Environmental Health Effects Research Series
                                             Health Effects Research Laboratory
                                            Office of Research and Development
                                           U.S. Environmental Protection Agency
                                    Research Triangle Park, North Carolina  27711


Research reports  of the Office of Research and Development, U.S. Environ-
mental Protection Agency, have been grouped into five series. These five broad
categories were established to facilitate further development and application
of environmental  technology.   Elimination  of traditional  grouping  was con-
sciously planned  to foster technology transfer  and a  maximum interface in
related fields. The five series are:
    1.    Environmental Health Effects Research
    2.    Environmental Protection Technology
    3.    Ecological Research
    4.    Environmental Monitoring
    5.    Socioeconomic Environmental Studies
This report has been  assigned to  the ENVIRONMENTAL HEALTH EFFECTS
RESEARCH series. This series describes projects and  studies relating to the
tolerances of man for unhealthful substances or conditions.  This work is gener-
ally assessed from a  medical  viewpoint, including  physiological or psycho-
logical studies.  In addition to toxicology and other medical specialities, study
areas include biomedical instrumentation and health research techniques uti-
lizing animals—but always with intended application to human health measures.
This document is available to the public through the National Technical Informa-
tion Service,  Springfield,  Virginia 22161.

                                           April 1976

Subcommittee on Chlorine and Hydrogen Chloride
         National Academy of Sciences
          National Research Council
    Committee on Medical and Biologic Effects
         of Environmental Pollutants
                Washington, D.C.
           Contract No. 68-02-1226
               Project Officer

              F. Gordon Hueter
      Criteria and Special Studies Office
      Health Effects Research Laboratory
      Research Triangle Park, N.C. 27711

      This report has been reviewed by the Health Effects Research Laboratory,
U.S. Environmental Protection Agency, and approved for publication.  Approval
does not signify that the contents necessarily reflect the views and policies
of the U.S. Environmental Protection Agency, nor does mention of trade names
or commercial products constitute endorsement or recommendation for use.
      The project that is the subject of this report was approved by the
Governing Board of the National Research Council, whose members are drawn '
from the Councils of the National Academy of Sciences, the National Academy
of Engineering, and the Institute of Medicine.  The members of the Committee
responsible for the report were chosen for their special competences and with
regard for appropriate balance.

      This report has been reviewed by a group other than the authors
according to procedures approved by a Report Review Committee consisting
of members of the National Academy of Sciences,  the National Academy of
Engineering, and the Institute of Medicine.

      The work on which this publication is based was performed pursuant
to Contract No. 68-02-1226 with the Environmental Protection Agency.


RALPH G. SMITH, University of Michigan School of Public Health, Ann

  Arbor, Chairman.

MARIO C. BATTIGELLI, University of North Carolina School of Medicine,

  Chapel Hill.

RALPH R. COOK, Dow Chemical Company, Midland, Michigan.

WARREN S. FERGUSON, Allied Chemical Corporation, Morristown, New


NORMAN LACASSE, Spring Mills, Pennsylvania.

WILBUR D. SHULTS, Oak Ridge National Laboratory, Oak Ridge, Tennessee.


JOSEPH COLUCCI, General Motors Research Laboratories, Warren, Michigan.

ROBERT DUCE, Graduate School of Oceanography, University of Rhode

  Island, Kingston.

GEORGE M. HIDY, Environmental Research and Technology, Inc., Westlake

  Village, California.

ALEX KATONA, Hooker Chemical Company, Niagara Falls, New York.

CHARLES G. KRAMER, Dow Chemical Company, Midland, Michigan.

RICHARD W. MC BURNEY, Diamond Shamrock Corporation, Painesville, Ohio.

BERNARD P. MC NAMARA, Edgewood Arsenal, Maryland.

ELIZABETH E. FORCE, Division of Medical Sciences, National Research

  Council, Washington, D.C., Staff Officer.

JAMES A. FRAZIER, Division of Medical Sciences, National Research

  Council, Washington, D.C., Staff Officer.


HERSCHEL E. GRIFFIN, Graduate School of Public Health,  University of

  Pittsburgh, Pennsylvania, Chairman.

DAVID M. ANDERSON, Environmental Quality Control Division, Bethlehem

  Steel Corporation, Pennsylvania.

RICHARD U. BYERRUM, College of Natural Science, Michigan State

  University, East Lansing.

RONALD F. COBURN, Department of Physiology, University  of Pennsylvania

  School of Medicine, Philadelphia.

T. TIMOTHY CROCKER, Department of Community and Environmental Medicine,

  University of California College of  Medicine, Irvine.

SHELDON K. FRIEDLANDER, W;  M.  Keck Laboratories, California Institute of

  Technology, Pasadena.

SAMUEL A. GUNN, Department of Pathology, University of  Miami School of

  Medicine, Florida.

ROBERT I. HENKIN, National Heart and Lung Institute, National Institutes

  of Health, Bethesda, Maryland.

IAN T. T. HIGGINS, School of Public Health, University  of Michigan,

  Ann Arbor.

JOE W. HIGHTOWER, Department of Chemical Engineering, Rice University,

  Houston, Texas.

ORVILLE A. LEVANDER, Nutrition Institute, Agricultural  Research Center,

  Beltsville, Maryland.

DWIGHT F. METZLER, Kansas State Department of Health and Environment,


I. HERBERT SCHEINBERG, Department of Medicine, Albert Einstein College

  of Medicine, Bronx, New York.

RALPH G. SMITH, Department of Environmental and Industrial Health,

  School of Public Health, University  of Michigan,  Ann  Arbor.


                                                CHAPTER 1


     Each year, many millions of tons of chlorine are produced to meet the demands of the chemical

industry and to satisfy the demand for chlorine in the purification of domestic water supplies.  As a

consequence of the manufacture and use of this element, some chlorine gas escapes to the atmosphere.

In addition, the action of sunlight on chloride-containing aerosols has been shown to produce small

amounts of chlorine.  Occasionally, exposure of populations to high concentrations of chlorine has

occurred, usually as a result of accidents involving the transportation of chlorine by rail, truck, or

barge.  For a brief time, during World War I, chlorine was intentionally used in warfare, although by

most standards it was not a very effective weapon.

     Hydrogen chloride is also an important basic chemical, and its close relationship to chlorine

makes it desirable to consider the two substances together in discussing environmental effects.

     The purpose of this report is to discuss the medical, biologic, and environmental effects of chlorine

pollution in the lower atmosphere.  The next three chapters discuss the natural and anthropogenic sources

of pollution by chlorine and hydrogen chloride, the varied industrial and other usages of chlorine and

hydrogen chloride and the quantities consumed, the atmospheric chemistry of their transformation and

transport processes, and their spatial distribution.

     Later chapters deal with the effects of chlorine and hydrogen chloride on man, animals, vegetation,

and materials.  Chapters 9 and 10 present the summary and conclusions and offer recommendations for

consideration in future studies.  Methods of monitoring and analyzing aqueous, gaseous, and biologic

samples for chlorine and hydrogen chloride are discussed in the Appendix.

     Unless stated otherwise, "chlorine" refers to the element and "hydrogen chloride" to the molecule

HC1.  "Gaseous chlorine" refers to the element when it is present as the diatomic molecule.  It should

be understood that gaseous chlorine and hydrogen  chloride in the atmosphere are complexed with

condensation nuclei of unspecified chemical composition.

     A balance was sought in apportioning the representation of expertise and interests of industry and

academe in studying the two chemicals in question.  Each participant in the study was asked to prepare

a section of the report based on a review and evaluation of the published information obtained from

national and international sources that were available up to July 1, 1974.  The summary, conclusions,

and recommendations for each section were prepared by its author and these were consolidated to form

Chapters 9 and 10.  The drafts of individual chapters were reviewed and appropriately revised by

members of the Subcommittee on Chlorine and Hydrogen Chloride.  The complete manuscript was also

approved by the Committee on Medical and Biologic Effects of Environmental Pollutants.
                                                 - 1  -

                                   CHAPTER 2



       Industrial production of chlorine in the United States has grown and

continues to grow at a high rate.  In 1972,  9, 859, 800 tons of chlorine were

produced,  compared with 5, 142, 876 tons in 1962 (an increase of about 6. 7%

per year),  and productionwasprojected to increase at the rate of approximately
                          77, 98
7% per year through 1974.        The major commercial sources of chlorine

are the electrolysis of water solutions of the alkali chlorides  (96. 6% of total

installed U.S. production capacity in  1972) and the  electrolysis of fused sodium

chloride-calcium chloride salt mixture, in -which chlorine is obtained as  a by-

product of  sodium production (slightly under 3.4% of total installed U.S.
capacity  in  1972).    Because the largest users  of chlorine are the chemical

industry  (approximately 70% of total consumption) and the pulp and paper
industry  (approximately 18% of total consumption,    the number of  sources

of possible chlorine emission tends to be restricted,  compared, for example,

to the number of sources of possible emission of the oxides of sulfur and nitro-

gen.   Chlorine emission control is generally effective and has been  in wide-

spread use in  industry for  many years.

       The 7. 7% average annual growth in  the industrial production  of hydro-

chloric acid (100% basis*)  in the United States over the period 1962-1972 has

slightly outstripped the 6. 7% average annual growth in the production of

chlorine.   In 1972, 2,  198,  140 tons of hydrochloric acid (100% basis) (22. 3%

of the chlorine tonnage) were produced, compared with 1,052, 116 tons in 1962
^"100% basis" means on the basis of equivalent anhydrous hydrogen chloride.

(20. 5% of the chlorine tonnage).    Production of hydrochloric acid (100%

basis) is projected to increase over the next few years at an average annual
rate of approximately 5-7%.     In the United States, hydrogen chloride is
produced  by three major processes:     as a byproduct of the chlorination

of organic compounds; by reaction of chloride salt with sulfuric acid (the

Mannheim process) or with sulfur dioxide,  steam (water), and air (oxygen)--

the Hargreaves process--at high temperature to produce salt cake (sodium

sulfate) and hydrogen chloride; and by  reaction of chlorine with hydrogen gas.

Only one large plant using the Hargreaves process is still in operation in the
United States.    In common with chlorine production, industrial hydrogen

chloride production is confined largely to a few chemical organizations that

use one or more  of the three major processes and that use an estimated

55-60% of the total production.   Theoretically, the essentially anhydrous

gaseous hydrogen chloride produced via the three routes (with chlorine,

chlorinated organic compounds, other organic materials, and other chemicals

in the gas stream.) represents a significant atmospheric emission control

problem.   In practice,  however, such potential emission is most commonly,

effectively, and inexpensively controlled by scrubbing the main exit-gas
stream and any tail-gas stream with water to produce hydrochloric acid for

use,  sale, or disposal; and other  emission control systems have been developed

to meet special industrial requirements.

       The burning of huge amounts of chloride- or chlorine-containing fossil

fuels--coal and fuel oil--is a very large  source of emission  of hydrogen chloride

gas to the atmosphere. The magnitude of the problem is discussed further in

the section on Combustion of Fuels. *  Increasing effort is being directed

toward the development of adequate and economical scrubber systems for

*Page 21

the control of emission of sulfur dioxide,  nitrogen oxides, and hydrogen

chloride from coal- and oil-fired industrial heating plants and electric generatiH

plants,  such systems are not now in general use in the United States.

        The incineration of chloride- or chlorine-containing refuse, paper,

and plastics  (particularly polyvinylchloride) is another important source of

emission of hydrogen chloride gas to the atmosphere.  The magnitude of this

source  is also unknown and is being  looked into.

        There is evidence that hydrogen chloride gas  is emitted to the

atmosphere in the exhaust resulting  from the combustion of hydrocarbon fuels

in transportation.  If it is  emitted, data to determine its  extent are not  avail-

able.  Hydrogen chloride from such  a source would probably  be in the form of

hydrochloric acid aerosol  because of the water present in exhaust.  The only

transportation fuel considered even potentially significant as  a source of

hydrogen chloride gas emission is motor gasoline that contains the ethylene

dichloride scavenger used -with lead  antiknock compounds.  The potential

for hydrogen chloride gas  emission from transportation sources will decrease

significantly, as  the EPA imposes regulations to decrease the lead content of


        The National Aeronautics and Space Administration (NASA) Office of

Space Science (OSS) Launch Vehicle and Propulsion Programs,  in a final en-

vironmental statement published in July 1973, indicated that,  with respect to

global or even national  significance,  the contribution of NASA launch vehicles

for automated missions to environmental pollution appears to be much smaller
than that of other sources.      The environmental effects of hydrogen chloride

gas emitted from rocket engines in tests,  launches,  on-pad accidents,  and in-

flight abort situations have been considered.

    Concentrations of hydrogen chloride gas in the ambient atmosphere

have not been reported.  Under normal atmospheric conditions,

hydrogen chloride is an aqueous acid aerosol; usually low relative
humidity may allow it to exist as anhydrous hydrogen chloride.      There

has been one report of hydrochloric acid aerosol concentrations in the
atmospheric air near a Russian magnesium plant.    Studies of hydrochloric

acid aerosol concentrations in atmospheric air have undoubtedly been

hindered because of the unavailability of an analytic method -with high

specificity for hydrogen chloride itself.   Most analytic methods for hydrogen

chloride are based on its acidity or on total-chloride determination,  and

these conventional methods are subject to interferences from other

contaminants commonly found in atmospheric air (see the Appendix).

    Determinations of background concentrations  of chlorine in the  ambient

atmosphere have not been reported.  The  air in  a 6-square-mile area around

a 1961 chlorine tank-car derailment in Louisiana was sampled for  chlorine

    Minute quantities  of hydrogen chloride gas are present in volcanic gases,

but it is readily converted to hydrochloric acid aerosol by the moisture  in

the air.

   All human body fluids contain chlorine:  blood at 0. 45% (expressed as
sodium  chloride) and gastric juices at 0. 4-0. 5%  (as hydrochloric acid).


The formation of hydrochloric acid in the gastric juices is closely associated

with the parietal cells of the gastric glands; one  accepted theory is that the

hydrochloric acid forms in the absence of carbonates as a result  of the inter-
change  of ions between sodium chloride and carbonic acid.     Nothing in the

literature suggests that emission of chlorine or hydrogen chloride gas to the

atmosphere results from biochemical reactions;  it is extremely  unlikely that

chlorine or hydrogen chloride gas can be emitted to the atmosphere as a result

of biochemical reactions.
    Chlorine at low concentrations may be formed by atmospheric reactions.

For example,  chloride compounds and nitrogen dioxide may react to form

nitrosyl chloride, which can decompose photochemically to yield  free chlorine

and nitric oxide.  Free chlorine may also be formed in the atmosphere by  the

reaction of chloride ion and ozone.*

    It is pointed out in Chapter 4 that there is  considerable circumstantial

evidence (measurements of the chloride: sodium ratio in the atmosphere in

West Coast cities) that sea salt particles (sodium chloride) in the presence of

moisture undergo attack by acid-forming gases,  such as nitrogen dioxide,  to

release hydrogen chloride gas.   In urban areas,  where concentrations of

nitrogen dioxide may be relatively high, the chloride: sodium  ratio is much

lower than -would be expected if it were reduced by  addition of only soil

dust to  the sea salt aerosol.  See Chapter 4 regarding this an other possible

atmospheric reactions leading to the formation of hydrogen chloride gas.

*See also page  103



       Chlorine.  The major processes for the production of chlorine in the

United States are the electrolysis of water solutions of alkali chlorides via

diaphragm or mercury cells and (to a much smaller extent) the electrolysis

of a fused sodium chloride-calcium chloride mixture (Downs process).  Other

processes used for the production of chlorine include the electrolysis of mag-
nesium chloride fused with other chlorides,    the electrolysis of hydro-
chloric acid,    and a process wherein chlorine is obtained as a byproduct

of the reaction of potassium chloride with nitric acid and oxygen to form
potassium nitrate.    Those three processes together account for only

approximately  0. 1% of chlorine production and details on them in the litera-

ture are sparse.

       Diaphragm- and mercury-cell processes accounted for approximately
96. 6% of the chlorine produced in 1972 (about 72. 4% and 24. 2%, respectively).

Detailed descriptions of these  processes can be found in several reference
         87, 200,415,480
sources.                 Slightly under 3.4% of the  chlorine manufactured
                                                                         81, 87
in this country is produced as  a byproduct of the Downs fused-salt process.

       There were 68 plants producing chlorine in the United States in 1972;

they are  listed  in  Table 2-1, with the type  of process used, the year of initial

chlorine  production, and the kinds of containers filled.

       The major sources of atmospheric emission  of chlorine from the pro-

duction processes are the blow gas resulting from the liquefaction of chlorine;

the vents from  returned tank cars,  ton containers, and cylinders; the vents

from storage tanks,  process transfer tanks, and tank cars during handling and

storage of liquid chlorine;  the process for the removal of water from chlorine

gas; emergency vents; the  air blowing of depleted brine in mercury-cell plants;
and occasional  equipment failure (especially compressor breakdown).

                          TABLE 2-1


Le Moynec


Muscle Shoals

Pine Bluff6

Delaware City**

Brunswick '?

East St. Louis"

Calvert Cityc
Calvert City"
Baton RougeCj^
Baton Rouge
_ , C-

Stauffer Chemical
Olin Corporation
Diamond Shamrock
Chemical Co.
Diamond Shamrock
Chemical Co.

U.S. government

The Dow Chemical

Diamond Shamrock
Chemical Co.

Olin Corporation
Allied Chemical
Brunswick Chemical

Monsanto Company

Vulcan Materials

B.F. Goodrich
Chemical Corp.
Pennwalt Corp .

Ethyl Corporation

Allied Chemical










, 1952






De Nora 22 x 5 (mere.)

Olin E8 (mere.)
De Nora (mere.)

De Nora 24 x 2M (mere.)

Hooker S (diaph.)

Dow (diaph.)

De Nora 18 x 4 (mere.)

Olin E11F (mere.)
Solvay V-100 (mere.)

Hooker S4 (diaph.)

De Nora 18 x 6 (mere.) ('62)

Hooker S,S3A,S3B (diaph.)

De Nora 24H5 (mere.)

Olin E11F (mere.) ('67)

Downs (fused salt),
Hooker S3D (diaph.)
Allen-Moore (modified diaph . ) ,
Hooker S4 (diaph.) ('68)


	 S -


- T S -

	 S -

	 S -
- - S -

_ _ _ _

- - S -

C T S -

_ _ _ _


	 S -

- - S -

BASF Wyandotte Corp.  1959
Diamond D3 (diaph.), Uhde 30 sq.
  m. (mere.)('64), Hooker S4

New York
  Niagara Falls^
                                             TABLE 2-1

                          CHLORINE PLANTS IN THE UNITED STATESa - (Cont'd)


Lake Charles


St. Gabriel0







New Jersey

Kaiser Aluminum &
Chemical Corp.
PPG Industries,

The Dow Chemical
Stauffer Chemical
Hooker Chemical

Sobin Chlor-Alkali

The Dow Chemical
Hooker Chemical
Corp. :
BASF Wyandotte
Pennwalt Corp.

Vicksburg Chemical

Stauffer Chemical
Co. of Nevada

Linden Chlorine
Products Inc .
Vulcan Materials













Hooker S3B (diaph.)

Columbia N 1, Hooker
S3B (diaph.), De Nora
48H5 (mere.) ('69)
Dow (diaph.)

Uhde 30 sq. m. (mere.)

Hooker S4, C-60, H-2

De Nora 24H5 (mere.)

Dow (diaph.)

Hooker HC-3 (diaph.)

Hooker S3B (diaph.)

Diamond D3 (diaph.) ('60)


Hooker S (diaph.)

BASF-Krebs ('69)

Hooker S (diaph.),

- T S B

- - S -


	 S -

- - S -

	 S -

	 S -

— — S —

C T S -

	 S -

- - S -

- T S -

	 S -
E.I. du Pont de
  Nemours & Co.
Hooker Chemical

                                 Hooker  S4  ('68)
Downs (fused salt)
                                                       Hooker S,S3A, Gibbs
                                                         (modified diaph.)('61)
                                 - T S -

                                              TABLE  2-1

                          CHLORINE PLANTS  IN  THE  UNITED  STATESa - (Cont'd)

Niagara Falls^

Niagara Falls

North Carolina
Q f
Canton jj
o f
Pisgah Forest ij



Oregon •


Hooker Sobin
Olin Corporation
Allied Chemical

Allied Chemical
Champion Inter-
national Corp.
Olin, Ecusta

Detrex Chemical
Industries, Inc.
RMI Company
PPG Industries Inc.
Diamond Shamrock
Chemical Co.

Oregon Metallurgi-
cal Co.
Pennwalt Corp.

Olin Corporation
E.I. du Pont de









Uhde 20 sq. m. (mere.)

Olin E11F (mere.) ('60)
Allen-Moore (modified diaph.)
Solvay Process SD 12 (merc.)(
Solvay S60 (mere.) ('53),
Hooker S4 (diaph.) ('68)

Solvay V-200 (mere.)

Hooker S (diaph.)

Sorensen (mere . )

Olin E11F (mere.)

Downs (fused salt)
Columbia (diaph.)
Diamond D3 (diaph.) ('59)

Alcan (magnesium)

Gibbs, Gibbs (modified
diaph . ) , Diamond
(diaph.) ('67)

Olin E11F, E812 (mere.)
Downs (fused salt)
- - S -

- - S -

- - S -



— — S —

	 S -
- T S -
C T S -



	 S -
Texas        ,
  Cedar Bayou
  Corpus Christic
  Denver Cityc
  Nemours & Co.
Velsicol Chemical
  Deer Park
Mobay CheayLcal Co.   1972
PPG Industries, Inc.  1938
Vulcan Materials Co. 1947
The Dow Chemical Co. 1940
Diamond Shamrock     1938
  Chemical Co.
Hooker S4 (diaph.)('69)
             Uhde (HCI)
             Columbia N 1, N 3  (diaph.)
             Hooker S (diaph.)
             Dow (diaph.), Dow  (magnesium)
             Diamond (diaph.),
             De Nora 18 SGL (mere.)
                                - T  S -

                                - -  S -
                                C T  S B,

West Virginia
  New Martinsville
                                                TABLE  2-1

                              CHLORINE PLANTS IN THE UNITED  STATES'2  -  (Cont'd)

Houston ,,

Point Comfort0

Port Neches


Washington ,?
Bellingham jj

Ethyl Corporation
Shell Chemical Co.
Champion Inter-
national Corp.
Aluminum Co . of
Jefferson Chemical
Co . , Inc .
American Magnesium

Hercules , Inc .

Hooker Chemical
Pennwalt Corp.








Downs (fused salt)
Hooker S4 (diaph.)
Hooker S (diaph.)

De Nora 2^ -x. 5 (mere.)

Hooker S3B (diaph.)

VAMI (magnesium)

Hooker S3 (diaph.)

De Nora 18 x 4 (mere . )

De Nora 14 TGL & 24H5
(mere.) ('67)
Hooker S3 (diaph.)

Gibbs (modified diaph.)
- - S -
_ _ _ _
_ _ _ _


_ 	 _

_ _ _ _

	 S -


	 S -

- T S B

C T S -
Allied Chemical      1953
PPG Industries Inc.  1943
Solvay S60  (mere.)

Columbia N  1, N 3, N  6
  (diaph.), Uhde 20 sq. m.

  So. Charleston

Wisconsin    ,,
  Green Bay J^

  Port Edwards0

      —     st
                      FMC Corporation
                      Fort Howard Paper    1968
                      BASF Wyandotte Corp. 1967
                      PPG Industries
Hooker S3B (diaph.)('57),
Hooker S4 (diaph.)('67)
Hooker S4 (diaph.)

De Nora 24H5  (mere.)

De Nora (mere.)
- T S B

                           TABLE 2-1

                                 ft 1
aDerived from Chlorine Institute;   excludes plants being built.

 C=cylinders, T=ton containers, S=single-unit tank cars, B=barges.

 Electrolytic plant producing caustic soda, chlorine, and hydrogen
 from brine.

 Electrolytic plant producing caustic soda, caustic potash, chlorine,
 and hydrogen from brine.
 Not operating.

 Electrolytic plant producing metallic sodium and chlorine from
 molten salt .

 Nonelectrolytic plant producing chlorine and potassium nitrate .

Electrolytic plant producing  caustic potash, chlorine, and hydrogen
 from brine.
 Electrolytic plant producing magnesium and chlorine from molten
 magnesium chloride.
 Electrolytic plant producing chlorine and hydrogen from hydrochloric
 Includes both Texas and Oyster Creek divisions.

     Chlorine and caustic are produced concurrently in electrolytic diaphragm

and mercury cells.  An electric current decomposes a chloride salt that is

fed to the cell as a water solution.   Chlorine gas is liberated at the anode

of the cell.  In the diaphragm  cell, hydrogen is liberated at the cathode,

and a diaphragm is used to prevent contact of the chlorine that is  produced

with the hydrogen or alkali hydroxide that is  formed simultaneously.  In  the

mercury cell, liquid mercury is used as the  cathode and forms an amalgam

with the alkali metal.   The amalgam is  removed from the cell and reacted

with water in a separate chamber, called a denuder,  to form alkali hydroxide

and hydrogen.

     Both chlorine and hydrogen are produced in the electrolytic diaphragm and

mercury cells.  Hydrogen gas saturated with water vapor leaves the cell at the

top of the cathode or denuder compartment.   Chlorine gas leaving the cells

from the anode compartment is saturated with water vapor and is cooled to

remove some of the water.  In the operation  of the diaphragm cell,  cooling

may be indirect or by  direct contact  with cold water, as in a  blow-gas absorber.

Chlorine gas from mercury cells is usually cooled indirectly with cold water.

After water cooling, the gas is dried further  by direct contact with  strong

sulfuric acid.  The dry chlorine  gas  is then compressed for in-plant use or

refrigerated to liquefy it.  Approximately half of the chlorine produced in the

United States is produced as a liquid.

     Electrolysis of a fused sodium chloride-calcium chloride mixture occurs in

the Downs cell  at a temperature  of about 550  C,  producing molten elemental  sodium

and gaseous chlorine.   The lower-density sodium and the chlorine percolate  sepa-

rately through the molten salt bath to a  submerged conical collection dome,  where

an outer annulus and an inner nickel  dome remove the molten sodium  and hot gaseous

chlorine.  The  chlorine  is cooled indirectly and then handled by methods  similar to

those used in association with diaphragm and mercury cells.


      The potential emissions are described in the following paragraphs.

      Gaseous chlorine is present in the blow gas  resulting from the liquefac-

 tion of chlorine.  The chlorine content of blow-gas streams normally ranges

 from 20 to  100 Ib/ton of chlorine produced with diaphragm cells and from
 40 to 160 Ib/ton of chlorine produced with mercury cells.     Methods  of

 removing chlorine from these streams are summarized later in this Chapter.

      It is common practice to apply suction to returned tank cars,  ton con-

 tainers,  and cylinders to remove liquid chlorine remaining in the vessels

 before inspection and cleaning.  The amount of chlorine thus removed varies

 considerably, but averages about 450 Ib for a 55-ton tank car (or about 8 Ib/ton
 of carrying capacity).     The recovered  chlorine from tank cars is usually

 sent to the operating system for process  chlorine handling, but plants find

 it convenient to send minor quantities of chlorine  to a caustic scrubber to

 avoid upsetting their operating systems.

     A common method of transferring chlorine involves the use of air
 padding.  After transfer, it is necessary  to vent the air, which now contains

 a relatively low concentration of chlorine, because the transfer  is normally

 completed before  equilibrium  can be reached.  Data from 19 plants (in response

 to a questionnaire for a study) show that the quantity of chlorine flushed out

 with the  padding air during the loading of  shipping containers with liquid

 chlorine varied from 1.1 to 60 Ib/ton of chlorine liquefied, with an average
 of 17 Ib.    The chlorine removed  during tank-car loading is  transferred

 to other  plant uses, returned to the process, or treated in a scrubber.   In

 many newer plants, submerged pumps are used to transfer liquid chlorine.

 Although pumps eliminate the loss of chlorine related to padding, emergency

 venting (usually to a caustic scrubber) is  necessary for pump  repair and
 general maintenance.    Another method  of transfer is to apply  suction on the

*Use of compressed air above the surface of a liquid to transfer the liquid to
 another  vessel.                      -14-

receiver or vessel to which a transfer is to be made and connect the dis-

charge from the compressor to the vessel that contains the chlorine to

be transferred.  This  is somewhat similar to transfer by air, except that
neither  tank  requires any venting.

     Chlorine gas is normally cooled to condense water vapor and then

dried further in scrubbers with concentrated sulfuric acid.  The potential

loss of chlorine with the water that condenses from cell gas varies from

4 to 12 Ib/ton liquefied and depends  on the type  of cell, cell temperature,
and location  of drip connections in the chlorine  gas system.     In modern

practice,  the water that condenses can be passed to the plant water  collec-
tion system through a  limestone pit      or acidified and steam-stripped  to a

chlorine content of less than 10 ppm  (0. 1-0. 2 Ib of chlorine per ton  liquefied)

in a process vessel before disposal.   Chlorine stripped from the water con-

densate is  recovered by piping it back to the cell-gas stream ahead  of the

first indirect-contact cooler.

     Chlorine seals and other sources of infrequent emission are usually

connected to an emergency scrubber, although in other cases  such emission

is vented to the atmosphere.  In either event, alarms   and electric  tie-in

connections are usually provided to permit prompt shutdown or  changes  in
operating procedures to limit the duration of the emission.    Seals on

chlorine headers,  provided  to prevent back-pressure at the cells, commonly

used to  be  vented to the cell house or to the atmosphere.  Although in  an

emergency they must handle the full  capacity of the cells connected  to the
header, the seals blow only infrequently and for short periods.    Modern

practice is to pipe  the  seals to a lime or caustic scrubber designed  to absorb

all the cell chlorine produced.   The shaft seals on liquid-seal chlorine com-

pressors are usually piped so that a  stream of sulfuric acid is fed into the

 compressor.  Carbon-ring reciprocal compressors usually have a double

 stuffing box vented to a caustic scrubber or the suction of the compressor.
 This effectively prevents emission to the atmosphere.    Storage-tank vent

 lines are  usually connected to a disposal scrubber.  The relief connection

 from the  safety valves may be vented to the atmosphere or to an emergency

     Recycled brine in mercury-cell plants is saturated with chlorine.  This

 brine is usually vacuum-treated,  air-blown, or both, to remove residual

 chlorine before  resaturation.  Concentrations of chlorine encountered in the

 vent gas are usually low, and recovery in a water or carbon tetrachloride

 absorber  is not economical.  Consequently, such gases are normally used for

 in-plant purposes,  such as water chlorination,  or are sent to lime or  caustic

 scrubbers for disposal or vented to the atmosphere.  Although air-blowing of

 depleted brine is common,  it is by no means universal.  For  example, some

 plants air-blow  and re-treat only a 5-10% sidestream, and several plants dis-

 pense with this procedure entirely.  The questionnaire  responses indicated that

 11 plants  treat depleted brine by air-blowing:  seven use the recovered chlorine

 for in-plant processes, three send it to scrubbers, and one vents it to the

     Minor  emission of chlorine in cell rooms can lead to emission to the

 atmosphere.  In the operation of diaphragm cells,  this results from leakage

 at dogleg  connections (those between the cell and the main chlorine header)

 due to improper assembly or overpressure at the  cell and from cell renewal.

Modern control  techniques and developments include operation at a slight

negative pressure (approximately 0. 5 in. H  0 gauge) in the chlorine header,
 the elimination of packed joints in dogleg assemblies  through  improved de-

 sign,  and essentially complete draining of chlorine-containing brine from the

cells into the caustic system before cell renewal.  In some mercury cells,

the discharge end box has a removable cover for servicing.   End boxes are

connected to a common suction header to prevent chlorine gas from entering

the cell room -when the  covers of the end boxes are opened.  Chlorine ex-

hausted from the end boxes is usually neutralized with lime  or caustic in a
scrubber system.

     Hydrogen  Chloride.  In 1972,  90% of the hydrochloric acid  (100% basis)

produced in the United States was manufactured as a byproduct of the chlorina-
tion of organic  compounds.     Byproduct hydrogen chloride is produced in

the manufacture of  chlorinated benzenes, chlorinated toluenes, vinylchloride,

fluorocarbons,  carbon tetrachloride,  toluene diisocyanate, glycerin,  linear

alkylsulfonate detergents,  chloroform, methylene chloride,  methylchloride,

trichloroethylene, perchloroethylene, chloral, hexachlorocyclopentadiene,
                                                         190,227, 276
chlorinated paraffins, ethylchloride, and other substances.

Thus, hydrogen chloride is a byproduct in any manufacturing process in which

chlorine is used to  substitute a chlorine atom for hydrogen in a chemical com-

pound.  Hydrogen chloride also is produced as a byproduct when a saturated

chlorinated compound is dehydrochlorinated to produce an unsaturated compound

that contains one less chlorine atom than the saturated chlorinated  compound

precursor.  Hydrochloric acid is produced from byproduct process hydrogen

chloride by absorbing the hydrogen chloride  in water after the organic materials

associated with it are removed by condensation,  absorption,  or adsorption.

The atmospheric contaminants that can be emitted during the manufacture of

hydrochloric acid from byproduct process hydrogen chloride include hydrogen

chloride, chlorine,  chlorinated organic compounds, and other organic materials.

The type and quantity of contaminants vary with the type of process, the operating

conditions,  and the  type of exit-gas  control systems.


     In a cooperative study report   of the Manufacturing Chemists' Associa-

tion, Inc., and the Public Health Service, published in  1969, hydrogen chloride

emission data and data on other  trace emission from byproduct plants were

obtained from 17 plants by questionnaire.  In addition, hydrogen chloride-

containing stack gases  from four other byproduct plants -were sampled by a

Public Health Service team as part of the overall cooperative study project.

It was  concluded in the cooperative study that hydrogen chloride emission to

the atmosphere usually totals less that 0. 5% of the tail-gas  volume.  This

is a relatively small quantity of hydrogen chloride;  tail-gas volumes for plants

reporting range from 2 to 550 cfm, with  an average  of 40 cfm.

     Adequate control equipment is available to prevent emission of more

than 0. 5% hydrogen  chloride, or about 0. 5 Ib/ton of  acid produced.

     In the event of  an  emergency  shutdown of a hydrochloric acid plant (pro-

ducing acid by absorbing hydrogen chloride gas in water), the hydrogen chloride

gas source should be shut down first.   Liquid flow to the absorption equipment

should always be sufficient to keep all tubes or packing wetted and thus prevent

hydrogen chloride emission to the atmosphere. Some weak acid will be made

during this shutdown period, but that can usually  be  corrected by producing acid

somewhat stronger than normal later.  The liquid flow should be greater than

that required for surface  wetting, to prevent hydrogen chloride  emission during

routine shutdowns and startups.
     In a survey  prepared for the Office of Air Programs  of the Environmental

Protection Agency and reported in 1972,  25 chlorination processes involved in

production of 14 organic chemical products (one containing no chlorine) and

two chlorine-containing inorganic chemicals (phosgene and synthesis hydrogen

chloride) were examined to determine their air pollution potential.  The manu-

facture of the  selected  14 organic chemical products consumed 64. 3% of the


chlorine produced in 1970.  Excluding the two inorganic chemical chlorination

processes and five organic chemical chlorination processes that produce no

hydrochloric acid byproduct,  10 of the remaining 18 chlorination processes

that did produce hydrochloric acid byproduct were listed as having no hydrogen

chloride emission factor (pounds of hydrogen chloride emitted per ton of product).

Emission factors for the other eight chlorination processes were 0. 001  (for

three processes:  chlorination of ethylene, chlorination of benzene, and hydro-

chlorination of ethylene), 0. 002 (for two processes:  chlorohydrination of

allylchloride and then hydrolysis and chlorohydrination of propylene and then

hydrolysis), 0. 02 (for one process:  hydrochlorination of ethanol),  and  0. 2

(for two processes:  dehydrochlorination of 1, 2-dichloroethane and  chlorination

and then dehydrochlorination of acetylene).  With one insignificant exception,

the emission factors were estimated on the basis of  little or no census or

experimental information and are averages for all sources using the processes

in question.
     The  synthesis process   accounted for 5. 6% of the hydrochloric acid
(100% basis) produced in 1972.     In this  process, high-purity (98-99. 7%

pure) hydrogen chloride gas is produced by burning chlorine in a slight excess
of hydrogen.      The high-purity gas is desirable for organic compound or

drug synthesis and the manufacture of reagent-grade acid.  Synthesis  plants

differ in detail,  because of differences in  raw-material sources and qualities

and plant  capacity.  However, all plants have a chlorine burner,  including

safety and control devices,  and absorption facilities  for the production of

hydrochloric acid.  Hydrogen chloride formed in the combustion  chamber can

be cooled and  absorbed in water or cooled, dried with sulfuric acid, and com-

pressed for pipeline distribution.   Some plants  liquefy dried synthesis-process

hydrogen  chloride and revaporize the liquid to meet  fluctuations in captive and

merchant sale demands.  In the cooperative study project of the Manufacturing

Chemists'  Association, Inc. , and the Public Health Service, hydrogen chloride

emission data from three synthesis plants were obtained in response to ques-
tionnaries,   and emission factors--pounds of hydrogen chloride emitted per
ton of 20 Be /(31. 5% acid)--of zero,  trace, and < 0. 035 were reported.  In the

plants surveyed, no additional air pollution control equipment was used after

the tail-gas (lean-gas) absorption tower.  In the survey prepared for the Office

of Air Programs of the EPA, an emission factor of 0. 1 was reported for  the
hydrogen chloride synthesis process.   According to the survey report,  that

emission factor was estimated on the basis of little or no census or experi-

mental information and is an average for all sources using the synthesis


     In 1972,  4.4% of the hydrochloric acid (100% basis) manufactured in the

United States was  produced by the reaction of  sulfuric acid with sodium chloride

(Mannheim process) or by the reaction of sulfur dioxide, steam (water), air
(oxygen), and sodium chloride (Hargreaves process).     The Mannheim process

is operated at about 1000 F and the Hargreaves process at 800-1000 F,  to pro-
duce hydrochloric acid and  a salt cake (sodium sulfate) coproduct.      In

addition to  hydrogen chloride gas, both sulfuric and hydrochloric acid mists

are emitted from Mannheim process plants.  In general, emission  from such

plants is greater than that from byproduct or synthesis-process plants.  Data

reported by manufacturers  and collected by actual test showed hydrogen chloride

emission factors of 1. 3-3. 8 Ib/ton of 20 Be* acid produced.  These  factors are

probably higher because of poor operation and maintenance and, in some  cases,
poor design of absorption systems.    In the Mannheim furnace operations,

losses of hydrogen chloride can also occur through leaks at the furnace and
through removal of hot salt cake.      No quantitative data are available on

the magnitude of such losses to the atmosphere from the Hargreaves process.

Combustion of Fuels

     The combustion of fossil fuels,  particularly coal,  produces a major  con-
tribution to the chloride content of the atmosphere.  In  one recent study,

it was  concluded that high concentrations of chloride occur in areas of heavy

industrialization and that this chloride is generated largely by combustion of

fuels.  This is confirmed by seasonal variations, which show high concentra-

tions during the winter months in urban areas.   The chloride:sodium ion ratio

of seawater is about 1. 8:1, and a map of the United States giving average  ratios

for the years  1960-1966 shows very high values in industrialized areas, indi-

cating  anthropogenic sources of chloride ion.
     A literature review  conducted under a  Public Health Service contract

cited 11 references  pertaining to  the prevalence of chlorine in coal and its

emission as hydrogen chloride during coal-burning.  In a reference not cited
in the literature  review,  Gibson and Selvig     indicated that tests on 24 coal

samples from 12 states yielded chlorine content of 0-0.46%, with a mean  of
0. 128%.  In one key reference cited in the literature review,  lapalucci et  al.

concluded that the chlorine content of American coal ranges from 0. 01 to  0. 5%

and that the burning of coal containing chlorine is associated with a serious

pollution hazard.  They assumed  that an 800-MW power plant is burning coal

with 0. 2% chlorine and concluded that hydrogen chloride is discharged from the

stack at 11,000  scf/hr, or 4, 560  tons/year.  They performed experiments with

pulverized coal  containing 0. 1-0.4% chlorine at carbon combustion efficiencies

of 94-98% and found that 93-98% of the chlorine was emitted as hydrogen chloride;

the remainder was left in the ash. To verify these results under actual condi-

tions,  they sampled the stack of a local power plant after burning a bituminous

coal containing 0. 087% chlorine; only 1. 5% of the chlorine was retained in the

ash, with the balance being emitted in the stack gas as hydrogen chloride.

We consumed 1, 053 billion pounds of coal (largely bituminous) in the United

States in 1970,  and it is estimated that we will consume 1, 230 billion pounds
of coal in 1975.      The data of lapalucci e_t al. can be used in estimating

the potential hydrogen chloride emission from coal-burning.  For example,

if it is assumed that  the average chlorine content  of coal is 0. 128% and that

95% of it is converted to hydrogen chloride, then approximately 1. 28 billion

pounds of hydrogen chloride gas were emitted to the atmosphere from the

burning of coal  in the United States in 1970.

     No supplementary quantitative literature references have been found re-

garding hydrogen  chloride emission during coal-burning.

     Fuel oil contains small amounts of chlorine and can therefore emit

hydrogen chloride when burned.  Few pertinent literature references  are
available,  but a study on fuel-oil combustion published in 1962     cited two

1938 reports on chloride  emission.  It has  been reported that 500 Ib of hydrogen

chloride are produced per day per 100, 000 persons by using oil for domestic
     Increasing effort is  being directed toward the development of adequate

and economical scrubber systems  for the control of emission of sulfur dioxide,

nitrogen oxides, and  hydrogen chloride from coal- and oil-fired industrial

heating plants and electric generating plants,  but such systems are not now

in general use in the  United States.

Waste Disposal

     "Incineration of refuse always produces at least two waste products,

residue and combustion gases.  Except for low^'burnout^ of the refuse,  the

residue is usually not a significant disposal problem because it is low in

volume,  sterile, and its offensive  odors have  been removed. . . . The com-
bustion gases,  however,  can be a significant problem  because  of their

contribution to air pollution.  The primary air pollution concern is with

particulate  emissions rather  than gases and odors	air pollution control

devices are basically designed for the removal of particulate matter, with
some incidental removal of pollutant gases. ..."     The above comments

indicate that concern over the control of incinerator combustion gases is  a

recent development in the United States.  The primary reason is that, conn-

pared with other sources, incinerators contribute relatively little  gaseous

emission.  In November  1965, 267 incinerators that burned municipal refxise
in the United States were identified.       They had a nominal rated capacity

of 76, 300 tons/day (approximately 28 million tons/year).  Projections of

municipal incinerator capacity show an increase from the  1970 capacity of

approximately 82, 000 tons/day  (approximately 30 million tons/year) to about
160,000 tons/day (approximately 58 million tons/year) in 1980.

     Results published in 1968 of the  first national survey of solid wastes--

made by representatives of the  Solid Wastes Program of the Public Health

Service, state agencies,  and  consultants--show that approximately 5. 32 lb
of municipal solid waste per person per day is collected.    The survey,

based on a large sample  consisting of 92.  5 million people  (46% of the U.S.

population) in 33 states, permits the calculation of a national municipal solid

•waste collection figure of approximately 195 million tons/year.  In the survey,

projections  on a national scale showed that the amount of solid wastes to be

collected through municipal and  private agencies will rise to 8 lb per person

per day by 1980.  The per capita projection coupled with the population projec-

tion would permit daily refuse disposal requirements to be projected.

     The EPA has estimated  that the municipal solid waste collected in 1967

was disposed  of by municipal systems that included incineration (10%), open

burning (44%), and other (46%);  "other" included sanitary landfill,  ocean dumping,


and composting.      Another source has estimated sanitary landfill at 10% and
incineration at 9-12%, unregulated dumping representing the balance.

     For the purpose of estimating control costs and emission reduction

efficiencies in 1977,  EPA said that all open burning in existing municipal

systems would be discontinued by 1977, with 25% of the waste that is now

being burned openly going to new municipal incinerators and 75% to sanitary


     One incinerator emission that is generating a great deal of concern is

that of hydrogen chloride gas from the combustion  of chlorine- and chloride-
containing refuse.  Kaiser and Carotti    corroborated previous findings

that hydrogen chloride is generated by burning normal refuse (e. g. , paper,

salt in food, grass, wool, leather, etc. ) without the presence of plastics.

During burning, most of the chlorine present in the normal refuse and in the

polyurethane and polyvinylchloride materials added to the base refuse in the

test work was evolved as hydrogen chloride.  No free chlorine gas or phosgene

was detected.  The chloride ion  concentration in the flue gas after the burning

of the normal base refuse averaged 511 ppm (0.0511%).

     Although analysis  of paper  products indicates  that the chloride content
       35,47                                             47
is low,        approximately 0. 03-0. 16 wt %, two examples   cited in the

literature demonstrate  that the amount of hydrogen chloride emitted from the

incineration of paper can injure  plants.  La both examples, the plant injury

was caused by hydrogen chloride emitted from a hospital incinerator burning

trash consisting of 80-90% paper products.

     It is the presence  of chlorine-containing plastics,  however, and especially

polyvinylchloride plastics, in the solid municipal refuse fed to incinerators

that has become a concern of ecologically minded persons.  That is because

polyvinylchloride and polyvinylidene chloride plastics differ from most other


plastic materials involved, in that they generate hydrogen chloride on incinera-
tion.  In Kaiser and Carotti's study,    for example,  addition of polyethylene

and polystyrene plastics to normal base refuse (without plastics  initially) had

no effect on chloride ion emission,  because they contain no chlorine.  Addition

of polyurethane foam resulted in slight increases, to 689 ppm (0. 0689%)  for a

2% addition to the base refuse and 751 ppm (0. 0751%) for a 4% addition.

Addition of polyvinylchloride  to the  normal refuse increased chloride ion

emission to 1, 990 ppm (0. 1990%) for a 2% addition and 3, 030 ppm (0. 3030%)

for a 4% addition.
     Truss    indicates that the combustion of pure polyvinylchloride  pro-

duces hydrogen chloride at about 58 wt % in the resulting combustion gas

and is an important source of the hydrogen chloride  that results  from refuse
incineration.  Eberhardt,     in discussing European practice in refuse in-

cineration,  indicates that the chlorine content of polyvinylchloride in house-

hold  refuse is about 50% and that, when the polyvinylchloride is heated to
over 446 F, the chlorine appears as hydrochloric  acid.  Reimer and Rossi

in Hamburg, found a linear relationship between the amount of hydrogen

chloride in an incinerator  flue gas  and the amount of polyvinylchloride  added

to the chloride-containing  refuse for test purposes.  For example, at a 4%

polyvinylchloride in the refuse, the hydrogen chloride content of the  flue ga.s

was 4, 000  mg/scm compared with 10, 500 mg/scm at 9% polyvinylchloride.

An approximately linear relationship was also  found between the concentration

of chlorides in the fly ash  and the amount of polyvinylchloride added  to the

refuse for  test purposes.  With 3. 5% polyvinylchloride in the feed refuse,

the fly ash chloride concentration was about 3%; with 9% polyvinylchloride,

the fly ash chloride concentration was 6. 5%.  In contrast,  the chloride con-

tent of the  slag, which ranged between 0. 28 and 0. 37% over the whole range

of polyvinylchloride additions, was little affected by the polyvinylchloride con-

tent of the refuse.  The latter observation is consonant with the belief that,

at the actual temperatures  of incineration, the chloride-containing materials

also decompose, to give gaseous hydrogen chloride, -which must either be

reacted with the fly ash or  appear  in the flue gases.
     According to Warner £t aL ,     at incineration temperatures of

170-300 C,  the  polyvinylchloride in refuse being incinerated decomposes,

giving off hydrogen chloride.  At temperatures above 300 C, ignition is

well advanced; at 400-700 C, where the main burning occurs,  the gaseous

products are a mixture  of water, carbon monoxide, carbon dioxide,  and

hydrogen  chloride from any chlorine-containing compounds present (in-

cluding inorganic chlorides, such as salt).
     Warner ejb aL ,     recognize the  difficulties of attempting to correlate

and compare data from different sources as to the  classification of  solid

wastes, but indicate that it is clear that the composition of refuse has changed

since 1939.  In  particular,  ashes have largely disappeared and been replaced

with combustible material,  such as paper and plastics, whereas the amounts

of other inorganic materials, such as glass and metals, have increased.

     According to a survey made for the Department of Health, Education, and
Welfare,     the packaging industry contributed 51.7 million tons to the total

residential, commercial, and industrial waste load in the United States in  1966.

The plastic content of that contribution was estimated to represent approximately

2% of the United States total "collectible refuse"  load.
                   50 5a
     Warner et^al. ,     indicate that the  fraction of plastic in the solid waste

load in 1980 is expected to  be about 2. 8%, up from  2% in 1970.  They also

indicate that Debell and Richardson, Inc. ,  estimates indicate that in 1970

about 54% of the plastic solid waste was polyolefin, about 20% polystyrene,

about 11% polyvinylchloride,  and 15% all other, including cellulosics.  For

packaging wastes only, polyolefins are nearly 75%, polystyrene nearly 20%,

and polyvinylchloride a little over 6% of the "big three" totals.
     Huffman and Keller     indicate that the total amount of plastic found

in the waste  stream in 1970 has been estimated at 3. 25 million tons, or about

2% of the municipal solid waste load, and that 70% of this waste plastic is

polyethylene and polypropylene, 17% is polystyrene, and the remaining 13%
                                                                            50 5a
is polyvinylchloride (or about 0. 26% of the municipal refuse).  Warner et al.

conclude that the present polyvinylchloride content in collectible refuse is

0. 20-0. 25%, compared with 0. 1-0. 5% in the other countries of the world

(except Japan, where it is 2-3%).  According to a  1971 report of the National
Industrial Pollution Control Council,      polyvinylchloride makes up less

than 0. 15% of all collected household,  commercial,  and industrial waste.
     In a recent investigation by Kaiser and  Carotti     of the chlorine con-

tents of refuse components,  all organic fractions were found to  contain some

chlorine, probably largely as sodium chloride.  Less than half the chlorine

was  present  in chlorinated plastics.

     It is possible to estimate the maximal hydrogen chloride emission poten-

tial from refuse incineration in the United States through use of the above and

other cited data.  Thus, assuming a polyvinylchloride content of 0. 25% in

collectible refuse and a chlorine content of 50% for the polyvinylchloride  com-

ponent,  an estimated refuse chlorine content of 0.  125% would be contributed

by the chlorinated plastic  component.  If, in addition, less than half the chlorine

present in the refuse is  due  to the chlorinated  plastic contribution, a total refuse

chlorine content of 0. 25% may be calculated.   Although only limited data  are

available on  the direct determination of the chlorine  content of refuse,  Kaiser
and Carotti      list a 0. 50% chlorine content of a typical municipal refuse,


 and a Homer and Schifrin, Inc. ,  report done under an EPA grant     lists

 a 0. 13-0. 32% chlorine content based on analysis of three samples of residen-

 tial solid waste.  If it is assumed that the average  chlorine content  of refuse

 is 0. 25%, the maximal atmospheric emission potential for hydrogen chloride

 gas due to the incineration of refuse in 1970 was 75, 000  tons.

     Although the average chlorine content of municipal  refuse appears to

 be  2-3 times the average chlorine content of coal,  the quantity of coal burned

 in the United States each year is approximately 20  times as great as the amount

 of municipal refuse incinerated.

     Increased  emphasis on removal of particles from the gases emitted from

 incinerator stacks will promote the installation of the very efficient wet scrubbers

 for control of this pollution problem.   Wet scrubbers also provide favorable con-

 ditions for removing such  gases as  sulfur dioxide  and hydrogen chloride  and

 organic acids out of the flue-gas stream.  However,  these gases tend to form

 active acids in water solution, and the scrubbers,  ducting,  fans, and  stacks

 must be constructed of materials that can withstand acid corrosion.

     It is only in the last few years that true wet-scrubbing systems,  as

 differentiated from crude spray chambers or wet baffles, have been applied
 to municipal incinerators,  and fewer than 10%  of the  incinerators have them.

 T ranspor tation

     Although emission of particulate matter,  including  chlorides, in auto-
              218                                                  517
motive exhaust     and aerosols presumably formed by such emission

have been studied for some time,  there appears to  be little or no published

 information on the measurement of gaseous chlorine  or hydrogen chloride
in exhaust from any mode  of transportation.                       In fact,

 there is no evidence that such gaseous emission exists.  Hydrogen chloride,

if present, would probably exist as hydrochloric acid aerosol,  because of

the water in exhaust.

     Although there are no data, one can calculate the maximal theoretical

amount of gaseous chlorine or hydrogen chloride that could be  emitted from

mobile  sources.  In this discussion,  the gaseous combustion product is assumed

to "be hydrogen chloride.  The major source of this chlorine would be the ethylene

dichloride scavenger used with  lead antiknock compounds.  Some other organi-

cally bound chlorine may be present in hydrocarbon fuels, but  analysis of  several
naphthas showed chlorine concentrations of about 1-6 ppm,    a very low concen-

tration when compared with about 300 ppm, which may be present in leaded

gasoline as part of the antiknock additive.  Lead antiknock compounds are  not

used in diesel and jet fuel, and  those used in aviation gasoline  do not contain

a chlorine scavenger.   Therefore,  the only fuel to be considered as a significant

source  of chlorine is motor gasoline.   The calculation can be made as follows.

     Data from the U. S.  Department of the Interior, Bureau of Mines,  show
1971 domestic  gasoline consumption at 92, 953 million gallons.    The aviation

gasoline volume was 751 million gallons, leaving 92, 202 million gallons.  An
arithmetic average of data from more than 50 U. S.  cities     indicates that

premium-grade gasoline sales were 49. 3% of the total,  or 45,456 million

gallons. The  remaining 50. 7%, or 46, 746 million gallons, is assumed to  have

been regular grade, although  it also includes subregular and super-regular or

middle-premium fuels.  The average  of data from two Bureau  of Mines motor
gasoline surveys          showed that the average lead content was 2. 55 g  of

lead per gallon for premium grades and 2. 05 g/gal for regular grades.  A

small amount  of gasoline  is unleaded, although sales data are generally not

made public.  The unleaded premium  gasoline sold in the eastern and  southern

states does not present a  problem, because  samples of this  gasoline are included

 in the Bureau of Mines average for all premium grades.  The subregular un-

 leaded gasolines,  however, are not included in the regular-grade average;

 therefore, the calculated total volume  of regular-grade fuel, 46,746 million

 gallons, should be reduced by perhaps 0. 5%, resulting in a leaded regular-

 grade volume of 46, 512 million gallons.  Using the average lead contents of

 regular and premium fuels and the volumes of each, the total amount of lead

used  in antiknock  compounds in the U.  S. in 1971 was 211, 263,000 kg,  or

 about 232, 900 tons. (The Bureau of Mines reported that about 264, 000 tons
 of lead was used for production of  antiknock compounds,     but some of
the product was exported.
      According to Ethyl Corporation,      the composition of tetraethyl lead

 (TEL) motor mix is as follows:

                                                       wt %
                  lead alkyl                            61.48

                  dye                                   0.0621

                  ethylene dibromide                   17. 86

                  ethylene dichloride                   18. 81

                  inhibitor and inerts                    1. 79

The chlorine:lead weight ratio in the mixture is 0. 342:1.  The total amount

of lead used in antiknock compounds was calculated to be about 232, 900 tons,

so the amount of chlorine used would be about 79, 650 tons.

     The major particulate matter in automotive exhaust is reported to be
lead II bromide chloride (PbClBr),          but other chlorine-containing solids

have also been identified,  such as the ammonium lead II bromide chloride
complexes (2NH  Cl'PbClBr and the alpha and beta forms of NH Cl»2PbClBr).
                4                                             4
Average data from two vehicles operating both on a city driving cycle and at a

constant 60 mph indicate the following product distribution (the calculated

chlorine:lead weight ratio for each compound is also shown):

                                         wt %       ClrPb (wt)

                PbClBr                    48         0.171:1

                NH  Cl'ZPbClBr           45        0.257:1
                2NH   Cl'PbClBr             7        0.513:1

The composite chlorine:lead weight ratio in  the particulate-product mixture is

then calculated to be 0. 234:1.  If all the lead used in antiknock additives, about

232, 900 tons,  is converted during combustion to those three compounds, the

amount of chlorine in the mixture would be 54, 500 tons.   The remaining chlorine,

about 25, 150 tons, would then conceivably be emitted as about 25, 870 tons  of

hydrogen chloride. This is the maximal amount of hydrogen chloride that

could be  emitted from the combustion of motor gasoline in the United States.

The quantity actually emitted is probably much less.  It seems reasonable  to

assume that other chlorides may be formed,  such as lead dichloride and ammonium

chloride, as well as hydrocarbon chlorides, thereby reducing the amount of

hydrogen chloride. It is also probable that a small amount of the hydrogen

chloride  ends up in the crankcase oil.

     In comparison with the maximal calculated hydrogen chloride emission of

25, 870 tons,  Gerstle  and Devitt estimated that gasoline combustion may have

contributed only 4, 500 tons of hydrogen chloride in 1969,  or only about 0. 5%
of the total from all combustion processes.      These authors also indicate

that gaseous chlorine does not result from combustion. In any case, hydrogen

chloride  emission from mobile  sources will decrease in future years, as the

lead content of gasolines is decreased.

      Some indication of this reduction can be obtained from Figure  2-1, dis-
 played     by William Ruckelshaus,  former EPA Administrator.  The figure

 demonstrates that mobile-source lead emission will decrease drastically,  as

 the use of unleaded gasoline increases owing to catalytic emission control

 system requirements (top curve).  If,  in addition, EPA imposes phased reduction

 of the average lead content of all motor fuels,  the overall lead emission reduc-

 tion would be even faster (bottom curve).

      Concurrent with the reduction in mobile-source lead emission  is the obvious

 reduction in  chlorine-compound  emission. The EPA estimates that about 200, 000

 tons of lead will be emitted in  1973 from mobile sources.  This is equivalent to a

 maximal hydrogen chloride emission of about 22, 000 tons.  The maximal hydrogen

 chloride emission from  1973 to 1985 would be reduced in proportion to the  reduc-

 tion in lead emission shown in Figure 2-1. For instance, with lead reduction

 only through the phasing in of lead-free gasoline, maximal hydrogen chloride

 emission will be less than about 10, 000 tons/year by 1978 and less than about

 5, 000 tons/year by 1982.  If, in addition,  EPA imposes the phased reduction

 of the average  lead content of all gasolines (as  shown in the figure),  maximal

 hydrogen chloride emission will be less than about 10, 000 tons/year by 1976

 and less than about 5,000 tons/year by 1978.

 Automated-Mission Spacecraft

      The NASA Office of Space Science Launch Vehicle and Propulsion Programs

 is responsible  for the launch of approximately  20 automated spacecraft per year.

 These spacecraft  contribute in a variety of ways to the control and betterment

 of the environment (e.g., meteorologic satellites).  However,  adverse environ-

mental effects  might result from these activities with respect to air quality,

water quality,  noise, and reentry of  launch-vehicle debris.   No chlorine emission

 to the atmosphere in association with rocket tests, launches, on-pad accidents,

 or in-flight abort  situations has been observed  or postulated.


    0 -


    20 -


tj   40-

c   50-

§   60-



    90 -

                                                                    r 200
                                     Lead Free Reductions Only
                 Lead Free
                 and Leaded
             73   74  75  76   77  78   79  80   81   82   83   84   85

FIGURE 2-1.  Projected reductions in lead emission resulting from EPA
lead regulations.

     A 1973 final environmental statement of NASA OSS launch vehicles and

propulsion programs indicates that environmental pollution by these vehicles
appear to be very low.       This conclusion  is supported by Table 2-2 (from

the final environmental statement), which compares various emission sources.

No significant impact is expected from normal current and planned NASA space-

craft activities.  The possible effects of some kinds of accidents or flight failures

involving Titan vehicles may be  of marginal  significance.

     In a summary of environmental impact, it is indicated that:

         1.  In normal launches, effects are limited to the immediate

             vicinity of the launch pad.

         2.  In accidents or abort situations,  a  limited area -within the

             facility boundaries is possibly subjected to hydrogen

             chloride  concentrations above  the public exposure limit,

             if there is an on-pad fire or an abort  of a Titan III E/Centaur

             or  Titan  III C.  No significant  effects  are expected for other


         3.  In development and testing, no significant environmental

             effect is  produced. The Titan  III E/Centaur (in development)

             and the Titan II C  (operational) are NASA's largest vehicles

             in terms  of quantity of propellant,  total vehicle mass, length,

             diameter, and thrust at zero altitude.  Table 2-3 summarizes

             the estimated maximal radius  of ground-level effects for

             Titan HI  E/Centaur or Titan III C.  Table 2-4 lists the re-

             ported and estimated human, plant, and animal exposure

             criteria used to estimate the environmental impact of pro-

             pellant and combustion-product air pollutant emission that

             might arise from normal and emergency NASA OSS launch

             vehicle and propulsion program activities.


                                   TABLE 2-2

             Comparison of Emissions into the Lower Atmosphere*

                        Emission, 10  kg/year	
                        CO        NO         HC1       SO       Ash
	x	2	

NASA Launch Vehicles

    for automated
            (a)                                                          (d)
    missions            0.414     0.00014    0.060                0.11
            (b)                                    (c)
Automobiles           56,200     5,720       4.1
             (b)                                     (c)
Power Plants               90     3,200         610      13,400   4,400
                  (b)                                (c)
Trash Incineration      6,890       450         180
Jet Aircraft               270       90
   Based on first stage propellants,  1969-1971 average.
   For 1966.  Source:  "The Federal R&D Plan For Air-Pollution Control By

   Combustion-Process Modificaton",  January ,  1971,  PB  198-066.
   Estimates from Gerstle and Devitt,  "Chlorine and Hydrogen Chloride

   Emissions and  Their Control",  Paper No.  71-25, Air Pollution Control

   Association,  1971.
    Al  0  from solid propellants.
      2  3
                                                           o c c
 *R,eprlnted from National  Aeronautics, and Space Administration,

                                   TABLE 2-3

       Summary of Estimated Maximum Radius of Ground Level Effects for

                         Titan HIE/Centaur or Titan IIIC *
 Normal Launch

 Cold Spill

 On-pad Catastrophe

 Low Level Destruct

 Engine Test
Maximum Radius
at which Exposure
Exceeds Criteria


Criteria Not

Criteria Not

Criteria Not


N  O
  2  4






 *Reprinted from National Aeronautics and Space Administration355.

**For uncontrolled populations.  Criteria for normal operations assumed for

  normal launch and engine test.  Emergency criteria used for accidental



Controlled Populations'8' Uncontrolled Populations '^'




NO (N 0 )
L i*

TLV. 1C)





Short-Term Exposure from Emergency Plants
10 min.





Limits (5), ppm Ordinary Operations, ppm Exposure, ppm Sensitive
30 min. 1 hr. 10 min. 30 min. 1 hr. 10 min. 30 min. 1 hr. (1)

20 10 4 2 2 — 125 (8) 500/-<49)(;1)

25(9> - -
20 10 l l 3<« 2 2.5/2<1A>

20 10 1^8) _-_ <25/4^'^^

50 30 O.S^8^ — <31/4^51^
(jj (a) Controlled populations consist of persons with known medical histories, subject to periodic health checks,
"•* under the control
of the res
ponsible agency. Such persons are normally employees with jobs that will poten

1000/1 (14)


1000/1 (1A)



and generally
tlally result

Human exposure criteria are
normally based on experimental
animal exposures using a number
of species and considering the
most sensitive species tested.
Hence, human exposure criteria
are probably applicable to most
animals. Birds could be an
exception as they are rarely
used as test animals.

     in exposure to known contaminants.
(b)   Uncontrolled populations consist of persons with unknown medical histories, not subject to periodic health checks, and
     not generally controlled by the responsible agency.  The general public is included in this classification.
(c)   No short duration exposure criteria for controlled populations appear applicable for ordinary launch operations.
     Threshold Limit Values (TLV) are time-weighted concentrations for 7 or 8 hour work days and a 40-hour work week,
     except that the values for HC1 and N02 are also considered ceiling values not to be exceeded. '*'  TLV18 are thought
     to be conservative for short duration exposures of controlled populations for relatively infrequent normal operations.
(d)   While there are no criteria for short-term exposure of uncontrolled populations to HCL which have official standing,
     the values quoted here have been proposed by a responsible organization after careful study of the problem (See Reference 6)
(e)   Based on 1.5% Carboxyhemoglobin  in 1 hour exposure.  See Reference 7.
(f)   There are no officially accepted criteria for short-term exposure of uncontrolled populations to nitrogen oxides.
     The criteria given here have been proposed by a responsible organization after careful study.  (See Reference 10).
(g)   Arbitrarily set equal to the 8 hour Industrial TLV: i.e., 1/48 of the acceptable Industrial dose.
(h)   Based on hydrolysis to HC1.  In subsequent discussion, AlCl-j is considered only in terms of its contribution to overall
     HC1 levels.
(1)   Concentration in ppn/exposure tisse in hours.
(J)   Epinastic response In tomatoes.  Toxic  response (leaf abscission) generally observed at -1Z CO for 1 to several days.
(k)   No observable effect on Nephrolepls in an exposure of 1 to several days.

                (Reprinted from National Aeronautics and Space Administration;  5 reference numbers pertain to
                    references In original publication.)

      The final environmental statement concludes that hydrogen chloride emis-

 sion from the Titan vehicles represents  the only environmental hazard of signifi-

 cance.  It concludes that this hazard is modest; even under unfavorable meteoro-

 logic conditions, it is assumed to be confined to controlled areas.

      The final environmental statement assesses the environmental effects of

 operations involving the current and near-future launch vehicles that will be

 used up to about  1980.  The Space Shuttle, which is intended to replace most

 of the current family of launch vehicles and is expected to be operational by

 about 1980,  will use a main engine propellant consisting of a mixture  of liquid

 hydrogen and oxygen; the propellant will produce only water vapor and free
 hydrogen from the  combustion process.



      In the chlor-alkali industry,  emission of chlorine originating from blow

 gases, tank-car blowdowns, air-blowing of mercury-cell brine, and air-padding

 of liquid-chlorine storage tanks can be prevented or controlled by using the

 chlorine so  produced for  chemical requirements -within the plant; neutralizing

 the chlorine in alkaline scrubbing units to form disposable, nonvolatile sub-

 stances, such as calcium and sodium hypochlorites; or scrubbing the  chlorine

 from the gas streams with a solvent like water, alkaline brine,  or carbon tetra-

 chloride and recovering the chlorine.

      The principal emission from chlorine manufacture is the chlorine present

 in the noncondensable gases that are separated from  liquid chlorine during lique-

 faction.  If  liquid chlorine is not produced (as in a paper mill plant), the plant

will have  no blow gas and therefore no chlorine emission from this source.

Where liquid chlorine is produced, emission varies according to the -waste

treatment system and the chlorine content of the blow gas.  Table 2-5 shows

the concentrations and amounts of chlorine that may be emitted with or with-

out control system.

                                   TABLE 2-5

               Chlorine Emission from Liquefaction Blow Gases
                   in Diaphragm- and Mercury-rCell Plants
                                                Chlorine Emission Factor,
   Type of            Chlorine  Concentration    lb/100 tons of chlorine
   Control	    in Exhaust, vol %	    liquefied	
   None                       20-50                    2,000-16,000

   Water absorber           0.1-4.5                      25-1,090

   Caustic or lime             0.0001                        1

      It is  common practice to operate at condensing pressures and temperatures

that represent an economic optimum.   If chlorine in the blow gas will not be used

and chlorine must be neutralized, it is economical to condense at higher pressures

or lower temperatures,  or both, to reduce the chlorine in the blow gas.  If useful

byproducts can be made  or the chlorine in the blow gas is recycled or recovered

in some other manner, it is usually more economical to allow the chlorine con-

centration  in the blow gas  to increase in lieu of operating at relatively high

pressures  or low temperatures,  or both.  The quantities of chlorine in blow

gas are increased by operating above  cell rated capacity when the chlorine con-

densing facilities are adequate only at rated capacity and by having air in the

system on  startup of a new cell circuit or after a shutdown, which seriously

reduces the liquefaction  efficiency.
a.                                           87
 Derived from Cooperative Study Project. . . .

      Table 2-6 summarizes present practices for the treatment of chlorine

in blow gas as  reported in 24 questionnaire responses.

                                  TABLE 2-6
                       Processing of Blow-Gas Chlorine

       Process Used	                No. Plants

       Sent to  alkaline scrubbing equipment                       7

       Sent to  absorptive scrubbing equipment                    4

       Vented  to atmosphere                                     0

       Sent to  in-plant processes                                 11

       Not indicated                                              2

                  Total                                           24

      Tables 2-7 and 2-8 give emission and operating data from chlor-alkali

establishments using blow-gas treatment.  Table 2-9 gives data on handling

chlorine from shipping-container vents during loading, as  reported in 19

questionnaire responses.  In all  cases except two, chlorine removed during

tank-car loading was transferred to other plant uses, returned to the process,

or treated in a  scrubber.  In the two exceptions, collection was not complete,

and chlorine was vented  at 10 and 140  Ib/day.

      In-Plant  Utilization of Chlorine-Containing Blow Gas or Waste Gas in the

Chlor-Alkali Industry.  Waste chlorine has been used to  manufacture chloro-
         150                                        460             273
benzene,     hydrochloric acid,  sulfur monochloride,      and bleach.      It has

also been used  to chlorinate river water to prevent algae buildup  in cooling
towers and to treat waste water before discharge.
 ^                                           87
 Derived from Cooperative Study Project. . . .

                                                           TABLE  2-7

                             Emission and Operating Data  from  Chlor-Alkali
                                Establishments using  Blow-Gas  Treatment
                                                                              Plant number
Chlorine production, tons/day 490
Liquid chlorine capacity, tons/day 370
Cell typed
Description of control equipment

Tower diameter, in. OD
Height of packing, ft
Type of packing

Materials of tower construction

Sources of inlet chlorine

Scrubbing liquor and strength at test, % by
Liquor circulation rate, gal/min
Liquor temperature, °F
Scrubber pressure drop, in. H2O
Inlet rps rate, sclm at 32° F, 1 atm wet
Outlet gas rate, scfm at 32° F, 1 atm wet
Inlet chlorine concentration, vol %. wet
Outlet chlorine concentration, vol %, wet
Inlet carbon dioxide concn., vol %, wet
Outlet carbon dioxide concn., vol %, wet
Chlorine mass efficiency, %
Chlorine emitted, Ib/day
Chlorine emission factor, Ib chlorine/100 tons
chlorine liquefied
Stack plume opacity, %
M and D
Two milk-oHime
falling film towers
None; 4-in. standard
pipe launderer
Concrete sections

Blow gas, process
Two caustic-packed
towers in parallel
2-in. Intalox saddles and
ceramic tiles
Titanium-lined steel

Blow gas. brine blowing.
btowdown, tank car ! process blowdown, tank


car venting
4 and 17





Packed-tower water absorbed under

Alternately stacked

1-and 1-1/2 in.
Intalox saddles
Rubber-lined steel

Blow gas only










Two milk-of-lime cascade
baffle towers in parallel
None; 3-ft overlapping
Hetron, glass-matte rein-
Blow gas,*1 cell end boxes.

tank car vents

112 200
3.5 2

1.1 201
13.1 ! 1.41


•Based on sampling by the Public Health Service.
"Actual liquid production at time of test was 195 tons/'
 day. Production changed to 180 tons/day to agree with
 total chlorine in blow gas/100 tons chlorine liquefied for
 tests 2, 3, and 4 performed at a later date.
c Liquid production based upon absorber chlorine load.
dD = diaphragm; M = mercury.
elnside diameter.
'Height of tower*, no packing employed.
BAfter scrubbing in alkaline brine.
hNot measured.
'Combined exhaust rate from both stacks.
'Calculated by material balance.
''Not detected.
'Foaming present in scrubber.
m Determined by extrapolation.
"Exhaust sent to powerhouse stack.
°No observation.
      (Reprinted from  Cooperative  Study Project.

                                                  TABLE 2-8

              Questionnaire Emission Data from  Chlor-Alkali Plants  with

                                    Blow-Gas  Treatment Equipment

Type of cell
Rated capacity, tons/day
Scrubbing liquor

Liquor flow, gal/min
Inlet liquor conditions
Nominal Cl Concn., g/liter
Temperature, °C
Outlet liquor conditions
Nominal Cl concn., g/liter
Temperature, °C
Tower diameter, in.

Height of packing, ft

Type of packing

Materials of construction

Inlet gas temp., °C
pressure, psig
chlorine, vol. %
Outlet gas temp., °C
pressure, psig
chlorine, vol. %
Outlet gas flow, scfm
Efficiency of scrubber, %
Total chlorine emitted.
Plant number
5% NaOH ; 5% NaOH






Rubber lined

tons/day ; nil
Lb chlorine emitted solidus j
100 tons of liquid






























0 : 0
0 * 0
180 ' 390

' N.D.

1, -

12 13
1 14
260 130 112
Ca(OH)] i Na(OH) | Waste
; alkali'

73 50

10 0 0




28 30


40 35
72 i 72

Chemical ! 8- x 12 in.
stoneware . clay
rings ; tile

Concrete Concrete Concrete
40 3 35 to 40
0.14 15
1 15 7
32 40 i 30 to 35
0 0 ! N.D.k
600 120
100 100








50 i




22 25«












Berl saddles



 •Design data.
 bD = diaphragm; M = mercury.
 CAII output is liquid CI2.
 dLiquid Clj product » 308 tons/day.
 'Reported use of vats containing Ca(OH)] slurry.
 'NaOH. NaHCOj.NajCOj.
9Not applicable.
kNot detectable by odor.
'Water absorber vented to caustic scrubber; chlorine emissions reported as zero.
(Reprinted  from Cooperative Study Project. ...     )

                                         TABLE 2-9

      Questionnaire  Data  on Handling  of Chlorine from Shipping-Container

                                   Vents During  Loading
                                                    Plant number

Rated capacity.
Liquid capacity.
tons/day Cl,
Quantities of Clj.
trorn tank car
loading, tons/day

Frequency of tank
car loading,
no. /day
Tons of chlorine
tank car loading

Tons of chlorine
evolved/ 100 tons
of chlorine

Treaiment of tank
car waste chlorine:

















































8 9

180 50
a a

2.0 0.25 to

a 1

0.25 to

1.1 0.5 to

- X












1 to 2


1.3 to

. X









































































bPer week.
"8-hr day.
(6-hr day.
h 0.5% vented = 10 Ib/day.
'140 Ib/day vented.
 (Reprinted from Cooperative Study Project. ...    )

      Absorption of Chlorine without Recovery.  Alkaline scrubbers that use

 caustic or lime to react with waste chlorine to form sodium and calcium

 chloride and hypochlorite are suited for treating dilute tail  gases (less than

 1% chlorine).  When chlorine concentrations are higher several percent--

 other control methods that permit recovery of pure chlorine are more attractive

 economically.  Absorption efficiencies of nearly 100% are attainable in alkaline

 scrubbers at modest equipment cost.  Waste chlorine  in the blow gas from the

 liquefaction system and that originating from the air-blowing of depleted brine

 and other sources are generally combined and sent to  a packed tower using

 caustic liquor or a spray tower using a lime slurry.  Recent developments in

 improved scrubber design include the use of high-density polyethylene or poly-

 propylene packing shapes and the increase use of fiber-reinforced plastics

 (FRP) to replace stainless steel,  rubber- and polyvinylchloride-lined steel,
 and other metallic alloys for scrubber bodies.

      Both reactions that can be used to remove chlorine  in alkaline scrubbers,

                     ZNaOH + Cl 	> NaCl + NaOCl  + H O
                                 2                       2

 and                  2Ca(OH)  +  2C1 	^ Ca(OCl)  + CaCl + 2H   0,
                             22             222

are exothermic, proceed rapidly  to completion,  and are irreversible over a
wide range of concentrations, if high temperature  and  low pH are avoided.

      Seven of the 24 plants  that responded to questionnaires in  the  cooperative
 study cited previously   use alkaline  scrubbers  to control blow-gas emission,

 and the absorption efficiencies exceeded 99% in all of them (Table 2-8). Source

 tests were performed  on two lime scrubbers and one caustic scrubber.  Absorp-

tion efficiencies of 99% or higher  and  exit chlorine concentrations of less than

 10 ppm in the vents were found in all three cases.


      Alkaline  scrubbing systems are used extensively in the chemical process

industry,  to remove chlorine from chlorination process tail gases being emitted

to the atmosphere.  Alkaline scrubbing normally takes place after organic or

inorganic chemical removal, such as condensation,  solvent scrubbing,  or water

scrubbing for hydrogen chloride absorption.

      The formation of hypochlorites in waste chlorine gas  neutralization by

alkaline media creates a pollution control problem within the plant confines and

with respect to external receiving waters.  If the hypochlorite is riot decomposed,

chlorine gas will be released on contact with acid streams.  To eliminate the

hypochlorite disposal problem, the hypochlorite is decomposed in the scrubber

with heat and a low concentration of metallic ion  catalyst (Hooker Chemical

Corporation, private communication).  The hypochlorite ion is decomposed to

innocuous chloride ion and oxygen:

                                     A   >       .   2
                          OC1~  catalyst"  Cl~+-| 0

      Recovery of Chlorine by Absorption and Stripping.  In contrast with

scrubbing systems that involve neutralization and disposal of chlorine,  various

absorption techniques  can be used to recover waste  chlorine.  This is especially

useful where high chlorine concentrations (greater than 10%) favor economical

recovery.  Such systems contain an absorber to remove chlorine from the gas

stream  and a stripper to recover the absorbed chlorine  from the rich absorbing
liquor.  Collection efficiencies are generally better  than 90%.

      Blow-gas columns using water for absorption  are  particularly useful in

some diaphragm-cell chlorine plants.  A cooler-stripper is integrated into  the

main cell chlorine purification system. Cold water  is passed  counter currently

to the chlorine-containing gas stream in an absorption tower filled with ceramic

packing.  Overhead gases, too low in chlorine for its economical recovery, can


   sent to alkaline scrubbers or discharged to the atmosphere.   Bottoms from

the tower,  rich in dissolved chlorine,  are  sent to a desorption tower consisting

of a direct-contact cooler and a steam-stripping section.  Hot chlorine-cell gas

is used to strip the chlorine partially from the cold water while the cell gas is

simultaneously cooled.  The remaining chlorine is removed by direct contact
with live steam.  One such process is  described in detail in a patent.

      Two diaphragm-cell chlorine plants indicated use of water absorbers in
response to a questionnaire.     One of these, having an exit chlorine concen-

tration of 3%, directs vent gases to a caustic  scrubber that virtually eliminates

chlorine emission to the atmosphere.  The other uses an absorber designed to

give an absorption efficiency of 97%, corresponding  to an inlet-gas chlorine

concentration of 11% and  an exit-gas chlorine  concentration of 0. 3%.  If vent

gases are considered to contain chlorine in excess of allowable limits, ab-

sorption efficiencies as high as 99.4%  can  be  obtained at a somewhat higher

cost--the cost of steam used in stripping.  As an alternative, a secondary

water scrubber can be used, with the water effluent  sent to disposal.  In any

event,  it is good practice to provide an alkaline scrubber for emergency use,

in case  the chlorine in the vent gases becomes excessive.
     Oldershaw ^Jb aL      have described  a system for the thermal stripping

and recovery of chlorine  from 32% hydrochloric acid produced in an absorber

handling a feed-gas stream containing  75 mole % hydrogen chloride,  15 mole

% chlorine,  and 10 mole % inert substances.

     Another type of blow-gas absorber uses carbon tetrachloride as the
solvent to recover chlorine from gas streams.    Carbon tetrachloride con-

tacts the waste chlorine in a packed tower and releases it in a steam-heated

recovery tower consisting of a stripping section and a rectifying section.    One
questionnaire response   indicated that chlorine  recovery in the absorber is

nearly 100%.  Stern     indicates that the recovery of chlorine is much more

nearly complete when carbon tetrachloride,  as opposed to water, is used as the

      An unpatented process   uses sulfur monochloride to recover waste

chlorine through formation of sulfur dichloride in an absorber.  Chlorine can

be distilled from the  dichloride and recovered, or the mixture of sulfur mono-

chloride and dichloride can be marketed.
                                                        82                  231
      Patented systems include those using alkaline brine,    stannic chloride,
                     392                         264
hexachlorobutadiene,      and ethylene dichloride.       The cited cooperative
study   concludes that the alkaline brine system is used in mercury-cell  plants

to some extent,  but that the other three  systems have no commercial significance.

      Adsorption Systems.  A patented recovery system uses  silica gel to
adsorb chlorine from waste streams.      In a regeneration cycle,  the ad-

sorption zone  containing silica gel with chlorine adsorbed thereon is subjected to

reduced pressure,  thereby desorbing chlorine and permitting  its recovery.

Thereafter, at least a portion of the previously recovered chlorine-free gas

stream from the adsorption cycle is passed  through the desorbed silica gel to

strip the final traces  of adsorbed chlorine.  The recovery system is claimed

to provide chlorine recovery efficiencies of  90-98% from noncondensable  gases

originally containing  chlorine in concentrations below about 15%.  Chlorine can

also be removed from very dilute gas  streams with activated carbon.  The

carbon can be reactivated by hydrogen gas at nominal pressure and  temperature,

forming hydrochloric acid,  which can be readily absorbed in water.

Hydrogen Chloride

      It has been indicated that the byproduct process accounted for 90% of the

U.S. hydrochloric acid (100% basis) production in  1972.  The hydrogen chloride

is produced as a result of substitution chlorinations of organic compounds

and the dehydrochlorination of saturated chlorinated compounds.

     The use of anhydrous hydrogen chloride in hydrochlorination and oxy-

chlorination reactions has dominated the use of hydrochloric acid (100% basis)

in the production of organic chemicals in recent years. In processes using

hydrochlorination (except hydrochlorination of alcohols) or oxychlorination,

hydrogen chloride leaving  the primary reactor is not absorbed in -water, but

is passed through an indirect-contact condenser for removal of condensable

organics before the hydrogen chloride and noncondensable organics are re-

cycled to the process.  Hydrogen chloride is emitted only in the purge that

removes inert materials from the recycled-gas  stream.

     Tail-gas  concentrations of contaminants emitted from a typical byproduct

plant are often reduced by scrubbing in a packed tower behind the final process

tower.  Venturi scrubbers are also used occasionally.  If hydrogen chloride

is the only component to be removed, water is universally used as the scrubbing

agent,  as  shown in Table 2-10.  Water  scrubbers can reduce hydrogen chloride

concentration  to less than  0. 1 Ib/ton of acid produced.  Alkaline  scrubbing is

sometimes used, if the gases contain substances like chlorine or phosgene,

which are not  readily absorbed in water.

     Removal  of organic materials from exhaust gases poses a separate

design problem for each specific compound.  In the chlorination of benzene,  the

hydrogen chloride from the reaction is scrubbed with recycled benzene  for

hydrocarbon removal and then absorbed in water forming 20 Be hydrochloric

acid (31.5%  hydrogen chloride).  A tail-gas absorber  is also used,  and the
major air pollutant is benzene.    In the chlorination of methane to form carbon

tetrachloride, the reactor  effluent containing organic chlorides, hydrogen chloride,

excess methane,  and traces of chlorine is  cooled and fed to  the hydrogen


                                      TABLE 2-10

     Emissions from By-Product Hydrochloric  Acid Manufacturing Plants^




BP 11






tons per day



















Exit gas conditto if


























Water jets on
storage tanks
Water scrubber
Caustic sciubber

Water scrubber
back up
Phosgene decom-
position towers
Fume jet

Closed system

Closed system
Na3COj scrubber
Caustic scrubber

Water scrubber

Water scrubber

None for HCI,
CCI, scrubber
for chlorine
Substances other
than HCI entering
Air, hydrogen, carbon
monoxide and dioxide
Trace Inerts
Air. carbon dioxide

Air, benzol

Nitrogen and Phosgene

Water vapor

Air. organic]
Methane, nitrogen.
Chlorine, R Cl
Nitrogen, traces of


carbon dioxide

Pounds HCI .mined
per ton of 20° 84
acid produced"








NA not ivailibl*.
    *Rtpmentl 0.6 percent HO or li
    "^ntad Vry PHS s*mp
recovery system.  The first column in this system is an absorber designed

for efficient hydrogen chloride removal.   The bulk of the absorbing liquor

is the azeotrope in the hydrogen chloride-water system (about 20. 24 wt %

hydrogen chloride).  The rich acid is thus above the azeotrope and allows

stripping of anhydrous hydrogen chloride.  The second column distills  off

the anhydrous hydrogen chloride for other uses and produces,  as a bottoms

product, the azeotrope required for the first column.  The gases from the

absorber are washed with caustic soda to remove final traces of hydrogen
chloride and are  then ready for recovery of organics.    In the production

of trichloroethylene by the chlorination of acetylene to tetrachloroethane  and

then the  dehydrochlorination of  tetrachloroethane to trichloroethylene,  the

hydrogen chloride, the trichloroethylene  main product,  and the unconverted

tetrachloroethane from the dehydrochlorinator are fed to a stripping column,

where hydrogen chloride  is stripped-off overhead and absorbed in water to

form hydrochloric acid.  A tail-gas absorber is installed after the hydrogen
chloride absorber for final process emission control.
     Oldershaw et a_L     describe and give a flowsheet for a system designed

to make  32 wt % hydrogen chloride from gases containing chlorinated hydro-

     A study prepared for the Office of Air Programs of the EPA   contained

the following general conclusions: Chlorination processes are usually designed

to give high-efficiency containment of potentially hazardous emission of chlorine,

hydrogen chloride, and chlorinated hydrocarbons within the process.   They do

not always have control equipment installed exclusively for the purpose of

preventing emission, but typically they have gas-cleaning devices to collect

unreacted gases and vapors, so that they can be recycled to the process.  The

cost and the obnoxious character of the materials provide incentives for high-

efficiency (over 95%) cleaning of the exit  gases.   The collection methods are


condensation, adsorption,  and absorption.  Condensers and solid adsorbents

are generally used to collect materials for recycling to the process.   The

data available on adsorption are  sparse,  but metal oxides, molecular sieves,

silica gel,  activated carbon, and alumina have been used.  The adsorbent is

used to collect and concentrate dilute components in exit gases.  Absorption

systems are most commonly used for final gas-cleaning.   Scrubbing  liquids

include water, caustic solutions, lime and  limestone slurries, carbon tetra-

chloride, sulfur monochloride, benzene,  and toluene.  Where high-efficiency

scrubbing is practiced with organics,  absorbent losses will be the main

atmospheric pollutant--e. g. ,  where toluene or  benzene is  used to clean emis-

sion from equipment handling phosgene.  Generally,  because of the cost, such

systems are used only for very hazardous materials.

     Byproduct hydrogen chloride plants  are adjuncts to other processes;

therefore,  they may be affected by upsets that occur in the process in which

the hydrogen chloride is evolved.  Good controls and secondary scrubbing

systems can reduce the possibility of increasing emission  resulting from such

     The design, operation, and  maintenance of direct hydrogen chloride syn-

thesis plants results in no significant emission  of hydrogen chloride.   During

startup and shutdown,  it is possible for chlorine and hydrogen chloride to be

released into the air.  Normally, an inert purge system is a part of the control

system, and any chlorine, hydrogen, or hydrogen chloride present in the system
is purged through the  absorber-cooler and tails tower before a shutdown.

Other control and safety devices  include automatic shutoff  valves and seals

on inlet gas lines, flame sensors,  and ignition devices on the outlet duct to

prevent the delivery of an  explosive mixture of  gases,  instead of hydrogen


       There are three basic methods of controlling atmospheric  emission from

  Mannheim furnaces:   proper operation, an efficient emission collecting system,

  and effective maintenance.  Proper operation assumes good design  and  results

  in maximal product  recovery,  thus reducing the possibility of  hydrogen chloride

  emission.  An adiabatic  wet-scrubbing tower that uses hydrochloric acid has

  had good results in scrubbing and cooling furnace gas.   To reduce atmospheric

  emission, a scrubber system can be installed on the tails-tower exhaust.

  Scrubbers used for  this  purpose include venturi scrubbers and  packed  water-
  scrubbing towers.

     The most widely used hydrogen chloride absorption unit is the falling-film

system.   It consists  of a falling-film cooler-absorber and a small packed tails
       196, 263
tower.          The  gases and the absorbent, which is usually weak acid,

enter at  the top of the absorber,  and the hydrogen chloride is absorbed in the

liquid wetting the inside of the  tubes.  The absorption is limited by the number

of tubes,  which determines the amount of wetted area available for absorption

and cooling.  After passing through the falling-film absorber, the  gases pass

through a tails tower, where the  remaining portion of the hydrogen chloride

is reduced to less than 0.  5% of the exit gas.  Fresh water, used as the

absorbent, is fed to the tails tower,  and a weak acid  feed to the top of the
falling-film unit is the product.    A falling-film absorption system is shown

in Figure 2-2.

     The falling-film absorber's greatest virtue is its ability to produce strong

acid (37-40%) without detectable vent loss.  On the basis of equipment cost and

technical factors--including desirable liquid loadings, feed-gas hydrogen chloride

concentration,  overall heat-transfer  coefficients,  and desirable gas  velocities

in the packed tail-gas scrubber--good engineering design indicates that the tail-

gas scrubber should  handle about one-third of the hydrogen chloride  gas fed to

                                                        FRESH WATER IN
                                                          INERTS OUT
                                                          TO ATMOSPHERE
                                                           TAILS TOWER
                                                              GAS FLOW
                                                               WEAK HYDROGEN
                                                               CHLORIDE GAS
                                                               FROM FALLING
                                                               FILM ABSORBER
                                                               TO TAILS TOWER
                        PRODUCT OUT
FIGURE 2-2.  Falling-film absorber with external piping and  tails  tower.

 the cooler-absorber plus all the inert substances if -water is the absorbent.

 If 20% acid is the absorbent, the tails tower will have to scrub only one-

 fourth of the hydrogen chloride plus all the inert gas entering the cooler-

     In recent years,  systems of falling-film absorbers have been used for

 recovering hydrogen chloride from gases as dilute in it as about 5-10%.  This

has been accomplished by increasing the mass-transfer  surface, adding one or

 two absorbers, and increasing the length of the tubes.  Another method is to

 raise the total pressure on  the system and  thus increase the partial pressure
 of hydrogen chloride in the  feed gas and improve the driving force.

     For design of industrial equipment, Gaylord and Miranda    have pre-

 sented equations for correlating the mass-transfer  coefficient for hydrogen

 chloride gas  in falling-film absorber-coolers.  Earlier work also covered
                                                                    89, 109
 correlations  for predicting  the performance of falling-film absorbers,

and mass  transfer in a commerical hydrogen chloride recovery unit has recently
been studied.

     The other common type of hydrogen chloride absorption system is the
                                      87, 232, 366
 so-called  adiabatic absorption  system.             Any  concentration of

hydrogen chloride in the feed gas can be accommodated by this equipment.

Acid strength up to 34% is easily made in adiabatic  systems.  Attempts to

produce stronger acid will result in rapidly decreasing absorption efficiency.

     The process is simple. Feed gas with hydrogen chloride is introduced

to the bottom of a packed contact tower, and the gas is counter currently con-

tacted by the absorbing medium, usually water.  Weak acid may be used

instead  of or -with water.  If weak acid is the sole absorbent, the efficiency

will range from 95% to more than 99%, depending on the  weak acid concen-

tration and the later hydrogen chloride vapor pressure.  If pure water is the

absorbing fluid, concentrated product acid  can be made,  with almost 100%
recovery of hydrogen chloride.

     Because "adiabatic" absorption (the process is actually operated at constant

temperature, rather than at constant enthalpy) is a hot  process, pure hydro-

chloric acid can often be produced from contaminated feed gases.  Byproduct

hydrogen chloride from chlorination operations contains small quantities of

chlorinated hydrocarbons.  If these compounds have relatively low boiling

points,  they will not condense in the acid, and a high-purity product is made.

However, compounds of high boiling point will condense and contaminate the


     Hydrogen chloride emission from the falling-film and the adiabatic ab-

sorbers may be effectively controlled by installing any of several types of

scrubbers after the  tails tower  (in the case  of the falling-film unit)  or after

the adiabatic tower  (in the case of the adiabatic unit).   In both types  of ab-

sorber  units, the maintenance at all times of liquid flow adequate to wet the

absorption surfaces is vital in reducing emission to the final scrubber.

     Packaged commercial systems are also available for production of

.reagent-grade acid  or anhydrous hydrogen chloride through distillation of

commercial-grade 31.5%  hydrochloric acid.  The spent acid from such units

is the azeotropic mixture (20. 24% hydrochloric acid).  These systems yield
no emission to the atmosphere,  because the manufacturing systems  are closed.

                                CHAPTER 3


      A recent survey prepared for the  EPA Office of Air Programs   con-

cluded that approximately 81. 0% of the chlorine produced in 1970 was used

in the production of chlorinated organic and inorganic products,  about 16. 0%

in the pulp and paper industry,  and about 3. 0% in water  sanitation.


      Table 3-1 lists 16 major products to which consumption of at least 1%

of the chlorine used in 1970 could be attributed.  Table 3-2 lists 12 products

whose manufacture required relatively minor  quantities  of chlorine.  Subtrac-

tion of the chlorine requirements for the five inorganic chemicals in these

lists (hydrogen chloride, phosgene, calcium hypochlorite, phosphorus tri-

chloride,  and sulfuryl chloride)  indicates a chlorine requirement for the

production of the remaining 23 organic chemicals of 67. 4% of the chlorine

produced  in 1970, leaving a 13. 6% requirement for the production of inorganic

chemicals and miscellaneous other organic chemicals.  For comparison,
Table 3-3 lists the 1965 estimated end-use distribution of chlorine.

      The 14 organic major products listed in Table 3-1 consumed an esti-
                                                               2, 190, 227
mated 64. 2% of chlorine production in their manufacture  in 1970.

The 23 processes involved  in the manufacture of the 14 products were  classi-
fied into five types,  as follows:

      Liquid-phase chlorinations at less than 100 C and near atmospheric

     pressure (generally,  addition reactions)--typical example:

           Cl  + C  H     90 C fr.  C H Cl  .
              2     24    7 psig W    24   2

                                 TABLE 3-1
                     Major Products from Chlorine
                                       Required Production of Chlorine,
                                       millions of pounds

Carbon tetrachloride, CC1
Chloroform, HCC13
Epichlorohydrin, C H OC1
3 5
Ethylchloride, C H Cl
2 5
1, 2-Dichloroethane, C H Cl
24 2
Allylchloride, C H Cl
3 5
Hydrogen chloride, HC1
Methylchloride, H CC1
Methylene chloride, CH Cl
2 2
Monochlorobenzene, C H Cl
6 5
Phosgene, COC1
Propylene oxide, C H 0
3 6
Tetrachloroethylene, C Cl
2 4
1, 1, 1-Trichloroethane, C H Cl
23 3
1, 1, 2-Trichloroethylene, C HC1














1, 500



2, 140







1, 340





7, 070

1, 550


1, 550


1, 650

2, 630

3, 580

2, 700

1, 820
2 3
Vinylchloride, C H Cl
2 3
Total chlorine production
Derived from Air Pollution from

4, 750
Chlo rination

13, 180
19, 500
4, 340

35, 980
45, 500


                              TABLE 3-2
                   Minor Products from Chlorine-

Ethylene oxide, C H 0
2 4
Chloral, C Cl HO
2 3
Dichlorobenzene, C H Cl
64 2
Benzene hexachloride, C Cl
6 6
Calcium hypo chlorite, Ca(OCl)
Chloroparaffins, (C -C )C1
10 30
1, 2-Dichloropropane, C H Cl
36 2








Monochloroacetic acid, C H O Cl 40
Pentachlorophenol, C Cl OH
6 5
Phosphorus trichloride, PCI
Sulfurylchloride, SOC 1
Vinylidene chloride, CH = CC1
2 2
Derived from Air Pollution from





2, 510
of pounds

— — _












of Chlorine,

— - _












Chlorination Processes.

                                   TABLE  3-3

               Estimated End-Use Distribution of Chlorine,  1965

End Use	                  Fraction of Total, %

Inorganic chemicals                                    9

Organic chemicals                                    65

Pulp and paper                                        17

Water and sewage treatment                            4

Miscellaneous                                          5

    Total                                              100
a                          140
 Derived from Faith et al.
      Hydrochlorinations at less than 200 C and at 40 psig (addition reactions)-

      typical example:

                     HC1 +  C  H    40 C      C H Cl.
                              2  4  40 psig^    2  5

      Vapor-phase chlorinations at over  500 C  and at 2-15 psig (generally,

      thermal substitution reactions)--typical example:

                      2C1   + CH    500 C      CH Cl   + 2HC1.
                          2       4   15 psig ^      2   2

      Vapor-phase dehydrochlorinations at over 600 C and at less than 60 psig

      (thermal cracking reactions that drive off hydrogen chloride)--typical


                      C H  Cl    900  C      CH  =CHC1 -f HC1.
                        24    2  50 psig       2

      Vapor -phase oxychlorinations at 300 C and 75 psig, namely:
      C  H  + 2HC1 + J._0    300 C          C  H  Cl   +H  0
        24           22  50-100 psig        242    2  .

      Some dual-step processes were included in only one classification,

      because the products of thedual-step reactions are the only ones on

      which there are production data.  For example, trichloroethylene

      is made by these two reactions:

                         2C1  + C  H  _    C H Cl
                            2     22              22   4

      and                C  H  Cl   _ C HC1   + HC1.
                           224           2     3

The first reaction is a mild addition reaction at 50 C and atmospheric pressure,

and the second is a thermal dehydrochlorination, carried out at about 600 C.

There are no production figures for tetrachloroethane; therefore, trichloro-

ethylene was placed in the fourth type, dehydrochlorination.

     Other aspects of the classification were the multiple reactions that can be

carried out with  one raw material.  Ethylene can be chlorinated,  chlorohydrinated

(with hypochlorous acid), or hydrochlorinated (with hydrogen chloride).

     Starting with the 23 processes involved in the  production of the 14 major

organic chemicals, and excluding three hydrochlorination processes for produc-

tion of methylchloride, ethylchloride, and vinylchloride (because no chlorine

is used or produced in any stage of the processes), we are  left with 20 processes
with a chlorine emission potential.  Of these 20 processes, the survey  lists

13 as having no chlorine emission factor (pounds of chlorine emitted per ton of

product).  Emission factors for the other seven processes were 0.0003 (for one

process,  chlorination of carbon disulfide),  0.001 (for two processes, chlorination

of ethylene and hydrochlorination of ethylene),  0. 002 (for two processes, chloro-

hydrination of allylchloride and then hydrolysis and chlorohydrination of

and then hydrolysis), and 20.0 (for two processes, thermal chlorination of

propane  to produce carbon tetrachloride  and thermal chlorination of propane

to produce perchloroethylene).  With two insignificant exceptions,  the emission

factors listed are estimates based on little or no census or experimental informa-

tion and  are average values for all sources using the processes in question.

In the two thermal chlorination processes listed as having a chlorine emission

factor of 20.0, the source of the emission is the purge stream for removing

inert materials on the dry chlorine recycle.  Impurities in the process  raw

materials require continuous purge, but  the processes are indicated to  have no

control system on the purge stream.

     In the manufacture of inorganic chemicals, much chlorine is required  for

the production of synthesis hydrogen chloride, metal chlorides  (including those
                                              437           425               402
of aluminum,  zirconium, silicon and titanium),     bromine,     hypochlorites,
          191                       496                  314
phosgene,      phosphorus chlorides,     sulfur chlorides,     and cyanuric
chlorides.      There are no quantitative indications in the literature that the

emission of chlorine is a problem  in these operations,  but it  should be noted

that, in general,  all emission from the processes must be carefully controlled,

because  of the hazardous nature of the products or of the other  raw materials

used.   Conventional vent-gas scrubbing devices based on water, alkaline solu-

tions,  or solvents are used for emission control in these processes.

Pulp and Paper

     The pulp and paper industry uses four basic techniques--acid chlorination

in dilute solution, alkaline hypochlorite bleaching,  caustic extraction, and chlorine

dioxide bleaching--in various combinations and sequences to bleach paper pulp and

to purify dissolving  pulps to obtain high concentrations of alpha-cellulose.   The

simplest bleaching sequences consist of hypochlorite only or  chlorination followed

by hypochlorite and  are used mainly for bleaching de-inked ledger stock and


de-inked stock containing some  ground wood.  The increased  demand for pulps

with higher brightness and equal or greater strength has led mills  to add a

chlorine dioxide  stage  (or stages) with or without a hypochlorite stage.

     Acid chlorination is almost always the first step in bleaching  wood pulp,
whether for paper or for chemical cellulose.       The treatment consists of

injecting the required quantity of chlorine  gas into the unbleached stock

(either  directly or through a water injector),  mixing chlorine and stock

intimately to ensure uniform treatment of  all fibers, and retaining the  slurry

until chlorine absorption is  almost complete.  Chlorination is usually carried

out in an upflow tower with a retention time of 60-90 min at the prevailing

tonnage  rates. Improved design of chlorine water injectors, in-line mixers,

and retention towers has been reported to  produce savings  in bleaching chemi-

cals,  either in chlorine for  chlorination or in hypochlorite  or chlorine dioxide
for later bleaching sequences.     Such improved design will reduce the

chlorine emission potential  from the chlorination step.

     Hypochlorite bleaching with either sodium- or calcium-base liquor is

now almost universally carried  out at high density in continuous towers--

either downflow or upflow.   Fully automatic,  continuous systems have been

developed for both sodium and calcium hypochlorite manufacture and offer

many major advantages,  including lower chemical costs due to complete
utilization of the chlorine added.

     In  1962,  five principal methods of generating chlorine dixoide from
                                                  372                       391
sodium  chlorate were in use throughout the world.      According to Rapson,

a delicate balance among the rates of three fundamental reactions--

                     HC10   + HC1	> HC10   + HC10,
                           3                         2

                     HC10   + HC10 	>  2C10  + H  0,
                           32                  22

                     and HC10 + HC1 	>  Cl   + H  0
                                                    2     2


determines the rate of production of chlorine dioxide and the ratio of chlorine

to chlorine dioxide produced.  Processes for chlorine dioxide generation

commonly use a final 3-4% sodium hydroxide solution for  absorption of the

chlorine vented from the chlorine dioxide absorption tower.

     Chlorine gas emission from pulp and paper mills can be controlled.  In

one Kraft mill bleach plant, waste gas discharges containing over 1 ton  of

chlorine per day were  combined and scrubbed with a 4% caustic solution,
with recovery of 96% of the waste chlorine as hypochlorite bleach liquor.

In another installation, chlorine (0.43 Ib/lb of chlorine dioxide) not  absorbed

in the chlorine dioxide absorber solution is absorbed in dilute sodium hydroxide

or injected into a flowing milk of lime solution to produce hypochlorite (the
choice depends on bleach plant requirements).

Water and Waste Treatment

     The utility of chlorine in water treatment is attributable to its  toxicologic

characteristics and its oxidative capacity.  Chlorine is used to destroy bacteria

and other microorganisms and to modify the chemical characteristics of the

water being treated.   The principles of water chlorination are highlighted in
Figure 3-1.

     An  important subcategory in water treatment is the use of the toxicologic

characteristics of chlorine  to  control fouling of heat-exchange surfaces with

biologic  material in fresh-water cooling circuits and to control adverse  growth
of marine fouling organisms in seawater cooling circuits.   White     states


     1.   All waters--fresh or salt--are capable of growing  slime

         on heat exchange surfaces.

      2.  All cooling water systems, whether for power stations, oil

         refineries,  or other industrial uses,  should be chlorinated to

         maintain the efficiency of the heat exchange  systems.

      3.  No microorganism can develop a chlorine tolerance.  The

         residual tolerance varies depending on the species.

      The utility of chlorine in waste treatment is attributable to its toxico-

logic characteristics,  its oxidative capacity, and its  adaptability as a coagulant.

The most important application of chlorine in  sanitary waste treatment is in dis-

infection; alteration of physical and chemical characteristics  is the most general

use for chlorine in industrial waste treatment. The principles  and practices of
the use of chlorine in -waste treatment are highlighted in Figure 3-2.
               293,294           512
      Laubusch          and White    have dealt extensively with the need to

consider chlorination equipment in the water and waste treatment as a total

system to include the following elements:

            Sufficient equipment for adequate dosage (dual, standby

            systems  should ordinarily be provided in community

            water supply operations to protect the public health).

            Proper rapid mixing at the point of application.

            Suitable contact chamber after  rapid mixing,

            giving a distribution of contact time approaching

            the ideal time of unity (ideal plug  flow).

            Continuous residual control of the chlorine metering

            equipment based on the amperometric method of  re-

            sidual determination.

             Final monitoring of residual chlorine at the end of

             chlorine contact time.

             Appropriate alarm functions to warn of malfunction

             in the total system and safety interlocks for automatic


     Although this publication lists a chlorine-emission accident in an

American filtration plant in 1969 that caused  two fatalities and a chlorine-

emission accident in an American swimming  pool in 1971 that was serious

(although it caused no fatalities), the dearth of  such reported incidents indi-

cates that emission of chlorine from water and waste treatment  operations

does not constitute a significant environmental  problem.


     Table  3-4 lists two estimated end-use distribution patterns for hydro-

chloric acid (100% basis).

                                   TABLE  3-4

          End-Use Distribution of Hydrochloric Acid (100% Basis)

End Use
Metals industry
Food -processing
Oil-well acidizing
of Total, %
a.                       140
 Data from Faith et _a_l.
b                            234
 Data from Chemical Briefs.



                                                     >.  '''''''
                                                      TOXIC IT y

                                                      • DESTROYS PATHOGENS
                                                      • CONTROLS NUISANCES
                                                      • REDUCES TASTES t, ODORS

                                                      • FORMS CHLORAMINES
                                                      • FORMS ORGANIC
                                                          CHLORAMiNES AND
                                                          AND SUBSTITUTION


                                                      • IRON (1C)
                                                      • MANGANESE (1C)
                                                      • NITRATE NITROGEN
                                                      • SULFATE
 FIGURE 3-1.   Principles  of water chlorination.   (Reprinted  with permission

 from Laubusch.   H)
                                         SANITARY AND
                                 INDUSTRIAL WASTES CHLORINATION
                             FOOO PROCESS/KG

                               EEfcT SUGAR
                               MEAT PRODUCTS
                               PACKING HOUSE
                               MILK PRODUCTS

                             METAL PROCESSING


                               OIL INDUSTRY
                                                         WASTE CONDITIONING
                                                          COOLING WATERS
                                                          PROCESS WATERS
                                                          ASTE TREATMENT
                                                          STREAM CONTROL

                               CCXE PL.ANT
                               DYE MFC.
                               GAS MFG.
                               PHENOLS 1 S.P

                            PULP AND PAPER

                               WHITE WATER


                               WOOL SCOURING
FIGURE  3-2.   Typical applications  of  chlorine in  waste  treatment for resource

conservation and pollution abatement.    (Reprinted with  permission from


It should be recognized that accurate national end-use consumption tonnages

for hydrochloric acid (100% basis) are difficult to estimate and that few of

the attempts at estimation are published.  Attempts to estimate end-use con-

sumption tonnages from reported production or shipment figures (including

interplant transfers) are  subject to error, because the reported shipment

figure for each year since 1947 has represented less than 50% of the  reported
production figure for the  corresponding  year.      In addition,  actual production

of byproduct hydrochloric acid (100% basis) is considerably in excess of what is
recovered and reported,     and the disposition of the unreported production

from  the dominant byproduct processes  is unknown.  Unusual regional supply-

and-demand situations for hydrochloric  acid (100% basis)  tend to confuse the

national end-use consumption picture  further.   Finally, end-use consumption

tonnage estimation for hydrochloric acid (100% basis) is made more difficult,

because of the many chlorination processes wherein  anhydrous hydrogen  chloride

is used in conjunction with or as a substitute for chlorine.

     Anhydrous hydrogen chloride in hydrochlorination reactions leading to

ethylchloride, methylchloride, vinylchloride,  1, 1, 1-trichloroethane, and

1,1, 1-trichloroethylene and in oxychlorination  reactions leading to vinylchloride

and trichloroethylene has dominated the use of hydrochloric acid (100% basis) in

the production of organic chemicals.  Another significant use for anhydrous

hydrogen chloride is in the production of chloroprene,  the monomer for pro-

duction of neoprene.  Potential hydrogen chloride gas emission  from such

processes has been discussed in Chapter 2.

     The aqueous acid is used in the production of dyes and dye intermediates,

in the preparation of chlorides from alcohols,  as a catalyst in organic reactions,

in the preparation of pesticides,  and in the preparation of pharmaceutical-grade

chemicals,  such as adipic acid, citric acid,  amine hydrochlorides, and aconitic

acid.      The use of the aqueous acid has grown tremendously in the metal
and industrial cleaning field, but particularly in steel-pickling applications.

Since 1964, a large percentage of the steel companies in the United States have

switched to hydrochloric acid using the conventional horizontal pickling baths

after minor modification. Inhibited hydrochloric acid is also used for the re-

moval of sludge and hard-water scale from boilers, heat exchangers, pipes,

and other industrial equipment.  Oil-well acidizing operations use a large

tonnage of inhibited hydrochloric acid to dissolve subsurface limestone  or
dolomite formations, thereby decreasing the resistance to oil or gas flow.

Finally, hydrochloric acid is used in a host of other applications, ranging

from the extraction and processing of minerals to the hydrolysis of proteins
and starch and reactivation of bone char and  charcoal in sugar refining.

     Emission of hydrogen chloride gas from industrial operations  that use

hydrochloric acid is not judged to be a significant atmospheric pollution problem,

because of the strong affinity of the gas for water.  Depending on  such factors

as the strength of acid,  the temperature of use,  the type of equipment, the local

ventilation, and the emission control devices, various problems of  environment

control and corrosion control are encountered.  Equilibrium pressures  of

hydrogen chloride increase markedly with temperature, especially  over acid

solutions containing more than 20% hydrogen chloride; equilibrium pressures
over dilute acid (under  20%)  may be considered negligible.

                                CHAPTER 4



Natural Atmospheric Chlorides

     Particles.  The ocean is the primary natural source of chlorine

present in particles (hereafter referred to as particulate chloride) in

the atmosphere.  There is good evidence of a direct relationship between

the gaseous chlorine compounds in nonurban air and atmospheric sea salt

particles.  Most of the sea salt particles that remain in the atmosphere

longer than a few minutes are produced by the breaking of bubbles at the

sea surface.  These bubbles may be formed by breaking waves and by rain-

drops and snowflakes that strike the water surface.  Except under some

local conditions, breaking waves (whitecaps) are by far the most important


     The mechanism of salt particle injection into the atmosphere by bursting

                                                                            / O
bubbles has been studied extensively and is reviewed in detail by Blanchard.

There have been only two detailed attempts to estimate the annual global

production of atmospheric sea salt particles, those of Eriksson-*-" and

Blanchard.^  Both authors determined the production rate by calculating

the amount of salt removed from the atmosphere by precipitation and dry

fallout, making various assumptions as to the particle concentrations in

the atmosphere, the effective particle deposition velocity, the strength

of the wind (which affects the atmospheric particle number and size distri-

bution), and the average salt content of rainfall.  The two estimates dis-

agree by a factor of about 9, Blanchard estimating a salt production of

10 x 10   kg/year, and Eriksson, 1.1 x 10^ kg/year.  Eriksson's estimate has been

quoted commonly, and his figure is generally used for the annual sea salt pro-

duction, 09,238,400 but Blanchard's calculation appears equally reasonable


and must also be considered.  Thus, the best estimates are that the sea salt
production is 1. 1-10 x 10   kg/year and results in a particulate chloride pro-
                    1 O
duction of 0. 7-6 x 10   kg/year,  as  shown in  Table 4-1.  Approximately 90%

of this is returned to the ocean surface,  and  10% is deposited on the continents.

     There have been a number  of estimates  of the  global injection of soil and
rock -weathering products into the atmosphere,  ranging from 7 to 500 x 10
         178,209,325,378,400                      325
kg/year.                       According to  Mason,     chlorine accounts

for about 0. 02% of the mass  of crustal rocks. Applying this  figure the various

estimates result in a range of global annual  production of particulate chloride
from crustal weathering of only  0. 0014-0. 10  x 10  kg (as  shown in Table  4-1)--

far less  than oceanic production.

     Estimates of the production of atmospheric particles  by volcanoes vary
            9         209,400           9         378
from 4x10   kg/year         to 25 x  10  kg/year     (there is even one  esti-
                9         178
mate of 150 x 10   kg/year.      Assuming an average chlorine content of
igneous rocks of 0. 032%    results in a chloride production estimate of
0. 0013-0.008 x  10   kg/year in particles from volcanoes--again far less than

oceanic production.

     Almost no quantitative data are available on the production of atmospheric

particles by forest fires.  Estimates of particle production range from 3 to
        9         209,400
150 x 10  kg/year.          Chemical analysis of forest fire particles are

also lacking, but even an assumption that 1%  of the particulate mass is

chloride--a very high value--re suits in a maximal particulate  chloride pro-
duction from forest fires of only 1.5x10  kg/year.

     Gases.  There  has been considerable controversy concerning the source
of the natural gaseous chlorine species present in the atmosphere.  Duce

has reviewed the various arguments in this problem.  It has not been determined.

what chemical species  of chlorine are present in the gas  phase in the undisturbed


                                  TABLE 4-1


                                              Estimated Production Rate,
     Source	                      10   kg of Chloride per Year

     Sea salt                                           700-6, 000

     Crustal weathering                               0.0014-0.10

     Volcanoes                                        0.0013-0.008

     Forest fires                                         «1.5

atmosphere.   Two sources have been suggested for gaseous chloride in un-

contaminated air:  sea salt particles and volcanism.

     The most commonly accepted view is that the gaseous chlorine con-

stituents found in uncontaminated marine air  are released from sea salt

particles.  A number of reactions have been suggested that would result in

this release.

     Sea salt particles  exist as saline droplets in the atmosphere at relative

humidities above 70%.  Over the sea,  the relative humidity in the lower few

hundred meters of the atmosphere  averages 70-80%.  Even at lower humidi-
ties, these particles are surrounded by a thin envelope of water.  Cauer

suggested that the aqueous chloride in aerosol particles  reacts with ozone

to form chlorine, which later escapes from  the particles.  He envisioned the

reactions as:
                O    + Cl   	> O     +  CIO
                  3(g)       (aq)     2(g)        (aq)                 (1)

and CIO       +  2H     + Cl    	> Cl     +H  O                 (2)
         (aq)      (aq)       (aq)       2(g)     2  (1).

 These reactions were studied in detail by Yeatts and Taube,     who found
 Eq.  1  to be rate-determining.  Eriksson     points out that,  on the basis

 of Yeatts and Taube's rate measurements, it would take several thousand

 years  for the chloride in sea salt particles to be converted to hypochlorite

 with the concentrations of ozone normally found in nonurban air, although

 the conversion may be  10-100 times faster in urban air, with higher oxygen

 concentrations. This suggests that chloride oxidation by ozone is probably

 not a major mechanism of release of gaseous chlorine compounds from
 atmospheric sea salt.  In addition,  Zafiriou     has pointed out that chlorine

 would  probably undergo relatively rapid photolysis in the atmosphere,  with

 the ultimate  product possibly being hydrogen chloride.
     Eriksson    believed the gaseous chlorine compound  in marine  air

was hydrogen chloride  released from sea salt particles.  He suggested that

 sulfur  trioxide, formed by the oxidation of sulfur dioxide,  dissolves in the

 particles,  lowering the pH and releasing hydrogen chloride.  The following

must be considered:

                   HC1   	>HC1   ;       K = 10    .              (3)
                       (aq)          (g)

 The pressure of hydrogen chloride (pHCl) in equilibrium with the saline

 droplets is given by

                   pHCl  = 10      a   * a                              (4)
                                   H   Cl"

 The chloride concentration will vary from the seawater value, 0. 55 M, to

 a maximum of about 6-7 M at low humidities, and the activity coefficient for

 chloride will be approximately 0. 7.  If all the gaseous chlorine species are

present as hydrogen chloride, its partial pressure in the atmosphere is about

10   atm.  (See also the following section).  According to Eq. 4, the equi-

librium pH of the sea salt particles would vary from 2. 2 (for 0. 55 M chloride

to 3. 3 (for 7. 0 M chloride).   These pH values appear rather low for sea salt
particles.  Junge     has pointed out that the ammonia concentration in the
marine atmosphere is sufficient to keep  the pH higher.  Blanchard   has

shown,  however, that there  are  approximately equal amounts of chloride and

surface-active organic film  material in sea salt particles in the marine atmo-

sphere.  The presence of  this organic material as a compressed film  on the

surface of a particle would probably influence the transfer of gaseous  species

across the droplet  surface,  and  it is possible that simple considerations of

ionic  equilibria are not valid in this situation.

     It has also been suggested that nitrosylchloride, NOC1, may be the
initial form of gaseous chlorine  in marine  air.  Junge     found that the

nitrate content of sea salt particles in coastal areas of the northeastern

United States was greatest for the giant particles,  those  containing most of

the  chloride.  He further determined that the presence of nitrate in  the aero-

sols depended on the presence of both nitrogen dioxide and sea  salt particles.
On the basis  of Junge1 s results,  Robbins et a_L     studied the following reac-


             NaCl    + 2NO  	>NaNO     + NOC1                  (5)
                  (s)        2(g)          3(8)         (g)

and          NOC1    + H  O  	>HC1    + HNO    .                (6)
                   (g)     2  (1)         (g)        2(1)

     The  reaction of Eq.  5 with  bulk moist sodium chloride was slow, but

complete--!, e. , all the nitrogen dioxide  was reacted. With sodium chloride

aerosols, however, the reaction was rather  rapid, but incomplete; the authors

suggested that that ruled out Eq.  5.  Also, any nitrosylchloride formed  should

be rapidly hydrolyzed according to Eq.  6,  giving hydrogen chloride and nitrite
                         258                                              *
as final products.  Junge     however,  had found no nitrite in his analyses.
     Robbins jejt ai.     then suggested that nitrogen dioxide is hydrolyzed

in the gas phase,

                   3NO    -1- H  O  	>2HNO     + NO  ,            (7)
                       2(g)     2  (g)           3(g)      (g)

and the nitric acid, HNO , is later dissolved in the sea salt droplets.  They
found that, -with the excess water available, about 5% of the nitrogen dioxide

was converted to nitric acid.   The decrease of the sea  salt particle pH on

dissolution of the nitric acid would result in the release of hydrogen chloride

according to Eq.  3.  This explanation, however,  suffers from the  same problem

as the sulfur trioxide mechanism: it appears unlikely that the pH can become

low enough on the particles for the particles to be in equilibrium with the gaseous

chlorine  compounds observed in the marine air, assuming that the chlorine is

present as hydrogen  chloride.  Thus, it is clear that,  if the gaseous chlorine

compounds in marine air comes from salt particles, strict ionic thermodynamic

considerations, such as those above,  cannot describe  the  situation adequately.
     Petriconi and Papee     have suggested that highly reactive transient

pernitrite intermediate oxidants can be  formed photolytically in saline solutions

that contain nitrate and that these strong oxidizing agents may result in the re-

lease of halogen-containing gases from  seawater and atmospheric  sea salt

particles.  It is very likely that photochemical reactions play an important

role  in the chemistry of atmospheric chlorine compounds.
 Recent work by Schroeder and Urone     with sodium chloride particles
 and nitrogen dioxide showed that Eq.  5 proceeds rapidly,  but depends on
 surface area..  They suggest that this may be an important source of atmo-
 spheric nitrosylchloride.  More work is clearly needed on this subject.

     If gaseous chlorine in some form is released from atmospheric sea

salt particles, the chloride:sodium ratio on the particles  should be lower

than that in seawater, which is 1. 80:1.   Unfortunately, and surprisingly,

very little information is available  on the chloride:sodium ratio in marine
aerosols.  Junge     found a mean  atmospheric chloride:sodium ratio of
(1.79 +.?):! along the Florida coast.  Chesselet ej: al_.    found that the

ratio  in particles  collected over the North Atlantic was (1. 72 +_ 0. 03):1,

suggesting a chlorine loss of 4-5%.  The mean ratio found on sea  salt parti -
cles in Puerto Rico by Martens et aL     was (1. 57 +_ 0. 1 6): 1, suggesting
a gaseous  chloride loss of approximately 13%.  Wilkniss and Bressan

measured  the ratio  on particles collected from surface air over 'the Atlantic

and Pacific.   They found a mean  ratio of (1. 88 +_ 0. 34):1 for particles  >^ 2 ym

in radius  and  (1.40 +_ 0. 26): 1 for  all particles  >0. 2  ym in radius.  The latter

figure would represent about a 22% chloride loss,  and their results  suggest

that the chloride loss is from  the smaller particles.  These studies indicate

that there  may be a 5-20% loss of chloride on sea  salt particles relative to the

chloride:sodium ratio in seawater.
                     324                       516          389
     Martens ^t aL ,     Wilkniss and Bressan    and Rahn    investigated

the variation in the  chloride:sodium ratio with particle size. Wilkniss and

Bressan,  in laboratory bubbling experiments,  found a depletion in the ratio

relative that in seawater on the smallest particles collected (radius,  f_ 0. 4 pm).

Martens ^t al. found a very pronounced  tendency toward chloride  loss from the

smallest sea salt particles collected in ambient air both in Puerto Rico and in

the San Francisco Bay area.   This  chloride loss from the  smallest particles

was also noted by Rahn at inland  sites in northern  Canada.  Martens et al.

found that  chloride losses from the particles were approximately  inversely

proportional to the particle radius, with over 90%  of the chloride  on the smallest

particles (radius 0. 2-0.4 nm) lost and less than 10% of the chloride on

the largest particles (radius,  >  5 um) lost.  They suggest that the  chloride

loss may be  controlled by a gain of hydrogen ion,  which depends on particle

surface area.

     A few recent observations  at a  remote location off the shore of southern

California have shown anomalously high  chloride:sodium ratios in aerosols.
On the basis of aerometric and meteorologic considerations,  Hidy et al.

have argued  that anthropogenic sources cannot be  responsible for these high

ratios.  They have speculated that there may be a connection between removal

of hydrogen chloride by absorption into aged aerosols in the middle and upper

troposphere  and the material that reaches the surface of the western Pacific

from large-scale subsidence of air around the Pacific high-pressure area.
Their  arguments are supported by Gillette and Blifford's evidence    of

increasing chloride: sodium ratio with altitude over the Pacific Ocean.
     In the relatively polluted San Francisco Bay area,  Martens et  al.

showed that there was a relationship between gaseous nitrogen dioxide and

absolute chloride loss from the particles calculated from the chloride-.sodium

ratio for the total particle distribution.  They suggest that this supports the
second hypothesis of Robbins et  al. ,      i. e. , Eq.  7.   Their data indicate

a loss of about 0. 06 micromole of chloride per standard cubic meter (SCM)

for every micromole of nitrogen dioxide.  If the chloride loss  is a result of

nitric acid interaction, the amount of nitric acid taken up by the particles

would  represent about 6% of the  available nitrogen dioxide.
     In Puerto Rico, Martens et al.      found a relatively constant chloride

loss from the sea salt particles,  about 0.006 micromole/SCM.  Assuming a
natural background nitrogen dioxide concentration of 0. 04-0. 07 micromole/SCM

and assuming that 6% of this nitrogen dioxide were converted to nitric acid and


taken up by the aerosol, approximately 0. 002-0. 004 micromoles of hydrogen

ion per standard cubic meter could be  supplied to the particles.  This is about

half that required to balance the loss of chloride.  The authors point out that

sulfur dioxide conversion to sulfuric acid may also be important in explaining

the overall chloride loss that they found in Puerto Rico.

     Volcanoes have  also been suggested as a source of gaseous chlorine in
uncontaminated air.  Valach     believed that the amount of hydrogen chloride

released from sea salt owing to the dissolving of sulfur trioxide in the particles

could not account for the total gaseous chlorine observed in the atmosphere.  He

based this belief primarily on the fact  that,  in general, the chloride:sodium ratio

on bulk particles is only 50-20% below the ratio in seawater,  and he held that the

su If ate: sodium ratio is  not  sufficiently above the  seawater value to account for

the amount of gaseous chlorine  observed in air, which  is approximately half the

particulate chlorine concentration in the lower troposphere.  Valach did not con-

sider the possibility of nitric acid addition to the  particles.  He suggests that the

gaseous chlorine is hydrogen chloride, but that only 10-20% of it could be from

sea salt, with the rest volcanic in origin.
     Eriksson     estimated  the total worldwide  volcanic production of
gaseous chloride to be 9 x 10  kg/year, a figure  with which Valach agreed.

Much of this gaseous chloride probably goes directly into local groundwater

or the ocean.  Assuming that 15% of the particulate chloride produced by the

ocean is converted to gaseous chloride results in an estimate of global produc-
tion gaseous chlorine from sea  salt particles of 1-9 x  10    kg/year.  Thus,

apparently,  less  than 10% of the gaseous chloride is volcanic in origin.

     The relative importance of other  natural sources  of gaseous chloride

is unknown.  Such sources  could include forest and grass fires and acidic

soils,  especially near coastal areas, -which might release hydrogen chloride.


Until the magnitudes of these and the previously discussed sources are de-

termined with some precision,  there will continue to be large uncertainties

in our understanding of the natural cycle of chloride compounds between  the

earth, the  atmosphere, and the oceans.

Natural Background Concentrations in Remote Locations

     Particles.   There have been numerous measurements of the concentration

of salt particles in marine  air.   Some of the most extensive  studies have been

made by Woodcock in Hawaii.  Figure 4-1  shows a typical number distribution

of sea salt particles  of different weights and sizes in the marine atmosphere at
various wind forces in Hawaii.      It is apparent that both the number of parti-

cles and their upper  size limit increase with increasing wind speed.  This is a

direct result of increased wave action and  bubble formation.  These results were
confirmed  by Lodge     in  Puerto Rico.  With improved collection techniques,
Woodcock    has recently  extended his studies to show that  salt particles as

small as 0. 01 -0. 001 picogram (pg), with radii of 0. 2-0. 2/
                                 WIND FORCE  NUM3ER OF
                                           SAMPLING DAYS -
                                                I      I
                                                     22.1 <70%
                                                     55.0  91%
                                                     110.0  99%
              10°     10
102     I03      I04     I05
FIGURE 4-1.  Number and weight of sea salt particles 800-1, 000 m over

the ocean near Hawaii as a function of wind force.  Three short transverse

lines on each curve mark the first quartile,  median, and third quartile weight
distribution points.  (Derived from Woodcock.     )

in sea salt and that from anthropogenic sources.  Rahn     found surface

level chloride concentrations of 0. 1-0. 3 pg/SCM at a remote site in the

Northwest Territories in Canada,  over 2, 000 km from the ocean.  Atmo-

spheric chloride concentrations were found to be < 10 ng/SCM at the geo-

graphic South Pole on the Antarctic polar plateau, 2, 800 m above sea
level.      The number of chloride particles  with radii greater than 10  um

is very low near ground level in interior portions of the United States.
Reitan and Braham     found only two such particles per  standard cubic
meter in central Illinois.  Semonin    reported that the concentrations of

the largest chloride particles over the midwestern United States showed no

clear relationship to the advection of marine air masses, thus suggesting

that these particles are nonmarine in origin.
                   97                 61
     Crozier et^ al.   and Byers e_t al_.   demonstrated the presence of

sea salt particles at various altitudes over the central United States, and
Twomey    made a similar study over central Australia.  Byers et al.

found that the  concentration of particles containing chloride  with radii

greater than  3ym increased in the first few  hundred meters over the

land and then was relatively constant up to an altitude of about 4 km.  The

concentration  of chloride particles with radii over   Sum was actually

greater over land than over the ocean above approximately 2 km.  This is

the result of the stronger vertical mixing  of the atmosphere over land areas.

     Gases.  There are very few  measurements of gaseous chlorine species
                                         255, 258
in the uncontaminated atmosphere.  Junge         measured gaseous chloride
in coastal regions of Florida and Hawaii,  Duce jet al.     in Hawaii,  and
                74                   56
Chesselet _et al.   and Buat-Menard   over the North Atlantic Ocean and

in coastal areas of western France.  The  atmospheric concentrations observed

by these authors  are  summarized in  Table 4-2.  The mean sea-level gaseous


                                                        TABLE 4-2

                                Gaseous and Particulate Chloride in the Marine Atmosphere
Gaseous Chloride
concentration, pg/SCM
i— •

Florida, coastal258
Hawaii, coastal
Hawaii, coastal116* 350
North Atlantic,56
No. samples
Particulate Chloride
concentration, yg/SCM
No . samples
Gas: Par tide
  sea level
Hawaii, 3,000 m255
Hawaii, 3,500 m





 chlorine (as chloride) concentrations found vary from 2 to 4  pg/SCM.  These

 results are in remarkable agreement and suggest that the gaseous chloride

 concentration is much less dependent on such factors as wind speed and pre-

 cipitation than is particulate  chloride.  This again supports a longer residence

 time of gaseous chloride.  The gaseous chloride concentration decreases by a

 factor of about 2 from the surface to 3, 000 m in Hawaii.

     The  ratio of gaseous to  particulate chloride measured at sea level ranges

 from  0. 2:1  to 0. 9:1 (Table 4-2).  The variation in this  ratio is determined

 largely by the variation in the particulate concentration, which depends heavily

 on wind speed, collection of local spray,  rainfall,  elevation, etc.  As an average,

 however,  it appears that the  gaseous chloride concentration is about half the

 particulate  concentration near sea level.  The measurements at 3, 000 and 3, 500

m above sea level show that the  gaseous chloride concentration is at least 20

 times the particulate concentration at those elevations.

     Precipitation.  The chloride content of precipitation in uncontaminated air

has been investigated primarily  in the marine environment.   Concentrations

 of chloride  in rain at sea level range from a few tenths  of a milligram to tens
 of milligrams per liter, depending on wind  speed and sea state. Junge

 summarized the results of many analyses of rainwater for chloride before

 1962.  The  chloride content of rain decreases with altitude and distance from
 the coast in Hawaii,     with  a mean concentration of about 7 mg/liter at sea

 level decreasing to 0. 15 mg/liter at an altitude  of 2, 200 m (a distance of 40 km

 inland).  The chloride concentration also  varies  inversely with rainfall intensi-

     The chloride:sodium ratio in rain in marine air is  generally at or slightly
                                   134,259,420              114
below the seawater ratio of 1. 80:1.              Duce e_t ai.     showed that

the ratio does not vary appreciably -with rainfall  intensity or  raindrop size.


     In continental areas, the chloride content of precipitation decreases

rapidly as one moves away from the coast.  This is shown clearly in

Figures 4-2 and 4-3, which present the results of the analyses  of rain
samples collected in the United States.

     The geographic distribution of chloride: sodium  ratios also is instructive

in showing the influence of urban areas on total atmospheric chloride content.

Figure  4-4 shows the ratios for  1960-1966 based on data from the  U.S. Na-
tional Precipitation Network.      The ratio is  1. 8 for seawater, and it can

be seen that in only a few places is  the ratio much  larger--mainly in the Mid-

west and in upper New York state.  It is  interesting that analysis of earlier

rainwater data failed to display such high ratios in large urban  areas (e. g. ,
Junge and Werby    ).

Relation of Chlorine to Other Halogens in the Natural Atmosphere

     Bromine.  Analysis of atmospheric particles  in marine  air for bromide

and chloride has shown that the bromide:chloride ratio in these particles col-

lected  over the ocean or on the coast is somewhat lower than the seawater
                              116,117                      349
ratio of 0. 0034:1.  Duce et ai.         and Moyers and Duce     found  the

ratio on particles collected in these regions of Hawaii to range  from 0. 0005:1

to 0. 003:1, with an average of about 0. 002:1.   However,  rain collected inland

in Hawaii showed  ratios that were roughly twice the seawater ratio.
                117                      349
     Duce jrt aJ.     and Moyers and Duce     measured the bromide and

chloride concentrations in different-size particles in Hawaii and used a cascade

impactor  for particle collection.  The total particulate bromide concentration

was about 9 ng/SCM.  The variations in chloride and bromide concentrations

and bromide:chloride ratio for 12 impactor  samples are shown  in Figures 4-5

and 4-6.  The shape of the  size distribution curve is  similar  for the two ele-'

ments;  the bromide:chloride ratio tends to be  lower for intermediate particle


FIGURE 4-2.  Average chloride concentration in rainfall over  the
United States, in milligrams per liter, July 1955-June 1956
(Reprinted with permission from Junge and Werby, 1958).

                                                                                          0.85    0.5199

                                                                                        <* 0.63
                                                                                                         O 1.26
             FIGURE 4-3.  Average chloride concentration in rainfall over  the United  States,  in milligrams
             per  liter, 1960-1966.   (Reprinted  from Lodge et al.307)

         FIGURE 4-4.  Average chloride:sodium concentration ratios,  1960-1966.  (Reprinted  from Lodge et al.307)


                                                  ;   I   i    r
                                                                           f)  "
                                                                         10°  «=
                                                                      in-1 r-
                                                                      ID  —<

                           i   I

A   B
                                 F  Tot.  A
                                   CI S
F  Tot
 FIGURE 4-5.  Mean size-concentration distribution for chloride, bromide,
 and iodide from a 20-m tower on the coast of Hawaii.  Cascade impactor (CI)
 stages A-F have approximately 100% collection efficiencies for particles
 of >10 ym on stage A, 5 ym on stage B, 2.5 ym on stage C, 1.2 ym on stage
 D, 0.6 ym on stage E, and 0.3 ym on stage F.  Tot.,  total concentration
 for all sizes collected.   (Derived from Movers and Duce.  49,350)

i—i—i—i—i—i	r
              Cr/Cl 1
                            1   1
    1   L
              A   B  C.  D  E   F
B  C   D  li   F  Tot.
  FIGURE 4-6.  Mean halogen ratio variation with particle size for particles
  collected from a 20-m tower on the coast of Hawaii.  See Figure 4-5  for
  further details.  (Derived from Moyers and Duce.349,350)

size.  Similar results were obtained by Duce ^t al_.      The major mass

of bromide is found on particles with radii of 1-5/am.  Particulate bromide

was also measured in Antarctica and ranged from about 1 ng/SCM at the

coastal McMurdo site (about 300 km from open water) to about 0. 5 ng/SCM
at the South Pole,  2, 800 m above sea level.
                     349                 118
     Moyers and Duce     and Duce jet  al.     also measured the  concen-

tration of gaseous bromide in Hawaii and Antarctica.  The chemical form

of the gaseous bromide is  unknown, like that of chloride.   Concentrations

found in these locations are given in Table 4-3.  Near sea level in Hawaii,

approximately 80-90% of the total bromide is in the gas phase, compared
with about 35-40% of  the total chloride.  Moyers and Duce    point out that,

over a reasonable pH range, simple therrnodynamic  considerations suggest

oxidation  of bromide  to bromine by oxygen in the  sea salt particles, and re-

lease of the bromine  to the gas phase can  explain the concentration of gaseous

bromide found in marine air,  whereas  simple release of hydrogen bromide

cannot.  Photochemical reactions probably play an important role in  the
                                          527                   349
chemistry of gaseous bromine compounds.     Moyers and Duce    point

out that the high bromide:chloride  ratios in rain collected in Hawaii can be

explained quantitatively by the dissolving of gaseous  bromine or hydrogen

bromide in the  rain at the  pH  of rain found in that area (5-6). Previously,
Seto^t al.    had shown that the chloride:sodium ratio in rain collected

in that area did not vary with  respect to altitude or distance from the sea,

indicating that the high bromide:chloride ratios in the rain are due to bromide

gain,  rather  than chloride  loss.
                117                       350
     Duce et aL     and Moyers and Duce     suggested that the tendency

for the bromide: chloride ratio to increase on the smaller particles could

result from the collection  of nonmarine particles containing bromide, perhaps


                      TABLE 4-3

Halogen-Compound Concentrations in the Natural Atmosphere

(— 1


Hawaii, sea
McMurdo, Antarctica,
sea level-'--'-8
South Pole, Antarctica,
2,800 m118
Chloride, yg/SCM
Gaseous Particulate

2.7 + 1.7 4.5 + 1.3

0.7 + 0.08

Bromide ,

46 + 13

7.9 + 2.

7.4 + 2.

8.6 + 2.8

0 0.96 + 0.37

6 0.43 + 0.06
Iodide, ng/SCM

Gaseous Particulate

8.1 + 3.5 2.

2.2 + 0.6 0.

2.7 + 0.8 0.

5 + 0

93 +

49 +




anthropogenic.  This was also suggested by Cadle     to explain the high

bromide:chloride  ratios found in stratospheric aerosols.
      Moyers and Duce     calculated that gaseous  bromide had  a residence

time approximately 7 times that of particulate bromide in marine air.  With

a particulate residence time similar to that of chloride, 2-4 days, this would

result in a gaseous bromide residence time of 2-4 weeks.

      Iodine.  There has been considerable interest in the atmospheric chemistry
                                             69, 104, 115, 116, 205, 280, 343, 499
of iodine in marine air for  a number of years.

Iodine appears to  behave very differently from chlorine and bromine in marine

air.   Atmospheric particles and rain in marine air have iodide:  chloride ratios

ranging from 100  to 1, 000 times the ratio in  seawater, although the sea is al-

most certainly the source of both elements in uncontaminated air.  The high

ratios in the  atmosphere are the result of either iodide enrichment on  the sea

salt particles when they are produced at the sea surface (perhaps owing to an

association of iodide with surface-active organic material present on the sea

surface) or iodide gas escape from  the surface of the  sea with later deposition

on the surface of the particles.
                 117                      350
      Duce e± al_.     and Moyers and  Duce     measured the iodide and

chloride concentrations on  different-sized particles in Hawaii with a cascade

impactor for particle collection.  The  total particulate iodide concentration
is approximately 2-3 ng/m  .  The variations in iodide and chloride concen-

trations and iodide:chloride ratio with  particle size  are shown in Figures
4-5 and 4-6.       Clearly,  the maximal iodide concentration is on smaller

particles than the maximal  chloride concentration,  resulting in an increase

in the iodide:  chloride ratio with decreasing size.  Similar results were obtained
              117                                                           118
by Duce et ai.      Particulate iodide was also measured at antarctic stations,

and the concentrations are  reported in Table 4-3.


      Gaseous iodide -was also measured by Moyers and Duce     and
Duce et ai.     in Hawaii and Antarctica and the concentrations found are

reported in Table 4-3.   Like those of bromide and chloride,  the chemical

form of gaseous iodide is unknown.   Approximately 70-75% of the total

iodide is in the gas phase near sea level.
     Laboratory studies by Miyake and Tsunogai     and Martens and
Hariss     with iodine-131 tracer have shown that gaseous iodine can be

released from seawater by photochemical oxidation of iodide in the sea.
Seto and Duce     questioned the validity of these experiments, inasmuch as

nonradioactive gaseous iodine was removed from the air coming into the

model system, thus upsetting any equilibrium between gaseous  and aqueous
iodine relative to ambient conditions.  Moyers and Duce     point out that,

at the concentrations of iodide and iodate present in seawater and iodine gas

present in the atmosphere (assuming it is iodine),  gaseous iodine should  be

dissolving in the  sea,  rather than released, if simple ionic thermodynamics

      Seto and Duce     show evidence that particles are enriched in iodide

when they are formed at the sea surface and that the iodide is associated with

organic material.  They point out, however, that the enrichment of iodide

found by this mechanism is only 10-20% of that found in ambient marine air,

and they state that gaseous iodide is  clearly a major factor in determining the

iodide enrichment on particles.  The mechanism for getting this additional
gaseous iodide into the  atmosphere is still unknown.  Moyers and Duce

suggest, on the basis of thermodynamic considerations of iodide, iodate,  and

gaseous and aqueous iodine, that atmospheric  sea  salt particles should be a
perfect sink for atmospheric iodine.  Duce et al.    pointed out that the

iodine:chlorine ratio on sea  salt particles was inversely proportional to particle


radius.  This distribution would occur if the majority of iodine on the particles

resulted from gaseous iodine diffusion to the particle  surface.  This idea was
                      396                  350
supported by Robbins.     Moyers and Duce    also point out,  however,

that the iodine:chlorine  ratio variation with particle size parallels the
atmospheric residence time of particles,  as reported  by Esmen and Corn.

They suggest that the increase in iodine on  the particles may be controlled

by the rate at which the  thermodynamically stable species of iodine, iodate,
is formed on the aqueous particles.  Moyers and Duce    state that iodine

is not the thermodynamically stable species in the gas phase.   Reactions  with

both methane and hydrogen to form methyliodide and hydrogen iodide are

thermodynamically favorable but kinetically very slow.  Other  organic species
may also be present.  Lovelock  et al.     have recently reported the presence

of methyliodide over the ocean.  They believe that this is the major  form of

gaseous  iodine in marine air and that its source is  the marine biomass.

Photochemical reactions involving gaseous iodine species are probably  very important
but little work has been  done on  this  subject.

      Quantitative estimates of the atmospheric residence time of gaseous
and particulate iodine have not been made.  Duce ^t al. ,     using measure-

ments at coastal and inland antarctic  stations,  found that particulate and

gaseous  iodine both  have longer  residence times than  the bromine species,

which were  2-4 days and 2-4 weeks,  respectively.

      Fluorine.   There have been very few  studies  of  fluoride in the uncon-
taminated atmosphere.   Carpenter    summarized the results of rain analyses

for fluoride and pointed  out that  the fluoride:chloride ratios in rain samples,

almost all of which were collected in  continental areas, •were 10-1, 000 times
                              67              458
the seawater ratio.  Carpenter    and Sugawara     conclude  that fluoride is

preferentially (relative to chloride) injected into the atmosphere from the sea

surface,  thus explaining the high ratios.


      However, Wilkniss and Bressan        have investigated the chemistry

of fluoride and chloride in rain,  as well as atmospheric particles in the field

and in the laboratory.  They do not report fluoride concentrations, but they find

that,at midocean sites, away from the influence of land, the fluoride:chloride

ratio in particles is near or a  little below the seawater ratio,  suggesting that

chemical fractionation during  sea salt particle production is not occurring to

any important extent.   This was supported by model studies in the laboratory.

Atmospheric particulate samples collected over the ocean, but near the east
coast of the United States, by Wilkniss and Bressan     showed fluoride:chloride

ratios from 2 to 25 times the seawater ratio.  The authors point out that these

high ratios are most likely due to the incorporation of continental material into

the marine aerosol that they •were  sampling.   This is probably also the explana-

tion  for a large part of the high ratios found in precipitation.   Wilkniss and

Bressan also measured the ratio in the  rain collected in Hawaii and found it

equal to or less than the seawater  ratio at altitudes up to about 500 m, but

considerably higher at higher altitude.  The reason for the increase is un-

certain,  but it is probably related  to the fact that the mass of continental

aerosols is greater than that of sea salt particles  at higher altitude.
      Wilkniss and Bressan     present laboratory evidence that gaseous

fluoride  is released from sea salt particles.   The relation between gaseous

fluoride  and the high fluoride:chloride ratios  in rain is  not known.  No attempt

has been made to measure gaseous fluoride,  except in the marine atmosphere,

and the importance of sea salt particles as a  source of  gaseous fluoride has
                                67                             9
not been investigated.  Carpenter   suggests that  as much as 10  kg of fluoride

per year, as hydrogen fluoride,  may  be released to the atmosphere from vol-
                  308              "       9
canoes.  Lovelock      reports that about 10  kg of fluorine-containing com-

pounds,  such as the freons and sulfur hexafluoride, are released into  the

atmosphere each year.  This is equivalent to about 2-4x10  kg of fluoride

per year.  Trichlorofluoromethane and sulfur hexafluoride  have been measured
in the atmosphere in a remote area of southwest Ireland by Lovelock.

Concentrations measured in westerly winds off the ocean were 0. 01 ppb for

trichlorofluoromethane and 0. 029 ppt for sulfur hexafluoride.  Concentrations

were about 10 times greater with easterly winds off the European continent.


Sources  of Urban Atmospheric Chlorides

      Despite the possibility of significant amounts of chloride-containing ma-

terial in urban atmospheres,  very few measurements have  been published.

In urban air, chlorine-containing compounds can exist in gaseous form or

combined with material in aerosols.   Particulate chloride has been identified

primarily with lead halides from motor-vehicle emission and with natural

sodium chloride mixed with material  of urban origin.  The  chloride associ-

ated with lead should be  in  submicrometer  particles, but sea salt will in-

fluence heavily the composition of larger particles in cities to the leeward

of oceans or  influenced at times by influxes of marine air.  Some typical
particle  size observations reviewed by Lee and  Patterson    are shown in

Figure 4-7.  The data available suggest that the bulk of the  particulate chloride

will normally be found in the  fraction larger than a few  tenths of a micrometer

in diameter.   Comparison of Tables 4-2 and 4-4 suggests that the concentrations

of particulate chloride in urban air are similar  to those in the nonurban,  marine

atmosphere.  However,  the total urban and nonurban chloride concentrations

are very different.

      The gaseous compounds are  believed to be principally hydrogen chloride

and chlorine,  although organohalides also have been observed including tri-

chlorofluoromethane,  methylene chloride,  and DDT.  Hydrogen chloride  is








I  I  I   I  I   I
          III   III
I   I  I   I

     FAIRFAX •

                                 VEST COAST URBAN AEROSOL
                                 (LUDWIG, et a1_. 1966)
     0.01 0.05  0.2 0.5 1   2
                5   10   20  30 40  50 60 70  80
                 I MASS < DIAMETER
                                                      90   95
     FIGURE  4-7.   Cumulative particle size  distributions
     of chloride  in Chicago; Philadelphia;  Fairfax, Ohio;
     and the West  Coast.   (Reprinted  with permission
     from Lee and  Patterson.296)

thought to be more prevalent than chlorine,  except near special isolated


Ambient Concentrations in Urban Areas

      Particles and Gases.   Because the urban concentration of chloride

generally has been found to be very low,  compared with those of other

pollutants, this material has not been studied in detail in cities in the United

States.  Interestingly, most of the estimates for  gaseous chlorine species in

city air must be derived from sources outside the United States.

      Some total chloride concentrations are listed in Table 4-4.   Particulate

chloride concentrations are  listed in Table 4-5.  The gaseous chlorine species

(as chloride) appear to dominate.  The available  information on ambient chloride

in urban air is scarce and poorly documented, but the values listed suggest an
upper limit of  <  100 yg/m   away from specific sources in American cities.

This appears to be about 10  times or more larger than  the concentrations in

the middle-latitude nonurban air.

      Pesticides.   The extensive use of pesticides for agricultural purposes

must be considered in the atmospheric chemistry of chlorine. Although most

of the pesticides used are high-molecular-weight organohalides,  there is some

evidence of an  unusually high volatility in the  atmosphere at concentrations

below the parts-per-billion range.  For example, the widespread dispersal of

DDT in the oceans cannot be explained readily by the fallout of large aerosol

particles from insecticide sprays.  More direct evidence of volatilization
comes from laboratory experiments of Safe and Hutzinger.

      The halogen-containing pesticides should also be  susceptible to photo-

decomposition  in the atmosphere.  Very little is  known about such reactions
under atmospheric conditions, but Hutzinger _e_t al.     have speculated about

reactions involving polychlorinated biphenyl compounds  (PCB's).


                                                   TABLE 4-4

                          Concentration of Particulate Chloride in Urban Atmospheres
Los Angeles
Fairfax, Ohio
San Francisco
Niles, Michigan
Date Concentration, yg/m3 Reference
•si n
Ludwig et al. u
P. K. Mueller et al. (in Miller
e_t al.341
Lee and Patterson 70
Lee and Patterson29"
Lee and Patterson29^
John et al.2^7
Rahn e_t al.389

                                                      TABLE  4-5

                              Concentration  of  Total  Chloride in Urban Atmospheres
Concentration, ug/nr'
Windsor, Ont.
Donora, Pa.
Niagara Falls,
New York
Berlin (near
incinerator —
1,500 m downwind)
Japan, Tokushima
Japan, Tokyo -
Germany (near
potassium plant —
2,000 m downwind)


1,500 (without

0 - 949
0 - 459
0 - 291.0
0 - 104
1.5 - 168
0 - 570
38 - 132
10 - 23
52 (maximum)
<15 (generally)
91.8 - 150

Lahmann and

Okita and Nakamura-'"-'
Matsuoka et
Environmental Sanitation

     Although the fate of airborne pesticides constitutes an important

aspect of atmospheric pollution chemistry, chloride from these materials

is generally found in concentrations of nanograms per cubic meter or less

away from sources.  Therefore, their contribution to the atmospheric chloride

burden is considered negligible, compared with that of other sources.

     Precipitation.  Significant amounts of chloride have been found in

rainwater samples.  It was noted earlier that rainwater sampling indicated

that chloride content generally decreases away from the seacoasts, except

for cases of anomalously high concentrations in some cities.  A comparison

of chloride in rainwater between selected cities and nonurban areas is

shown in Figures 4-2 and 4-3.  The systematic surplus of chloride in rain-

water in cities, particularly in the Midwest and East, suggests the influence

of anthropogenic sources, presumably fuel combustion and industry.

Dispersion of Chlorine Compounds in the Atmosphere

     There are no known anomalies in the dispersion of chlorine compounds

in the atmosphere.  Thus, the material from anthropogenic or natural sources

is expected to be transported and mixed by air motion in essentially the

same manner as other trace contaminants.  The dispersion of contaminants

in the atmosphere has been a subject of extensive investigation for many

years.   The general methods for estimating mixing rates and transport have

been reviewed by several investigators (e.g., Wanta^^).

     General transport and dispersion are common to all materials emitted

into the atmosphere, and a variety of information is available elsewhere;

these subjects will not be treated further here.   It should be pointed out,

however,  that chlorine gas is denser than air.  Under very stable atmospheric

conditions with light winds, chlorine compounds tend to concentrate near

the ground.

Transformation Process
     Chlorine compounds can react chemically in the atmosphere  to be

transformed into several classes of materials, including oxidized

species.  The atmospheric reactions of gaseous chlorine compounds

have been studied to an appreciable extent only in the recent years.

It is anticipated that photochemical reactions that produce atomic

chlorine will be of greatest interest, because they may play a  role

in the behavior of atmospheric ozone.  Several reactions of potential

importance can be written, as follows:
     RC1 + hv (185  R + Cl

     C12 + hv (X< 475 nm) ->• Cl + Cl
     Cl + 02 + M r= C100 + M    (1)


Cl + 03 + CIO + 02
CIO + 0 + Cl + 0,
     Cl + H2 -»• HC1 + H         (1)

     Cl + CH4 -»- HC1 + CH3      (1)

     Cl + CO + M £ C1CO + M    (2)

     CIO + CO -»• C02 + Cl

     Cl + H02 -»• HC1 + 02

     Cl + OH ->• HC1 + 0

     CIO + 03 -* C102 + 02      (1)

     CIO + NO -»• N02 + cl       (1)

     CIO + CIO -> C102 + Cl     (1)

     HC1 + OH -»-'  H20 + Cl      (1)
                                     (Reaction is very rapid, owing
                                      to the high intensity of
                                      visible light)
(This pair of reactions constitute
 the primary mechanism proposed
 for the destruction of ozone in
 the stratosphere)

(Main reactions forming HC1,
 which serves as a chlorine
                                     (Data are needed on this reaction)

                                     (Atmospheric concentration of OH
                                      is low)

                                     (Reaction is very slow)

                                     (Competes with CIO + 0 ->• Cl + 02)

                                     (Atmospheric concentration of
                                      CIO is low)
                                     (Important step for regenerating
                                      Cl atoms in stratosphere)

      The possible mechanisms for chlorine catalysis in the stratosphere

 following photolysis of a chlorine compound have been reviewed in

 detail by Watson 505b and by Rowland and Molina    3.  Their potential

 importance to air pollution appears to have been recognized a few

 years ago by Johnston.      Reaction rates have been reported for the

                                                                   1 fiftfl
 systems cited with numbers in parentheses — (1) Hampson and Garvin

 (2) Burns and Dainton 60.

     It is possible that many reactions would be important in both

 the troposphere  and the stratosphere if gas-phase chlorine compounds

were ever to reach significant concentrations.   What constitutes a

 significant concentration would be a function of the light intensity,

 the total atmospheric pressure, and the abundance of radical scavenging

material, such as particulate matter.

     The most significant reactions of chlorine compounds in the

atmosphere would occur after the photochemical dissociation of gas-phase

hydrogen chloride, chlorine, or other chlorinated compounds to produce

free chlorine atoms.   Molecular chlorine is rapidly photolyzed by

visible solar radiation.   It can be considered as a steady source of

Cl atoms.  Gaseous hydrogen chloride,  requiring higher energy for

dissociation, would be expected to be of photochemical significance

only at higher altitudes, where there is an abundance of low-wavelength

radiation.   However,  even in the stratosphere photolysis is less

important than the reaction of HC1 with OH.

     Once the chlorine atoms have been produced, they will proceed to

catalyze chain reactions  and produce other reactive free-radical species,

until they are removed from the atmosphere.   The removal processes consist

only of radical-radical recombination reactions and scavenging by

particulate matter or water droplets.

     The low concentration of radical species in the troposphere makes

the recombination reactions very slow, so the major termination reactions

would be expected to occur on particle surfaces.  At higher a.ltitudes,

where the radical population would be greater, the recombination

reactions should be of greater significance.  However, even for the

stratosphere these recombination reactions are believed to be relatively


     In either case, the free radicals would be expected to react mainly

with molecular species in which a free-radical species would always be

generated as one of the products.

     Many of the chlorine chain reactions rely on the production of the

CIO free radical.  The principal formation reaction is Cl + 0^ -»• CIO + 02

(in the stratosphere).  Other, speculative, possible reactions are included

in the foregoing list.  Free-radical reactions of these types can also

occur with hydrocarbons or water, producing other free radicals, such as

OH, HOO, RO, and ROO, all of which will have many reactions of their own.

Hence, the importance of the role of chlorine as a sensitizing agent in

the atmosphere is limited only by its concentration and the presence of

radical scavengers that terminate the free-radical production chains.

     In the lower atmosphere, the principal reactions of hydrogen

chloride are assumed to be physical and probably involve water or


     Recently, considerable concern has been expressed about the

increasing ambient concentrations or organochlorine compounds, particularly

the chlorofluoromethanesC'Freons").  An extensive review of the problem


is given by Rowland and Molina     .  The chlorofluoromethanes, e.g.,

CCl^F  and CC1 F, and similar materials, such as carbon tetrachloride

and methyl chloride, are believed to be stable in the troposphere,

without major removal paths.  After diffusion into the stratosphere,

they may dissociate in ultraviolet radiation to form chlorine atoms

which can undergo catalytic reactions with stratospheric ozone.

Such predictions have raised concern about anthropogenic organohalogen

compounds emitted at the ground.  The NAS/NRC Climatic Impact Committee's

Panel on Atmospheric Chemistry, chaired by Dr. H. S. Gutowsky, will

report later on the effects on stratospheric pollutants on the ozone


Tropospheric Processes in Urban Atmosphere

     Sodium chloride and presumably other halogen-containing salts

undergo attack by acid-forming gases to release hydrogen chloride

gas (see eqs. 5 and 6).  There is considerable circumstantial evidence

of this effect from measurements of the chloride:sodium ratio in West

Coast cities.  In urban areas, where relatively high concentrations of

nitrogen dioxide may be present, the chloride:sodium ratio  is much

lower than would be expected from sea salt if it were reduced by

addition of soil dust to the aerosol.

     Pierrard -*81 discussed the implications for atmospheric chemistry

of the photodecomposition of lead halides from auto exhaust.

Experimental observations suggested that the rate of release of

chlorine from lead bromochloride, for example, would be 0.8-1.3x10""

micromole/cm^-sec per milliwatt per square centimeter of sunlight.

For conditions of heavy freeway traffic, where lead


bromochloride concentrations can be as high as 30 yg/m ,

Pierrard calculated that the photochemical release of chloride

from such aerosols would be about 0.1 ppb/hr.  For the

residence time of air masses of about 1 day in Los Angeles, for

example, this release would give a negligible amount of chlorine

atoms in polluted air.  Robbins and Snitz 397 ftave measured the

loss of chloride from lead halides in air and have found that

the chloride is volatilized independently of sunlight.  The

loss rate of chloride observed by these investigators was

exponential in the chloride:lead ratio, with the time constant

of 0.003 + 0.002 per minute.


     Although chlorine may be present initially in gaseous

and particulate form, the transformations that its compounds

undergo will not remove chlorine from the atmosphere.  The

removal processes are uncertain.  However, the role of aerosols

and rain are identified as potentially significant.  Gaseous

chloride may also be absorbed at the earth's surface either by

the oceans or by soil.  The path of removal of chloride is

probably through aerosols and by water cloud processes.  These

processes have been described for other reactive trace gases by Hidy

                                  /*      o                               ^o
atmosphere by fallout is 5.1 x 10~° yg/cm -sec, corresponding to 3.1 x 10

     It is difficult to determine the relative importance of dry fallout

or impaction and precipitation for the removal of chloride from uncontaminated

air.  In his studies of the global sea salt budget, Blanchard^ estimates that,

for wind speeds of 12 knots in Hawaii, the average salt removal from the


of chloride per square centimeter per second.  The calculated value for rain-

                                                              —f\      9
fall removal of chlorine under the same conditions is 5.8 x 10   yg/cm -sec.

Thus, approximately 35% of the salt is removed by dry fallout, and 65% by

precipitation (assuming that all the chloride in the rain comes from the

particles).   In Eriksson's J  study of the global sea salt budget, he makes

calculations based on river runoff and rainfall chloride concentration in

Scandinavia.  He estimates that approximately 50% is removed by dry fall-

out, and 50% by rain.  Silker,^32 using measurements of beryllium-7,  suggests

that rainfall is the primary mechanism for aerosol removal over large areas

of the tropical oceans.  From these estimates, it appears that perhaps 50-75%

of the particulate chloride is removed by rainfall, and 25-50% by dry fallout.

     The residence time of atmospheric sea salt particles depends, of course,

on particle size.   Junge^" ancj Eriksson    made estimates of the residence

time of sea salt particles over the ocean.  These are presented in Table 4-6.

For the major mass of atmospheric chloride, with particle radius of 1-3 ym

(at 90% relative humidity), the residence time is apparently about 1-4 days.


     The gaseous chloride species in the atmosphere must be removed by rainfall,

adsorption op,, particles,  or direct uptake by the earth's surface.   Data on this

subject are almost completely lacking.  Duce    has pointed out that, for

                                                      TABLE 4-6

                           Calculated Residence Times of Sea Salt Particles  over  the  Ocean

Sea Salt
Particle radius, um (90% R.H.) 1>3
Residence time, days:
Eriksson133 3.5
Junge257 1.9
Particle Mass, g
io-11 io-10 io-9
2.6 5.5 11

1.0 0.6 0.5
1.6 1.0 0.3

 rainwater in marine air in Hawaii with a pH of 5-5.5 and a chloride concen-

 tration of 1 mg/liter  (or 10~^'^ M), the pressure of hydrogen chloride in

 equilibrium, according to Eq. 4, should be about 10    atm, one ten-millionth

 of the partial pressure of gaseous  chloride actually observed, assuming that

 it is hydrogen chloride.  Thus, hydrogen chloride should dissolve in rain

 readily.  However, Duce et^ _al.    showed that the chloride:sodium ratio did

 not vary with rainfall intensity or raindrop size and suggested that the ex-

 change of gaseous and dissolved chloride was a minor factor in the variation

 in chloride concentration in the rain.   This again supports the suggestion

 that gaseous chloride has a longer residence time than particulate chloride

 over the ocean.  The small variation in gaseous chlorine compounds during

 rain in Hawaii found by Junge^" and the fact that chloride:sodium ratios in

 rain are generally below the seawater ratio of 1.80:1 also suggest that pre-

 cipitation may not be a very rapid removal mechanism for gaseous chlorine


     Gaseous pollutants are also known to be exchanged with vegetation.

     91 7
 Hill,    for example, has reported experiments on the rate of absorption

 of chlorine by alfalfa.  His studies indicate that,  the more water-soluble

 a gas, the higher the uptake in plants.   Wind speed  and light intensity were

noted to influence absorption.  The rate of uptake of chlorine increased

with increasing gas concentration in air over a range.   At higher concen-

 trations of this pollutant,  the absorption was partially limited by closure

 of stomata.

     The extent to which gaseous chlorine compounds  adsorb on the surface of

atmospheric particles other  than sea salt is unknown.  The surface of the

ocean, with a pH of 8.3, may be a significant sink for gaseous hydrogen

chloride,  but there are no experimental  data available to support this.  The

land surfaces, vegetation, alkaline soils, etc., are also undoubtedly efficient

sinks, but again there is no quantitative information available.  This is

clearly a subject for future research.

     From the very limited data available, it is difficult to estimate a

residence time for gaseous chloride in the uncontaminated marine atmosphere,

but it is instructive to see what ranges of values can be obtained.  We

will make the simplifying assumption that naturally occurring gaseous chloride

is essentially absent over the continents.  We will assume from the meager

data in Table 4-2 that the average gaseous chloride concentration over the

ocean is 3 Pg/SCM from sea level to 700 mb, 1.5 Mg/SCM from 700 to 400 mb,

and 0.75 yg/SCM above 400 mb.  With an atmospheric volume over the oceans

of about 2.9 x 10   SCM, this results in 4.7 x 109 kg of gaseous chloride

present in the marine atmosphere at any time.  Combining this value with

the previously estimated gaseous chloride production rate of about 100-900

x 10  kg/year results in a gaseous chloride residence time range of 2-17

days.  This range could be increased by up to 25%, if some of the gaseous

chloride produced in the marine atmosphere is found over the continents,

as it certainly is.   Although these numbers must be considered as very

tentative, they are, at least, in a reasonable range.


     There is ambiguous evidence that some atmospheric pollutants, such as

carbon dioxide and aerosols, have a measurable influence on the radiative

transfer of heat in the atmosphere or on the perturbation of cloud formation.

Thus, there may be concern that the chloride-containing pollutants would

reach concentrations that could influence the earth's weather.  Because of the

low concentration of chloride gases in the ambient air, it is unlikely that

 such material would strongly influence the radiative transfer processes

 in  the lower atmosphere.   However, the tendency for hydrogen chloride

 and chlorine to dissociate with light absorption may make them of potential

 importance in the ozone cycle.  This may be of concern, particularly in the

 upper atmosphere, in the use of large rocket boosters in the space-shuttle

 program, in which rocket engines emit locally significant quantities of hydrogen

 chloride and chlorine.

     Chloride in airborne particles might be a disturbing influence in the

 nucleation of water droplets or ice in clouds.  It is well known that sea

 salt or other hygroscopic particles larger than 0.1 um in diameter are good

 cloud condensation nuclei.  Soluble chloride particles found in an urban

 environment might add active condensation nuclei to the nonurban background.

 The low mass concentrations of particulate chloride combined with the possi-

 bility of removal of chloride by acid-gas reactions on particles appears

 to weaken the potential influence of chloride with respect to condensation

 nuclei.  Schaefer    has speculated that lead halides, especially lead iodide,

will make a significant change in ice nuclei concentrations downstream from

 cities.  Lead iodide has been used as a nucleation or cloud seeding agent in

 a manner similar to that of silver iodide. -^  However, some crude measure-

ments of ice nuclei taken upstream from Los Angeles and in Los Angeles, as

 reported by Hidy et al.,    did not provide any evidence of this kind of


     There appears to be no evidence of any influence of anthropogenic

chlorides on weather.
                                     -110- '

                                    CHAPTER 5


     The natural history of a disease (including intoxication) taids to become

evident at first through the most advanced cases.   It is ordinarily only then

that the early, more limited, subtle characteristics of the problem are

recognized.  These prodromal characteristics may or may not be similar to the

more obvious ones.  With chemical exposures, this can happen for a variety

of reasons; dose, duration of exposure,  threshold of response, interspecies

and intraspecies variability, etc.

     In many cases, the responses of a biologic system to chemical exposures

appear to depend on both the dose and the duration of exposure.  Observations

of effects of acute exposures to high concentrations of a chemical may con-

tribute little to the understanding of the effects noted at the other end

of the scale.  Chronic exposure to low concentrations of hydrogen chloride

is a case in point.  Acute high-concentration exposures produce irritation

of the respiratory tract;^22  chronic low-concentration exposures apparently

produce no respiratory problems, but cause erosion of the teeth.   '


     Chlorine, regardless of its divergent sources and variety of uses, is

found in only two states:  gas and liquid.

     Although liquid chlorine can cause eye and skin burns, the most common

state of chlorine in adverse exposures is the gaseous state.   Therefore,

the most important route of exposure is inhalation.  Less significant routes

of exposure to the gaseous state are ocular and cutaneous.


     Chlorine is a most reactive element and readily combines with a variety

of organic compounds and radicals well justifying its reputation of a general


protoplasmic poison.  Its reactivity is epitomized by the readiness with
which it displaces other halogens, bromine and iodine in particular, from
their salts.295
     Chlorine persists as an element only at very low pH (less than 2); in
less acid solutions (such as living tissues), it rapidly converts to hypo-
chlorous acid (HOC1).  29  Hypochlorous acid apparently penetrates the cell
wall easily, promptly reacting with cytoplasmic proteins to form N-chloro
derivatives that destroy the cell structure.295  Although the toxic sequence
of the process is not clearly established, cell-wall damage is one of the
most immediate effects of chlorine.  Radioactive-tracer studies by Friberg
have demonstrated that small amounts of chlorine are effective in disrupting
bacterial wall permeability, which leads to leakage of the marker into the
              IS 2
watery medium.     This cell-wall lesion explains the acute effects of
chlorine:  its edematogenic effect and its corrosive injury of exposed
surfaces.  The biochemical correlates of this injury have been studied
almost exclusively in microbiologic models.
     The inhibition of carbohydrate metabolism was originally suggested
on the basis of the decreased glucose oxidation observed in bacteria treated
                                1 87
with a dilute chlorine solution.     The reactivity between sulfhydryl groups
and chlorine and the evidence of inhibition of sulfhydryl-dependent enzymes
have suggested this as the most likely site for the action of chlorine.2'9
This hypothesis has been challenged.   Experiments with viruses suggest
that compounds active toward sulfhydryl groups are not always virucidal. '
Inactivation of RNA appears important in chlorine toxicity, as documented in
recent observations of virucidal effects.
     Lethal effects on elementary forms of life (bacteria,  fungi, etc.) exposed
to chlorine in water occur at about 1 ppm (range, 0.05-5.0 ppm)  with contact


duration of a few seconds (range, 1-120 sec).  However, some bacteria (such as

Mycobacterium tuberculosis) and some fungi (such as Aspergillus niger) require

much higher concentrations—in excess of 50 ppm.

     Oxidation has been traditionally considered an important step in the

germicidal action manifested by hypochlorous acid and other halogenated

species.  This mechanism was proposed some 70 years ago^"^ as the basis of

cellular necrosis and bactericidal effect.  However, as clearly outlined

by Morris,3^6 the temptation to formulate mechanism of bactericidal action

on the basis of oxidation potential is not justified.  Hydrogen peroxide,

for instance, with a strong oxidation potential, has very limited bactericidal

strength.  Analysis by electron-spin resonance spectroscopy of radicals

associated with oxidation does not indicate the presence of atomic oxygen.  ®

In fact, the nature and importance of the reactivity or presence of "activated"

oxygen often mentioned in the old literature remains unsubstantiated, in the

opinion of a recent reviewer.


     Chlorine is used to treat public drinking water supplies and the water

supplies and effluent of sewage treatment plants, textile mills, power plants,

and various other industries.  Some industries chlorinate continuously; in

others, in which chlorination is used to control marine fouling, the practice

is to "slug" with high concentrations for short periods.  Chlorine added to

water containing nitrogenous materials rapidly forms chloramines.  The ultimate

toxicity to various forms of acquatic life depends on the concentrations of

chlorine and chloramines and on species variability.  In the life cycle of the

fathead minnow, for example, egg production reportedly is the link most

          «.   ,-,  .,    305> 336> 358> 529
sensitive to chlorine.

     Aside from aquatic animals, it has been reported that chronic ingestion

                                                           O O£

of chlorinated water produces vascular changes in chickens.



Lethality of Single Inhalation Exposures to High Concentrations

     The toxicity of inhaled chlorine varies greatly in different reports.

The variability might be related to type, size, or shape of exposure chambers,

to completeness of mixing of chamber atmosphere, to mode of operation (whether

static or dynamic), to variations in gas absorption in chamber or animals,

to method of determination of concentration of airborne chlorine, to species,

to concentration, to exposure time, etc.  Underbill compared the experimental

results on dogs and found them consistent when dogs were exposed individually,

but inconsistent when they were exposed in pairs.

     There is also confusion in the terms used in the literature to describe

the airborne toxic dose.  Haber introduced the concept of mortality product

or lethal index (the Haber product of mortality) -.°^  the product of the

concentration of gas inhaled (in milligrams per cubic meter) and the exposure

time (in minutes) that will kill animals.  This product, as considered by Flury

and cited by Sartor i, was considered to be the minimal lethal value.     After
the advent of statistical treatment of data, the term LCten was introduced.

Ct is a measure of airborne dose or total exposure:  C refers to concentration

(in milligrams per cubic meter), and t refers to time (in minutes).  The product

Ct is expressed in milligram-minutes per cubic meter (mg-min/m ) .   The term LCt^

indicates the dose (Ct) that is lethal (L) to 50% of an exposed population.

     There are some weaknesses in the use of Ct.  There is no provision for

differences in breathing rates between individuals.  However, this difference

seems to lose importance when groups of animals are compared.  For a given

substance, Ct values developed with low concentrations and long exposure times

are greater than those developed with high concentrations and short exposure

times.  The former situation affords a better opportunity for detoxification.

In reporting Ct values, the exposure time should be mentioned.  Despite these

weaknesses, Ct values do provide a convenient and useful measurement of total

exposure or airborne dose.

     The general results indicate that there is much species variation in the

toxicity of chlorine.  Mice are more susceptible than dogs, and (although this

is less adequately documented) cats seem more susceptible than mice.^1"

     Information on lethality of chlorine in animals appeared in the literature

as early as 1887.148 

     Exposure to chlorine at 900 mg/m  (300 ppm) for 1 hr may kill cats,

rabbits, and guinea pigs by asphyxiation.136  Dogs rarely die after a 30-min

exposure to concentrations less than 1,900 mg/m  (650 ppm) and never after a

30-min exposure at less than 800 mg/m3 (280 ppm).     Brief exposure to air

containing chlorine at 3,000 mg/m3 (1,000 ppm) kills horses.  8

     Weedon et _al.    exposed mice, rats, and houseflies to chlorine at

2,900, 725, and 183 mg/m3 (1,000, 250, and 63 ppm).  They also exposed the

flies to 47 mg/m  (16 ppm).   The animals were exposed for 16 hr or until

death.  It is known that deaths occur after, as well as during, exposure

to chlorine.  Thus, it is likely that many of the animals had received

lethal doses at some time before death occurred.

     The animals exposed at  2,900 mg/m  showed little early excitement.

There was dyspnea, lacrimation, and foaming secretion of the nostrils.

One mouse died in 21 min, and all were dead by 50 min.  At 725 mg/m , the

mice showed lacrimation during the first hour, and then dyspnea, terminal

prostration, and convulsion.  All the mice were dead in 8.4 hr.  The first

rat died in 6.4 hr, and all  died by the sixteenth hour.  At 183 mg/m , there

were fewer effects and no deaths.  Animals that died or were sacrificed for

gross autopsy immediately after exposure showed distention, with foaming,

 hemorrhagic  fluid in the lungs, and some congestion of the liver at all chlorine

 concentrations.  Weedon et al.    gave the Lt_-,  that are shown in Table 5-1.
                        --                50's

                                    TABLE 5-1


                Lt  ,  for Chlorine Exposures of Various Species—
                   Chlorine concentration, mg/m-3
                           2,900      725      183         47

45 240 840
28 440 >960
53 440 >960
—                       508
 Data from Weedon et al.
     Weedon et al. produced time-mortality regression lines by plotting their

data on log-probit paper.  The size of their published graphs made accurate

reading of the values somewhat difficult.  Several values from each graph were

used to compute new lines by the Bliss method.  Computed times to death for

various percentages of the populations are shown in Table 5-2, and the values

in Table 5-2 were used to calculate the LCt   values shown in Table 5-3.

     Silver and McGrath    exposed two strains of mice to chlorine for 10 min

and found LCt,.^,  of 15,200 + 1,900 mg-min/m  and 17,300 + 2,400 mg-min/m3.

The lowest concentration, 730 mg/m , killed two of 20 animals.  Values derived

from their graphs are shown in Table 5-4 .

                                         TABLE  5-2

               Lt's  for Various Percentages of  Population Exposed  to  Chlorine—
               Lt, min
Chlorine concentration,
killed, %
Houseflies Mice
45 28
2,900 mg/nr Chlorine concentration, 725 mg/m3
  —Computed from regression lines of Weedon et^ ^al_.     The recalculation  allows  direct
   comparison with other values given in this chapter. 158> 433>
                                         TABLE 5-3

                      LCt's for Chlorine Exposures of Mice and Rats—
             LCt, mg-min/m
Chlorine concentration, 2,900 mg/m3 Chlorine concentration 725 mg/m3
killed, %




—Calculated from data of Weedon et

                                  TABLE 5-4

             Dose-Response Regression Data for Lethality in Mice

                     Exposed to Chlorine for 10 Minutes3-

          Dose-Response Regression Data
Miscellaneous Mice
killed %
Chlorine Concen.
mg/m3 LCt,
Chlorine Concen.
LCt , mg-min/m
— —
a                                433

"Derived from Silver and McGrath.

     In another investigation, Silver e± al.    found an LCt _ of 19,600 + 1,900


mg-min/m  for a third strain of mice exposed to chlorine for 10 min.  Deaths

occurred at all concentrations.  The lowest concentration to cause death was


1,100 mg/m .  Most of the deaths were due to pulmonary edema.  Some deaths

occurred in the presence of slight edema accompanied by congestion, and deaths

of a third type seemed to be related to secondary pneumonia.  LCt's are shown

in Table 5-5.  The derived LCt's from Weedon ^t _al.    for mice are much higher

                            433 434
than those of Silver et al.    '     The former recorded deaths as they occurred

during exposure, but Silver et al. included deaths that occurred after exposure.

Shortly after exposure, the mice pawed at their noses and mouths.  Labored

breathing, gasping, yawning, and spasmodic contraction of the intercostal

muscles began soon thereafter.  The mice convulsed shortly before death.

During a 10-day observation period after a given dosage, the number of deaths

                                    TABLE 5-5

               Dose-Response Regression Data for Lethality in Mice

                       Exposed to Chlorine for 10 Minutes^-
Killed, %
Dose-Response Regression Data
Chlorine Concentration, mg/m3

LCt, mg-min/m3
"Derived from Silver et al.

per day was roughly constant.  There were no pathologic findings in

survivors 10 days after exposure. ^3^

     In mice exposed for 30 min by Schlagbauer et al. , the LCcQ dose (with

95% confidence limits) was 381 (range, 318-456) mg/m3, or 127 (range, 106-152)
ppm, for a 4-day observation period.     The LCt   was 11,430 (range, 9,540-13,680)

mg-min/m .   In exposures of 3 or 6 hr at 10, 22, or 40 ppm, deaths occurred

as a result of bronchospasm or pulmonary edema.  Concentrations of 2.5-10 ppm

for 8 hr/day for 3 successive days were not lethal.  This was a Ct of 13,920

mg-min/m3 for 1 day (29 mg/m^ x 480 min) or 41,760 mg-min/m3 for 3 days.

     In dogs, deaths occurring in the first 3 days (most died within 24 hr)

are due to immediate effects of the chlorine gas. ^6  in animals that survive

beyond the 3 days, the pulmonary edema subsides, and the animals later die

of bronchopneumonia or recover.  Table 5-6 shows some results of exposure

of dogs to chlorine for 30 min, and Table 5-7 is a Bliss calculation based on

these data.

     Table 5-8 summarizes information on the lethality of chlorine in various


Toxicologic Effects of Single Lethal or Near-Lethal Exposures

     Studies in animals have generally confirmed and expanded the knowledge

obtained from human exposure to chlorine during World War I.  Immediately

on exposure there is bronchoconstriction and a reflex slowing of respiration.

The bradypnea is followed by tachypnea.  Pulmonary edema, which develops

rapidly, is followed by plasma loss and hemoconcentration.  Anoxemia, acidosis,

and cyanosis appear.  Body temperature is increased by small doses of chlorine

and decreased by moderate or high doses.  As death approaches, the pulse rate

increases and blood pressure decreases to the point of shock.  This section

summarizes briefly the experimental basis of what is known about the effects

of chlorine.

     Sudden Death.  Sudden death without pulmonary lesions in man during WWI

has been attributed to reflex action by Vedder    and to "respiratory

paralysis" by Gilchrist.      In studies with unanesthetized and anesthetized

(with ether)  dogs and cats, the inhalation of pure chlorine produced a long

expiration, respiratory arrest for 20 sec or more, and then slower-than-normal

breathing.  These changes in respiratory rhythm were abolished by cutting the

vagi.   '     Intratracheal injection of pure chlorine produced cardiac

arrest in anesthetized dogs and cats.  Section of the vagi before injection

prevented cardiac arrest.

                                    TABLE 5-6

                Acute Deaths (within 72 Hours) in Dogs Exposed to
Concentration, mg/m3
16- 800
for 30 Minutes^

Median Fraction killed
Ct, mg-min/m3 within 72 hr, %
12,240 0
42,750 6
52,200 20
61,800 43
71,250 50
80,700 87
139,350 92
^Derived from Underhill.486'487

                                    TABLE 5-7

                      LCt's for Chlorine Exposures of Dogs3-

Fraction Killed, %     LCt, mg-min/m3     95% Confidence Limits, mg-min/m3

         1                 30,562                   21,418-43,611

        16                 47,678                   40,122-56,657

        30                 55,781                   49,455-62,916

        50                 66,455                   60,428-73,084

        84                 96,628                   77,395-110,860

        99                144,501                  100,441-207,889
-Derived from Underhill.486'487

                     TABLE 5-8

Lethality of Single-Inhalation Exposures of Animals



Not stated
Most animals
Most animals
Not stated
Not stated
Chlorine Concentration, mg/m3
to Chlorine
Exposure Time, min
Ct, mg-min/m3
Toxicity Value
LCt 158
TO 433
TO 434
T ft- JVO 	
T /-> f JvJo —
LL.CC- rt
Mortality ,
Mortality ,
Lethal for most'
Serious or
Mortality ,

TABLE 5-8 - Continued

Animals	  Chlorine Concentration, mg/m3  Exposure Time, min  Ct, mg-min/m3  Toxicity Value

Not stated                2,530                      30             75,900      Mortality    ,

Not stated6-                  50                      30              1,500      Toxic148>

Not stated6-                 100                      30              3,000      Fatal148
     exposures until death; LCtjQ calculated from Ct at time when 50% of animals had died
 during exposure.

-"Mortality product" means "lethal Ct" or "minimal lethal Ct."

—Determined by Bliss method.

—No data or references to support toxicity values.

-§-No data.  Reference is made to Sayers et^ al.410a Ind. Eng. Chem. 26:1251, 1934;
 Haggard,1843 J. Ind. Hyg. 6:397, 1923-24; and Berghoff.32

•^Wachtel^OO quotes Flury and Zernik,    who quote Lehman-Hes; fatal values given for man;
 basis for values not given.

                 o o n
     Mayer et^ a^.    noted that irritant vapors in the upper respiratory

tract decreased or arrested respiration and circulation in rabbits and

dogs.  In some animals, the respiratory arrest was fatal.  Irritant

vapors that were inhaled deeply or through a tracheal cannula, so that

they penetrated into the bronchi and lungs, produced an acceleration of

respiration.  The two reflexes were antagonistic.  Simultaneous acceleration

of the upper and lower respiratory tract caused the respiratory rhythm to be

disorganized, spasmodic, and convulsive.  The reflex causing the polypnea

does not occur if the vagus nerve has been cut before inhalation.  Tachypnea

that had begun was abolished by section of the vagus nerve.

     Bronchoconstriction.  Gunn-^4 found that the respiratory excursion of

the lungs of anesthetized rabbits subjected to artificial respiration at

constant pressure was reduced for about 1 min when chlorine was breathed.

Gilpin,171 in a similar experiment with decerebrate rabbits, found that

chlorine caused an immediate spasm.  Bronchospasm in pithed cats subjected

to artificial respiration was relieved by stramonium fumes.-"-^  The intravenous

administration of atropine was believed to have an antispasmodic action in

unanesthetized rabbits that had been exposed to chlorine.'0

     Effects on Ciliary Activity.  In 1915, Hill213 reported that chlorine

in water at 1:300 stops the movement of cilia.  Schultz431 found that the

cilia of the tracheal mucosa were paralyzed after pure chlorine was intro-

duced into the trachea; it is assumed that the animals used were unanes-

thetized dogs or cats.  Cralley noted that irreversible cessation of the

mucociliary activity of sections of excised rabbit trachea occurred at ex-

posures to 30 ppm for 5 min.  and 18-20 ppm for 10 min.93  However, reversible

ciliostasis was noted after exposure at 200 ppm for less than a minute and 20 ppm(

for 2.5 min.

     Respiratory Rate, Pulse Rate, and Edema Formation.  Underbill    exposed

112 dogs to chlorine at 160-6,340 mg/m3 for 30 min.  Inhalation of high con-

centrations of chlorine caused immediate respiratory arrest and broncho-

constriction.  The average respiratory rate increased from 20 per minute to

about 35 per minute during the first hour after exposure.  It gradually

subsided to about 25 per minute 13 hr after exposure.  The pulse rate de-

clined slightly during the first 4 hr after exposure followed by a rapid

increase to double the normal rate at 10 hr.  This pulse rate was maintained

for 24 hr.   These respiratory and cardiac changes corresponded to the develop-

ment of pulmonary edema, which was measured in dogs sacrificed periodically

beginning 30 min after 30-min exposure.^°"  The edema develops rapidly; it

was noted at the first sacrifice, which occurred 30 min after a dog had in-

haled a concentration of 2,590 mg/m3 for 30 min.  Edema was present up to

the last sacrifice, 312 hr after exposures of animals to chlorine at

1,450-2,930 mg/m3.

     Other investigators have reported on the effect of chlorine on respira-

tion, pulse rate, and blood pressure.  Concentrations of 29,000 mg/m3 and

58,000 mg/m3 initially caused a gradual, slight increase in blood pressure,

with little change in respiration, in rabbits anesthetized by chloroform.

After 4 min, respiration became slower and deeper.  The heart rate was

slower, but blood pressure was maintained.  At 5% min, respiration suddenly

became convulsive, and blood pressure, irregular.  At 6% min, respiration

and blood pressure failed suddenly.  The heart continued to beat for several

minutes.  Artificial respiration was ineffective when given 2% min after

respiration ceased.

     The respiratory rate of rabbits anesthetized by a chloroform-ether

mixture or ether alone increased during exposure to 580-2,900 mg/m3,.

     The pulse rate of dogs was decreased during exposure to 522-580

and higher concentrations.

     Temperature.  After lethal exposure of dogs to chlorine, the body

temperature decreased from a normal of 39 C to about 35 C in 4 hr.  Death

followed, 12 hr after exposure.  After less severe exposure, there was an

initial decrease in temperature and a gradual recovery in 24 hr.

     Hemoconcentration.  Underhill^°° found that the hemoglobin concentra-

tion in dogs severely poisoned with chlorine increased to as high as 178%

of normal.  In some that survived, the concentration reached 145% of normal

during the pulmonary edema stage.

     Blood Pressure.  The blood pressure in dogs and cats decreased soon

                                                             9 o t^ft 914
after exposure to chlorine, during the period of bradycardia. ^'J0»  H

The decrease occurred before edema or asphyxia and was accompanied by

constriction of the splanchnic vessels.    The pressure  remained low when

edema was fully developed.  As death approached, the pulse became rapid and

the blood pressure decreased to the point of shock.

     Blood Oxygen.  Bunting et al.   exposed dogs for 30 min to chlorine

concentrations of 1,970-2,840 mg/m^.  The oxygen saturation of arterial

blood decreased from a normal 98% to 60-67% 10 min after exposure.  Immediately

after a 30-min exposure of dogs, Underbill^   found that the venous oxygen

concentration had decreased from 12.1-15.5 vol % to 6.2-8.2 vol %.

     Acid-Base Balance.  The effects of inhaled chlorine on acid-base

balance have been studied in dogs.  Immediately after a 30-min ex-

posure to concentrations of 1,670-3,330 mg/m , acidosis was seen.  The pH

was reduced from 7.2-7.33 to 6.96-7.03.  There was a moderate increase in

carbon dioxide tension and a slight reduction in bicarbonate concentration.


In animals that were mildly affected, the acid-base displacement returned

to normal in 5-7 hr.  In one dog, the acidosis persisted even after 19 hr.

     Changes in urinary excretion were correlated with those effects.^87

There was an increase in urinary acidity and an increase in excretion of

ammonia acid phosphates.  Excretion of total nitrogen, creatinine, and

uric acid was increased, especially on the second day after exposure.

Chloride excretion was decreased at the time of hemoconcentration and

increased after later dilution.  Hjort and Taylor^O also reported a

rapidly increasing acidosis in dogs exposed for 2-7 hr to chlorine at

2,400 mg/m3 (800 ppm).

     Cause of Death.  Underhill °' attributed death to pulmonary edema and

hemoconcentration.  He considered the former as only an indirect cause of

death.  The conclusion was based on the knowledge that maintenance of

increased oxygen concentration in the arterial blood (above normal) did

not prevent death.  Some animals died with much less edema than others,

and some survived with an "apparent excessive quantity of fluid in the lungs."

When hemoconcentration was prevented, animals survived, despite pulmonary


Pathologic Findings after Single Exposures

     Mice.  In the studies of Silver et al.,    mice were exposed to various

concentrations of chlorine for 10 min.  Most deaths were attributed to pul-

monary edema.  In some, death occurred with slight edema accompanied by

congestion; in others,  death seemed to be related to secondary pneumonia.

Klotz278 found thrombi in arterioles, venules, and capillaries of mice

after chlorine exposure.

     Dogs.  Sudden death during exposure to high concentrations of chlorine

has been noted in dogs and men.^86,498  xhj[s has been attributed to respiratory1


     Dogs that died 1% min after exposure to high concentrations of chlorine

were autopsied immediately.^°°  The peripheral vessels did not bleed.  The

lungs were retracted to about one-third of the chest cavity.  They were

greenish-gray and like India rubber in appearance and consistency.  On

section, they were greenish-gray, dry, bloodless, and friable.  The trachea

and bronchi were gray and dry.  The heart was dry and in systole.  The right

side of the heart was slightly dilated and contained thick blood.

     In dogs that died 1-24 hr after exposure, the smaller bronchioles were

constricted, with almost complete closure of the lumen.     It has been

suggested that the constriction might have resulted from sectioning of the


     In dogs that died 48 hr after exposure, there was necrosis of the

epithelial lining cells of the trachea, the bronchi, and the walls of the

alveoli that communicated directly with the terminal bronchioles.  The

affected epithelial cells were eosinophilic, and the nuclei were pyknotic.

Cell death was indicated by nuclear staining with trypan blue.  A layer of

fibrin coated the surface of the trachea or bronchi where the necrotic

epithelium had sloughed.  Stripped-off sheets of epithelium often blocked

the bronchiolar lumen.   Most of the alveoli were filled with edematous fluid;

others were emphysematous.  Fibrin was deposited on many alveolar walls.

                                                                r-I Q

Alveolar capillaries were congested, but no thrombi were found.

     The edema had begun to subside 2-4 days after exposure.  At that time,

pneumonia was noted in 95% of the dogs.   '      Acute inflammation was noted

on the surface and in the cells of the trachea and bronchi.  The pneumonia

was peribronchial or lobular.  Bronchioles were often obstructed by fibrin

exudates, and the alveoli were atelectatic.  Rapid regeneration had occurred

in the epithelial linings of some bronchioles, the bronchi, and the trachea.

     In dogs that died 5-10 days after exposure, pneumonia and abscesses

were common.  Winternitz et al.    and Lambert^'  showed that organisms

normal to the mouth invade the lungs after chlorine poisoning.

     Animals that died or were sacrificed 15 and 193 days after exposure

                                     9QO SI 8
had patchy emphysema and atelectasis.   '     The latter was associated with

mucopurulent plugs and chronic inflammatory changes in the bronchi.  There

were also obliterated bronchioles surrounded by pneumonia.  Poor physical

condition often accompanied the more extensive pulmonary lesions.  Dogs

that made good recovery had few or no pulmonary lesions at the time of


     Koontz reported insignificant scars and areas of organization and

hemorrhage in dogs sacrificed 14-20 weeks after exposure.

Effects of Repeated Inhalation or Ingestion

     Lethality of Exposure for 3 Days.  Mice were not killed by being exposed

                                                          O Q C
to chlorine at 2.5-10 ppm 8 hr/day for 3 consecutive days.

     Resistance to Disease.  Repeated inhalation by rabbits and guinea pigs

of chlorine at 5 mg/m  (approximately 1.7 ppm) for 1 hr daily for several

days caused deterioration of the nutritional state, blood alterations, and

decreased resistance against infections.  Under similar experimental condi-

tions, a concentration of 2 mg/nP (approximately 0.7 ppm) was not toxic.

     Repeated exposure of rabbits to 2-5 mg/m^ over periods of up to 9

months caused weight loss and increased incidence of respiratory disease.

     In guinea pigs, the inhalation of small quantities of chlorine

accelerated the course of experimental tuberculosis.-^

     Other authors have reported on guinea pigs with experimental tubercu-

losis that were exposed to chlorine in air diluted 1:200,000 for 2-4 months.

The gas did not seem to influence the development of the disease.

     Pulmonary Disease in Rats.  Various studies have been done on rats

with spontaneous pulmonary disease (SPD) and specific-pathogen-free (SPF)

rats to evaluate differences in response to chlorine."»130,281  Rats with

SPD were compared with similar rats that had been exposed to chlorine.  The

disease is characterized by goblet cell proliferation, excessive mucus secre-

tion, and focal damage to the lung periphery.  Exposure to chlorine accelerates

the course of the disease process.130  gpj- rats show very few goblet cells

and no lymphoid cuffing.  The SPF animals tolerate higher doses of chlorine

than the diseased (SPD) animals.  After exposure to chlorine, the lungs of

the diseased animals show changes that resemble human chronic bronchitis

more closely than the lungs of the SPF rats.2^

     Thirty female rats weighing 120-140 g were exposed to the air in a

chlorine factory for 5 hr/day for 4 months.  The upper respiratory tracts

became inflamed, and body weights were lower than those of controls.  Early

leukocytosis was followed by leukopenia on termination of the experiment,

at which time the estrus cycles were longer, and fertility and the number

of animals in estrus were lower.-5

     Multigeneration Test.  Water containing chlorine at 100 mg/liter was

well tolerated when drunk over the whole life span by 236 BDH rats in seven

consecutive generations.  There were no toxic effects on fertility, growth,

blood, or as observed in the histology of liver, spleen, kidneys, or other

organs.  The incidence of malignant tumors was the same in control and

experimental animals.  The life span was not influenced.

     Reproduction in Rabbits.  Sklyanskaya and Rappoport exposed animals to

chlorine in air at concentrations of 0.002-0.005 mg/liter for 9 months.^36

Six rabbits produced normal offspring.  In two cases, macerated fetuses

were found in the peritoneal cavity.


     Scheele of Sweden first prepared chlorine gas in 1774.^u^  Because

it was liberated from hydrochloric acid and thought to contain oxygen,

it was called oxymuriatic acid gas.  Others, because of the then popular

phlogiston theory, referred to it as dephlogisticated muriatic acid.  In

the early 1800's, Sir Humphry Davy considered the elemental character of

the material, and the term "chlorine" (from the Greek "chloros," meaning

yellowish green) was coined. ^

     Not long afterward, the medical implications of the gas were recognized.

In 1824, Dr. William Wallace of Dublin published a work entitled "Researches

Respecting the Medical Powers of Chlorine Gas.'"^8  Kastner, obviously aware

of the adverse effects of the material, in 1825 produced an article about an

"Antidote for Inhalations of Chlorine."265  ^ series of laboratory and field

observations have followed.

     A wide variety of effects have been reported to be associated with acute

and chronic exposures to chlorine gas:  cough, conjunctivitis, fever, headache,

anorexia, nausea, vomiting, befuddled sensorium, pulmonary edema, anxiety

and other neuroses, anosmia, tuberculosis, nephritis, bronchitis, asthma,

pneumonia, pleurisy, meningitis, chronic tachycardia, neurocirculatory

asthenia, chronic laryngitis; valvular heart disease, keratitis, acne, dental

caries, and pulmonary fibrosis.  Some are, some probably are not, related to

chlorine exposures.19,31,287


Experimental Observations
     Determinations of Odor and Irritation.  Although much of the experimental
work has been done with animals, some controlled studies have been made with
human volunteers.  Matt, in the late 1800's, stated that it was possible to
work uninterruptedly in the presence of chlorine at 1-2 ppm.   '     Vedder
and Sawyer, in 1924, published dose-response data that they had determined
                                     A QQ
experimentally with human volunteers.     They listed the concentrations
and durations of exposure that produce various effects—from odor detection
to death (0.01-3.0 mg/liter).  They did not elaborate on how they had de-
termined human death experimentally.  Beck, in 1959, reported on odor threshold
            O                                                    O /
of 0.15 mg/m  (0.05 ppm) and noted the possibility of adaptation. ^
Leonardas et^ al., in 1968 reported the odor threshold as 0.314 ppm.
Aside from the reports from eastern Europe, much of the dose-response informa-
tion from other work seems to be related to these studies.

     Russian Test Techniques.  The Russians have published some of the data
on human responses to chlorine.  Their studies are interesting, but care
must be taken in interpreting their data, because they use concepts and
methods alien to most scientists trained in the West.  Even in their work
on the physiologic responses of odor and irritation, their protocols are
sufficiently different from those of other scientists to make the direct
comparison of threshold values difficult.
     They seem to attach great significance to the reflex effects of
chlorine—changes in higher nervous activity.  Although they regard such
changes as protective adaptational reactions, and not pathologic in the
true sense of the word, they assert that such effects "prove" that conditions
have deviated from the physiologic optimum and that the organism is thus being
adversely affected by the environment.      Many western scientists disagree
with this interpretation and doubt the value of such studies.


     The following is a brief discussion of some of the Russian test

techniques.   In some cases, effects are noted below the Russian-recognized

odor threshold.  It has been suggested that this is related to which nerve

endings are stimulated—olfactory or trigeminal (odor or irritation).
     •  Odor Threshold:  Reproducibility of odor threshold is reported

     to have been obtained by means of a cylinder pair  (Figure  5-1).

     The apparatus  is arranged  to allow a  trained observer to make

     rapid  comparisons  between  clean air and various  calibrated con-

     centrations of a chemical.  On the basis  of this method,  the

     odor  threshold of  chlorine is reported  to be 0.7 mg/m3.
 FIGURE 5-1.  Schematic drawing of apparatus for determination of odor
 threshold concentration.  (Original sketch of inhalation setup does
 not itemize components.)  (Reprinted from Styazhkin."0 )

•  Respiratory Tract Responses;  Changes have been noted in

the rhythm, frequency, and amplitude of respiration after ex-

posures to chlorine gas.  They develop apparently only at con-

centrations perceived subjectively as odor or irritation.  At

lower concentrations, no effect on respiration is reported to


•  Optical Chronaxy;  Chronaxy is a measure of the excitability

of nervous or muscular tissue.  It is the minimal time that a

current of twice the threshold strength (the rheobase) must

flow to excite a tissue.  To measure optical chronaxy, an

electrode is placed on the orbit of the eye near the upper lid,

and a baseline is established, with phosphene (a sensation of

light) as the desired response.  Simultaneous inflation pf a

chemical may produce a shift in the baseline.  According to

Pavlov's teachings, excitation of the cerebral cortex in one

region can cause inhibition in other regions, on the basis of

the law of negative induction.  Russian literature reports

that, under the influence of the breathing of a gas, the

chronxy changes:  as a rule, it becomes longer under the

influence of odorous substances, demonstrating a reduction

in excitability of the central nervous system.  In other

words, excitation arising in the olfactory region of the

cerebral cortex causes inhibition of the visual region.

This change disappears quickly on cessation of olfactory

stimulation.  Chlorine does not affect chronaxy at concen-

trations equivalent to odor threshold.395,457

•  Visual Adaptometry;  The ability to distinguish a light signal

in darkness can be defined in terms of threshold luminosity, as

well as rapidity of adaptation in darkness.   Simultaneous or

previous exposure to a chemical may alter visual performance,

according to the Russian literature.  The visual adaptometry test

demonstrates one of the problems of Pavlovian doctrine:  moderate

stimuli tend to increase and stronger stimuli tend to reduce

neural activity.  With some substances, such as sulfur dioxide

and furfural, changes in light sensitivity may be noted at con-

centrations only one-third of the odor threshold.  With chlorine,

alterations are noted only at concentrations perceptible by smell.

•  Plethysmography;  The inhalation of a chemical may be monitored

by plethysmographic techniques—that is, by encasing a finger in

a volume-sensing device or plethysmograph.  Volume change depends

on the vascularity of the tissues.  Chlorine does not appear to

affect the vascularity of peripheral tissues at the lower ranges

of exposure related to odor threshold.395
Additional Russian techniques are used in behavioral toxicology-

particularly conditioned reflex measurements.   It is uncertain,

however, whether chlorine significantly affects such tests.

      In conclusion, this array of measurements of physiologic re-

      sponses adds little to the interpretation of the effects of

      chlorine at low concentrations.  It appears likely that significant

      biologic effects of exposure to chlorine at relatively low concen-

      trations are confined to odor and mucous membrane irritation.

      Treatment of Respiratory Diseases.  Smith, in 1893, discussed the

possibility of "disinfecting human beings with chlorine and bromine".  9

Kuster, in 1915, reportedly used chlorine successfully to "cure" menin-

gococcus and diphtheria carriers. *°  Army medical officers noted that,

after the introduction of chlorine as a war gas in 1915, there seemed

to be decreased respiratory problems among front line troops.1^5

Baskerville, in 1919, was of the opinion that small amounts of chlorine

decreased the incidence of respiratory diseases among workers.    In

1922, a study was done in Camp Perry, Ohio, using chlorine gas for

the treatment of the common cold and bronchitis, with reportedly good


     Vedder and Sawyer did follow-up studies on the Camp Perry study and

made observations on chlorine workers at Edgewood Arsenal during World

War I.  It was noted during an influenza epidemic that the post's

chlorine workers had decreased morbidity, compared with workers not

routinely exposed to chlorine gas.   On the basis of their experiments,

they believed that chlorine at 0.015-0.020 mg/liter (5-7 ppm) inhaled

for an hour had a "distinctly curative value in common colds, influenza,

whooping cough, and other respiratory diseases in which the infecting

organisms are located on the surface of the mucous membranes of the

                      / Qft
respiratory passages."     The key,  they thought, was for the exposure

to be of sufficient strength and duration to produce a concentration of

1 ppm on the fluid lining the respiratory tract.

     In addition to the over 930 patients treated by Vedder and Sawyer,

Gilchrist reported in 1924 on another 900 patients who were so treated,

again with allegedly good results.  It must be noted that, in Gilchrist's

study, cure or improvement was based on patient history, not medical

examinat ion.

Field Observations

     Some studies on the effects of chlorine exposure have been done under

controlled circumstances with medical observation during the course of the

exposure, but the bulk of the material on the effects has been derived from

studies of chlorine exposures "in the field":  war gases during World War I,

catastrophic accidents, chronic industrial exposure, and industrial hygiene

surveys.  Aside from the latter, in which trained observers were exposed

during the course of field measurements of chlorine, it is often difficult

to reconstruct the exact degree of exposure and thus determine accurate

dose-response data.

     Acute Exposures During World War I.  The effects of chlorine on man

were not generally recognized by either the public or the scientific

                                                                      l fift
community until after its introduction as a war gas on April 22, 1915.

Although it was replaced by other agents after being used by both sides

several times, the labels "war gas" and "poison gas" persist.

     During the initial attacks, many of the Allied troops, unprepared

and unprotected, were victims of chlorine gassing.  The exact number is

difficult to determine, because the British originally listed deaths from

this cause under the general heading of "killed in action."  Gilchrist and

Matz reported that the U.S. War  Department determined  that  70,752 men,

                                                                      i /r Q

were casualties as a result of gassing, including 1,843 with chlorine.

     Among the 1,843, few deaths occurred.  Because of disagreement as to

what pathologic effects chlorine could be related to, there was and is less

than universal agreement as to the number of disabilities attributable to

gassing during World War I.  The government apparently accepted a number of

cases of tuberculosis, cardiovascular disease, and nephritis as being re-

lated to wartime exposures to chlorine.  Even so, the number was small.

     Meakins and Priestly examined 700 Canadians some 4 years after they had

suffered massive chlorine exposure; 16.4% were found unfit for work, 11%

                                                                  O o Q

because of heart trouble and 3.5% because of asthma or bronchitis.

     There are other studies of victims of war gases by British, French,

and American investigators.  Most of the retrospective analyses mention

bronchitis,  emphysema, and other respiratory problems as possible sequelae

of chlorine exposures.

     Catastrophic Accidental Exposures.  A number of catastrophic accidental

exposures to chlorine have occurred,:both here and abroad.  Some incidents

involved individuals, and others, large groups.

     In 1947, approximately 1,000 persons were exposed to high concentrations

of the gas when a chlorine cylinder leaked into a ventilator of a Brooklyn

subway.  Some 208 required hospitalization, and 33 of these were followed for

16 months.   There were no deaths, and, by the methods used for evaluation,

                                    7 *}
none had detectable residual damage.'-3

     Approximately 150 longshoremen were exposed during an accident in

Baltimore in 1961.  A number of them had follow-up of 2-3 years.  The authors

believed that there were indications of permanent damage.  No deaths occurred.282

     The derailment of a freight train near a small Louisiana community in

1961 caused 6,000 gal of liquid chlorine to spill.  A low wind dispersed the

cloud of gas over an area of several square miles; 7 hr after the accident,

concentrations up to 400 ppm could be detected 75 yards from the wreck area,

at a location considered only "moderately contaminated."  Of the 100 people

affected, 17 were hospitalized.   An 11-raonth-old died with pulmonary edema.

From 3 to 7 years after exposure, 12 of the victims were studied.  Chest

X ray did not reveal significant abnormality.  All subjects were free of

symptoms, except a 53-year-old man, a heavy cigarette-smoker with evidence

of pulmonary emphysema.  Occasional blood-gas abnormalities and marginal

pulmonary-function values were noted, but the authors could not refer them

to injury experienced at the time of the accident.  Rather, cigarette-

                                                                    O^o cii
smoking, obesity, and pregnancy appeared to be the relevant factors.   '

     Seven chemical workers, exposed in separate accidents, have been

                       9 Q
studied by Beach et al_. °  Although all recovered completely, three experi-

enced respiratory failure, and all presented radiographic evidence of pul-

monary congestion.  In one case, extensive pulmonary edema cleared after

several days.  Six of the seven underwent spirometry and measurement of lung

volume and transfer factor 8 weeks after discharge; only one had an obstructive

pattern, with increased residual volume and normal diffusion, and the other

five had values within normal ranges.^3

     In 1969, fumes leaked from a filtration plant in Cleveland, killing

two people.  Kaufman and Burkons studied 18 of the 35 affected and found

that a single acute exposure did not result in measurable permanent clinico-

physiologic abnormality.270  Adelson and Kaufman reported on the two that

died.  Abnormalities were noted  in the lungs of both and in the kidneys and

brain of the one who survived longer. -'-

     In 1968, Dixon and Drew reported the death of a chemical worker who

was exposed to chlorine for about 30 min.  Death was attributed to pulmonary


     The Washington Post reported, in 1971, that 36 people were hurt by

 inhaling chlorine fumes at a swimming pool.

     Similar reports have come from Europe.  Romcke and Evensen reported

 on the explosion of a railway tank containing 15 tons of chlorine in

 Mjondalen, Norway; 85 people were injured, and three died. ™  Hoveid did

 a follow-up study some two decades later and concluded that the after-

 effects in the survivors were few and trivial.

     Eight people died and 241 were injured in a cellulose factory in Walsum,

 Germany, when a tank broke and released 17 tons of liquid chlorine. ^

     Chronic Exposures in Industry.  Some population groups, notably

 industrial workers, are chronically exposed to chlorine.  A number of

 reports have discussed the correlation of pathologic effects with chronic

 exposure to low concentrations.  Documentation of the threshold limit values

 notes that the older literature states that a concentration of around 5 ppm

 causes respiratory complaints, nasal mucous membrane inflammation, increased

 susceptibility to tuberculosis, and corrosion of the teeth in workers chroni-

 cally exposed.

     In 1967, Ferris ejt fil.     noted that men working with chlorine had some-

 what poorer respiratory function  and more shortness of breath than those

 working with sulfur dioxide,  but that both groups had a lower prevalence of

 respiratory, disease than that of the local male population.  They appreciated

 the phenomenon of self-selection; those in the general population with respira-

 tory disease would actively avoid jobs that would aggravate their symptoms.

     Chester et_ a±. ^-> noted that the immediate effect of acute chlorine ex-

 posure, an obstructive ventilatory defect, cleared rapidly, but that workers

 chronically exposed seemed to have a decreased maximal midexpiratory flow.

This was most marked among chlorine workers who smoked.

     In a study of 332 chlorine-cell workers, generally exposed to less than

                   OT O
1 ppm, Patil et_ al_.    found no statistically significant signs of symptoms

on a dose-response basis.

     Industrial Hygiene Surveys.  Trained industrial hygienists have recorded

their subjective responses to chlorine and have attempted to correlate them

with simultaneous measurements  (Table 5-9).   These were not controlled experi-

ments, but casual observations during the course of regular work.  Apparently,

no attempt was made to find the thresholds of the various responses.  The re-

sults are nonetheless interesting.

     It should be noted that observations made by the same person late in the

day after previous exposure are frequently less discerning than those made

earlier in the day (H. R. Hoyle, personal communication), indicating possible

adaptation.  This acclimation was not as pronounced as has been noted with

other chemicals, such as ammonia; the differences in concentration for similar

subjective responses between the industrial hygienist, with relatively short

exposures, and the workman on the job, with more chronic exposures, were not


     It is interesting to note in Table 5-9 the overlap for odor between

"none" (0.08-2.9 ppm) and "strong" (2.2-41 ppm) and the overlap for respiratory

irritation between "none" (0.08-2.9 ppm) and "intolerable" (2.6-41 ppm).  The

difficulty of constructing a dose-response relationship from symptomatology

alone, as was attempted by Hoveid, can be appreciated.^28

Immediate Effects of Acute Exposure

     The immediate effects of chlorine exposure are basically odor and

irritation.  The odor threshold has been reported in western literature to

be as low as 0.02 ppm3™ and as high as 3.5 ppm.     Comparable figures in

Russian literature are 0.1 mg/m   (0.03 ppm)  and 3 mg/m3 (1 ppm).^85  Minimal

                                     TABLE 5-9
                         Subjective Responses to Chlorine
Easily Noticed
Chlorine Concentrati
in Air, ppm
1.1 -
1.9 -
2.2 -41
Chlorine Concentration
in Air, ppm
0.08- 2.9
1.95- 2.9
1.92- 4.23
2.6 -41
               Eye Irritation






Chlorine Concentration
in Air, ppm	
0.08- 2.9


•^Data from H. R. Hoyle, personal communication.

mucous membrane irritation has been reported in western literature from

0.2379 to 16 ppm,498 and in Russian literature, from 1 to 6 mg/m3 (0.3-2

     Man's olfactory organ, although less sensitive than that of many lower

animals, is able to react to some substances diluted to picograms (10~^^g)

per liter of air.  This sensitivity varies with the odor, with the individual,

and, in some cases, with the duration of exposure.  A person exposed to rela-

tively low concentrations of chlorine may rapidly lose the ability to detect

its odor, so potentially harmful concentrations of chlorine may not cause

sufficient odor or irritation to give adequate warning and alert the person

to avoid the exposure.  Laciak and Sipa^"' concluded that chlorine workers

had significant olfactory deficiency, which increased with length of employ-

ment, and that workers with lower olfactory efficiency suffered intoxication

more often and more severely.

     Vedder and Sawyer 9  determined experimentally the concentrations at

which the odor of chlorine was plainly perceptible 0.010 mg/liter (3.3 ppm)

and at which slight irritation of the throat was noted after exposure for

1 hr 0.02 mg/liter (6.6 ppm) and after 3 min 0.048 mg/liter (16 ppm).

Hoyle (personal communication) reported that odor threshold concentration varied

from 1.1 to 2.7 ppm (average, 1.6 ppm), that respiratory irritation threshold

concentration varied from 1.95 to 2.9 ppm (average, 2.6 ppm), and that the

eye irritation threshold concentration was 7.7 ppm.  De Nora and Gallone-^-05

gave 1.0 ppm as the lowest concentration that would cause slight symptoms

after exposure for several hours, 3.5 ppm as the odor threshold concentration,

4.0 ppm as the highest concentration that can be breathed for 1 hr without

serious effects, 15.1 ppm as the throat irritation threshold concentration,

and 30.2 ppm as the coughing threshold concentration.  Petri3?9 reported

that the odor or taste threshold concentration is 0.02-0.05 ppm and the

 respiratory  or  eye  irritation  threshold concentration  is  0.2-0.5  ppm.

 Leonardas _et__al_. 299 reported an odor threshold concentration of 0.314  ppm;

 this was the lowest concentration at which all four members of a  panel could

 positively recognize  the odor  of chlorine.

     Joyner2->3  reported minor  first-degree burns of the skin secondary to

 chlorine vapor  exposures, but  did not estimate concentrations or  durations

 of exposure.

     In the  Russian literature, Takhirov,464,465 reporting on 238 tests made

 on 11 test subjects, noted that the minimal perceptible chlorine  concentration

 ranged between  0.8 and 1.3 mg/m3 (0.25-0.4 ppm), with  the average being 1 mg/m3

 (0.3 ppm).    He  also reported that the maximal nonperceptible chlorine  concen-

 tration was  0.7-1 mg/m3 (0.2-0.3 ppm), with the average being 0.8 mg/m3

 (0.25 ppm).  In all test subjects, the odor of chlorine was clearly perceived

 at 3-4 mg/mj  (1-1.3 ppm); at such concentrations, all  subjects had acute

 irritation of upper respiratory mucosa, and some had a reflex cough and

 conjunctival irritation.  At 1.3-2 mg/m3 (0.4-0.6 ppm), most noted the

 chlorine odor and had slight nasal irritation, and some complained of  con-

 junctival irritation.  Some complained of slight nasal irritation at even

 lower concentrations.

     Styazhkin^56 reported 0.7 mg/m3 (0.2 ppm) as the chlorine odor threshold

 concentration.  Lazarev^°^ cited 3 mg/m3 (1 ppm) for odor and 1-6 mg/m^

 (0.3-2 ppm)  for mucosal irritation.   Ugryumova-Sapozhnikova^SS concluded

 that the olfactory organ can "sense" a chlorine concentration of  0.3 mg/m3

 (0.1 ppm) and stated that others had reported the "sensing" concentration

 at 0.1-0.5 mg/m3 (0.03-0.2 ppm).

     At higher  concentrations, the irritation becomes pronounced,  with

marked cough, dyspnea, and conjunctivitis.   At sufficiently high  concen-

 trations, pulmonary edema or even death may occur.   Some of the victims

of chlorine exposure during World War I had minimal to no significant

pathology of their lungs, as determined by autopsy.  It was postulated

that they died as a result of laryngeal spasm secondary to sudden large

exposure to irritating chlorine gas.^"^

     Zielhuis528 stated that 30 ppra for 30 min was potentially lethal.

Vedder and Sawyer^8 reported that 0.30 mg/liter (100 ppm) was tolerable

for only a few seconds and that 30 min of exposure at 3.0 mg/liter (1,000 ppm)

was lethal.  De Nora and Gallone,105 however, reported that 40-60 ppm was

dangerous in exposures of 30-60 min and that 1,000 ppm would be fatal after

but a few deep breaths.

Latent Effects and Sequelae of Acute Exposure

     Asthmatic people often display acute bronchospasm or bronchial obstruction

when exposed to nonspecific respiratory irritants.  The occurrence of asthma,

or rather the aggravation or relapse of asthma, in conjunction with exposure

to chlorine is seldom reported in the literature.^1  it is of interest that

not only has inhalation of low concentrations of chlorine caused an asthmatic

attack, but ingestion of chlorinated water has been associated with the

occurrence of asthmatic relapse. ^°  Sheldon and Lovell^l refer to a

53-year-old asthmatic housewife.  Each time she visited an indoor swimming

pool, she experienced severe asthma within a few hours after being exposed

to the air contaminated by the swimming-pool water, which had a chlorine

load of 4-6 ppm.  This patient once developed such an extreme attack of

wheezing within an hour of entering the pool area that she was forced to

leave the building, thus immediately obtaining relief.  Her asthmatic com-

plaints increased on Monday nights, after her weekly washing with a liquid

chlorine rinse.  When she discontinued the chlorine rinse, she experienced

no further aggravation.

      Hoveid,228  £n ^s follow-up study of  the chlorine gas accident in

Mjondalen, Norway, using symptomatology and dose-response data from U. S.

Bureau of Mines  Technical Paper 248, attempted to derive relative exposure

doses of the victims.  He believed that all those hospitalized were exposed

to concentrations of at least 30 ppm and that many were exposed to 60 ppm.

He concluded that the after-effects, some  two decades after exposure, were

few and generally trivial; the most common complaint was dyspnea.  A number

of authors are of like opinion, that single acute exposures cause no permanent


     Other authors disagree.  Kowitz et al. studied the accident in Baltimore

in which 150 longshoremen were accidentally exposed to chlorine.  They felt

that sufficient  abnormalities of pulmonary function were found to suggest

permanent damage.^82  vfeill et^ _al. , on review of their data, disagreed.

     There is disagreement as to whether pulmonary edema, when it occurs,

has its onset immediately after exposure or is delayed.1^6  There is also

some disagreement as to the role of chlorine inhalation in the development

of pulmonary infections.   Pneumonia and infectious bronchitis have been

reported, as has tuberculosis, but many authors doubt the role of chlorine

in the latter disease.168»511

     The immediate effect of exposure of the respiratory surface to chlorine

may be involvement of the most distal airways and may persist as latent sequelae,

which are not readily documented by most routine tests of function.  For

instance, in 19  subjects (mean age,  35.3 years)  who were accidentally exposed

to chlorine several weeks (mean, 3.5 months) before testing, the most common
abnormal pulmonary function was closing volume.      The closing volume

test has been introduced in recent years,    and  appears to be a most sensitive

measure of disorder of  the peripheral (or "small") airways.334

     Pathology of other organ systems has also been reported.   Gastric

ulcers, when they occur, may be stress ulcers and not result from the

direct action of chlorine on the gastric mucosa.194  Changes in brain and

kidney tissue of victims who die a couple of days after exposure may be

due to hypoxia associated with pulmonary edema, rather than a direct toxic

effect of the gas.   The development of valvular heart disease is questionable.

Chlorine produces its effect by localized reaction, and no systemic effects

are thought to occur.

     Both liquid chlorine and gaseous chlorine can produce ocular damage.

The production of any changes in the internal structures of the eye, however,

                                                                     1 O Q
is not reported to have occurred in either acute or chronic exposure.

Effects of Chronic Exposure

     A number of authors have studied the effects of chronic exposures to

low concentrations of chlorine.  Ferris et al.    reported on observations

made during the winter of 1963-1964 on a group of pulp-mill workers exposed

to chlorine and oxides of chlorine in the process of bleaching pulp.  They

were compared with workers who were exposed to sulfur dioxide.  The population

was observed during a 2-month period, with the use of a respiratory question-

naire, simple pulmonary-function tests, and environmental determinations.

The average cumulative exposure duration was 20.4 years.  The chlorine con-

centrations during the surveillance period were reported to be around 0.001 ppm.

But they were known to have peaked as high as 64 ppm before the study, so

the target population represented a mixture of people with acute and chronic

low-concentration exposures to chlorine and oxides of chlorine.  The authors

did not consider the difference between the two groups to be statistically

significant.  There was significantly less respiratory disease in the total

mill population than in the general male population of the town.  They did

 not  consider  the low prevalence of disease in the working population indicative

 of the "safety" of the pollutants to the general population.

     McCord   reported on a case of chronic intoxication in a worker chroni-

 cally exposed to chlorine at concentrations up to 15 ppm.

     Kaufman  and Burkons '^ noted that workers with occupational exposures

 to chlorine of 5-30 years had persistent obstructive airway defects and

 mild hypoxemia.

     Chester  et^ ai^.   studied workers who, for the most part, had chronic

 exposures to  chlorine at less than 1 ppm; some of them, on occasion, had

 acute exposures of sufficient dose to require oxygen therapy (>30 ppm ? ).

 Three of 139  had significant impairment of ventilatory function.  Compared

with controls, the exposed group had a significant reduction in maximal

midexpiratory flow.  This was even more marked when an exposed group of

 smokers was compared with a control group of nonsmokers.  This may indicate

 that smoking  and chlorine exposure have additive or synergistic noxious

 effects.   The authors suggested that the changes seen in their patients and

                         O QO
 in those of Kowitz et^ al.    could represent peribronchial cicatrization

 secondary to  chlorine inhalation.

     Patil et^ al.3'3 studied 600 diaphragm-cell workers in a number of

chlorine manufacturing plants in North America.   Exposure data and medical

evaluations—including chest X ray,  electrocardiogram,  pulmonary-function

tests,  and physical examinations—were collected for 332.   On a time-weighted

average,  exposures ranged from 0.006 ppm to 1.42 ppm;  most were exposed to

less than 1 ppm.   By history, tooth decay showed a moderate degree of dose

response, but this was not confirmed by examination.  The authors believed

that no statistically significant  signs or symptoms on a dose-response

basis were found.   Some minor hematologic changes were noted, as were some

symptoms, such as nervousness,  shyness, and anxiety.  The authors were not

convinced that the latter were associated with chlorine exposure itself,

but thought that they might be due to some other factor in the chlorine-

cell room.

     In light of this, it is interesting to note that the victim of an

accidental chlorine exposure often exhibits a variable degree of acute

anxiety.75,165  xhis anxiety is lessened if the patient is treated calmly

and with confidence.283  jt has been observed that the industrial worker

who has experienced multiple acute exposures does not manifest the high

                                                                    O Q O
degree of acute anxiety as does the victim unaccustomed to chlorine.

     A number of authors have noted not only acute transient psychologic

reactions, but also some longstanding problems.  Chasis et^ al.'3 observed

in 16 of 29 patients anxiety reactions with phobias, hysterical phenomena,

and psychosomatic dysfunction for periods of 1-16 months after exposure.

     Chloracne, a form of chronic skin lesion, has been reported among

workers engaged in the production of chlorine by the electrolytic process.

It is thought that a contaminant created by the reaction of chlorine with

the tars in the anode cells produces the lesion, and not chlorine itself.148

In confirmation of this, similar lesions are seen among those who are not

exposed to chlorine gas but are working with various chlorinated aromatic

hydrocarbons—the chloronaphthalenes, chlorophenyls, chlorophenols, etc.9°

The offending agents are thought to be reaction contaminants—various

chlorinated dioxins.274'329

     Finally, the phenomenon of tolerance, so often reported in the literature,

should be mentioned.  Sequential exposure appears to modify significantly

the outcome of the individual response in some people.291>431  The mechanism

is not understood, although the same phenomenon has been described for a

variety of irritant and toxic gases.453  xt has been noted that men may work

without signs of discomfort in an atmosphere where the concentration of

some irritants has accumulated gradually.  The same atmosphere may be

intolerable to persons entering the contaminated area from fresh air.

When a "tolerant" person leaves the contaminated atmosphere for 10-30 min,

the tolerance is lost, and reentry into the contaminated area is objectionable.

The degree and duration of tolerance may be different for different irritants

and for different concentrations.

     Animal experiments indicate that development of a high degree of

tolerance is possible.  Jancso^3 an(j porszasz and Jancso383 have shown

that, after serial injection of capsaicin, a strong irritant, into guinea

pigs and rats, known irritants failed to produce their typical effects when

                                                                     O / /
applied to skin or eyes.  The desensitization may persist for months. ^

     Chlorine gas recognition (odor) also appears to be influenced by

previous exposure, in that the threshold concentration may tend to rise

in prolonged or repeated exposure. ^»°   Perhaps related is the discrepancy

in the literature in regard to those characteristics.  For instance,

observations gathered on chronically exposed workers seem to suggest an

analogous tolerance with respect to both odor and mucosal irritation.395,456

Mutagenesis, Teratogenesis, and Carcinogenesis

     There is no evidence of mutagenic, teratogenic,  or carcinogenic effects

of chlorine in human beings.

     Pregnant women exposed to chlorine have gone to term with no reported

complications.  Women exposed to chlorine in their place of employment had

normal pregnancy, delivery, puerperium, and lactation, and their infants

were of normal weight.^35

     No increased incidence of lung or skin malignancies has been reported

among chlorine workers.

     Table 5-10 summarizes the available data on the threshold and limit

values for chlorine, and Table 5-11 gives some examples of the available

chlorine concentration limits.

Short-Term Public Exposure Limits (STPL's)

     On the grounds that there is no justification for submitting the public

to appreciable risk from chlorine in situations where exposures can be pre-

dicted, the NAS-NRC Committee on Toxicology has recommended "short-term

public exposure limits."  (Table 5-12).  The Committee believes that none

of these concentration-duration combinations presents any health hazard.

Public Emergency Limits (PEL's)

     On the grounds that,  under some emergency conditions, the public may

be exposed to concentrations of chlorine in excess of the STPL's, the NAS-NRC

Committee on Toxicology also recommended "public emergency limits."  (Table

5-13).  The human response to these combinations of concentration and duration

may be perception of a strong odor or irritation of the mucous membranes,

                                                                              Q C f
but the effect is thought  to be reversible and to involve no serious sequelae.


     Airborne hydrogen chloride exists in the anhydrous state and as a

hydrochloric acid aerosol, i.e., as microdroplets of a solution of hydrogen

chloride and water.  Because anhydrous hydrogen chloride is highly hygroscopic,

exposures to this material are potentially more dangerous to the biologic

system than exposures to hydrochloric acid aerosols.  It insults not only

by corrosion, as does the  acid, but also by desiccation. ^-  This very affinity

for water, however, makes  general environmental chronic exposures to low con-

centrations of anhydrous hydrogen chloride extremely unlikely.  Even in

industrial settings, where anhydrous hydrogen chloride may be used in quantity,

                                   TABLE  5-10

                     Summary of Chlorine Thresholds and Limits
 Chlorine  Concentration,
   ppm    	  Remarks          	        	 References
Range of reported odor thresholds
TLV, OSHA time-weighted average
Permissible concentration; 8-hr working
Men can work without interruption
There might be slight irritation
Pennsylvania short-term limit for 5 min
Permissible excursion for 15 min based
on TLV
Recommended as 60-min EEL3-
Stinging or burning in the eyes, nose,


                           and throat and perhaps headache due
                           to sinus irritation; may be watering
                           of eyes, sneezing, coughing, bloody nose
                           or blood-tinged sputum                    206

          4              Recommended as 30-min EElA                  528

         >5              Severe irritation of eyes, nose, and
                           respiratory tract, which becomes in-
                           tolerable for more than a few minutes     528

          5              Recommended as 15-min EEl£                  528

          7              Recommended as 5-min EEL3-                   528

        14-21            Dangerous for 0.5-1 hr                      206

        35-51            Lethal in 1-1.5 hr                          151
"Emergency exposure limit; for an emergency in a manufacturing area and its
 neighborhoods, storage facilities, and surrounding areas, and during trans-
 port of the chemical; suggested by Zielhius in 1970.528

Established Limits                 TABLE 5-11

                     Examples of Some Established Limits for

                             Chlorine Concentration
Threshold limit value (TLV):   3 mg/m3 (1 ppm); for 15-min
  excursion; 9 mg/m3  3 ppm                                               7

Russian maximal allowable concentration:
  industrial, 1 mg/m3 (0.001 mg/liter)                            .      239

Recommended EEL for submarine crews:  3 ppm for 60 min                  357

Pennsylvania short-term limits:       3 ppm for 5 min                   377

Maximal allowable concentrations in populated areas:

  Average 24-hr concentration, 0.03 mg/m3 x 1,440

  Maximal single concentration,
                 0.1 mg/m3 (Russian figures)                            301

Recommended EEL's for occupational exposure:                            377

                        60 min, 3 ppm
                        30 min, 4 ppm
                        15 min, 5 ppm
                         5 min, 7 ppm

International MAC's in the workplace:                                   100

       German Federal Republic,     2 mg/m3 (1968)
       German Democratic Republic,  1 mg/m3 (1963)
       Great Britain,               3 mg/m3 (1955)
       Hungary,                     1 mg/m3 (1956)
       Poland,                      1 mg/m3 (1959)
       Yugoslavia,                  3 mg/m3 (1957)
       Czechoslovakia,              3 mg/m3 (mean MAC, 1969)
                                    6 mg/m3 (peak MAC, 1969)
Occupational Exposure Limits,
Department of Labor, Occupational Safety and Health Administration:
          3.0 mg/m3 (1 ppm)

                                   TABLE 5-12

                 Short-Term Public Exposure Limits for Chlorineg.

             Duration, min      Chlorine Concentration, mg/m   (ppm)

                  10                         2.9  (1.0)

               30 and 60                     1.4  (0.5)
—Values are tentative.  The STPL's are to be considered time-weighted
 averages, with maximal excursion factors of 3 for the 10-min concen-
 tration and 2 for the 30- and 60-min concentration.  Any excursions
 above the STPL should be compensated for by an appropriate reduction
 in the duration of the exposure.  Adapted from National Academy of

                                   TABLE  5-13

                      Public Emergency Limits  for  Chlorinef.

          Duration, min      Chlorine Concentration, mg/nr* (ppm)

               10                           8.7  (3)

            30 and 60                       5.8  (2)
""Values are tentative.  The PEL's are ceiling  limits  and  are not to be
 exceeded.  Derived from National Academy of Sciences.

 exposures  to the anhydrous state are unlikely, because the material fumes

 in atmospheric humidity and forms the aerosol.  Because of these hygroscopic

 properties, it must be assumed that published reports deal with hydrochloric

 acid aerosol unless they specifically state otherwise.

     Exposures to gaseous hydrogen chloride are limited to the external

 surface of the body (integument and conjunctiva) and the lining of the

 respiratory tract (teeth and mucous membranes of the mouth, nose, pharynx,

 trachea, etc.).322


     The mechanisms of action of hydrogen chloride may be conveniently

 described in two parts:  molecular and elementary biochemical effects and

 disturbed function.

 Molecular and Elementary Biochemical Effects

     Hydrogen chloride is readily soluble in aqueous medium, up to concen-

 trations of 72 wt %, at 20 C.   It is also soluble, to a smaller extent, in

 organic solvents.27°  in water, hydrogen chloride dissociates almost com-

 pletely, because its pK is -7.  This occurs in the following fashion:

                        HC1 + H20.  5  R30+ + Cl~

     The hydrogen ion is readily captured by the water molecules, with pro-

duction of hydronium ions, in which the proton is attached to the rest of the

                                       2 2*5
molecule by a coordinate covalent bond.

     Reciprocally, the hydronium ion becomes a donor of a proton, responsible

 in turn for a variety of reactions with organic molecules.   For instance,

protons, by virtue of their well-recognized catalytic property, may effectively

                         f\ o
cleave organic molecules.     Among others, hydrolysis of peptides and of

esters may well assume major importance in the production of injury, inasmuch

as these are components of the cellular wall.  Furthermore, hydroxylation of

carbonyl groups and polymerization, as well as depolymerization, of organic

                                                          f\f 27
molecules are reactions caused by this catalytic property. °»^'

     With the loss of membrane integrity, the injured cell can readily be

depleted of cytoplasmic components, and cellular death may follow rapidly.

However, the dose-response relationships at realistic concentrations are

not known.

Disturbed Function

     Necrosis, or cellular death, is obviously the most serious functional

effect of acid burn.  Erythema and edema usually precede it, although edema

is probably the most characteristic manifestation; it occurs in any tissue

that bears the brunt of the exposure.  Edema of the cornea and conjunctiva,

skin and surface mucosae,315 and deep respiratory tissues has been described

in connection with substantial or massive exposure.

     Experiments with rodents suggest a discrepancy between animal species

in regard to hydrogen chloride toxicity.  Rats, for instance, survive at

concentrations that are most effective in killing mice, guinea pigs, and

rabbits.101'315  Death is attributed principally to respiratory injury with.

emphysema, atelectasis, and pulmonary edema reflecting th,e extent of the


     Residual alveolar injury may persist in animals sacrificed 14 days

after exposure.101  Differences in severity or type of injury have not been

detected between aerosol and vapor phases of hydrogen chloride.     The en-

vironmental temperature seems to have some importance, with morbidity and

mortality higher at 37 C than at 20.298

     The genesis of pulmonary edema, including the variety caused by inhaled

chemicals, has been reviewed recently.     Changes in permeability and liquid

transport across cellular membranes are associated with histologically evident

damage of the alveolar epithelium and endothelial cells.

     The sequence of fluid accumulation, beginning around bronchioles and

later involving alveolar spaces, has been well described by Staub.

     An analogy of the ultrastructural changes associated with hydrogen

chloride inhalation has been described in association with aspiration of

gastric juice.5

     The effect of community exposure concentrations (i.e., air pollution)

remains undocumented and hypothetical.


Single Exposures to Hydrogen Chloride Vapor and Aerosol

     The effects of hydrogen chloride vapor on animals were reported as

early as 1886 by K. B.  Lehmann.-^°  Lehmann's data are given in Table 5-14.

     Banner et al.     exposed mice and rats to hydrogen chloride vapor

or aerosol for 5 or 30 min.  The vapor concentrations were 3,200-57,290

ppm for 5 min and 410-6,681 ppm for 30 min.  The aerosol concentrations

were 6,571-62,042 ppm for 5 min and 1,204-6,640 ppm for 30 min.  The LC5Q

values are shown in Table 5-15.

     Gross examination of animals that died during or shortly after exposure

revealed moderate to severe emphysema, atelectasis, and pulmonary edema.

Recovery was not complete in animals that survived 14 days.

     The lowest concentrations that caused death in these experiments by

Darmer et_ al.    are shown in Table 5-16.

     Dose-response regression lines calculated from the data of Darmer

et_ a^.101 (Table 5-17)  are shown in the Figures 5-2 through 5-9.

                                  TABLE 5-14

               Effects of Single Exposures of Hydrogen Chloride

                      on Cats, Rabbits, and Guinea PigaJL
         Hydrogen Chloride
         Concentration      Exposure
Animals  mg/m^ (ppm)	
Cats and    150-210
rabbits    (100-140)

Rabbits  2,000 (1,350)
pigs       450 (300)

Rabbits  5,000 (3,400)
Time, min  CT, mg-min/m^  Effects
Up to


54,000-75,600  Salivation, rhinorrhea,
                 no sequelae

   150,000     Respiratory irritation,
                 corneal opacity

   162,000     Cloudy cornea, catarrh

   450,000     Death 2-6 days after
—Data from Lehmann.

                                   TABLE 5-15

        LC      of  Hydrogen Chloride Vapor and Aerosol in Rats and Mice3.
Vapor :
JU'Jj 	 . 	 _ 	 . 	
LC , mg/m3 (ppm)
5 Min
60,100^ (40,898)
20,200^ (13,750)

45,600 (31,008)
16,500 (11,238)

30 Min

6,90Qb (4,701)
3,90Qb (2,644)

8,300 (5,666)
3,100 (2,142)
—Data from Darmer et^ al.101

—Values not given in original paper.

                                  TABLE 5-16

    Lowest Concentrations of Hydrogen Chloride Vapor or Aerosol that Caused
Death in Experimental Rats and Mice-


Time, min

Lowest Concentration
Causing Death
mg/m^ (ppm)
48,507 (32,255)
4,768 (3,20Qb)
3,990 (2,678)
1,690 (1,134)

28,775 (19,312)
13,496 ( 9,058^)
4,336 ( 2,910^)
1,794 ( 1,204k)


~Data from Darmer et al.
—Lowest concentration tested.

                                   TABLE 5-17

          Bliss Dose-Response Regression Data for Lethality of Hydrogen

                  Chloride Vapor and Aerosol in Mice and Rats-3-
Killed, %


LCt, mg-min/m






.—Data  from Banner  et al.

CT.s....(mq Jrri ri/xu". in) '..
I  ,000
 Ct (mg min/cu

                 r   r  ?
                             I  I
                                                                   O>  «•*  en
                                                    iiH!M '• r 1  ;
                                                        ''LIMITS  OF
                50,000        100,000

                           Ct (mg 'min/cu m)

                                           r  r
  84:  _

  15  -
         -FIGURE'.5-4 .LTTHALXts- (nig! min/cu- rn'};:AN'd--9^
                 ;-[.i.JO MICE FOLLOWING TOTAL-BODY1. E

I  . i   ,  .  •  .  :  .i   I  .


                                        Ct (mg

mln/cu m)

                                :   i   III1'—!1   :     !•   I   i
                             AND.. 95s:cwRiBtN'CEXxHlTs'idE4: YOROGEN: CHLOR
  J_L  I JJJl
   '  LP  LL1 l
  •T—r-~r -t-TT-:
  50,000        100,000

       Ct  (mq min/cu m)


   84 -
•-.  50 - -—

                                                                          O»  -4  O» 10

                                                                          !   I   !  !
  99 -
  84 - '--:--
  15  -
                             CHLORIDEJAEROSOLS iTO. RATS FOLLOWING.
                                   EXPOSURE-FOR-5 MINUTES.

                                 Ct (mg min/cu m)

                                                   _                • !    I   '  i
                                                   min/cu m)

              LETHAL  :CTs! (itg .mitr/cir m)--'AND;9i?iro'NFID!ENCE:bMlT.S:.O.U
              CHLORIDE  AEROSOLS
                 TOfRATS FOLLOWING TO
                   '-  30

50,000       100,000
         Ct  (mg  min/cu m)

     Mucociliary activity of excised rabbit trachea ceased permanently after

exposed to hydrogen chloride vapor at 600 mg/m  (400 ppm) for 0.5 min, at

90 mg/m3 (60 ppm) for 5 min, and at 45 mg/m3 (30 ppm) for 10 min.93

     Table 5-18 summarizes the available toxicity data on hydrogen chloride.

Repeated Exposures to Hydrogen Chloride Vapor

     Machle ^t _al_.    exposed animals to hydrogen chloride gas at 0.05-20.5

rag/liter for periods of 5, 15, 60, 120, 360, 720, 1,800, or 7,200 min.  One

to six concentrations were used for each period.  The exposures of 720 and

1,800 min were carried out 6 hr/day for 2 and 5 consecutive days, respectively.

The 7,200-min exposure was carried out 6 hr/day for 5 days/week for 4 weeks.

In each of 31 experiments, three rabbits and three guinea pigs were exposed;

in the 7,200-min experiment, an adult female monkey was also used.  The re-

sults of these tests are shown in Table 5-19.  Deaths in the guinea pigs

were attributed to acute respiratory damage.  High concentrations caused

necrosis of the trachea and bronchi, edema, atelectasis, emphysema, and

damage to pulmonary blood vessels.  Gross pathologic changes were noted in

the livers of 45 of 57 guinea pigs that died, and pulmonary lesions were

noted in guinea pigs that died or were sacrificed between 1-18 months after

exposure.  The rabbits were more resistant to the immediate effects of hydrogen

chloride, but died later from pulmonary or nasal infections.  Severe lesions

were noted in the livers of 16 of 51 rabbits that died.

     Ronzani    noted only slight unrest of the animals and irritation of

the eyes and nose in rabbits, guinea pigs, and pigeons exposed to hydrogen

chloride at 150 mg/m3 (100 ppm) for 6 hr/day for 50 days.  The hemoglobin

concentration was only slightly diminished. " Table 5-20 summarizes the

available toxicity data on repeated exposures to hydrogen chloride vapors.

     Table 5-21 shows a gradation of Ct's with corresponding toxicologic


                                  TABLE 5-18

              Summary of Toxicity of Single Exposures of Animals

                          to Hydrogen Chloride Vapor

Hydrogen Chloride
mg/m-* (ppm)	
 5,000  (3,400)
 1,000  (650)
 6,500  (4,350)
   450  (300)
 2,000  (1,350)

 5,500  (3,700)
Time, min    Ct, mg-min/m^
 150-210(100-140)    up to 360
60,000  (40,898)
 6,900  (4,701)
47,500  (32,255)
            4,250  (2,910)
 3,870  (2,644)
20,200  (13,750)
 1,760  (1,204)
            4,750  (3,200)

Deaths         148
100% deaths    315
100% deaths    315
Cloudy cornea  148
  distress     148
No deaths      315
              Running nose,










LL* t _
Lowest dose
Lowest dose
Lowest dose
Lowest dose






                                  TABLE 5-19

                 Toxicity of Hydrogen Chloride Gas in Animals3-
Hydrogen Chloride
No. Rabbits No. Guinea Pigs mg/m^
3 3 6,500
3 3 1,000
3 3 5,500
33 100
3 3 50
Time, min
a                       QIC
"Data from Machle et al.

—Mild inflammatory reactions in bronchi, with peribronchial fibrosis and
 lymph node hyperplasia, in guinea pigs; lobular pneumonia and pulmonary
 abscesses in rabbits.

                                                                            100% deaths

                                                                            100% deaths

                                                                            No deaths


                                                                            No effects,
                                                                              no patho-

                                       TABLE  5-20

            Summary of Repeated Exposures of Animals  to Hydrogen  Chloride  Vapor
Hydrogen Chloride
Concentration      Exposure   Daily
mg/nr* (ppm)	  Time, min    Ct, mg-min/m-*  Effect
  guinea pigs    100   (65)
  guinea pigs,
  and monkeys     50   (33)

  guinea pigs,
  and pigeons    150   (100)
Inflammatory reaction
  in respiratory
  tract                315
No effects, no
Unrest, irritation
  of eyes and nose     148
—360 min/day for 5 days.

—360 min/day for 20 days.

-360 min/day for 50 days.

                        TABLE 5-21

      Ct's and Effects Produced by Hydrogen Chloride

                     Vapor in Animals

Effect	      Ct, mg-min/m3

Lethal to 100%                          200,000 - 450,000

Lethal to 50%                           100,000 - 300,000

Cloudy corneas, catarrh                     150,000

Irritation, rhinorrhea, salivation           50,000

Rare deaths or pathology                    <10,000

     Tables 5-18 and 5-20 indicate that mice are more sensitive to the

lethal effects of hydrogen chloride vapor than rats, guinea pigs, rabbits,

or monkeys.  Also, within a given species, the degree of damage produced

by hydrogen chloride is related to the Ct over the known ranges of concen-

tration and exposure.  The LCt   for mice is about half that for rats.

     It is indicated also that irreversible toxic effects or death would

occur only rarely after single exposures of 5 min or more at a Ct of

               _                                                            3
10,000 mg-min/mj or less, even in mice.  The LCt,-n is about 100,000 mg-min/m

for mice and about 250,000 mg-min/m-^ for rats when the exposure time is 5

or 30 min.  At the LCtcQ clouding of the cornea occurs in rabbits and guinea

pigs.  The studies of Lehmann    and of Ronzani-*-^ in rabbits and guinea

pigs indicate that irritation, salivation, and rhinorrhea occur at a Ct of

about 50,000 mg-min/m3.

     The studies show that, in rabbits, guinea pigs, and monkeys, daily

                       3         ^
Ct's of 18,000 mg-min/m  (50 mg/m  for 6 hr/day) for 20 days do not cause

any signs of irritation or morphology.

     Except for the effects on the eyes, skin, and respiratory tract, the

single mention of hemoglobin, and the liver pathology, there is little

published information on the effects of inhaled hydrogen chloride on the

various body organs or systems.

Intrabronchial Insufflation of Hydrochloric Acid

     Winternitz et^ al.519 insufflated 5 ml of 0.1-1% hydrochloric acid in

saline into the lungs of anesthetized rabbits.  The 1% solution caused death

within 3-5 min.  The lungs filled the pleural cavities.  The pleural surfaces

were tense and often hemorrhagic.  When sectioned, the lungs contained large

quantities of blood-stained fluid.   The tracheas and larger parts of the

bronchi  contained blood-stained fluid and hemorrhaged into the mucosa.

The 0.25% solution seldom produced sudden death.   Most of the animals came

out of anesthesia and later showed no untoward symptoms, except pulmonary

infection.  Animals sacrificed at intervals after insufflation showed

destruction of the epithelium of the bronchioles, the alveolar ducts, and

the alveoli.  There was exudation into the alveolar, interstitial peri-

vascular, and peribronchial tissues.  In some areas, there was consolidation,

with or without destruction in the alveolar walls.  Later, there was organiza-

tion of the exudate, necrosis, and proliferation of the epithelium and

bronchi.  Pulmonary parenchyma finally regenerated.

     Other investigators have reported the effects of intratracheal administra-

tion of hydrochloric acid solutions in rabbits,181  dogs,6^'183 and cats.302*503

Positive-pressure ventilation was considered an aid to survival in rabbits

and dogs.64,181,183  Ventilation with oxygen immediately after exposure to

the acid was said to spread the damage and to increase mortality in cats.


     Compared with chlorine, there is a paucity of data available on the

human effects of exposure to gaseous hydrogen chloride.  Aside from the

studies of Toyama et ^l.^81 in 1962, ten Bruggen Cate^69 ±n 1968, and

Leondardos et al.    in 1969 and the subjective-response data of industrial

hygienists in 1973, most of the material in western literature is derived

from much older studies.

     The Russians have reported on experimental work with human volunteers.

This work includes not only data on the physiologic response of odor, as

recognized in the United States, but also "odor" or reflex effects as de-

termined by changes in optical chronaxy, eye adaptation to darkness,

respiratory rhythm, or other test techniques not commonly used by experimenters

in other scientific communities.  Rjazanov,3^ ±n an article in 1965, discussed

 the  U.S.S.R. Criteria and Methods  for Establishing Maximum Permissible

 Concentrations of Air Pollution.

     In both anhydrous and aerosol forms, hydrogen chloride is a strong

 irritant, affecting  the conjunctiva and the mucous membranes of the

 respiratory tract.   Because of its solubility in water, the major effects

 of acute exposure are usually limited to the upper passages of the respiratory

 system and are of sufficient intensity to encourage prompt voluntary with-

 drawal from a contaminated atmosphere.  The warning properties are such that

 acute exposure causing significant trauma is limited to people who are pre-

 vented from* escaping.  In man, the effects are usually confined to inflammation

 and possibly ulceration of the nose, throat, and larynx.322  However, on

 rare occasions, laryngeal spasm or pulmonary edema may occur.  •*•

     According to Heyroth, "7 most people can detect 1-5 ppm, with 5-10 ppm

 being disagreeable.  He also noted, however, that others have stated that

 up to 35 ppm cannot be detected by either odor or taste.

     Leonardos et^ ^1.74 determined experimentally that the odor threshold

 concentration of hydrogen chloride was 10 ppm.

     Hoyle (personal communication), in rating subjective responses of

 trained industrial hygienists, reported that no response was observed at

 0.06-1.8 ppm, minimal response was noted at 0.07-2.17 ppm, the material

was easily noticed at 1.9-8.6 ppm, and a strong response was obvious at

 5.6-22.1 ppm (Table 5-22).

     Matt-^8 reported that work was undisturbed at 10 ppm, difficult at

 10-50 ppm, and impossible above 50 ppm.

     However, Sax^1-*- said that,  although short exposures to 35 ppm could

cause irritation of the throat,  work was possible at 50-100 ppm for an hour.

He noted that severe exposure could cause pulmonary edema or laryngeal

 spasm, with 1,000-2,000 ppm for brief periods being dangerous.

                                 TABLE 5-22

                 Subjective Response to Hydrogen Chloride^.


Easily noticed

No. Observations




Hydrogen Chloride Concentration, ppm
     Average        Range	



0.06 - 1.8

0.07 - 2.17

1.9  - 8.6

5.6  -22.1
%)ata from H. R. Hoyle (personal communication).

     In the Russian literature, Melekhina    reported the odor threshold

at 0.39 mg/m3  (0.26 ppm).  Styazhkin^56 stated that the odor threshold was

0.2 mg/m3  (0.13 ppm), and Elfimova,126 0.1 mg/m3  (0.067 ppm).

     Eye and skin burns have been observed at higher concentrations.  However,

it has been reported that flushing with copious amounts of water will prevent

most of the serious damage.322  This was confirmed by Nagao e£ al.3" in

1972.  They reported that, after application of IN hydrochloric acid solution,

the first damage to the living cells of the skin was not noted microscopically

before 120 min.  If the acidic solution remains in contact with the tissues

for relatively long periods, damage can occur.  For example, it is possible

that enough gaseous hydrogen chloride will go into solution in perspiration-

soaked clothes to cause dermatitis.322

     Ten Bruggen Gate, "^ in 1968, published a report on dental erosion

associated with exposures to various mineral acids, including hydrochloric

acid.  In most of the exposures, hydrochloric acid was in combination with

other acids, primarily sulfuric.  The pathologic effects observed were etching

and erosion of the front teeth.  However,  there was no apparent increase in

dental caries.  There was some correlation of severity of pathology with

degree and duration of exposure.

     Aside from dental erosion, no significant abnormalities have been

associated with chronic exposures to low concentrations of gaseous hydrogen

chloride.   Toyama et _al_.*°-'- noted that workers chronically exposed did not

exhibit the pulmonary-function changes observed in people acutely exposed

to similar concentrations; this suggests acclimation.

     Table 5-23 summarizes the reported effects of hydrogen chloride on man.

                                  TABLE 5-23

           Summary of Human Effects of Exposure to Hydrogen Chloride
Hydrogen Chloride
Concentration, ppm


















Effects or Comments
Few minutes  Lethal

30-60 min    Dangerous

   —        Brief exposures dangerous

   —        Work impossible

60 min       Intolerable
                            241, 449a



                            207, 148

                            411, 148, 202, 241
             Irritation of throat after
               short exposure            411

             Work difficult but possible 207, 148

             Undetectable by odor or
               taste in some             207

             Irritation                  450

             Work undisturbed            207, 148

             Odor threshold concentra-
               tion                      299, 451

             No organic damage           450

             Odor threshold concentra-
               tion                      207

             Optical chronaxy reflex
               threshold concentration   322

             Digitovascular toxicity
               threshold concentration   126

             Odor threshold concentra-
               tion                      340

             Threshold concentration
               for reflex effect on
               eye sensitivity to
               light                     127, 126

             Odor threshold concentra-
               tion                      456, 126

TABLE 5-23 - continued
Hydrogen Chloride   Exposure
Concentration, ppm  Time

Effects or Comments         Reference
                    3 mo
                   18 mo
                    6 yr
Odor threshold concentra-
  tion                      127, 126

Threshold concentration
  for change in rhythm and
  depth of respiratory move-
  ment                      127, 126

Earliest etching of tooth
  enamel in plant workers   469

Earliest erosion of tooth
  enamel in plant workers   469

Earliest erosion to expose
  secondary dentin in plant
  workers                   469

Mutagenesis, Teratogenesis, and Carcinogenesis

     No mutagenic, teratogenic, or carcinogenic effects of exposure of humans

to gaseous hydrogen chloride have been reported.

     Recent data indicate that gaseous hydrogen chloride and formaldehyde

can react in the atmosphere to form bis-chloromethylether, a reported

carcinogen.  This reaction does not occur at concentrations of hydrogen

chloride or formaldehyde at or below the current threshold limit value. 3;, 143,359

Combined Exposures to Hydrogen Chloride and Other Irritants

     Styazhkin    determined experimentally the odor threshold concentrations

of hydrogen chloride gas and chlorine simultaneously present in atmospheric

air.  He determined the odor threshold concentrations first for each chemical

individually and then for various combinations.  Expressing each chemical

as a fraction, determined by the experimental dose relative to the odor

threshold concentrations, he found that, when the sum was unity or more,

the odor of the combination was perceptible.  To express this in another

way, when X in the following formula is equal to or greater than 1, odor

is perceptible:

              yr _ concentration of Cl£ •  concentration of HC1

                  odor Threshold of C12  odor Threshold of HCl'

     Melekhina-^0 studied the threshold concentrations of combinations of

three mineral acids.   Using various concentrations of gaseous sulfuric, nitric,

and hydrochloric acids, he also found that the determination of odor threshold

concentration involved arithmetic summation.

 Established Limits

     Air quality  standards  for hydrogen  chloride  are  summarized  in Table

 5-24, and Table 5-25 presents short-term and emergency  limits  for  man.
                                  TABLE 5-24

               Environmental Air Standards for Hydrogen Chloride
Hydrogen Chloride Concentration, mg/nr*  (ppm)  Source
                   7 (5)                      TLV, ACGIH8a

                  — (5)                      West Germany, permissible
                                                work-station concentration^"'

                 0.7 (0.5)                    30-min mean average with
                                                maximum of 1.0 ppm267

                 0.015  (0.009)                Russian 24-hr maximal average267'328

                 0.05 (0.03)                  Maximum for single exposure267'328

                      (0.02)                  Czechoslovakian 24-hr maximal

                  —  (0.07)                  Maximal single exposure405
—Adopted by Occupational Safety and Health Administration.489

                                  TABLE  5-25

   Short-Term and Emergency Limits  for Public  Exposure  to Hydrogen Chloride^

Duration                              Hydrogen Chloride Concentration,  mg/m  (ppni)

Short-Term Public Exposure Limits;

              10 min                                  6  (4)

              30 min                                  3  (2)

              60 min                                  3  (2)

               1 hr/day                               3  (2)

               5 hr/day,
                3-4 days/mo                           1  (0.7)
Public Emergency Limits;

              10 min                                  10  (7)

              30 min                                   5  (3)

              60 min                                   5  (3)
"Derived from National Research Council Committee on Toxicology.

                                  CHAPTER 6



       Damage to vegetation due to chlorine gas was reported to have occurred

at least 100 years ago in  Europe, near brickworks,  clay product plants, and

chemical  plants.  In recent years, damage to vegetation from this gas has usually
been the result of accidental leakage,  breaks in a line,  etc.   Zimmerman

reported two cases of accidental damage to vegetation near Yonkers, N. Y.  One

case resulted from the  escape of gas from a cylinder at a swimming pool,  and the

other,  from an accidental leak at a factory.   About 30 species of plants were  in-

jured in these two cases,  including tree of heaven,  apple,  cherry, maple,  smartweed,
                                                                       *      4 54
basswood, dogwood, elm, ash,  sweetgum, hemlock,  oak,  and white pine.   Stout

reported chlorine  injury to lettuce and weeds growing near a sewer plant whose

chlorinating apparatus leaked.  The concentrations of chlorine in the ambient air

as a result of these accidents are not known.   However,  the phytotoxic potential

of chlorine has been determined by fumigation under controlled conditions.
       Haselhoff and Lindau     summarized the literature on chlorine and hydro-

chloric acid in 1903  and reported that Turner and Christison were probably the

first to have  investigated  experimentally the injurious action of chlorine and hydro-

chloric acid on vegetation.  According to Turner and Christison, an exposure to

2 ml of chlorine in ZOO ml of air for 3 hr was the  threshold dose needed  to cause

injury on mignonette.  Haselhoff and Lindau also summarized the work of Richardson,

•who exposed  spruce,  pine, cactus, myrtle, and mignonette to chlorine gas diluted to
*Common and scientific names of plants are listed in the appendix to this chapter.

1:5,000 for 12 hr.  The leaves dried up,  shriveled, yellowed, and died.  These

early results were obtained without adequate air circulation over the plants,  so

the stated concentrations should not be taken as representative of a.ctual outdoor

      In 1934,  Weiler     described chlorine injury to sugar beets and red clover.

The injury was characterized as white spots  on sugar beets and brown spots on the

clover leaves.  Weiler believed that the gas had entered the leaf via the stomata on

the upper side of the leaf, because the dead cells were found in  the vicinity of these

stomata and extending downward into the mesophyll.  Cells adjacent to the necrotic

tissue had  thickened walls. A strong layer of cork formed in the mesophyll below

the damaged area.  In clover,  the injury extended down into two or three layers  of

palisade  parenchyma.
                                 332                       333
      McCallan and Setterstrom,     McCallan and Weedon,     Thornton and
             477           18
Setterstrom,     and Barton   undertook an extensive cooperative project to deter-

mine  the comparative  toxicity of ammonia, chlorine,  hydrogen cyanide, hydrogen

sulfide, and sulfur dioxide gases to 18 species, including fungal and bacterial

plant  and animal pathogens, green leaves and stems,  seeds,  sclerotia, insects,

and rodents. Their fumigation  apparatus permitted a continuous flow of gases at

controlled  concentrations.  The exposure concentrations ranged from 1 to 1,000

ppm for periods of 1-960 min.  At 1, 000 ppm, the orders of toxicity of gases were

as follows:  for fungi and bacteria--sulfur dioxide, chlorine, ammonia,  hydrogen

sulfide, hydrogen cyanide; for seeds and sclerotia--sulfur dioxide, chlorine, ammo-

nia, hydrogen cyanide, hydrogen sulfide; for green leaves--chlorine,  sulfur dioxide,

ammonia,  hydrogen cyanide, hydrogen sulfide; and for green stems--no difference.

The plant pathogens included Sclerotium delphinii,  Rhizoctonia tuliparum, Botrytis sp. ,

Sclerotinia fructicola,  Pestalotia stellata, Glomerella cingulata, Macrosporium

sarcinaeforme, and Ceratostomella ulmi.  Sclerotia of the following plant patho-

gens were also fumigated:  Sclerotium delphinii, Botrytis sp. ,  and Rhizoctonia

tuliparum.  The  seeds  included soaked and dry rye and radish.  The green stems

and leaves included tomato, tobacco,  and buckwheat.   The order of sensitivity of

classes of organism was as follows for chlorine:  leaves,  fungi and bacteria, stems,

animals,  seeds,  and sclerotia.  Young cultures and sclerotia were much more sen-

sitive to chlorine than older ones.  With all plant pathogens and all gases, there

was a conspicuous delay in the visible growth of viable cultures after transfer to

fresh media.

Acute Injury
      Thornton and Setterstrom     reported that chlorine injury is manifested

by a discoloration of the leaf,  which eventually turns brown.  With tomato,  buck-

wheat, and tobacco, chlorine at 0. 46-2. 95 ppm for 20-480 min caused injury to

the older  leaves in the form of interveinal chlorosis, which -was followed by a

bleaching and breakdown of the entire leaf tissue.
      Benedict and Breen   fumigated 10 weed species to chlorine at a high

(2. 5 ppm) and a low (0. 5 ppm) concentration.   The fumigations were run from

approximately 10:00 a.m. to 2:00 p.m.,  to provide the maximal amount of sun-

light, so that the plant stomata would  be  open,  thereby ensuring optimal condi-

tions for marking.   The following plants  were fumigated:  annual bluegrass,

cheese-weed, chickweed,  dandelion, Kentucky bluegrass,  lamb's quarter, mustard,

nettle-leaf goosefoot, pigweed, and sunflower.   Necrotic areas were produced

between the veins on the broad-leaved plants, but they usually developed close

to the margin and with increased intensity of fumigation spread toward the midrib.

With the grasses, the markings first appeared as marginal streaks progressing

toward the main vein, in the region between the tip and the point -where the grass

leaf bends over.  The markings usually occurred alongside the veins.  Middle-

aged and older leaves were about equally marked -with necrotic areas and were

usually marked more  severely than new leaves. White to tan markings were

produced on mustard, annual and Kentucky bluegrass, chickweed,  nettle-leaf

goosefoot, and lamb's quarter.   Chlorine  sometimes  produced an overall bleach-

ing of the leaf without killing the tissue.  The  color was generally light green,

with some yellow occasionally.
       Zimmerman     fumigated 19 species of plants with chlorine at 0.46-

4. 67 ppm and found  16 were susceptible to injury at those concentrations.

Of the  susceptible species, those of most  interest were peach, coleus,  cosmos,

buckwheat, and hybrid tea.  Chinese holly, eggplant,  and tobacco had no visible

injury  from any of the treatments.  He stated  that the most characteristic: re-

sponse  of the various  species was spotting of the leaves similar to the effects

of sulfur dioxide.  The spots appear first  as cooked areas,  but turn straw-

colored or brown after a few days.  Threshold concentrations for acute injury

were reported  to be 0. 46 ppm for 1  hr  for buckwheat,  0. 56 ppm for 2 hr

for coleus, 0. 56 ppm  for 3 hr for peach, 0. 56 ppm for 2 hr for silverbell-tree,

1. 3 ppm for 2 hr for bramble, 1. 3 ppm for 0.  5 hr for bean and radish, and

1. 5 ppm for 0. 5 hr for rose.  Threshold concentrations and times  were not

given for  cosmos and hybrid tea.
       Brennan ej: al.    fumigated plants with  chlorine at 0. 10-1. 50 ppm for 4 hr.

They reported  considerable variation in the  symptoms produced, depending on the

species and the concentration of the gas.  At high concentration,  water-soaking

of the foliage and often wilting could be observed by the end of the fumigation

period.  Within a day or so fumigation, necrosis and bleaching of the leaves

developed.  A marginal necrosis developed in alfalfa and begonia, and scattered

necrotic areas developed on leaves of tomato, tobacco, and radish.  In general,

the necrotic  areas appeared between the veins, but there were exceptions.  In

monocots, the necrotic areas were produced between the veins,  giving the

appearance of streaks.  In onion and pine,  the necrosis appeared at the tip

and extended downward, as the exposure increased.  The markings on the

affected tissue varied from almost white or tan to brown.  Orange-brown

necrotic areas developed consistently in some species, such as apple, pine,

and maple.  At low exposure,  the typical response observed was  a bleaching

of the foliage.
      Brennan^taL    fumigated three species of pine with chlorine (short-

leaf,  slash, and loblolly).  The needles of all three species were visibly injured

by a 3-hr fumigation at 1. 00 ppm.

Chronic Injury

      Although  chronic fumigations have apparently not been run for chlorine,

it is logical to assume that chronic injury would result if the concentration of
the gas  were low enough during the fumigation.    Brennan^t al.   reported

that epinasty often occurred  after fumigation that -was insufficient to mark tomato

foliage.  Leaf cupping was sometimes produced on squash.  In Chenopodium,

there was a tendency for leaves to abscise  after fumigation.

Metabolic Effects

      There are no. reports  in the literature on the metabolic effects  of chlorine

gas on vegetation.

       Benedict and Breen   reported that,  of 10 weed species fumigated, mustard,

chickweed,  and sunflower were the most sensitive; dandelion, cheeseweed,

nettle-leaf goosefoot,  and annual bluegrass  were intermediate in sensitivity;

and Kentucky bluegrass,  lamb's quarter,  and pigweed were the most resistant.
B rennan jet al.    have reported that shortleaf, slash, and loblolly pines are

considerably more resistant to chlorine gas than many herbaceous species.

The threshold concentration for injury appears to be 1 ppm for a 3-hr exposure.

The results of work by a number of investigators with respect to sensitivity of

plaints to chlorine gas  are summarized in Table 6-1.
       Benedict and Breen   reported that plants under low soil-moisture con-

ditions were marked less than those grown under high soil-moisture conditions.

The age  of their •weeds also seemed to be important in affecting  this sensitivity;

the 6-week-old plants  were more sensitive than the  3-week-old plants.   The age

factor was confounded by soil-moisture stress,  inasmuch as  the 3-week-old

plants and the 6-week-old plants on dry soil were about equally marked by the

high and low concentrations of chlorine,  but the 6-week-old moist-soil plants

were  more severely marked at high concentration.
       Brennan et al.    reported that the presence of moisture on the leaves  of

plants did not seem to affect their  sensitivity to chlorine.  They also reported

that shade (darkness) has a tendency to minimize damage, if  the shade period

follows fumigation.  If the shade period precedes fumigation,  there is no effect.

Water stress, as well as closing of the stomata by artificial means, has a tendency
to reduce the sensitivity  of  tomato to chlorine gas.  Zimmerman    also reported

that water stress,  even  slight wilting,  causes plants to become resistant.

                                  TABLE 6-1
                 Relative Sensitivity of Plants to Chlorine Gas



Box elder


Crab apple

Globe -amaranth



Pin oak



Sugar maple




Tree of heaven

Tulip tree

Virginia creeper

Wandering Jew

a                             30                51                      195
 Data from Benedict and Breen   Brennan e_t a_l. ,    Haselhoff and Lindau,
                            332          426                               477
 McCallan and Setterstrom,     Shriner,     and Thornton and Setterstrom.
                        Annual blue grass








                        Nettle-leaf goosefoot



                        Pinto bean

                        Scotia bean



Balsam fir







Kentucky bluegrass

Lamb's quarter








       Brennan et al.     reported that pine trees in a hardened condition

were less sensitive  than those actively growing.

Accumulation of Chlorides
       Brennan et al.     analyzed tomato foliage for chlorine immediately

after fumigation at concentrations ranging from 0.40 ppm for 6 hr to 1.40 ppm

for 3 hr.  They found that the chloride content of the tissues was  related neither

to the degree  of chlorine exposure nor to the amount of damage produced by the

gas in these short-term fumigations.  However,  the chloride content of the

petioles was considerably higher than that of any other tissue fraction in the

plant. The  concentration in the  lower leaves was appreciably more  than that

in the top leaves.   Exposure of  the plants to an atmosphere of chlorine did not

alter the pattern of chloride distribution within the plant, and there was no

appreciable increase in the chloride content of any of the fractions after fumi-

gation.  They concluded that their evidence did not support chemical analysis

for chloride as a method of diagnosing chlorine injury caused by air pollution.
They also reported elsewhere   that the chloride content of pine needles

generally increased after chlorine fumigation, but the increment was propor-

tional neither to the degree of fumigation nor  to the extent of damage.

Indirect Effects
       Rjazonov    reported that Krasinskii had conducted studies to distinguish

between the effects of chlorine on the soil,  the root system, and the aboveground

part of plants.  Chlorine did not directly affect a plant's root system,  because

it almost immediately united with solid constituents to form chlorides.  Chlorides

are highly water-soluble, so they were easily washed out by subsoil water move-

ments, thereby depriving the soil of its original fertility and particularly of its

base  elements.

Mimicking Symptoms

        The general pattern of injury by chlorine is similar to that reported

for injury of some species by ozone--for example, mustard,  Italian prune,

and ginkgo.  Chlorine injury  of some conifers, such as larch, causes a

chlorotic needle mottle that looks very similar to oxidant-sulfur dioxide injury

of white pine.  Chlorine injury of white pine appears as a light to reddish-tan

necrosis of the needle tips.  Although the result is generally  lighter than tip-

burn caused by other pollutants, the injury could be confused -with acute ozone or

sulfur dioxide injury.


        The  effects of hydrogen chloride gas on vegetation were first noted in

Europe  and Great Britain in the vicinity of alkali plants during the midnineteenth

century. In the early days of the Le Blanc soda process, sodium chloride was

treated  with sulfuric acid, and hydrogen chloride gas was released  as an unwanted

byproduct.   Extensive studies on the damaged vegetation were undertaken at that
time by Haselhoff and Lindau.      Scrubbers installed at the various alkali works

in England between 1836 and  1863 removed at least 95% of the hydrogen chloride

in the stack gases.  In 1874,  the concentration in the stack gases was limited to
0. 45 mg/m  , and that in effect eliminated crop damage.  After the passage of the

Alkali Act of 1906 in Great Britian, there were no further reports of crop damage

by this  contaminant.
       In 1934,  Weiler    reported damage to plants by hydrochloric acid.   The

following plants were examined in more detail in the field:  osier, white thorn,

elm, linden, oak, lilac,  cherry tree,  plum tree, Virginia creeper, Oregon grape,

dragon  tree, strawberry, red currant, one species of Chenopodium, pine, and

spruce.  According to Weiler, the appearance of damage depended heavily on the

nature of the carrier of the acid and on the species examined.  Extensive  damage

in the form of dots or spots can be expected if the acid was carried by rain, dew,

or fog.   The most common type of damage was the peculiar ring formation on

the leaves.   This developed supposedly as a result of deposition  of droplets  of

dew that contained the acid on the tips  of leaves resulting in turn from the cool-

ing effect of heat radiation, which caused these drops to run off to a leaf edge

or tip.  Soot was also considered to be a carrier of the  acid.  The extent of

damage appeared to depend on the amount and concentration of the acid in  the

water droplet or soot particle.  The acid apparently diffused out of the droplet

in all directions and resulted in a rather uniform appearance in cases -where

the droplets affected the leaf.  The depression  in the leaf was small or large,

bowl-shaped or  jar-shaped,  shallow, or tapering in  a wedge shape.  The injured

areas appeared  brown on broadleaf  species and yellow on conifer species.  Acid

damage could be found not only on interveinal tissue, but also on the veins.
       In 1938,  Horicht    reported damage to forest trees in the vicinity

of soda-ash factories that released hydrogen chloride.  He attributed the damage

to the acid and noted that conifers were more susceptible than broadleaf species.

As will be  seen  later, the observation  on susceptibility  is not in  accord with ob-

servations of others, and no data were presented to  support it.
       In 1956,  Antipov   reported hydrogen chloride gas damage to ornamental

plants near a chemical factory in the USSR that released fumes once or twice a

month.   The affected plants included oriental poppy,  daisy,  belleflower, columbine,
bluets, and phlox.  Styazhkin     reported the death  of trees and  shrubs in. 1957 in the

vicinity of  the Solikansk magnesium plant (USSR),  where unpurified hydrogen chloride

gas was emitted through a stack 120 m high at 15 tons/day.  The maximal ground-
level concentration of 34. 0 mg/m  was measured 1, 000 m from the plant;
the maximal ground-level concentration at  3, 000 m was 17. 3 mg/m .
        Recently, Hindawi    reported damage to trees, shrubs and ornamental

plants in an eastern community in the United States in the fall of 1966.  Severe

damage was evident on specimens of maple, cherry, redbud,  rose, and begonia.

Hindawi attributed the damage to hydrochloric acid mist and chlorine emitted

from a nearby glass manufacturing plant.  Although no atmospheric air analyses

•were made by Hindawi, the damage was probably caused by hydrogen chloride

gas or hydrochloric acid  emitted by the reduction of silicon tetrachloride in high-

temperature ovens  to produce the fused silica  glass.  Hydrogen chloride is a

colorless hygroscopic gas and,  because of its  high solubility in water (82. 3 g/100

ml of cold water), readily forms aqueous hydrochloric acid.   Under normal

atmospheric conditions, it is an aqueous acid aerosol; but in unusually low rela-

tive humidity, it is anhydrous hydrogen chloride.  The toxic effects of high con-

centrations  of this anhydrous form may be more severe than those  of the  aqueous

form, because of the dehydrating action of the gas on exposed  tissues.
       In 1968, Wood    reported that smoke from the  combusion  of polyvinyl-

chloride insulation  at a wire salvage  operation in northern Pennsylvania caused

extensive damage to several northern hardwoods and attributed the  damage to

hydrochloric acid mist; there were no atmospheric air analyses. The damage

may well have been caused by the anhydrous or the aqueous phase of hydrogen
chloride.  Boettner and Weiss    reported that hydrogen chloride gas accounts

for 58% of the weight loss in the low-temperature fraction of polyvinylchloride

       In 1969, Bohne   reported hydrogen chloride gas damage to several

shrubs, trees, and flowers near a hospital  incinerator.

       The experiments of Haselhoff and Landau    and those of earlier re-

searchers—such as  Turner and Christison, Schroeder and Reuss, and Ramann

(all cited in Haselhoff and Lindau)--are of limited usefulness, because they •were

conducted without air circulation over the plants.   The gas concentrations used

in their experiments were obtained by evaporating  hydrochloric acid or by using

hydrochloric  acid of varying specific gravity in a closed vessel,  such as a bell

jar.  Only a summary of their observations is presented below.

       Symptoms observed  on broadleaf species by early investigators include

discoloration on the  margin of leaves and spotting in the central portion of leaves.

The discolorations ranged from white to brownish-yellow or  red, and sometimes

to black.  The spots observed in the central portion of the leaves were reported

to be transparent, except for small black dots that were thought to  be tannin  sub-

stances. When the gas concentration was increased,  the entire leaves collapsed

and turned brown.  The species tested included roses, buffalo currant, beech,

birch,  maple, oak, viburnum,  apple,  pear, and cherry.

       On narrow-leaf species, such as grain crops and meadow-grass, the tips

of the leaves  were affected and turned brown.  The edges of the leaves exhibited

a similar coloring.  High concentrations  of the gas caused  entire leaves to turn

brown  and limp.

       Conifer species — such as larch,  spruce, fir, and pine--exhibited such

symptoms as discolored needle  tips  and yellowing or browning of the needle

tips.  The affected tips had  a sharp border against a green base.

       One interesting observation reported in these early experiments was

that flower parts were affected.  The blue coloring material of flowers was

especially sensitive, particularly in chicory and cornflowers.  The color change
occurred within 12-15 hr.  With the exception of two or three reported cases,

flower parts are not sensitive to air pollutants.  It is interesting to note also
that Haselhoff and Landau     concluded from their literature survey and their

own experiments that damage to vegetation by the action of fumes containing

hydrochloric acid or chlorine on the soil or by the influence of their reaction

products in the ground is not probable.  Damage to vegetation by such fumes

could be brought about only by direct action on the above-ground  parts.

       Recent observations of field injury by hydrogen chloride gas include
                 217        520            48
those of Hindawi,     Wood,     and Bohne.    Hindawi reported that hydrogen

chloride injury on redbud and begonia consisted of a brown-orange color on the

margin of the leaf tissue and necrotic spots on the surface of leaves.   Premature

leaf abscission was  also noticed.  Damage  was reportedly similar to that caused
by hydrogen fluoride and sulfur  dioxide.  Wood    reported that  hydrogen chloride

caused chlorotic flecking of the  upper leaf surfaces and red-brown to black necrotic

spots on the leaves of northern hardwood species.  Tan necrotic  flecks and dis-

tortion of leaves were observed on the conifer species present in the area.  Broad-

leaves also exhibited leaf cupping.
       Means and Lacasse    tested  the sensitivity of 12 coniferous and broad-

leaf tree species to  hydrogen chloride gas.   The fumigations were conducted for

4 hr under controlled conditions at a temperature of 27  C,  a relative humidity
                                          4          2
of 78-85%, and a light intensity  of 1. 4 x 10   ergs/cm   -sec.  Under these con-

ditions, the only symptom  noted  on conifer  needles was a tip necrosis  on white

pine at 8 ppm,  on balsam and Douglas fir at 12 ppm,  and on Norway spruce at

19 ppm.  Austrian pine and arborvitae were not injured at concentrations  of 18

and 43 ppm,  respectively.  Symptoms on broadleaf species included marginal

and interveinal necrosis and necrotic flecking.  Tuliptree was injured at 3 ppm,

European black alder and black cherry at 6 ppm,  and sugar maple and Norway

maple at 7 ppm.  Red oak was not injured at concentrations up to 13 ppm.
       Shriner    undertook extensive experiments  to determine symptom

response  of tomato (cultivar Bonny Best) and chrysanthemum (cultivar Neptune)

to hydrogen chloride under  controlled conditions.   In tomato, severe injury in

the form of bronzing occurred at a concentration  of 4 ppm for 2 hr at a relative

humidity of 70% and a temperature of 30 C, but a  concentration of 10 ppm was

required to produce a similar effect for the same exposure duration when the

humidity was 50% and the temperature was  31 C.  Marginal leaf necrosis and

injury to the petiole occurred at a concentration of 5 ppm for 2 hr at a relative

humidity of 81% and a temperature of 33 C, but again a concentration of 10 ppm

was needed to produce similar symptoms when  the relative humidity was lowered

to 55% at  a temperature  of 31 C for 2 hr. Symptoms of glazing on the underside

of the leaf, leaf tipburn,  and necrotic flecking were produced at a concentration

of 3 ppm for  2 hr when the relative humidity was  65-72% and the temperature

31-33 C; a concentration of 8 ppm for 3 hr was  needed to cause those symptoms

at a relative humidity of 35%.  No visible injury developed -when the  concentra-

tion was 2-5 ppm for periods of 2-3 hr when the relative  humidity was 55-60%

and the temperature 30-31 C.  Even a concentration  of 8. 5 ppm for 3 hr caused

no injury  when the relative humidity was 23% at a temperature of 31 C.

       Chrysanthemum was much more resistant to  hydrogen chloride than

tomato.  The plants were severely injured,  with bronzing as the predominant

symptom, when they were exposed to 8-23 ppm for periods of 4 and  2 hr,

 respectively, and relative humidity of 65-70% and temperature of 30-31 C.

 Marginal necrosis and petiole injury occurred at 3. 5-8. 5 ppm,  respectively,

 for 3-hr fumigations at 31 C and relative humidities of 65 and 45%,  respectively.

 Glazing on the underside of the leaf, tipburn, and necrotic flecking occurred

 when the  concentration was 6 ppm for 5 hr at 60% relative humidity or  12 ppm

 for 2 hr at 52% relative humidity.  No injury developed at a concentration of

 2. 7 ppm for  2 or 3 hr at a relative humidity of 60% and 30 C.
       Chronic fumigations of tomato (Bonny Best) were performed by Godish
 and Godish and Lacasse     in 1970.  Chlorosis was the dominant symptom ob-

 served when plants were  fumigated  at 0. 70 ppm for 10 hr/day for 2 days.  The

 chlorosis was generally  interveinal and occurred most often on younger leaves

 and leaves of intermediate maturity.  A severe upward curling of the leaf margins

was  observed occasionally after the first 10 hr of fumigation and was almost always

 present after the second 10 hr. At  0. 40 ppm for  8 hr/day for 6 days,  no visible

 symptoms were observed on greenhouse-grown plants during winter.  However,

 for greenhouse-grown plants during May and June,  chlorosis developed at that

 concentration after the third or fourth consecutive fumigation.
       Haselhoff and Lindau    summarized the  -work of Wieler  and Hartleb

dealing with the physiologic impact of hydrochloric  acid.  However, their ex-

periments were performed by immersing plants in -water with hydrochloric acid

and carbon dioxide and counting the  number of bubbles evolved to determine  assimi-

lation rates.  In the hydrochloric acid solution, the number  of bubbles always de-

creased and the gas bubbles -were always smaller, indicating a considerable

decrease  in assimilation.  The plants tested included waterweed, beans,  oaks,

and red beeches.   They concluded that sulfurous acid decreases transpiration

and hydrochloric  acid decreases assimilation.

            175                        176
     Godish    and Godish and Lacasse    also reported several meta-

bolic effects associated with acute and chronic hydrogen chloride fumigations.

With acute fumigations of 8-10 ppm for 2 hr at a relative humidity of 40-50%

(when few or no symptoms developed), a 20-30% stimulation of the  respiration

rate was detected.  The respiration rate returned to normal within 24 hr.  As

the degree of injury increased, respiration rate became more and more variable,

and no statistically significant changes could be detected.

      Photosynthesis rates after fumigation at 8-10 ppm and a relative humidity

at or below 40% were about 90% of those of control plants.  These rates  were

corrected for respiration.  Although the rates were not statistically significant,

the changes indicate a trend toward inhibition of photosynthesis.  No visible

injury was present under these circumstances.  In situations in which symptoms

developed (10-50% of the leaf area injured), photosynthesis was reduced by as

much as 25% on a unit chlorophyll basis (i. e. , on the basis of the amount of

chlorophyll present, rather than on the basis  of the leaf area, because of the

obvious leaf injury).

     Transpiration rates were also decreased by acute  fumigation.,  At its

lowest point, the average transpiration rate of fumigated plants was 59% of

rate of control plants.  Transpiration returned to normal during the 12-hr

dark period after  fumigation.

     When plants  were fumigated at 0. 70 ppm for 10 hr/day for 2 days,  there

was  no significant difference  in respiration rate between control a.nd fumigated

plants when measured at 0, 24, and 48 hr  after fumigation and -when the  rate

was  based  on fresh weight. However,  a significant stimulation  of respiration

of fumigated plants was evident in each of  the sampling periods  on a dry-weight


     At 0. 40 ppm for 8 hr/day for 6 days, respiration rate at 0 and 24 hr

after fumigation was significantly reduced on either a fresh-weight or a dry-

weight basis.

     The photosynthesis rate measured before chlorosis became visible was

significantly decreased on a unit area basis.  However, no differences were

observed when the rate was expressed on a chlorophyll basis.  After symptom

development (24 hr after fumigation), there was no difference in the photosyn-

thesis rate based  on  leaf area. However,  fumigated plants had  a significantly

higher rate  if the  rate was  based  on  total chlorophyll.  It appears that, at or

near saturating light intensities,  the rate of photosynthesis in fumigated plants

is higher if  photo synthetic efficiency is measured under various light intensities
based on unit chlorophyll content.  At the highest light intensity (7. 6 x 10
ergs/cm  -sec), there were significant differences  in the rate of photosynthesis

between the two groups.  Thus, it appears that, if only a small amount of chloro-

phyll is destroyed, the remaining chlorophyll is better able to utilize light energy.

However, if the same data  are based on unit leaf area, the control plants have a

significantly higher rate of real photosynthesis at light intensities below saturation.

There is no difference between the two groups at the highest light intensity.  These

differences  clearly indicate that it would not be advantageous to  attempt measure-

ment of leaf function impairment  by using chlorophyll content as an index of injury.

     Transpiration rates of plants at chronic  fumigation concentrations were re-

ported to be slightly  decreased during  exposure at 0. 70 ppm.  Water loss was

significantly reduced (83% of the control value) during the 4 hr after fumigation,

but quickly returned  to normal by the end of the 4-hr period.

     Godish    also measured chlorophyll and pheophytin concentrations

after fumigation at 0. 70 ppm for 10 hr/day for 2 days.  Significant changes

in total chlorophyll and total pheophytin were detected immediately after

fumigation and 16 hr later.  Chlorophyll destruction or conversion did not

result in pheophytin formation.  Ratios of chlorophyll a to chlorophyll b a.nd

pheophytin a to pheophytin b did not indicate preferential destruction of indi-

vidual pigments.   Because no increase in pheophytin  concentration was found

in plants exposed to hydrogen chloride gas,  Godish concluded that the observed

destruction or conversion of chlorophyll was clearly not due to pheophytiniza-

tion.  The action of hydrogen chloride gas on chlorophyll is probably not due

solely to the acidic properties of the gas.
     Fisher    fumigated bean plants (pinto III) simultaneously with ozor.e and

hydrogen  chloride gas.  The injury observed depended on the concentrations of

the gases.  With  ozone at 0. 10-0. 20 ppm and hydrogen chloride gas at 1. 5-3 ppm

for 2 hr,  the injury consisted of an upper-leaf-surface stippling and flecking,

marginal  necrosis, veinal and interveinal tissue collapse on the underside of

the leaf, or interveinal tissue collapse of the underside of the  leaf alone.  With

ozone at 0. 20-0. 25 ppm and hydrogen chloride at 3-4 ppm, the injury consisted

of flecking or stippling with collapse of both surfaces of the leaf.  Symptom ex-

pression was highly variable,  and  only one symptom type was  present on a given

leaf.  The following mathematical  relationship was derived for ozone-hydrogen

chloride fumigations:

                                    2                           2
     R = -6. 23  -0. 10  [0  ] + 0. 02 [0 ]  + 0. 89 [HC1] + 0. 52 [HCl]   .
                       3           3

     The equation has the following limits:

     0. 0 < [0  ] < 25. 0,  where [0 ] is the ozone concentration in parts per
            3                  3
     hundred million.

     0. 0 < [HCl] < 4. 0, where [HCl] is the hydrogen chloride gas  concentration

     in parts per hundred million

     R is considered to be equal to zero,  if it is equal to or less than zero,

     where R is  the pinto bean response expressed as percent leaf injury.

     The equation describes approximately 90% of the data generated in Fisher's

     Fisher    reported that the threshold concentrations for injury to pinto

beans in  a 2-hr  fumigation were approximately 2. 6 ppm for hydrogen chloride

gas alone and 0. 18 ppm for ozone alone.  When plants were fumigated with both

pollutants simultaneously, the injury threshold concentration for hydrogen chloride

gas was lowered to 1. 2 ppm, but remained at 0. 18 ppm for ozone.

Morphology and Histopathology  of Hydrogen Chloride Injury
     Haselhoff and Lindau    reported  that the cells in white limp leaves of

fumigated rye appeared heavily bleached and shriveled,  and in some cells in

the vicinity of the vascular bundles there were brown or black deposits consisting

of tannin.  In pea leaves, the grains of chlorophyll appeared swollen, and tannin

deposits  filled some cells  nearly completely and colored them black.  Roses

exhibited  even heavier tannin deposits.  Montana pine exhibited a pale discolora-

tion of the needle, with browning and drying spreading from the tip.  In the assimi-

lation cells, the  grains of chlorophyll were bleached  out and were often no longer

clearly recognizable in outline.   The contents of the cell were often bunched

together,  later turned brown with continued drying, and finally disappeared,

except for small remnants.  In the first stages, often only the cuticula appeared

brown,  but the coloring of the membrane later  extended inward,  and finally the

greatest part of the membranes became brown  at the dry areas.  Haselhoff and

Lindau also reported an observation by Wieler  related to the red coloring  of the

guard cells of spruce.
            426                         428
     Shriner     and Shriner and Lacasse    examined the effect of hydrogen

chloride gas  in histologic studies and  related the type of visible symptoms ob-

served to the specific  leaf tissues that were affected.  They reported thai; the

under-leaf-surface glazing symptom appeared to be a result of the collapse

of the lower epidermal cells.   This was particularly evident in tomato.  They

attributed  this to the relatively large amount of air space  adjacent to the lower

epidermis inside the leaf,  in contrast with the palisade tissue.  The bronzing

symptom  on both tomato and chrysanthemum appeared to result from the collapse

of the lower epidermis, the spongy mesophyll,  and occasionally the palisade

mesophyll and upper epidermis.  Microscopic symptoms observed by Shriner
resemble  those described  by Solberg and Adams     for hydrogen fluoride; and
sulfur dioxide and by Bobrov    for  smog.  Shriner concluded  from his histologic

studies  that the gas entered the plants through the stomata because tissues nearest

the stomata were always the first to be damaged.  The substomatal  injury observed
closely  resembles what Bobrov   described as  "dehydration"  of cells lining the sub-

stomatal cavities of annual bluegrass  damaged  by smog.   The bronzing symptom  ob-

served by Shriner in tomato and chrysanthemum was very  similar to the "tan-colored

spot" symptom caused by hydrogen fluoride on  apricot and caused by sulfur dioxide

on pinto bean.

     According to Shriner, the order of tissue damage for tomato after entry

through the stomata appears to be as follows:  collapse of adjacent lower epi-

dermal cells and then disorganization and collapse of the spongy mesophyll.

Depending on the severity of damage, the palisade mesophyll may or may not

collapse,  and then the upper epidermis.  In chrysanthemum,  collapse of the

tissues was not as severe as in tomato.  Shriner postulated that this was be-

cause chrysanthemum cell walls were thicker than those  of tomato.

Factors That Modify Plant Response
     Shriner     listed a number  of factors affecting the response of tomato and

chrysanthemum to hydrogen chloride gas.  Of prime importance is the dose

(concentration  and length of fumigation).  The relative frequency and abundance

of stomata also appear to be important in the sensitivity of plants to this gas.

     The  relative humidity of the exposure environment appears to be the dominant
                                                              426            175
factor in symptom expression.  The results obtained by Shriner    and Godish

indicate that there is a relative humidity threshold above  •which injury will be

severe and below which injury will be minimal for a given dose of the gas.  Al-

though much time and effort have been expended in numerous  fumigations to de-

termine precisely what that threshold relative humidity is,  the question remains

unresolved.  The problem lies in the fact that the gas is hygroscopic.  There are

indications that, at relative humidities above 80%,  the damage is typical of that

caused by acid--i.e., small,  discrete flecks on the exposed leaves.  At relative

humidity below 80%,  the damage is  typical of that caused  by gas.

     Cell wall  thickness and amount of intercellular space appear to influence

the severity of symptom expression.  It should be noted,  however, that the

data base for this conclusion is extremely limited.

     Age of tissue appears to be important in symptom expression in relation

to the amount of chloride taken up by or translocated within plants.   Shriiier's

data suggest either that semimature tissue in tomato is capable of greater up-

take of chloride or that chloride  can be more  readily translocated to growing

points in that species.  It is interesting to note that, when the  source of chloride

is the soil,  a number of plant species normally tend to accumulate chloride in the

petiole.  Shriner reported petiole damage in both tomato and chrysanthemum,

suggesting some translocation from lower leaves.  It is also interesting that the

semimature tissue of tomato, which showed the greatest increase in chloride

content,  did not necessarily show the  severest symptoms.  A possible explana-

tion is that, as the leaf continues to grow and expand,  the chloride present in

the leaf is diluted.

     Shriner1 s chrysanthemum data show that chloride accumulates in mature

tissue in that species, although large increases were also noted in semimature

tissue.  Because Shriner fumigated chrysanthemum at much higher concentrations

of hydrogen chloride (7-18 ppm)  than tomato (2-5 ppm), it is not possible  to state

conclusively that translocation or greater uptake  occurs in tomato,  but not in


     Although Haselhoff and Lindau     reported  large differences in species

sensitivity to hydrogen chloride gas, the value of their data should be questioned,

because they were obtained without adequate air circulation over  the plants.  The
results obtained by Means and Lacasse     represent the only recent determination

of sensitivity of plant species to  hydrogen chloride  gas under  controlled conditions.

Unfortunately, only a few forest  tree species were  tested, and the experiments were

designed to determine the dose at which acute injury would occur. Their  data do

suggest, however, that broadleaf plants are generally more sensitive than
coniferous plants.  Limited experiments by Thomas     on sugar beets  suggested

that the marking threshold concentration for a few hours of exposure was about

10 ppm.
                                    11                        339
     The results of work by Antipov   and Means and Lacasse    with respect

to sensitivity of plants to hydrogen chloride are summarized in Table 6-2.

            426                         427
     Shriner     and  Shriner and Lacasse    measured  chloride concentrations

in tomato plants at various intervals after fumigation. Significant increases in

chloride  content occurred in all parts of fumigated plants.   Chloride concentra-

tion in foliar portions was higher immediately after and  24 hr  after fumigation

and then  decreased gradually.  Actively growing tissue appeared to have a greater

tolerance for  chloride than older leaves, which  exhibited symptoms readily with

smaller amounts of chloride taken up.  A 0. 14% increase in chloride occurred

in immature  secondary leaves after fumigation at 3. 5 ppm for 2 hr; an increase

of 0. 10% occurred in mature secondary leaves.  Roots showed the smallest

increase, 0. 002%.

     Shriner measured chloride  content based on fresh weight of tissues.

Tissues were homogenized in a top-drive macerator  in water.  The macerate

was centrifuged at 3, 500  rpm for 15 min,  and the supernatant was filtered.

The clear extract was buffered with 0. 1 N nitric acid-10%  acetic acid and titrated

with a  Buchler-Cotlove automatic chloride titrator.   Repeated extracts of the pellet

were titrated.  The results showed that the initial extraction contained 95 +_ 2% of

the free chloride in the cell sap of the test plant tissues.

                                   TABLE 6-2
              Relative Sensitivity of Plants to Hydrogen Chloride
       Caespitose phlox



       Garden daisy

       Oriental poppy


Black cherry


European black alder

Norway maple

Pinto bean

Sugar maple

White pine


Austrian pine

Balsam fir

Douglas fir

Garden iris

Garden lupine

Garden peony




Norway spruce

Paniculate phlox

Pheasant's eye pink

Plantain  lily

Red oak

Sweet William
a.                  11                         339
 Data from Antipov   and Means and Lacasse.

    It should be noted that determination of elements in plant material based

on fresh weight can lead to errors.  This is particularly true in dealing with

severely injured plants.  The injured tissues become disrupted and lose moisture.

This decrease  in fresh weight would be accentuated over time.  It would be prefer-

able to base measurements on dry weight.

Mimicking Symptoms

    The glazing symptom was first reported for peroxyacetylnitrate (PAN)
injury in California on a number of plant species.      This symptom has been

observed elsewhere in the United States and has been generally attributed to

PAN.  PAN has not been measured in areas other than  California or Utah,

because of lack of instrumentation.  It is possible that PAN has not been solely

responsible for this symptom every time it has been observed.

    Marginal leaf scorch has been reported to be  caused by salt (sodium or
calcium chloride) used on high-ways for deicing.       This  symptom closely

resembles the  marginal burning caused by hydrogen chloride gas.

                         Appendix to Chapter 6

               Common and Scientific Names  of Plants
Common Name



Annual blue grass





Austrian pine


Balsam fir








Black cherry


Box elder

Scientific Name
Adonis sp.

Medicago sativa L.

Poa annua L.

Pyrus sp.  L.

Prunus armeniaca.

Thuja occidentalis L.

Fraxinus  sp. L.

Pinus nigra Arnold

Rhododendron sp.  L.

Abies balsamea (L. ) Mill.

Tilia  sp.  L.

Phase olus

Fagus sp.

Polygonum sp.

Campanula sp.  L.

Be tula sp.

Rubus sp.

Prunus serotina Ehrh.

Houstonia sp.  L.

Acer negundo L.

Rhodotypos sp. Siev. and Zucc.

 Common Name


 Buffalo currant


 Caespitose phlox





 Chinese holly








 Crab apple






Douglas fir

Dragon tree
 Scientific Name
 Fagopyrum sagittaturn Gilib.

 Ribes aureum Wendland f.
Phlox sp. L.

Malva parviflora L.

Prunus sp.  L.

Stellaria sp.  L.

Cichorium intybus

Ilex sp. L.

Chrysanthemum sp. L.

Coleus sp.

Aquilega sp.  L.

Zea Mays JL.

Centaurea cyanus  L.

Cosmos sp. Cav.

Vigna  sinensis (L. )  Endl.

Pyrus sp. L.

Cucurbita sp.  L.

Dahlia sp.

Chrysanthemum sp. L.

Taraxacum  officinale Weber

Cornus sp.  L.

Pseudotsuga taxifolia (Poir) Britt.

Dracaena  draco

 Common Name	



 European black  alder


 Garden daisy

 Garden iris

 Garden lupine

 Garden peony







Hybrid tea

Italian prune

Kentucky bluegrass

Lamb's quarter






Scientific Name
Solanum melongena L.

Ulmus sp. L.

Alnus glutinosa (L. ) Ga.ertn.


Chrysanthemum sp. L.

Iris sp.  L.

Lupinus  sp.  L.

Paeonia  sp.

Geranium sp. L,.

Ginkgo biloba L.

Gomphrena globosa L.

Solidago sp.  L.

Tsuga sp.  (Endl. ) Carr.

Aescubus hippocastanurn L.


Prunus domestica L.

Poa pratensis L.

Chenopodium sp. L.

Larix sp. Mill.

Delphinium sp.  L.

Lactuca sp.  L.

Syringa sp.  L.

Convallaria sp.  L.

Tilia  sp. L.

Common Name	

Loblolly pine







Nettle-leaf goosefoot

Norway maple

Norway spruce



Oregon grape

Oriental poppy



Paniculate phlox






Pheasant's eye pink

Scientific Name
Pinus taeda L.

Acer sp.

Poa sp.  L.

Reseda lutea L.

Brassica sp. L.

Vine a minor L.

Nasturtium sp. R. Br.

Chenopodium sp.  L.

Acer platanoides L.

Picea abies L. Karst.

Quercus sp.  L.

Allium cepa L.

Mahonia (Berberis) aquifolium

Papaver sp.  L.

Salix viminalis L.

Oxalis sp. L.

Phlox paniculata  L.

Pisum satium

Prunus persica (L. ) Batsch.

Pyrus sp. L.

Capsicum sp.

Petunia sp.  Juss.

Dianthus sp.  L.

Phlox  sp. L.

Common Name
Scientific Name


Pin oak

Pinto bean

Plantain lily



Red beech


Red clover

Red currant

Red oak



Scotia bean

Shortleaf pine


Slash pine





Sugar beet

Sugar maple
Chenopodium sp. L.

Pinus sp.

Quercus palustris Muenchh.

Phaseolus vulgaris L.

Hosta plantaginea (Lam. ) Archers

Prunus  sp.  L.

Raphanus sativus L.

Fagus sp. L.

Cercis sp.  L.

Trifolium pratense L.

Rib e s sativum Syme

Quercus rubra  Du Roi

Rosa sp. L.

Elymus sp.  L.

Phase olus sp. L.

Pincus echinata Mill.

Halesia sp.  Ellis

Pinus caribaea Morelet

Persicaria sp.  L.

Picea sp.

Cucurbita sp. L.

Fragaria sp. L.

Beta vulgaris L.

Acer saccharum Marsh.

Common Name
Scientific Name


Sweet william



Tree of heaven

Tulip tree

Vibu rnum

Virginia creeper

Wandering Jew


White beech

White pine

White thorn

Helianthus sp. L.

Liquidambar styraciflua L.

Dianthus barbatus L.

Nicotiana tabacum L.

Lycopersicum esculentum Mill.

Ailanthus altissima (Mill. ) Swingle

Liriodendron tulipifera  L.

Viburnum sp.

Parthenocissus sp.  Planch.

Tradescantia sp.  L.

Elodea sp. Michx.

Fagus sp. L.

Pinus strobus L.

Crataegus sp.  L.

Heliopsis sp.  Pers.

                                   CHAPTER 7


     This chapter deals primarily with chlorine and hydrogen chloride as

nuisances.  That is, such subjects as acute and chronic toxicity to humans,

animals, and plants will be avoided.  Attention will be focused on the effects

of chlorine and hydrogen chloride on aesthetics and as chemical irritants!.

Also to be considered are their influence as agents that initiate or aggravate

corrosion of and damage to building materials and other property.


     The possibility of airborne emission of chlorine and hydrogen chloride

is unavoidably associated with their manufacture and use.  One of the first

large sources of hydrogen chloride was the use of the Leblanc process for

the manufacture of soda ash.311  This process can be summarized by the

following reactions:

                   H2S02 + 2NaCl  	>2HC1 ^  + Na2S04,

                    Na2S04 + 2C   	> 2CO- A  + Na2S,
                    Na2S + CaC03  	>Na2C03  + CaS,

                   CaS + C02 + H20	>   CaC03 + H2S, and

                         H2S + 202	>

     The net overall reaction is the production of soda ash and hydrogen

 chloride (the  intermediate products are recycled):

                   2NaCl + H20 + C02 	>2HC1  ^ + Na2C03.

     Naturally, the hydrogen chloride produced as a byproduct of soda ash

 could have been recovered as hydrochloric acid by condensation or scrubbing.

 When the Leblanc process was introduced into Great Britain in 1818, it was

 carried out on a small scale and the practice was to roast sulfuric acid

 with salt in an open furnace.  As a consequence of this, hydrogen chloride

 was released to the atmosphere.  The demand for hydrochloric acid and products

 that might have been manufactured from it was insufficient to permit marketing

 of all the acid produced; so most recovered hydrochloric acid would have gone

 to the sewer, and one pollution problem would have been exchanged for another.

     With the passing years, the production of Leblanc soda ash grew from

 90,000 kg (100 tons) in 1818 to more than 81 x 106 kg (90,000 tons) in 1864.

 The technology for condensing and scrubbing hydrogen chloride-bearing streams

 was well advanced by that time, but often the financial incentive to ensure

 the complete recovery of the hydrochloric acid did not exist, because of lack

 of demand for the product.   By 1864, it was customary to condense and scrub

 the effluent gases in packed columns and to vent the remaining gas through

 stacks as high as 150 m.  However,  because of the increased production, the

 total amount of hydrogen chloride vented to the atmosphere had increased

 beyond that of earlier times, when no attempts were made to recover the acid.

     According to Lunge,3H (p«  306) "the destruction of the vegetation

round the alkali-works was only too evident....It was impossible to ignore

 the nuisance caused by the smell, and the worse one that iron objects of all

kinds,  locks, window-fittings,  gutters,  etc.,  could not be kept from rusting,

that tools of mechanics were at once blunted, and that even window-curtains

were destroyed in a very short time."  Clearly, some type of controlling

legislation was needed.

     On July 13, 1863, the House of Commons passed an "Act for the More

Effectual Condensation of Muriatic Acid Gas in Alkali Works."10  This law,

which is often referred to as the Lord Derby alkali act, after one of its

chief sponsors, was to come into force on January 1, 1864, and expire on

July 1, 1868.  The alkali act was a considerable departure from previous

legislation.  Before 1863, some jurisdictions had passed laws banning

chemical plants, including Leblanc process plants, from within their limits.

This solved the local problem, but usually resulted only in a plant's re-

location to another site.  Of course, this in no way reduced pollution within

Great Britain.   Instead of this approach, the alkali act recognized the de-

sirability of the manufacture of soda ash and set up a system of monitoring

and control to reduce the emission of hydrogen chloride that inevitably

accompanies production of soda ash by the Leblanc process.

     The alkali act had four important provisions:

     1.  Emission of hydrogen chloride from Leblanc process plants were

to be no greater than 5% of the total hydrogen chloride produced.

     2.  An inspection system was set up, and the inspectors were empowered

to monitor plant emission whenever they desired.  If in their opinion the

plant emission exceeded the limit over a 4-hr period, the operator  could

be brought into court.

     3.  Operators of Leblanc process plants were required to register their

plants with the inspectors.

     4.  Operators convicted of a first offense were subject to a fine nc>t

exceeding 50 pounds.  Each additional conviction carried a fine not to exceed

100 pounds, and this fine could be applied for each successive 24-hr period

in which a violation was proved.


     Thus, the alkali act established a limit on emission, provided a system

of compulsory inspection, required registration of emission sources, and

penalized convicted violators.  This piece of legislation, unique at the

time, set a precedent for pollution control legislation throughout the

world.  However, a law is useful only if it is complied with and enforced.

     The year after the act went into force, all 64 Leblanc process plants

reported on were in compliance with the 5% emission standard, and 33 were

emitting none or no more than 0.1% of the total hydrogen chloride produced.

In 1866, all plants averaged less than 1% emission.     In 1867, the first

prosecution under the alkali act took place.  The Bridgewater Smelting Company

was convicted and fined 50 pounds for the release of large quantities of

hydrogen chloride.144

     The alkali act was a marked success, and there was said to be substantial

improvement in the environment of the neighborhoods of chemical works.  There-

fore, the act, which was to have expired in 1868, was renewed and made per-


     However, the alkali act needed improvement.  It said nothing about other

sources of hydrogen chloride, such as potential consumers, nor did it include

other offensive gases.  Thus, it was amended in 1874    to require that the

emission of noxious gases be controlled by the best practicable means.  Noxious

gases were defined as chlorine,  oxides of nitrogen, hydrogen sulfide, and

oxides of sulfur, except those arising from the combustion of coal.   The

emission standard for hydrogen chloride was further defined as not to exceed

0.2 grain/ft3 (about 0.46 g/m3).

     In the 110 years since the passage of the alkali act, it has been amended

periodically to include every conceivable gas or fume that might be considered

harmful, and it now governs all sectors of industry.   Through these many

alterations and extensions, the rational principles incorporated in the alkali

act of 1863 have remained unchanged.


     Such laws did not evolve in the United States, because the gross, con-

tinuous emission of hydrogen chloride of the early days of the Leblanc process

in Great Britain did not occur in the United States.  In fact, the Leblanc

process was never used in the United States.  Thus, in the early days of the

chemical industry in the United States, hydrogen chloride was not produced

as a largely or partially useless byproduct.


     Chlorine, hydrogen chloride, and the acid solutions derived from them

when they are dissolved in water are considered very corrosive.  Accordingly,

many studies have been carried out to determine their corrosive properties

and to evaluate the rate at which they attack materials.  These studies have

been limited mostly to the commercially significant concentrations in the

gaseous, liquid, and aqueous phases.  With the exception of a very rare

occurrence of catastrophic failure of equipment that results in a massive

release of chlorine or hydrogen chloride, those concentrations are much

greater than the ones with which we are primarily concerned.  There are some

data that pertain specifically to the very dilute gases and solutions that

are considered here, and other information can be inferred from fundamentally

similar systems of acids, oxidizing gases, and electrolytes.  Before a dis-

cussion of corrosion related specifically to chlorine and hydrogen chloride,

is it important that something of an understanding of atmospheric corrosion

be developed.

     Atmospheric corrosion of materials is a highly complex subject and can

hardly be treated fully here.  But it is necessary to consider what contributes

to it.  It must be realized that all the metals most commonly used should be

expected to react to form compounds, usually oxides, in the earth's atmosphere.

If they do not or if they do so only very slowly, it is because corrosion or

 reaction  is retarded by a protective coating.  The protective coating may

 have been applied purposely, such as paint, or it may have formed spontaneously,

 such as the iron oxide film on steel.  Any agent that either attacks the coating

 or interferes with its formation will accelerate corrosion beyond the "normal"


     The  normal rate of atmospheric corrosion is influenced by temperature,

 relative  humidity, sunlight, and the presence and characteristics of particu-

 late matter and trace gases.  Most chemical reactions are accelerated by an

 increase  in temperature, but a temperature increase may also slow corrosion

 by decreasing the relative humidity.  In the absence of moisture, little if

 any corrosion takes place, even in a very polluted atmosphere; none takes place

 in an unpolluted atmosphere.  A film of water will adsorb on a surface to a

degree that depends on the relative humidity and the affinity of the surface

 for water molecules.   When the surface is completely clean and dry, the circuit

 is open; no current can flow,  and no electrochemical reaction takes place.

When water is adsorbed on the surface, it acts as an electrolyte, allowing

 current to flow, and corrosion takes place.   Substances, such as carbon dioxide,

 that dissolve in the adsorbed water layer and cause additional ions to be formed

by hydrolysis aggravate the situation by increasing the number of ions available

to carry current.

     Inert particulate matter can cause erosion by impingement,  but we are

concerned here with its ability to act as an adsorption site for chemicals

and moisture,  which accelerate corrosion.  Also,  particulate matter can be

acid mists or solid particles,  such as sodium chloride,  which supply electrolyte

to the water film and often make corrosion products more soluble, helping to

expose fresh surface to attack.

     Many trace gases, including chlorine and hydrogen chloride, accelerate

corrosion through some of the mechanisms cited.  They dissolve in the adsorbed

water film to supply electrolyte and can in fact cause adsorption of additional

water by lowering the vapor pressure of the film.  Some can also effectively

increase the solubility of corrosion products through changes in the acidity

of the water film, and the ions produced in the water film can increase the

solubility of corrosion products, tending to expose fresh surfaces to attack.

     Anhydrous chlorine and hydrogen chloride are stored in mild steel tanks

and conveyed in pipelines and containers fabricated from mild steel.  At

ordinary temperatures, corrosion is negligible.  But chlorine and hydrogen

chloride are among the most corrosive of chemicals.  The reason that corrosion

of the steel does not occur is the absence of moisture.  Corrosion proceeds

via the adsorbed water film, and this mechanism will prevail as long as the

temperature of the material is above the dewpoint of the water vapor in the

surrounding atmosphere; below this temperature, bulk water will condense.

However, in the latter case, the chemistry of the process will be essentially

the same.  The corrosive properties of chlorine and hydrogen chloride are,

therefore,  inevitably related to the properties of the solutions that are

formed when they dissolve in water.

     Chlorine dissolves in water and, hydrolyzing to some degree, forms

hypochlorous and hydrochloric acid.  These ionize to form hydrogen ions and,

respectively, hypochlorite and chloride ions:
                   HOH + C10 x       HOC1      +      HC1
                                       OC1~        H+

     Hypochlorous acid is a weak acid and can be considered essentially not

ionized.  It is also a strong oxidizing agent and decomposes to form atomic

oxygen and hydrochloric acid:

                         HOC1  	> 0 + HC1.

     Hydrochloric acid is a strong acid and, for practical purposes, can be

considered completely dissociated.  The term "strong" should not be construed

to mean highly concentrated, inasmuch as the concentrations dealt with here

are very low.

     The corrosiveness of chlorine dissolved in water is due to four factors:

     1.  It is a strong oxidizing agent and can oxidize metals, their protective

coatings, and other materials.

     2.  It supplies a strong acid that can dissolve the passive, protective

oxide film on metals, exposing a fresh metallic surface to additional atmospheric

corrosion and can also dissolve the calcium carbonate contained in building

materials, such as limestone.

     3.  It supplies electrolyte, which accelerates galvanic or electrochemical

corrosion by increasing the conductivity of the adsorbed water layer.

     4.  It supplies chloride ion, which enhances corrosion of some metals by

the formation of chloride complexes that aid in the solubilization and dispersion

of corrosion products that,  in its absence, might remain to form a passive

barrier.  Chlorine ions are particularly offensive, because they can cause

intergranular corrosion and pitting,  which may far outweight apparent overall


     Hydrogen chloride dissolves in water to form hydrochloric acid, which is,

of course, no different from that formed when chlorine dissolves in water.

Itscorrosiveness is due to the last three properties responsible for the

corrosiveness of chlorine.

     It has been conceded that examples of economic damage caused by the

corrosive attack of trace amounts of atmospheric chlorine on metals and
other materials are lacking in the literature.  Stahl^6 (P*     states that

"the high reactiveness of chlorine with almost all metals (including iron,

zinc, tin, silver, and copper) as well as non-metals (including most organic

compounds) suggests that chlorine in sufficiently high concentrations would

corrode metals, discolor and damage painted materials, and damage textile

fibers.'1  The preceding statement is inarguable.  However, it is not known

what concentrations are sufficiently high to accelerate corrosion rates

significantly beyond  what is considered normal.  The key word here is

"significantly."  One might reason that any amount of chlorine would be

sufficient to cause an increase in the rate of atmospheric corrosion.  For

practical purposes, what is of interest is the threshold concentration at

which an observable increase in the rate of atmospheric corrosion causes

economic loss or damages the aesthetic properties of the surroundings.

     A great deal of material regarding the corrosive properties of chlorine

has been generated. 461,530  fjjig information, however, is of negligible value,

because it deals with concentrations that would never be reached in the

atmosphere.  Only a few references have been uncovered concerning accelerated

atmospheric corrosion due to the presence of chlorine.'"  A silver chloride

tarnish, in addition to silver sulfide, appeared on a silver test specimen

at one of the test sites where a peak chlorine concentration of 7 ppb and a

median chlorine concentration of 1.2 ppb were observed.  It is important to

note that other pollutants — such as hydrogen sulfide, nitrogen oxides, hydrogen

fluoride, ammonia, ozone, and particulate matter — were also present, most often

 in much larger  concentrations.  Therefore, one cannot say what the  influence

 of chlorine  by  itself was.  However,  the  test does  supply some useful  informa-

 tion,  in that chlorine will probably  always be accompanied by some  of  the

 other  chemicals in any industrialized area where chlorine is present.

     Test panels have been placed on  the  roofs of buildings in a chlor-alkali

 plant  to determine the corrosion rate of  aluminum and steel in the  atmosphere.  ^

 In areas of  the plant most likely to  be exposed to  chlorine in the  atmosphere,

 the corrosion rate of mild steel was  0.3-1.0 mil/yr  (7.6-25.4 ym/yr),  except

 at  an  open brine storage tank, where  the  corrosion rate was 5.3 mils/yr

 (134.6  ym/yr).  This last value is rejected, because the brine is the  obvious

 cause  of accelerated corrosion.  For  comparison, at three other areas  that

 were least likely to be exposed to chlorine or other chemicals from the plant,

 the corrosion rates were <0.1, 0.1, and 0.4 mil/yr  (<2.5, 2.5, and  10.2 pm/yr).

 Unfortunately,  no data were given on  the  atmospheric concentration  of  chlorine.

 Also,  it must be recognized that many other chemical species would be  expected

 to be present in the atmosphere of the highly industrialized area.  The corro-

 sion rates cited would not result in any economic losses, because corrosion

 rates of 1 mil/yr (25.4 ym/yr) or less are considered insignificant with

 respect  to structural integrity.  However, staining with iron oxide might

 be considered aesthetically displeasing.

     In another study, the atmosphere at various locations within a chlorine

 plant was simulated by mixing chlorine or hydrogen chloride and chlorine with

moist air.157  The results are presented in Table 7-1.   The concentration of

 chlorine is not given, nor is the water content of the air which can be

 significant in determining the corrosion rate.  The authors state that the

variation in the corrosion rate of steel is probably due to differences in

 the chlorine content of the atmosphere to which the test specimens were exposed.

                                        TABLE  7-1

                  Corrosion Rates  of  Various Metals Exposed to Chlorine

                       and  Hydrogen Chloride in  a  Chlorine  Plant—
Eip. No.

5 ...

9 ...

Corrosion Rates, Mils Per Year
Zr | Nl
6> »
0.04 •:
6" '
1 Slight or shallow pitting attack.
3 Moderate pitting attack.
5 Severe pitting attack.
4 Slight attack under spacer.
* Moderate attack under spacer.
8 Severe attack under spacer.
7 Specimens perforated by severe pitting attack.

Hast. C

Chlorlmet 3

7 -' '
0.4 i
0.2 i.4
0.3 *
Al 6061
Mo st
Mo st
a r containing alkaline
a containing MCI and
a containing HCI and
a containing HCI 	
a containing Clj 	
a containing traces of
a containing traces of
Mo st a contain!
Mo st a contain!
Mo Pt a contain!

Cls.'. ".'.'.'.'.

20 «
92 F
98 F
120 K
Mlld Steel
of Test.
Reprinted with permission from Gegner and Wilson.157

See, for example, the corrosion rates of mild steel in exposures 9 and 10,

for where the environment is described as "moist air containing Clo"; one

might expect the corrosion rates to be the same, but they differ considerably.

Hence, it is not possible to draw any conclusions regarding the data presented.

It is of interest, however, that the corrosion rates are much greater than

those presented in the Wyandotte study. '

     No significant data on the corrosiveness of hydrogen chloride in the

environment appear to be available (the same conclusion has been arrived

at elsewhere   ).  We find that interest has centered about concentrations

that are found in industrial manufacture and use.  ^

     No data on the corrosion rates of textiles or building materials, such

as limestone, in the presence of trace quantities of atmospheric chlorine or

hydrogen chloride could be obtained from the literature.  Nor is there any

evidence to indicate whether ambient atmospheric concentrations of chlorine

have a bleaching effect on textiles.


     Aggravated corrosion is defined as the corrosion that occurs when there

is a major release of, say, chlorine or hydrogen chloride and the concentra-

tions substantially exceed those which might prevail over an extended period

in the neighborhood of an emission source.  Because these events are rare

and brief, it follows that materials will be exposed to accelerated corrosive

attack only rarely and for very brief periods.   Consequently, data obtained

from long-term exposures are not useful.

     The concentration of any gas emitted from a point source at a given rate

is calculable.^29  However, the effects on materials of brief exposures to

chlorine or hydrogen chloride are not known.   One observation has been made

regarding property damage after a train derailment in which a chlorine car

was ruptured:  "Farm implements and tools were badly corroded and rusted

wherever they were exposed, particularly where dew had condensed on the

surface.1     ^P*   '  One would expect a similar result from a release of

hydrogen chloride.


     The mere definition of what constitutes an obnoxious odor is a formidable

task.  To be sure, there will be total agreement on whether some specific

odors are obnoxious—for example, a strong odor of putrefying meat.  The diffi-

culty arises when there is an attempt to set some sort of threshold above which

an odor is obnoxious.  The reason is that the only means of identifying an odor

as obnoxious is the capricious human sense of smell.  Furthermore, individual

sensitivities,  odor fatigue, weather conditions, and other factors complicate


     The olfactory threshold of chlorine and hydrogen chloride is discussed

in Chapter 5, and no details will be given here.  However, it might be pointed

out that the olfactory threshold is often used as the criterion for identifying

an odor as obnoxious.  Rjazanov goes further in considering subsensory effects

(such as changes in nervous activity) in labeling odors as obnoxious.395

It is not clear whether he used this criterion in the case of chlorine and

hydrogen chloride, but he does recommend the very low atmospheric chlorine

and hydrogen chloride concentrations of 0.03 mg/m-^ and 0.015 mg/nr , respectively,

as the maximal allowable exposure limits, averaged over a 24-hr period, for the

general public.

     Chlorine manufacturing plants have a characteristic odor that: those who

are experienced will identify as being not due to chlorine.  The odor is not

nearly as acrid as that of chlorine and is similar to the odor usually associ-

ated with organic compounds.


     In the manufacture of chlorine, small amounts of low-volatility

chlorinated organic compounds are produced by the reaction of chlorine

with graphite anodes and organic-based materials of construction, sealants,

and the like.  During operation of the plant, some of these chlorinated

organic compounds are deposited in pipelines and processing equipment.  When

they are opened to the atmosphere for cleaning or maintenance, some of the

compounds escape and, because of their low volatility, linger in the area

and impart their characteristic odor to the atmosphere.  This hypothesis is

at least partially borne out by the fact that a new plant, on starting up,

does not have the characteristic odor, but develops it after the first

maintenance or cleaning operation.

     The low-volatility organic compounds have been identified as poly-

chlorinated aromatic and aliphatic compounds, such as pentachlorobenzene,

hexachlorobenzene, hexachloroethane, and hexachlorobutadiene.  There may

also be opportunity for chlorine to react with ammonium compounds or amines

present in rainwater, process cooling water,  etc.  In such cases, formation

of monochloramine, dichloramine, and nitrogen trichloride might occur, although

it has not been established.   These also have a characteristic odor that differs

from that of chlorine.


     Actual discomfort  among the general population near chlorine and hydrogen

chloride emission sources will not occur under normal operating conditions.

Only when atmospheric concentrations are moderate or high because of accidental

releases of chlorine and hydrogen chloride will this potential exist.  The

threshold concentrations for human discomfort and accompanying symptoms are

discussed in Chapter 5.

     The chlorinated organic derivatives just discussed are highly unlikely

to produce any discomfort among the general population.  In fact, because of

the minute quantities involved, it is probably safe to assert that such an

occurrence is impossible.

     The chloramines and nitrogen trichloride can be rather irritating In

sufficiently high concentrations, although these concentrations are unknown.

If they are generated on the premises of chlorine plants, the amounts would

be too small to constitute a potential irritant to the public.


     It is well known that traffic and navigational hazards may be caused

by mist and smog, which are at least partially caused by the presence of

pollutants that act as nuclei for the coalescence of water vapor.  There

is no evidence in the literature that chlorine or hydrogen chloride has been

specifically identified as being at fault in this respect.  It is likely,

however, that they contribute, where present, with other chemical pollutants.

At what concentration this contribution is significant is unknown.

     When substantial amounts of hydrogen chloride are released into the

atmosphere, a white mist or cloud results from reaction with atmospheric

water vapor.  Under appropriate meteorologic conditions, such a hydrochloric

acid cloud can be sufficiently opaque as to impede traffic and interfere with

navigation.  No account of such an event has been found in the literature.

Industrial sources have indicated that such events occasionally occur, although

their frequency is not known.

     Another type of haze is associated with the reaction of ammonia with

hydrogen chloride or chlorine in the atmosphere.  The acid gases react with

the alkaline ammonia to form ammonium chloride salt,  which sublimes to a

white powder.  Such a phenomenon can occur where chlorine or hydrogen chloride

and ammonia are manufactured or used in proximity.  Again, it is known from

industrial sources that this occurs occasionally, but the frequency is not

known, nor has any mention of it been found in the literature.  It should also

be noted that a similar phenomenon can occur with the reaction, for example,

of ammonia, water vapor, and sulfur dioxide to form ammonium sulfite.

     The haze formed by the reaction of ammonia with an acid gas has a potential

for producing a navagational hazard or impeding traffic movement by lowering

visibility.  The haze may be white or blue, depending probably on particle size,

angle of light incidence, and viewing angle.

                                   CHAPTER 8



     Safety in the manufacture of chlorine has been a prime consideration

since the inception of the chlorine industry in the late nineteenth century.

Developments in processes and controls, in the handling of chlorine gas and

liquid, in the minimization of potentially dangerous impurities, and in the

packaging and transportation of liquid chlorine have enabled the industry to

produce and distribute thousands of tons of chlorine each day in the United


     Before a discussion of the various aspects of manufacturing safety,

it is pertinent to summarize the most common chlorine manufacturing processes

and the properties of chlorine.

     The majority of chlorine is produced by the electrolysis of sodium

chloride or potassium chloride brine solution; small quantities are produced

by the electrolysis of molten salt or hydrochloric acid.  Only the electrolysis

of brine will be treated here.

     Wet chlorine gas is produced directly by the electrolysis cells, wiuh

byproduct sodium hydroxide and hydrogen gas produced either directly (in

diaphragm cells) or indirectly (in mercury or amalgam cells).  The wet

chlorine gas is continuously removed from the cells by the partial vacuum

created by chlorine compressors.   It is pulled through demisters to remove

entrained salt, pulled through indirect- or direct-contact coolers to reduce

temperature and water content, and dried with concentrated sulfuric acid in

packed towers.  In some installations, the dried chlorine gas is further puri-

fied and cooled before compression by scrubbing the gas with liquid chlorine

reflux in a packed tower.


      Several  types of chlorine compressor systems are used.  The most common

are rotary compressors that use concentrated sulfuric acid as a seal liquor

and large multi-stage centrifugal compressors.  After compression to 35-150

psig  (it varies in different installations), the gas is transferred directly

to processes  that use gaseous chlorine or is cooled to 20° F (about 6.7 C)

or below in liquefiers to form liquid chlorine, which is then transferred to

pressurized tanks, where it is stored as a liquid until used or loaded for

shipment.  Tail gases from the chlorine liquefier, containing up to 50%

gaseous chlorine and noncondensable substances—such as hydrogen, nitrogen,

oxygen, and carbon dioxide—are processed by various means, either to produce

chlorinated products or to recover chlorine from the stream.

     Chlorine at ordinary temperatures and pressures is a greenish-yellow

gas with a pungent and irritating odor.   When diluted in air, chlorine can

be undetectable by sight, and its color cannot be used as a guide to its

concentration.  Because of its reactivity, chlorine is found in nature

only in combination with other elements.   Gaseous chlorine is approximately

2.5 times as heavy as air, so leaked chlorine tends to accumulate in the lowest

part of a building or area.   Liquid chlorine is clear, amber in color, and

about 1.5 times as heavy as water.  At atmospheric pressure, chlorine boils

at about -30 F (about -34.4 C) and freezes at about -150 F (about -101.1 C).

     Chlorine's characteristic odor can be detected at a concentration of

approximately 0.3 ppm in air.   Neither liquid nor gaseous chlorine is flammable

or explosive, but gaseous chlorine will support the combustion of some materials

under special conditions.  Chlorine is an excellent oxidizing agent and is very

active chemically with many substances.   Although dry chlorine does not react

with many metals, it is very reactive in the presence of moisture.

Materials of Construction

     Wet chlorine attacks most common metals, so rubber-lined, brick-lined,

glass, or ceramic equipment is often used in chlorine plants.  Acid-resistant

polyester or phenolic-based resins are used predominantly for pipe construction

in wet-gas systems, with polyvinylchloride (PVC) and polyvinyldichloride (CPVC)

also used for smaller-diameter piping.  Titanium is used for wet-chlorine equip-

ment, particularly for heat exchangers and low-pressure blowers.  (Dry chlorine,

however, readily attacks and can spontaneously ignite titanium).  Tantalum,

platinum, gold, and silver are also resistant to wet-chlorine attack.

     Dry chlorine gas and liquid (moisture less than 150 ppm by weight) are

normally handled in iron or steel equipment and piping.  Some stainless steels,

nickel, copper, Monel, brass, bronze, tantalum, and lead can also be useid for

dry chlorine.  Introduction of moisture will cause severe corrosion of these

metals (except for tantalum), so strict monitoring and control of moisture

in the process are of utmost importance in the handling of dry chlorine.

Overpressure Relief and Emergency Vents

     In chlorine manufacturing plants, chlorine is handled at pressures up to

250 psig.  Safe handling and chlorine emission control dictate the need for

overpressure protection and containment or neutralization of process gas streams.

     Primary overpressure protection for the electrolytic cells and the cell-

room chlorine piping system consists of a water seal.   This seal is often a

combination pressure and vacuum seal, with air pulled  in to avoid high

vacuum in the cells, or chlorine gas directed to a caustic scrubbing system

in the event of excessive header pressure.  Other designs incorporate a

separate header system in the cell room to divert cell gas to a caustic

scrubber if pressure on the cells exceeds several inches of water.

Water seals at the individual cells or the main chlorine header separate the

main chlorine collection piping from the weak gas header.

     Pressure vessels are protected from overpressure by rupture disks or

relief valves set to relieve at code-approved pressures.  Silver, tantalum,

or impervious graphite rupture disks are generally specified.  Spring-loaded

relief valves like those on chlorine tank cars are the most commonly used.

     On pipelines conveying liquid chlorine, expansion chambers are used to

prevent overpressure from thermal expansion in the line.  Often, 1-ton con-

tainers or chlorine cylinders are adapted for use as expansion chambers.

     Properly instrumented power-operated control valves are often used,

rather than check valves, in pipelines.  Rising-ball check valves, used

in chlorine tank cars and storage tanks,  are designed to check when excessive

flow occurs.  Spring-operated swing check valves have been used for dis-

charge piping from chlorine compressors.

     During plant startup and shutdown and during process upsets, emergency

vent systems are used to prevent release  of chlorine gas to the atmosphere.

Various designs are used for emergency vent systems, but all include piping

and equipment for the neutralization of chlorine gas in a caustic soda solution.

Piping and valves are designed to permit  alternate routing of chlorine gas from

various points in the process directly to the emergency vent system.  Remotely

operated valves are often used.   To neutralize the chlorine gas, weak caustic

soda is used to react with chlorine; this forms hypochlorite, and chlorates,  and

only the inert gases are vented.

     The caustic is generally circulated  through a packed tower or contained

in a sparger tank, where it contacts and  reacts with the chlorine,releasing

only inert gases to the atmosphere.

Hydrogen Explosions

     In the electrolysis of brine solutions, gaseous hydrogen is also p>roduced

in the cell gas, usually in concentrations below 1%.  Because chlorine and

high-concentration hydrogen can form explosive mixtures, prevention and con-

trol of excessive hydrogen generation in the cells is a major concern in

chlorine manufacture.

     Prevention of excessive hydrogen generation is based primarily on brine

purity and proper cell operation.  Metallic impurities in brine catalyze

hydrogen generation in electrolytic cells; therefore, brine purification

systems are designed to reduce metallic impurities.  Proper pH adjustment

and control, carbonation of the brine with soda ash or carbon dioxide, and

clarification and filtration are used to control brine purity.  The brine is

analyzed routinely to monitor brine quality.

     Proper cell operation depends on operator and instrument monitoring of

cell variables.  Periodic analyses of cell gas are run on individual cells

and on the main chlorine pipeline to determine hydrogen content of the cell

gas.  Often, hydrogen in the main cell gas stream is monitored continuously.

Backup analyses are routinely run on the compressed chlorine and tail ga.s

to provide further control.

     In diaphragm cells, the amount of brine in the cells and the caustic

flow from the cathode are monitored.  In mercury cells, individual cell

voltages and mercury are also monitored.  The proper mix of trained operators

and modern control equipment are used to control both brine purification and

cell operation to minimize hydrogen generation in the cells.

     Occasionally, excessive hydrogen is generated, because of a process

upset.  The response varies according to the individual circumstances, but

consists of:

      •  Immediate  addition  of  air  at  the  cells,  after  compression and

         after  liquefaction  to  bring the hydrogen content  in  both  cell

         gas  and  tail  gas below potentially  explosive limits.

      •  If required,  reduction of  electric  power to the electrolytic

         cells  or shutdown of the cell circuit  to keep  the hydrogen

         concentration of the various  streams below explosive limits  (the

         hydrogen content in the tail  gas  stream  is important, because

         the  removal of a portion of the chlorine in the liquefier concen-

         trates the hydrogen in the tail gas stream; increased hydrogen  in

         the  cell gas  can be well below explosive limits while that in the

         tail gas is at an explosive point).

      •  Troubleshooting to identify and eliminate the  cause  of increased

         hydrogen generation.

If excessive hydrogen generation is due to brine quality, the brine must be

treated  chemically to isolate  high metallic impurities and stabilize

the pH to bring brine quality  to normal.  If the cause is a malfunction of

an individual cell, the cell must be taken off line until the problem is


      In  rare instances, excessive hydrogen generation  can result  in an ex-

plosion.  Hydrogen explosions  generally occur in individual cells, at the

first-stage drying tower, in the liquefier, or in the  tail gas stream.

     Response to a hydrogen explosion depends on the cause, location, and

severity of  the explosion and  is determined primarily  by  the requirements for

personnel safety and  control of chlorine release.  Plant design,  emergency

planning, and personnel training are the keys to a safe and orderly re-

sponse to explosions  in a chlorine plant.   Strategically placed and re-

motely operated valves are used to direct all process gases to the emergency

vent system immediately, to minimize chlorine release to the atmosphere.


Remote cell-circuit trip switches, automatic compressor controls., and so

forth are incorporated into plant design specifically for emergency situa-


     Emergency planning and personnel training geared to specific emergency

situations ensure that the proper response to an upset condition will be

taken.  The emergency plan assigns responsibility to groups and individuals

in the plant for each of the critical activities that must be undertaken

immediately, to minimize atmospheric releases, protect plant personnel cind

people in the vicinity, and secure the plant after an explosion.  The

following are the most critical functions:

     •  Donning of adequate respiratory protective equipment by plant


     •  Accounting for all plant personnel.

     •  Removal of injured persons exposed to chlorine to safe areas

        and administration of first aid as required.

     •  Diversion of process gas streams to the emergency vent system.

     •  Shutdown of cell circuits to stop further production of chlorine.

     •  Isolation of damaged equipment to prevent further chlorine release.

     •  Assessment of extent of chlorine release to the atmosphere.

     •  Notification of local authorities and neighboring industry to

        apprise them of the situation and to initiate coordinated area

        emergency plan.

     •  Evacuation of affected area, if necessary.

     •  Securing of plant equipment.

     These functions, undertaken essentially simultaneously, apply to a

severe explosion in a critical pipeline or process vessel.   An explosion

in an individual cell or in the tail gas system would usually be met by

isolating only that cell or part of the plant.


     Chlorine plant hydrogen explosions are rare.  Therefore, emergency

planning must include continual training, emergency drills, formal review

of responses to specific upset conditions, and retraining.  The emergency

plan should be coordinated in advance with an area emergency plan  or with

the appropriate local authorities and nearby industries for assistance

and protection of people in the area.

Nitrogen Trichloride Explosions

     Ammonia can combine with chlorine to form nitrogen trichloride, NClo-

Nitrogen trichloride is a yellow, oily liquid that is soluble in all pro-

portions with liquid chlorine.   It is a highly explosive compound and,

when isolated, will detonate spontaneously at temperatures above 55-95 C

(depending on air concentration).

     In some areas of the United States, the salt deposits used for

chlorine production contain ammonium compounds.   The brines produced from

this salt can be treated with small amounts of chlorine gas and air-blown

to reduce the ammonia content before use in the chlorine cells.  At least

one plant in the United States  has used ultraviolet radiation of the cell-

gas stream to reduce nitrogen trichloride to chlorine and nitrogen.

     A significant point of nitrogen trichloride removal in many plants is

the chlorine purification tower, where liquid chlorine is used to cool

and reflux the main cell-gas stream in a packed tower.  Nitrogen trichloride

accumulates in the residue, or  "bottoms," of the purification column, where

it is diluted with an inert organic solvent.  In solution, nitrogen trichloride

is safe to remove from the column on a regular basis.

     Another significant factor in the reduction of nitrogen trichloride to

chlorine is the heat produced by chlorine compression.  In a chlorine-nitrogen

trichloride system, temperatures above 50 C promote decomposition of nitrogen

trichloride to chlorine and nitrogen, especially in the presence of iron compounds.


     Control of nitrogen trichloride and avoidance of nitrogen trichloride

explosions, therefore, depend on a variety of factors.  Regular analysis for

nitrogen trichloride in the cell-gas stream, liquid chlorine production, and

purification bottoms is essential.  Depending on plant design, a combination

of removal schemes can be used to reduce nitrogen trichloride to a safe con-


     The chlorine purification column, which removes nitrogen trichloride,

is the most vulnerable location for a nitrogen trichloride explosion in a

chlorine plant, particularly during an extended plant shutdown.  During a

shutdown, the liquid chlorine in the column will be vaporized and removed,

and the vessel temperature will increase.  The nitrogen trichloride, haraless

while at low temperature and diluted in chlorine, will become concentrated

unless other dilution is used.  Thorough rinsing of the column and piping

is therefore done during plant shutdowns to remove and dilute nitrogen tri-


     Nitrogen trichloride explosions are most likely to occur during a shut-

down of the plant, so response consists primarily of handling injuries to

personnel and damage to equipment caused by the explosion.  Other equipment

that could be the site of a similar explosion should be immediately secured by

dilution.  The cause of the nitrogen trichloride buildup must be found and

eliminated, to prevent future explosions.

Corrosion-Induced Pipeline and Vessel Failures

     After drying, chlorine is handled in an all-steel system—steel piping,

compressors, and vessels.  The introduction of any moisture into the system

can accelerate corrosion of the steel to the point of failure.  In extreme

cases, the moisture in the all-steel system can promote spontaneous combustion

of the chlorine (chlorine'fires").  Therefore, corrosion control in chlorine

handling systems depends on moisture control.


     The chlorine gas is passed through a series of packed towers counter-

current with concentrated sulfuric acid for drying.  The relative dryness

of the chlorine gas stream is controlled by the acid concentration in the last-

stage drying tower.  Virgin concentrated acid is added at such a rate as to

keep the last-stage acid concentration above the minimum that will yield dry

chlorine gas containing water vapor at less than 150 ppm.  When acid flow in

the drying towers is interrupted, the cell circuit must be shut down to prevent

moist chlorine from passing through the drying towers to the steel equipment.

The drying towers must be kept in proper operation at all times, and the gas

stream must be analyzed periodically or continuously for moisture, to verify

proper operation.

     Addition of air to the chlorine stream is another possible source of

moisture.  Automatic regenerative air driers capable of keeping moisture

content below 100 ppm in the air (dew point, -40 C) are used on compressed-

air systems in a chlorine plant.  Dryness is monitored through periodic

analyses run on the exit air from the driers.

     Regular inspections of piping and equipment in chlorine service are

essential in preventing corrosion-induced failures.  Sonic and x-ray testing

are also used on critical equipment and piping,  to ensure integrity of the

welds and steel.

     Hydrostatic testing of new or repaired piping systems and equipment is

standard procedure in chlorine plants.   After the hydrostatic test, the equip-

ment must be dried with steam and then purged with dry air.   Process and

storage vessels are hydrostatically tested regularly.

Fail-Safe Compression Systems

     The main chlorine compression system is the integral part of a chlorine

plant,  with regard to control of chlorine emission to the atmosphere.  The

cells are continuously producing chlorine, and the compression system must

remove the gas from the cells, compress it, and pump it through liquefac.tion

to storage.  Various compression systems are used for chlorine:  rotary com-

pressors with a sulfuric acid seal medium, multistage centrifugal compressors,

and reciprocating compressors.  Rotary  and centrifugal compressors are pre-

dominant; centrifugal compressors are preferred in the newer plants.  The

compression systems are designed to maintain a slight vacuum on each electro-

lytic cell,  to pull the gas through the cooling and drying steps to the com-

pressor suction.   Compressor discharge pressures vary from 35 to 150 psig.

Fail-safe design implies that no chlorine gas will be emitted under any cir-

cumstance—compressor shutdown,  power outage, power surge, or other equipment

or piping failure.  This has not been fully achieved for all contingencies,

but compressor system design includes many features that allow fail-safe

operation to be approached.

     The most difficult situations to provide fail-safe compression systems

for are complete power outages (assuming an electrically driven compressor),

compressor tripoffs, and cell circuit tripoffs.  In a complete power outage,

all additional chlorine production from the cells stops, but chlorine gas in

the system must be removed and there must be adequate provision to prevent

the chlorine pressure at the compressor discharge from backing into the

chlorine suction header, drying towers, and cell room.  In the case of a

compressor tripoff, the cells continue to produce chlorine gas, arid system

chlorine pressure can back into the cell room, as in a complete outage.  In

a cell circuit tripoff, the ceasing of chlorine gas production can create

compressor control difficulties.  If sufficient air is drawn into the system

before the compressor recycle control responds, a centrifugal compressor

can go into surge and stop pumping.

     The plant design must minimize the potential for chlorine release to the

atmosphere for these extreme cases.  The following describes several features

that are included in some plant compression designs.  It is not intended to

imply that all plants incorporate these features or that other approaches to

fail-safe compression systems are not being used.

     Automatic suction control in some systems includes butterfly-valve control

of the suction on the main chlorine header, in addition to compressor re-

cycle control.  Such a system provides relatively independent cell-room suction

control, with the compressor operation controlled by the recycle of gas from

the discharge back to the suction.  When a large change occurs in the amount

of chlorine being handled (owing to a power surge or a cell circuit shutdown,

for example), the compressor recycle operates to keep the compressor loading

constant.  The butterfly valve on the main chlorine header adjusts to the

changing pressure drop through the piping and equipment from the cell room

to the compressor suction, to maintain a constant negative pressure on the

cell circuit.  Wide-range control with this system has been difficult to

achieve, however, so the pressure-vacuum seal or weak-gas header system is

used to back up the suction controller.

     The pressure-vacuum seal system,  as described earlier, either pulls

air into the system to prevent excessive negative pressure on the cells or

diverts excessive gas to the caustic scrubber to relieve pressure.  On

pressure relief,  the gases are conveyed  to a nearby scrubber tower for

neutralization with caustic soda.   Other designs incorporate an auxiliary

header in the cell room.  This auxiliary piping conveys chlorine gas directly

to a caustic scrubber system and in this manner relieves pressure on the

main chlorine header.

     Some plant designs include interlocking relays between the main chlorine

compressor and the cell circuit; if the compressor trips off, the cell circuit

is automatically tripped off, also.  This has not gained wide acceptance, be-

cause of startup difficulties with the interlocking system and because many

plants use multicompressor systems, which obviate interlocks.  Compressor

reliability has been outstanding in the chlorine industry, with continous opera-

tion for a year or more not unusual.

     There have been several approaches to the problem of compressor discharge pres-

sure that backs into the cell-room chlorine header during compressor shutdown or

complete power outage.   Spring-loaded swing check valves on the compressor

discharge have given satisfactory service in some plants; in other locations,

their reliability is suspect.  Three-way, air-operated ball valves have been

used to isolate the compressor discharge to the emergency vent system.  Re-

motely operated valves  on the main chlorine suction header are also used to

divert this stream to the emergency vent system.

     Thus, there is a basis for compression system designs that approach

fail-safe in a chlorine plant.  Some situations, particularly those involving

equipment failure or malfunction, will cause some release of chlorine to the

atmosphere; the basic design elements discussed here will minimize such re-


Compressor Fires

     Chlorine "fires" with steel are self-sustaining chemical reactions

between chlorine and steel, accompanied by a high heat of reaction.  Chlorine

fires in a steel chlorine compressor can be caused by moisture in the chlorine

gas or sulfuric acid seal liquid (with a rotary compressor), localized high

temperatures from friction of moving parts or excessive gas temperature, and

oil or other organic contaminants.

     Moisture exclusion from the chlorine gas and air systems was discussed

earlier, and the same factors apply to compressors.  In addition, where

rotary compressors are used, concentrated sulfuric acid is the seal liquid

in the compressors.  Sulfuric acid strength must be monitored and virgin acid

added, to keep acid strength high enough to avoid a weak sulfuric acid reac-

tion with steel.  Sulfuric acid below a concentration of approximately 70%

is very corrosive to steel, and a byproduct of the corrosion reaction is

hydrogen gas, which presents a fire and explosion hazard.

     The reactivity of chlorine with such organic substances as oil can

contribute to a fire potential in a compressor.  Chlorine compressors

should be designed to isolate the lubricated bearings via air purged or open

distance pieces or chambers to prevent oil from*'"entering the compressor.

Valves and compressor parts are disassembled and washed in an inert organic

solvent before they are put into use,  so as to remove traces of machine

oils.  Because chlorine can be very reactive with many organic compounds, the

inert solvent should be a chlorinated  hydrocarbon, such as perchloroethylene.

     In the design of chlorine compressors, particularly high-speed centrifugal

compressors, consideration must be given to the effects of heat from the

friction of moving parts.   A detailed  discussion of chlorine compressor

design is beyond the scope of this report,  but accurate maintenance of metal-

to-metal clearances, the use of nonmetallic surfaces, and labyrinth seals

between compressor stages are incorporated into the machine design to prevent

localized high temperatures.

     In multistage compressors, integral compressor-housing cooling jackets

or auxiliary coolers between stages are needed to control the temperature of

compressed chlorine gas.  High-temperature protection includes alarm devices

at one temperature and machine tripoff at a somewhat higher temperature, with

maximal operating temperature generally limited to about 300 F (150 C).

Coolers are designed for low-pressure discharge of the cooling medium

(water or chlorinated solvent), to prevent the cooling medium from entering

the gas stream.  The cooling water is monitored regularly for evidence of

cooler leak.

     If a compressor fire occurs, the immediate responses are to vent the

machine to the emergency vent system, isolate the compressor from the system,

and flood the compressor and piping with dry nitrogen gas.  Because the

chlorine "fire" is a self-sustained reaction, the use of nitrogen to purge

residual chlorine from the machine and piping is the prime consideration

in extinguishing the fire.



     Chlorine is stored and shipped as a pressurized liquid in cylinders,

1-ton containers, single-unit tank cars, cargo tank trucks, and tank barges.

All containers used in the transportation of chlorine are controlled by federal

or other governmental regulations, and it is the responsibility of each person

transporting chlorine to know and to comply with all applicable regulations.

A brief summary of the design of each type container is given below.

     Chlorine cylinders (capacity, 1-150 Ib, or 0.45-67.5 kg) are of seamless

steel and of the "foot-ring" or "bumped-bottom" type meeting Interstate

Commerce Commission (ICC) or Department of Transportation specifications

for chlorine service.   All cylinders and 1-ton containers must be requalified

by hydrostatic test every 5 years; test records must be maintained for all

containers in use; and serial numbers and dates of tests must be stamped on

the containers.

     The only opening in a cylinder permitted by regulations is the valve

connection at the top.  A steel hood covers the valve.  Cylinders in an up-

right position deliver gaseous chlorine; they may be inverted to deliver

liquid.  The outlet-valve design includes a fusible metal plug that melts at

158-165 F (70-74 C) for overpressure relief.  Cylinders may be shipped by

truck, rail, or water in truck or carload quantities or less.

     One-ton containers are welded tanks 30-in. (76.2 cm) in diameter that

meet ICC specifications for chlorine containers.  The container is equipped

with two identical valves at one end; each valve is connected to an internal

eduction pipe.  The eduction pipes are so arranged that, when the container

valves are vertical, gaseous chlorine will be delivered from the upper valve

and liquid from the lower valve.  Most containers have six fusible plugs

(three at each end) that are designed to melt at 70-74 C for overpressure

relief.  The heads of the container are convex inward, with the sides crimped

inward to provide chimes for lifting the container.  The valves are protected

by steel hoods.   One-ton containers may be shipped in lots of 15 by rail

(multiunit tank cars) and by truck or water.

     Single-unit chlorine tank cars are built according to ICC regulations

in capacities of 16, 30, 55, 85, and 90 tons.  They are insulated to minimize

temperature and pressure buildup in transit and during storage and are designed

for unloading liquid chlorine directly to the user's vaporizing equipment or

process.  The only openings in a tank car are at the dome, where five valves

are mounted within a protective hood.  Two of the valves are connected to

internal eduction pipes for liquid chlorine withdrawal; ball check valves

are installed under the liquid valves to interrupt flow if the withdrawal

rate exceeds rated capacity.  Two valves are mounted directly on the dome

and are used for adding dry air or nitrogen to the vapor space to increase

liquid removal rates.  These valves are also used for depressuring and evacu-

ating the tank in the loading plant.  The fifth valve, mounted in the center

of the valve cluster, is a safety relief valve set to operate when the pressure

in the car reaches 75% of test pressure.

     Cargo tank trucks with capacities of 15-20 tons are also used.  The

dome and valve arrangements are identical with those of tank cars, except

that excess-flow valves are also required under the gas valves.   Tank trucks

are also insulated.

     Chlorine barges are of the open-hopper, double-skin type, with a number

of cylindrical tanks mounted horizontally.  Different configurations in

capacities up to 1,100 tons are in use and are regulated by the U.S. Coast

Guard.  All openings in a barge tank are required to be in the top.  Unlike

those in tank cars and trucks, valve arrangements are not uniform.  Depending

on the capacity of the individual tank, two or three safety valves rated at

300 psig are used on each tank (each barge has four tanks), with a variable

number of operating valves.  Under each liquid valve, excess-flow valves

are installed at the top of the eduction pipe.  Under each gas valve is a

different excess-flow valve designed to close if the operating valve is

broken off.   All valves are enclosed in protective hoods.  Underwater sonic-

detection devices are installed on chlorine barges to aid in locating them

if they sink.

     Proper handling of chlorine containers is essential in transportation.

Cylinders and 1-ton containers must be secured rigidly to prevent falling.

Cylinders should be transported and stored in an upright position and l^ton

containers should be transported on their sides on steel supports.  Valve-

protection hoods must be securely in place during movement of all containers.

     Exposure of containers to flame, intense radiant heat or high temperature

of any source is to be avoided.  Fusible plugs in small containers will melt

at around 70 C, and excessive chlorine vapor pressure due to increased

temperature in tank cars, trucks, or barges will cause the safety valves

to operate.  Intense local heat on the steel containers will increase corrosion

on the steel walls, and the steel will ignite at high temperatures (420-500°F,

or 215-260 C, depending on surface conditions, impurities, etc.)-  Response

to fires in transit consists of immediate removal of chlorine containers from

the fire zone.   If no chlorine is escaping, water should be applied to the

containers to cool them, if they cannot be moved.  If chlorine is being re-

leased, water should not be sprayed directly on the leak, because that would

increase the leakage rate.

     If a chlorine leak develops in transit, usually the best practice is

to continue moving the container until it is out of a populated area.

Properly trained personnel with protective equipment should then be dispatched

to secure the leak.  If necessary, the affected area should be evacuated.

Emergency kits have been designed to stop most leaks that may be encountered

in chlorine containers.  Three standard emergency kits sold through the

Chlorine Institute, Inc., are designed for cylinders, 1-ton containers, and

tank cars and tank trucks.  Because barge tank design is not uniform, kits

designed for specific barges are on board or at barge loading plants.  Pro-

ducers, repackagers, and many users of chlorine maintain emergency kits and

trained teams experienced in their use.  Motor vehicles that are used to

transport chlorine containers are required to have appropriate emergency

kits on hand.  The following general rules apply to most chlorine-container


     •  If possible, turn container so that gas, rather than liquid

        chlorine, escapes.  One volume of liquid chlorine is equivalent

        to about 460 volumes of gas.

     •  It is often advisable to move the container to an isolated

        area where it will do the least harm.

     •  If it is practical, reduce pressure in the container by removing

        chlorine as a gas to a user's process or disposal system.  The

        vaporization of liquid chlorine in the container will cool the re-

        maining liquid, reducing the container pressure and the magnitude

        of the leakage.

     •  Apply an emergency device to stop leakage.

     In the event of a wreck where chlorine is leaking, the affected area

should be evacuated and emergency assistance obtained.  Trained emergency

teams are available around the clock from any chlorine-producing plant.

     The Chlorine Institute has initiated CHLOREP, a 24-hr/day emergency

assistance program for the entire United States.  A call to a chlorine

producer or repacker or directly to CHLOREP will bring trained emergency

teams with suitable emergency equipment to the scene of a chlorine incident.

On arrival at the scene, the CHLOREP team, with support personnel in tele-

phone contact, will advise local authorities on evacuation, handling of the

leaking container, securing of the leak, and arrangements for removing damaged


     Of course, the first concern in the event of a chlorine leak should be

the protection of people.  All people downwind of a chlorine leak should be

removed from the area.  In the case of actual or potential large-scale chlorine

releases, meteorologic estimation of the atmospheric dispersion of the release

may be required for determining evacuation areas.  Only trained p«;rsonne.L with

suitable respiratory protection should approach the leaking container to move

it or to secure the leak.  Persons who inhale chlorine should be removed to

a safe area and given first aid, and emergency assistance should be sought

as soon as possible.



     Steel pipelines for both gaseous and liquid chlorine are used by the

U.S. chlorine industry for interplant transfer and customer delivery of

chlorine in some locations.  The distances involved have been relatively

short, with design of the piping systems providing a high factor of reliability.

     Chlorine pipeline systems have been installed both below and above ground.

Design considerations for the system include providing protection from traffic

and from heavy equipment.  Below grade, encasement of the piping at crossings

and cathodic protection must be provided.

     Chlorine pipelines are of welded carbon steel with flanged valves.

Expansion loops are used, rather than expansion joints, and there is access

to the line for cleanout, washout, and hydrostatic testing.

     Expansion tanks are provided for potentially isolated sections of the

line, and there are also pipeline depressurization and evacuation facilities.

The depressurization facilities usually include an evacuated tank and auto-

matic or semiautomatic controls for rapidly dumping the line pressure and

contents into the tank in case of a pipeline leak.

     Proper operation and maintenance of a chlorine pipeline include the

general equipment and piping practices discussed earlier.  Particular care

must be taken in the construction, repair, and drying of the pipeline.  Hydro-

static testing after repairs or modification of the line and at regular

intervals ensures the integrity of the pipeline.  X-ray examination of

welds is also used.

     Regular inspection of the external condition of the pipeline and inspection

and testing of cathodic protection systems are essential for safe pipeline

operation.   Any deficiencies on the piping,  cathodic protection system, or

support structures should be promptly corrected.

     Emergency procedures for leaks should be drawn up and personnel at

both ends of the pipeline should be well trained in these procedures.

Dry-run emergency drills, actual pipeline evacuation drills, and formal

review of procedures are integral parts of the emergency plan.

        Response to a pipeline leak will consist of shutting off chlorine

feed to the line, dumping of the pipeline contents into an evacuated vessel,

notification of emergency teams at both ends of the pipeline, and notifica-

tion of local authorities and industries.  The disaster team will immediately

don respiratory protective equipment and assess the impact of the chlorine

emission from the line.  If necessary, the affected area will be evacuated.

In general, the response to a pipeline leak will be dictated by the needs

to protect people and to minimize chlorine emission.


     Chlorine is commercially used in many varied processes ranging from a

few pounds per day, as in small water-treatment plants, to several hundred

tons per day, as in pulp and paper bleaching or organic chlorination plants.

As discussed earlier, safe use of chlorine depends on proper equipment design,

materials of construction, employee training, and emergency planning.  Chlorine

is received in cylinders, 1-ton containers, tank cars, tank trucks, and barges

or via pipeline.  Although most users store the chlorine in those containers,

some barge and tank truck users may require on-site storage tanks.  There: are

specific requirements for use of the various containers, but general guidelines

for safe chlorine handling will be discussed here.

Materials of Construction

     All chlorine commercially shipped has been dried, so steel is the pre-

dominant construction material for piping and vessels in a chlorine-consuming

plant.  Copper or Monel is often used for flexible connections to the con-

tainers, and tantalum, graphite, lead, and silver have been used for the

parts of instruments or rupture disks that contact chlorine.  Both asbestos

and lead gaskets are used.

     Where moisture may be introduced into the process, PVC, CPVC, ABS

(acryon-butadiene-polystyrene copolymer resin), polyester, phenolic-based

resin, Kynar,* and rubber-lined steel may be used for chlorine gas service.

Kynar has been successfully used where liquid chlorine must be introduced

into a water-containing process.

     Proper material selection is important in safe chlorine handling, and

specific questions should be directed to the chlorine producer or to the

Chlorine Institute.

Corrosion Control

     As in a manufacturing plant, control of corrosion of metal equipment

in a chlorine-using facility depends primarily on exclusion of moisture from

the system.  Dry chlorine gas or liquid is noncorrosive to most metals, but

the addition of small amounts of water to the chlorine will accelerate corro-


     Air systems used in conjunction with chlorine must be designed and

operated at a -40 C dew point or below.  Adequate protection from chlorine

flowing back into the air drying system must be provided, lest the chlorine

deactivate the desiccant.  Air systems used exclusively for the chlorine

system are recommended, to prevent the possibility that other uses of air

in the plant will pull the air system pressure below the chlorine pressure.

Multiple check valves should be installed between the chlorine and air systems

and cleaned regularly with inert solvent.
 A Pennwalt fluorocarbon resin.

     Blowers and compressors used for chlorine must be designed to prevent

water, moisture from the air, and oil from entering the chlorine system.

     Piping and equipment used for chlorine should be hydrostatically tested

after maintenance and periodically.  There should be regular external inspec-

tion of the chlorine systems, and deficiencies should be corrected immediately.

     Barometric loops should be installed where moisture may be sucked back

into the process or container.  All pipelines and vessels that are opened

should be plugged off immediately, to keep atmospheric moisture from entering

and causing corrosion.   No flame, welding, or other heat source should be

applied to a. chlorine-containing vessel or pipeline before it is purged and


     A further consideration in corrosion control in chlorine-consuming plants

is attack by liquid chlorine on many plastics, including PVC, CPVC, and ABS.

Where liquid may contact moisture in the process, Kynar pipe should be usud

for the liquid-chlorine piping.  The attack of plastic pipe by liquid chlorine

is caused by solvent attack of the plasticizer or lubricant used in pipe extru-

sion or molding by the chlorine.

Chlorine Unloading

     Specific recommendations for the design and operation of a chlorine un-

loading station should be obtained from the chlorine supplier or the Chlorine

Institute.  However, it is pertinent to summarize general guidelines for safe

chlorine unloading.

     Small Containers.   At the point where a chlorine cylinder is to be usied,

a special rack must be provided to which the cylinder may be secured by chains

or clamps.  If gaseous chlorine is to be removed, the rack must be designed to

hold the cylinder upright; if liquid chlorine, the rack must support the

cylinder on its shoulder and hold it at a 60-deg angle  (from horizontal).

Cylinders should be moved and handled with a hand truck, and a cradle must

be used to hoist them safely.

     One-ton containers must be used in a horizontal position and be firmly

chocked to prevent movement when in use.  The two outlet valves are arranged

vertically;  gaseous chlorine may be withdrawn from the upper valve, liquid

chlorine from the lower.  Hoisting of 1-ton containers is done with specially

designed lifting hooks that clamp into the chime on each end of the container.

A hoist or crane rated at 2 tons or more must be used.

     Cylinders and 1-ton containers should be stored and used in well-

ventilated areas and protected from heat.  The valve-protection hood must

be in place at all times, except when the container is secured and hooked

up for use.  Chlorine containers should not be stored near ether, ammonia,

hydrocarbons, turpentine, or other materials that are flammable or react

violently with chlorine.  Containers may be stored outdoors, provided they

are off the ground, to prevent moisture corrosion, and also provided that the

area is secure from tampering.

     The container valve must be closed each time use is discontinued

and it should not be used for flow regulation or throttling.

     The internal vapor pressure of chlorine in the container provides un-

loading pressure.  Padding of cylinders or 1-ton containers is not recom-

mended.  Valves, gauges, regulators, and fittings approved for chlorine

service must be used.  A flexible connection, usually seamless copper tubing

rated at 250 psig, is used for the connection between the container and  the

piping system.  A trained operator should be in attendance when chlorine is

being withdrawn, and the container should be secured if it is to be left


     Tank Cars and Tank Trucks.  Tank car unloading stations must be on

private railway sidings with locked switches or derails protecting the open

end of the siding at a distance of at least 50 ft (about 15 m).   DOT regula-

tions specify that a warning sign and (for nighttime unloading), a blue

lantern must be in place while a tank car is being unloaded.  The tank car

must be chocked and the brakes set while it is connected for unloading.

Chlorine cars should not be unattended while they are hooked up  for unloading.

     A flexible metal connection (either a copper piping loop or braided

Monel or stainless-steel flexible hose) is used to connect a chlorine  tank

car to the permanent piping system.  A remotely operated shutoff valve is

recommended for chlorine piping systems to limit chlorine release in case a

pipeline is broken.  Expansion chambers should be used if liquid chlorine

might be trapped in a pipeline.

     Chlorine tank cars may be padded with dry air or nitrogen (within

limitations).  On request,  chlorine producers will add a dry air pad when

the car is loaded, to improve liquid withdrawal rates.  Air pads must be

limited to the maximal pressure allowed by DOT regulations, which state

that the vapor pressure calculated at a liquid temperature of 105 F (about

40 C) must not  exceed the safety-valve rating.  Air quality must be strictly

monitored to maintain the -40 C dew point or lower, and all entrained oil

must be removed from the air.

     Because chlorine cars are well insulated, the heat required for

vaporization and withdrawal of gaseous chlorine cannot be obtained, and

liquid chlorine must be withdrawn from the car.  Internal excess-flow

valves in the liquid chlorine eduction piping limit withdrawal rates and

shut off flow if the rated withdrawal is exceeded.  Excess-flow valves

are designed especially to protect a chlorine tank car during transit.


     Design of piping systems, operating and maintenance procedures, and

materials of construction described earlier must be used in chlorine un-

loading systems.  Tank trucks are similar in design to tank cars, and similar

guidelines for unloading tank trucks apply.

     Barges.  Unloading of chlorine barges is regulated by the U.S. Coast

Guard, and the equipment and operating procedures specified by Coast Guard

regulations must be used.  The Coast Guard specifies that a double-braided

flexible-hose connector stamped for a bursting pressure of 1,500 psi be

used and provides for regular hydrostatic testing of all piping used in

chlorine barge loading and unloading.   Emergency shutoff valves, respiratory

protection, attendance requirements, etc., are all specified in the Coast

Guard regulations.

Other Engineering Safeguards

     Barometric legs or vacuum breakers must be provided to present suckback

of process fluids into chlorine containers.   Expansion tanks should be pro-

vided on piping to trap liquid chlorine between closed valves.   If liquid

chlorine is trapped in a line, it will expand because of a temperature

increase and can create enough internal pressure to burst the pipe.

     Remote shutoff valves should be placed at appropriate points in the

unloading system and process, so that  the chlorine supply can be isolated

quickly to prevent further release in the event of a piping failure.

     Chlorine-using plants should be designed to prevent release of chlorine

in the event of a process shutdown or  power outage or other utility interruption

and to limit release in the event of a piping or equipment failure.

Chlorine Vaporizers

     Gaseous chlorine can be withdrawn for use directly into a process from

cylinders and 1-ton containers at low flow rates.   However, where larger gas

flow rates are required or larger containers are used, vaporizers are used

to revaporize the liquid chlorine.

     Details differ widely in regard to construction of vaporizers, but they

all operate on the same principle.  Liquid chlorine is transferred from the

chlorine container to the vaporizing chamber, where heat is applied.  The

heat, generally from either hot water or steam, is used to boil the liquid

chlorine, and vapor is continuously delivered to the process.  Vaporizers

operate continuously and automatically, and the container pressure is

usually sufficient to deliver liquid to the vaporizer.

     Vaporizer design must provide for protection against flooding, adequate

vapor-liquid disengagement, and superheating of the vapor.  Vaporizers are

sized in excess of the peak load demanded by the process.  Because vaporizers

are constructed of carbon steel with steel or Monel heating coils, the maximal

temperature of the heating medium cannot exceed 250 F (121 C), and appropriate

pressure-relief and high-temperature alarms must be provided.  Design working

pressure of chlorine vaporizers is at least 250 psig, and an additional 1/8 in.

(0.3 cm) of corrosion allowance must be provided.

     The hazards that must be considered and provided for in the design,

operation, and maintenance of chlorine vaporizers are discussed below.

     Reliquefaction of chlorine gas downstream of the vaporizer must be pre-

vented by including a superheating section in the vaporizer.  Chlorine j;as

piping should be insulated from cold process lines and atmospheric conditions.

Liquid chlorine pockets in a gas system could present an overpressure hazard

after shutdown of the system.

     The  chlorine vaporizing system must be equipped with an overpressure

 relief device to protect against rupture.  Code-rated rupture disks and

 spring-loaded relief valves similar to those used on chlorine cars have been

 used for  vaporizers.  If a spring-loaded safety valve is used in series with

 a frangible disk, the section between them should be equipped with a pressure

 alarm to  warn of a leaking rupture disk.  Vents from the pressure relief

 device should be piped away from the working area, preferably to an absorption

 system.   A barometric loop must be provided to prevent suckback of the

 absorption liquid.

     Because steel corrosion by chlorine will be accelerated above 300 F

 (150 C),  there must be some provision for preventing operation above the

maximal design temperature of 250 F (121 C).   On steam systems, a 15-psig

 steam-regulating valve and a relief valve set to relieve at a steam pressure

below 121 C should be used.  Hot-water vaporizers should be designed with a

vented water jacket to prevent overpressure,  and high- and low-temperature

alarms for the heating medium should be used.  In vaporizer operation, liquid

chlorine must not be trapped in the vaporizer when it is shut down.   Shutdown

procedure involves first shutting off liquid  chlorine supply to the vaporizer

and then maintaining heat until a rapid fall  in vaporizer pressure indicates

complete revaporization of the liquid.  Closing the gas discharge valve of

the vaporizer while maintaining the heat supply will also empty the vaporizer

of liquid, with the pressure buildup in the vaporizer forcing the remaining

liquid to return to the container.

     If moisture is excluded,  the.chlorine side of the vaporizing equipment

does not represent a serious corrosion problem.   A corrosion inhibitor or

cathodic protection for the heating medium is advisable, because water or

steam may cause some corrosion.   The interiors of both the water or steam

and the chlorine sides of vaporizers should be regularly inspected.   The

vaporizer should be cleaned and hydrostatically tested periodically.  Uecause

the pressure of the heating medium will be less than the chlorine pressure in

a vaporizer, a leak will admit chlorine into the steam or water.   A conductivity

monitor or regular monitoring of atmospheric water or condensate discharge

points is used to discover evidence of internal leakage during operation.

     Where practical, barometric loops are used on the chlorine gas discharge

to prevent process fluids from being pulled back into the vaporizer.  Power-

operated control valves, automatic backpressure regulators, check valv«:s, low-

pressure controls and alarms, etc., are also used where process pressures are

above atmospheric pressure.  These devices must be regularly maintained, and

tested to ensure proper operation.  The emptying or changing of chlorine con-

tainers can result in changing the chlorine supply pressure and tempera.ture.

This can result in suckback of liquid chlorine from the vaporizer to the con-

tainer, possibly overfilling the container.  Storage of the next used con-

tainer at the same temperature as those being used and control of the supply

pressure at the time of container changing will prevent backflow of chlorine.

Vaporization of remaining liquid chlorine and shutoff of the gas discharge

valve before changing containers are other common ways to prevent suckback.

It is not advisable to use check valves in the liquid chlorine supply line,

because the chlorine container acts as an expansion chamber for the vaporizer

in normal operation.

     No case reports of nitrogen trichloride explosions in vaporizing equip-

ment are known.  Nitrogen trichloride concentrations are monitored and kept

very low by the U.S. chlorine industry.  In addition, the thermal decomposi-

tion of nitrogen trichloride to nitrogen and chlorine at high temperatures

and in combination with steel indicates that nitrogen trichloride will not

accumulate in chlorine vaporizers.  As a further precaution, the internal

 design  of  chlorine vaporizers  should provide unrestricted liquid chlorine

 flow, to prevent any pockets where nitrogen trichloride could accumulate.

 Internal refluxing of chlorine in the vaporizer is prevented by the super-

 heat sections.  Liquid-gas demisters are not recommended for vaporizer design,

 because some refluxing by the  demister could lead to an accumulation of nitrogen


     Flooding of a vaporizer with liquid chlorine and carryover of liquid

 chlorine into the vapor discharge line can occur if inadequate heat is

 supplied to the vaporizer, if  the vapor demand exceeds the vaporizer capacity,

 or if excessive padding of the chlorine container introduces high pressure

 into the vaporizer.  A properly sized gas control valve should be installed

 in the  vapor discharge line from the vaporizer to prevent exceeding the vaporizer

 capacity.  A low-temperature alarm and an automatic valve actuated by low

 temperature of the heating medium can also prevent flooding.  Air padding of

 cylinders  or 1-ton containers  is not recommended; tank cars may be padded

 with dry air or nitrogen under controlled conditions only.  Specific recom-

 mendations on air padding should be obtained from the chlorine manufacturer.

 Generally, no air pad will.be  required, because the chlorine vapor pressure

 will be sufficient to transfer  liquid chlorine from the container to the

 vaporizer.  Producers will add  air pressure to tank cars on request.

     Proper maintenance procedures must be followed, to ensure safe vaporizer

 operation.  The vaporizer must  be completely purged of chlorine and washed

 with water before burning or welding on the vessel or piping begins.   After

 repairs and inspection, the vessel should be retested hydrostatically, heated

 with steam, and then air-dried  to below a -40 C dew point.  All gaskets should

 be replaced after water is drained from the vessel.   After drying,  the vessel

 should  again be tested for leaks with chlorine vapor.  A cloth saturated with

*Use of  compressed air above the surface  of  a  liquid  to  transfer  the  liquid  to
 another vessel.

ammonium hydroxide is used at joints, flanges, etc., to find leaks.   (A

white cloud of ammonium chloride is formed when chlorine comes into  contact

with the ammonium hydroxide.)

     After a new installation, or when new pipes or valves are used, residual

oil must be washed off first  with an inert solvent, such as perchlorethylene.

     There should be regular  preventive maintenance and testing of safety

valves, check valves, automatic controls, and alarms on chlorine vaporizer

systems to ensure proper operation.

     No flame or other heat source should be applied to a chlorine vessel

or pipe without purging and washing, because excessive heat can spontaneously

ignite the steel.  All piping and equipment that is temporarily disconnected—

for example, the container connecting lines—must be plugged, to prevent

atmospheric moisture from entering the system and causing corrosion.

     These maintenance guidelines apply to all chlorine systems, including


     In summary, chlorine vaporizers are operated safely throughout  the

United States.  It is imperative that those operating the vaporizers under-

stand the operating and maintenance procedures and potential hazards involved.

With proper operator training, vaporizer operation is safe, easily controlled,

and relatively troublefree.

Piping Leaks

     The proper design and construction of chlorine piping systems are

essential, to avoid piping leaks.  Seamless schedule 80 steel pipe of 3/4 in.

(about 1.9 cm) or above should be used, with butt-welded or flanged  joints

used exclusively for 1 1/2-in. (3.8 cm) or larger sizes.  Tongue-and-groove

or raised-face flanges are recommended.  All pipe bends must be made hot. and

properly stress-relieved.  All valves must be of the indicating type, such as

rising-stem or indicating-ball valves.  Only valves and gauges approved

for chlorine service should be used.

     Before use, all piping systems must be cleaned thoroughly with an inert

organic solvent to remove traces of oil.  Valves and other equipment should

be disassembled and cleaned before use.  Piping systems should be hydro-

statically tested to 300 psig and dried to a -40 C dew point before use.

Final gas testing with dry air or nitrogen is followed by the introduction

of chlorine gas.

     All piping should be inspected regularly and any deficiencies noted

should be promptly corrected.   Periodic retesting of the piping is recom-

mended to ensure integrity of  the piping.

     Exclusion of moisture from the system, as discussed before, is the

most important means of avoiding piping leaks.

     Response to a piping leak involves shutting off further chlorine supply,

diverting the remaining pressure to neutralization facilities if available,

and initiating the emergency plan to prevent chlorine inhalation.

     A small leak should be corrected immediately, because chlorine leaks

will always get worse.   No repairs should  be attempted until the piping is

isolated and purged of residual chlorine.

     Each facility using chlorine should develop an emergency plan that includes

contingency procedures for possible chlorine releases.  The details of the

plan should involve minimization of the release and protection of persons in

the affected area.   Employee training in responding to specific release situations

and proper use of respiratory  protective equipment should be conducted continually.


     Anhydrous hydrogen chloride is a colorless, stable gas at ordinary

temperature.  In moist air, it produces white, corrosive fumes and is

readily absorbed by water to form dilute hydrochloric acid.  It has a boiling

point of -121 F (-85 C) at atmospheric pressure; at 68 F (20 C), it has a

vapor pressure of about 600 psig.  It is handled primarily as a gas, but is

also commercially distributed as a liquid under pressure.

     Although hydrogen chloride is not itself flammable, its reaction with

steel in the presence of moisture produces hydrogen gas.  This coproduct

hydrogen can present both a fire hazard and an explosion hazard.

Materials of Construction

     Anhydrous hydrogen chloride gas and liquid (moisture content, below 150

ppm) are commonly handled in steel piping and equipment.  Nickel-alloy ma-

terials, including some low-nickel stainless steels, can also be used.

     Schedule 40 steel seamless pipe for 3 in. (7.6 cm) in diameter and

larger is used for dry hydrogen chloride gas at up to 100 psig and at -15 to

350 F (-26 to 177 C).   Schedule 80 pipe is used for pipe smaller than 7.6 cm.

Alloy 20 gate, plug, and ball valves (rating, 150 psig) are commonly used.

Monel valves can also be used.

     For dry liquid hydrogen chloride, schedule 80 seamless piping systems

are used for all sizes, with alloy 20 valves  (rating, 600 psig).  Liquid

hydrogen chloride storage tanks must be constructed of a steel with good

low-temperature qualities; for most storage temperatures, carbon stetil is


     If the hydrogen chloride contains moisture at above 150 ppm, then

plastic or rubber lining or special alloys that are suitable for hydro-

chloric acid must be used for equipment and piping.

Corrosion Control

     In the presence of moisture, hydrogen chloride gas and liquid are very

corrosive to almost all metals.  Control of internal corrosion is therefore

based primarily on proper design of equipment, operating procedures, and

maintenance techniques to exclude moisture from the system.

     Because anhydrous hydrogen chloride is extremely soluble in water and

other liquids, piping design must provide barometric loops or vacuum breakers

to prevent suckback into piping and containers from the point of introduction

of the hydrogen chloride.  Other details to exclude moisture from specific

equipment must also be considered.  Air systems used in conjunction with

hydrogen chloride handling equipment must be operated at a -40 C dew point

(for moisture at 100 ppm) or below.

     Proper maintenance procedures include complete purging of piping and

equipment with dry air or nitrogen before work or burning on the equipment

and capping of all openings on disconnected equipment and piping to keep

moisture in the air from combining with residual hydrogen chloride and forming

corrosive hydrochloric acid.

     To prevent hydrogen explosions before the burning, welding, or repairing

of hydrogen chloride equipment, there must be an explosion test to verify

safe conditions.

     All metal equipment must be dried with nitrogen or dry air to below

a -40 C dew point before anhydrous hydrogen chloride is introduced.

     Acid-resistant paint should be used on buildings,  equipment,  and piping

in the vicinity of anhydrous hydrogen chloride equipment, and regular external

inspections should be conducted to identify and correct areas of external

corrosion.   Piping and vessels used in pressure service are hydrostatically

tested on a regular schedule, to ensure the integrity of the equipment.

Overpressure Relief and Emergency Vents

     Anhydrous hydrogen chloride equipment is protected against overpressure

by rupture disks or relief valves at code-specified ratings.   Where rupture

disks  are used, impervious graphite or silver disks are specified.  Relief

valves are generally of the spring-loaded type as used on chlorine tank

cars, but with silver lower frangible disks (lead lower disks are used for

chlorine relief valves).  The frangible disk shields the working parts of the

relief valve from hydrogen chloride until relief pressure is approached.

     The discharge of pressure relief devices should be directed to an ab-

sorber to prevent atmospheric release of hydrogen chloride.  Emergency

vents to the absorber are provided at stratetic points in the process, to

prevent atmospheric emissions due to equipment shutdown, power outage, or

reaction control problems.

     Additional precautions must be taken in the handling of anhydrous

hydrogen chloride liquid.  Expansion vessels should be provided for piping

systems where the liquid could be blocked between closed valves.  Thermal

expansion and increased vapor pressure due to a temperature increase can

create  a hazardous overpressure without expansion vessels.  For the same

reason, the design must include a way to prevent overfilling of an anhydrous

hydrogen chloride liquid container or vessel.

Tail-Gas Absorption and Emergency Emission Control

     Elimination of tail-gas streams of anhydrous hydrogen chloride and

emergency emission control are accomplished through absorption of the gas

in a water jet, fume scrubber, or packed tower that circulates water or a

dilute alkaline solution.  Absorber design must provide for the removal of

heat generated by the absorption process.  A barometric loop on the tail-gas

stream must prevent suckback of the absorption liquid into the process.

      Response  to a hydrogen chloride leak must be as quick as possible,

 because  the  leak will  increase in severity.  The leaking hydrogen chloride

 will  combine with atmospheric moisture and form corrosive hydrochloric acid

 at the point of leakage.  The acid will further attack the steel pipe or

 container and  increase the leak.  Proper respiratory protection and, in

 many  cases,  protective clothing should be put on before the leak is approached.

 A dilute aqueous ammonia solution or a cloth saturated with ammonia is used

 to find the  leak.  Where the ammonia vapor contacts hydrogen chloride, a

 white "smoke"  (ammonium chloride) will be formed.  When the leak is found,

 the defective piping or equipment must be isolated, purged of hydrogen

 chloride with dry air or nitrogen, and repaired or replaced.

      In the  event of a large emission to the atmosphere, a fog nozzle

 spraying large quantities of water should be used to absorb the hydrogen

 chloride until its source can be shut down.  Unlike chlorine, hydrogen

 chloride is very soluble in water, and fog nozzles are effective in con-

 trolling emission.   Care should be taken to direct the water away from the

 point of leakage to avoid increasing the leakage by aggravated corrosion.

     Protection of plant personnel and other persons in the area affected

 by a hydrogen chloride release must be the prime concern in the response

 to a release.  Emergency planning, personnel training,  and coordination

with local authorities should be handled as discussed earlier in this



     Anhydrous hydrogen chloride is transported as a pressurized liquid in

cylinders of 50 and 600 Ib (22.5 and 270 kg)  net,  truck tube and tank

trailers, and tank cars.   The pressure in anhydrous hydrogen chloride con-

tainers depends on the temperature of the liquid.   At 68 F (20 C),  the

pressure is about 600 psig;  it is less at lower temperatures.   Gaseous or

liquid hydrogen chloride may be withdrawn from cylinders, but  the larger con-

tainers are designed only for liquid withdrawal.   All containers used in the

transportation of anhydrous hydrogen chloride are controlled by federal, or

other governmental regulations, and it is the responsibility of each person

shipping, transporting, or using anhydrous hydrogen chloride to know and

comply with all applicable regulations.  The design of the containers commonly

used is discussed briefly below.


     Anhydrous hydrogen chloride cylinders are steel pressure vessels con-

structed in accordance with DOT specifications.  The 22.5-kg cylinders are

equipped with a top discharge valve and two safety devices designed to re-

lieve at pressures of 2,400-2,700 psig and temperatures of 158-163 F

(70-73 C).  One relief device is on the valve body, and the other is in the

concave cylinder bottom.  Gaseous hydrogen chloride is withdrawn from the

22.5-kg cylinder in an upright position, and the cylinder may be inverted

to withdraw liquid.  The 270rkg cylinders are handled on their sides and

are equipped with one discharge valve and three relief devices.  Two of the

relief devices are on the cylinder proper, and one is on the discharge valve.

They are rated at pressures of 2,400-2,700 psig and temperatures of 70-73 C.

The discharge valve is connected to an internal dip tube that permits with-

drawal of either liquid or gaseous hydrogen chloride by rotation of the

cylinder.  Cylinder valves are protected by a valve hood, which should be

in place at all times when the cylinder is not in use.  Normal cylinder

handling precautions must be taken for safe operation.  The cylinders must

be secured when stored, protected from dropping or striking, stored in a cool

dry place, and protected from sunlight or other heat sources.

     Anhydrous hydrogen chloride tube trailers are made in various sizes and

are basically multicylinders mounted on a trailer and manifolded together.

Common tube trailers transport 5-8 tons (4,500-7,200 kg) of anhydrous hydrogen

chloride, although other sizes are also used.  Each individual tube or

cylinder on a tube trailer has a block valve and relief devices designed to

relieve at pressures of 2,400-2,700 psig or temperatures of 70-73 C.  Manifold

designs, tube design, and configuration vary within the DOT specifications.

Manifold arrangements on tube trailers are designed only for liquid hydrogen

chloride withdrawal.  In tube trailer processing and refilling, care must be

taken to prevent overfilling an individual tube.  A vacuum is pulled on each

tube, the vacuum broken with dry air, the tube valve removed, and the tube

visually inspected for foreign matter.  If foreign material is present, the

tube must be cleaned before loading.  All tubes must be dried to below a

-40 C dew point.  Each tube is individually loaded by weight to a filling

density of not over 65% (percent ratio of the weight of hydrogen chloride

in the container to the weight of water that the container will hold).   A

few single-bore tank trailers in anhydrous hydrogen chloride service are

in operation under a special permit.

     Rail tank cars of various sizes are in use to transport anhydrous

hydrogen chloride, with the most common having capacities of 33 and 70  tons

(29,700 and 63,000 kg).   The cars are designed for liquid hydrogen chloride

withdrawal and are equipped with relief valves like those on chlorine cars.

The lower frangible disk in the relief valve is silver,  rather than lead,

as is used in chlorine cars.   A special DOT permit is required for selected

hydrogen chloride tank cars for specific routing to transport anhydrous

hydrogen chloride liquid.   The relief-valve setting for most hydrogen chloride

tank cars is 450 psig,  which is below the vapor pressure of liquid hydrogen

chloride at normal ambient temperatures.  The hydrogen chloride is refrigerated


to -50 F (-45.6 C) before loading into the insulated tank car.   This allows

30 days or more before the liquid temperature will approach the corresponding

vapor pressure to lift the spring-loaded safety valve.   The monitoring and

expediting of hydrogen chloride rail shipments and the  complete withdrawal

of all liquid hydrogen chloride by the consumer receiving the tank cars are

necessary, to prevent hydrogen chloride release.  The standard emergency kit

used for chlorine cars will fit most anhydrous hydrogen chloride cars to

control leaks, but its use must be accompanied by additional action to lower

the tank-car pressure, because the chlorine emergency kit is designed for

lower pressures than are commonly experienced with hydrogen chloride.

     Two properties of anhydrous hydrogen chloride can  be useful in responding

to in-transit leaks:

     •  Through withdrawal of gaseous hydrogen chloride from a container,

        vaporization of the liquid removes about 190 BTU/lb vaporized.

        This reduces the temperature of the remaining liquid and reduces

        the pressure in the container.

     •  Unlike chlorine, hydrogen chloride is readily soluble in water.

        In a situation where the container pressure must be lowered,

        gaseous hydrogen chloride can be withdrawn and  absorbed by

        water.  Use of a fog nozzle to spray water on an emission is

        effective in controlling the emission.

     General guidelines for responding to a hydrogen chloride leak are

similar to those discussed for chlorine.  The major differences are the

higher pressures used in transporting hydrogen chloride, the favorable water

solubility of hydrogen chloride, and the availability of the emergency devices

for all chlorine containers.


     Gaseous anhydrous hydrogen chloride is transported via steel pipelines

for interplant transfer and delivery to nearby customers.  Design, maintenance,

and safe operation of these pipelines involve the factors discussed earlier

in connection with the materials of construction and corrosion control.  The

design must permit adequate purging, washing, and hydrostatic testing.  The

line must be protected from being struck by traffic or heavy equipment, and

below-grade lines must be encased at grade crossings.  Underground pipe should

be cathodically protected from external corrosion.  The pipelines should be

all-welded steel, with expansion loops where required.

     Inspection of the external condition of the pipeline and periodic

hydrostatic testing of the line are important for safe operation.

     Emergency procedures for a hydrogen chloride pipeline leak primarily

involve shutting off of the gaseous feed to the pipeline and dumping of the

line pressure to the emergency vent absorber.  Protection of people in the

affected area and "fogging" of the emitted hydrogen chloride gas with water

to minimize the atmospheric release are integral parts of the emergency plan

for a specific installation.


     Recommended industrial hygiene practices for a chlorine or anhydrous

hydrogen chloride area in a plant are as follows.

Medical Aspects

     A new employee or one about to be reassigned to a chlorine or hydrogen

chloride area should receive a physical examination, and his medical history

should be reviewed.  The physical should be a thorough, general examination,

with emphasis on discovering evidence of chronic respiratory, pulmonary, or

cardiac difficulties.  A person with such chronic difficulty should not be

assigned to a chlorine or hydrogen chloride handling area.

     Routine medical surveillance involves regularly scheduled reexamination

of employees and review of recent illness history.

Plant Design, Operation, and Maintenance

     The engineering design of an area in which chlorine or hydrogen chloride

is to be handled must include proper ventilation, to avoid gas accumulation

in case of leakage.  There should be provisions for handling a process upset

without exposing employees to an atmospheric release.  Alarms, emergency

vent systems, absorption systems, etc., should be installed where appropriate.

High housekeeping standards should be maintained.  A formal emergency plan

for handling an atmospheric release should be devised, and employees should

be trained in its application.  Retraining and regular drills for specific

emergencies or release situations are important.

     Equipment and controls should be tested often to ensure proper operation

when needed.  Leaks should be promptly repaired.

Respiratory Protection

     Employees should be trained in the location and use of canister gas

masks and self-contained breathing apparatus.  It is recommended that every

employee entering a chlorine or hydrogen chloride area be provided with a

pocket escape respirator and carry it at all times.  The proper use, location,

and maintenance of the various respiratory protection devices should be

reviewed regularly.

     Periodic air sampling and determination of the weighted exposure of

each employee group is recommended for information and control purposes.

     Both chlorine and hydrogen chloride leaks can be easily found with

ammonia, and the characteristic odor of each below the recommended TLV can

be detected.  Prompt identification and correction of leaks are the main

criteria of an effective industrial hygiene program in a plant that produces

or consumes chlorine or hydrogen chloride.

                                CHAPTER 9

                         SUMMARY AND CONCLUSIONS


     Volcanic gases constitute the only known natural source  of emission

of chlorine and hydrogen chloride gases to the atmosphere, and the quanti-

ties of such emission are minute.  The formation of chlorine in low con-

centrations by atmospheric reactions has been postulated.  Atmospheric

reactions leading to the formation of hydrogen chloride gas in low con-

centrations have also been postulated.

     Commercial production of chlorine is a major and growing U.S.

industry.  A total of 9.86 x 106 tons (8.9 x 109 kg) of chlorine was pro-

duced in the United States in 1972, and production is projected to con-

tinue to increase at approximately 7% per year through 1974.  Chlorine

gas and liquid shipments in 1971 total about 4.2 x 10  tons (3.,8 x 109 kg),

or 45.4% of the total production of 9.35 x 106 tons (8.4 x 109 kg) in 1971.

     The production, shipment, and use of chlorine provide significant

opportunities for infrequent, localized emission of chlorine to the

atmosphere, through equipment or control system failure or transportation

accidents.  Improved engineering design (including the use of fail-safe

systems), improved selection of materials of construction, and appropriate

detailed local and national emergency plans are being used to minimize the

incidence and magnitude of such accidental releases of chlorine to the

atmosphere and to minimize their effects on the public.  No estimate can be

made of the chlorine emission to the atmosphere from such accidental and

noncontinuous emissions.

     Potential continuous emission of chlorine from production and use

is controlled by the recycling of exit gases to plant chlorination

processes, the neutralization of chlorine in alkaline scrubbing units,

and the scrubbing of chlorine from gas streams with a solvent and then

recovery of the chlorine from the solvent.  Scrubbing technology is well

developed, and the industrial use of such technology is extensively re-

ported in the literature.  The use of a final alkaline scrubber on the

process tail-gas emission to the atmosphere is common industrial practice,

regardless of the type of intermediate chlorine emission control technique.

     The chlorine emission factor for any production or use is a direct

function of the type of final emission control technique used to treat

the process tail gases.  The chlorine emission factor can be reduced to

a few parts per million (pounds of chlorine emitted per million pounds of

chlorine handled or product produced) through the use of final alkaline

scrubbing, but the absence of final alkaline scrubbing will permit chlorine

emission factors ranging up to values like 10-20 Ib of chlorine emitted

per ton of chlorine handled or product produced, depending on the process

and the chlorine emission control techniques (if any) used.  Processes

with chlorine emission factors in the range of 10-20 generally have no

emission control system on the purge stream.  A chlorine emission factor

of less than 1 is normally obtained when a nonalkaline chlorine emission

control system is used.

     In view of the nonuniformity in the techniques used to control potential

chlorine emission to the atmosphere, no attempt has been made to estimate

the maximal annual emission of chlorine to the atmosphere from continuous


     Commercial production of hydrochloric acid (100% basis) in the U.S.

in 1972 was 2.2 x 106 tons (2 x 109 kg), and production is projected to

increase over the next few years at an average annual rate of approximately

5-7%.  In 1972, 90% of the hydrochloric acid (100% basis) was manufactured

as a byproduct of the chlorination of organic compounds.  Theoretically,

practically all the hydrochloric acid produced by the three major routes

is available for release to the atmosphere as hydrogen chloride gas; in

practice, the potential emission is most commonly, effectively, and inex-

pensively controlled by scrubbing the main exit-gas stream and any tail-gas

stream with water.  Other emission control systems have been developed to

meet special industrial requirements.

     The published data indicate that adequate technology and control

equipment are available to reduce hydrogen chloride emission from byproduct

process manufacturing and from applications of hydrogen chloride gas to about

0.5 Ib/ton (0.25 kg/1,000 kg) of 20° Be* acid produced.  In such cases as

the manufacture of hydrogen chloride by the synthesis process, or where

hydrogen chloride is the only component to be removed from a tail-gas

stream, water scrubbing can reduce hydrogen chloride emission to less than

0.1 Ib/ton (0.5 kg/1,000 kg) of 20° B/ acid produced.

     If we assume that almost all continuous emission of hydrogen chloride

gas from primary manufacturing and applications is water-scrubbed to pre-

vent local public-nuisance and plant-corrosion problems and if we assume

a hydrogen chloride emission factor of 0.5 Ib/ton (0.25 kg/1,000 kg) of

20  B6 (31.5% hydrogen chloride) acid produced, then approximately 1,750

tons (1.6 x 10" kg) of hydrogen chloride gas was emitted to the atmosphere

in the United States in 1972 from such manufacturing and applications.  This

rough estimate also assumes the use of low concentration aqueous acid (less

than 20%, with negligible hydrogen chloride equilibrium vapor pressure)

for the bulk of the applications.

     It should be noted that the byproduct hydrogen chloride is believed

to be considerably in excess of what is recovered and reported and that

the disposition of such excess is unknown.  Consequently, these estimates

of hydrogen chloride gas emission to the atmosphere from byproduct process

operations are undoubtedly low, but no  reliable basis is available for

the development of a more accurate estimate.

     As is the case with chlorine, the production and use of hydrochloric

acid (100% basis) provide significant opportunities for infrequent, localized

emission of hydrogen chloride gas to the atmosphere, through equipment or

control system failure.  Transportation accidents with hydrochloric acid

(100% basis) are significantly less serious than chlorine transportation

accidents, because most hydrogen chloride is shipped as 18°, 20°, and

22  Be aqueous hydrochloric acid solutions and because the great affinity

of the gas for water permits reasonable control of large emission through

use of fog nozzles.  Improved engineering design (including fail-safe

systems), improved selection of materials of construction, and appropriate

detailed emergency plans are being used to minimize and control accidental

releases of hydrogen chloride gas to the atmosphere.

     On the basis of limited data, the public incineration of approximately

30 x 106 tons (27 x 10  kg)  of collected refuse in the United States in

1970 produced an estimated maximal atmospheric emission of 75,000 tons

(67.5 x 10  kg) of hydrogen chloride gas.   The hydrogen chloride emission

arises from the combustion of chlorine-containing plastics,  especially

polyvinylchloride, in the refuse and from the combustion of  other components

*18% 20P, Ti  Be'  is 27.9%, 31.5%,  and 35.2% acid,  respectively.


of the refuse that contain chlorine or chlorides, probably largely in, the

form of common salt (sodium chloride).  No free chlorine or phosgene has

been detected in the exit gases from refuse incineration.  Only in the last

few years have true wet-scrubbing systems, as differentiated from crude

spray chambers or wet baffles, been applied to municipal incinerators to

afford favorable conditions for removing such gases as sulfur dioxide,

hydrogen chloride, and organic acids from the flue-gas streams.  At present,

fewer than 10% of incinerators have wet-scrubbing systems.  The projected

increases in public incinerator capacity to 58 x 10  tons (52 x 10" kg) and

in the plastics component of refuse from the present 2% to 2.8-3.0% by 1980

will significantly increase the potential for hydrogen chloride emission

to the atmosphere, even if the present percentage distribution of polyolefins,

polystyrene, and polyvinylchloride in the plastics component of refuse re-

mains unchanged.

     The combustion of fossil fuels, particularly coal, produces a major

contribution to the chloride content of the atmosphere in the form of

hydrogen chloride gas emission.  The United States consumed about 526 x 10"

tons (474 x 109 kg) in 1970.  If it is assumed (using published data) that

the average chlorine content of coal is 0.128% and that 95% of the chlorine

is converted to hydrogen chloride gas, it is possible to estimate the maximal

hydrogen chloride gas atmospheric emission due to coal burning in 1970 at

0.64 x 10  tons (0.6 x 10  kg) although methods are available for control

of emission of sulfur dioxide, nitrogen oxides, arid hydrogen chloride from

coal- and oil-fired industrial heating plants and electric generating plants,

these methods are not in general use.

     There appears to be little published information on the measurement

of gaseous chlorine or hydrogen chloride in exhaust from any mode of trans-

portation.  In fact, there is no evidence that there is such gaseous emission.

Although appropriate exhaust analysis data do not exist, one can calculate

that the maximal theoretical amount of hydrogen chloride gas (the con-

taminant assumed to be emitted) that could be emitted from mobile sources

burning motor gasoline in the United States in 1971 is approximately 26,000

tons (23.4 x 10  kg).  It seems reasonable to assume that other chlorides—

such as lead chloride, ammonium chloride, and hydrocarbon chlorides—may

be formed, so even this maximal theoretical emission of hydrogen chloride

gas is probably high.  In any case, such postulated hydrogen chloride

emission from mobile sources will decrease significantly in future years,

as the lead content of gasolines is decreased.

     The contribution of NASA launch vehicles to environmental pollution

due to emission of hydrogen chloride gas appears to be much smaller than

those of other sources of such pollution.  Hydrogen chloride emission from

the Titan vehicles represents the only environmental hazards of significance

contributed by NASA OSS Launch Vehicle and Propulsion Programs, and NASA

concludes that this hazard is modest and that, even under unfavorable

meteorologic conditions, it is estimated to be confined to controlled areas.

The NASA conclusion is based on an assessment of the environmental effects

of operations involving the current and near-future launch vehicles that

will be used up to about 1979-1980.  The Space Shuttle, which is intended

to replace most of the current family of launch vehicles and is expected

to be operational about 1979-1980,  will emit only water vapor and free

hydrogen from the combustion process.


     There is very little information on the concentrations of gaseous

chlorine compounds in the nonurban atmosphere.  There is no direct evidence

of their chemical form, but it is generally believed to be hydrogen chloride.

In marine air, the gaseous chlorine concentration near sea level is about

3 yg/SCM, where particulate chlorine (in sea salt) generally ranges from

1 to 10 yg/SCM.  The source of the gaseous chlorine in marine air is; not

definitely known, but it is probably atmospheric sea salt particles.

Volcanism may be a less important source.  Experimental evidence suggests

that the residence time of gaseous chlorine is longer than that of the

chlorine present on particles.

     There is very little information on the nature and concentration

of chloride in urban air of American cities.  On the basis of a few limited

data, it appe'ars that the concentrations of total chloride exceed those

in nonurban and marine air by a factor of about 10 and that they are; in the

range of 10-100 yg/m , away from sources.  The principal chloride-containing

gas in urban air is expected to be hydrogen chloride.  Data on particulate'

chloride in cities are also scarce, but the available information suggests

that such concentrations are similar to those in the uncontaminated marine

atmosphere—less than 5 yg/m .  Halogen-carrying pesticides contribute little

to the chloride burden, although they are known to decompose in the atmosphere.

     Chlorine compounds can undergo a variety of photochemical reactions

in the atmosphere that may be potentially significant in ozone formation

and removal.  Hydrogen chloride can be released from particulate chloride

by reactions of acid gases, such as nitrogen dioxide, in the presence of


     At the concentrations currently known, there is no evidence that

chlorine compounds play any significant role in the chemistry of polluted

atmospheres or in inadvertent weather modification.

     With the exception of pesticides, chlorine-containing compounds are

expected to be removed rapidly from the atmosphere.  Their residence time

in urban air should be similar to that in nonurban air.  Rough calculation

indicates a gaseous chloride atmospheric residence time of 2-17 days.

     The most crucial problem at present in dealing with the urban chemistry

of airborne chlorine is the lack of data on ambient concentrations of

gaseous and aerosol chlorides.



     Excessive exposures to chlorine have proved fatal to both man and

microbe.  But, as Paracelsus said in the early 1500's, dosis sola facit

venenum ("the dose alone makes a poison").  This is true for chlorine.

One of the earliest applications of chlorine was as a war gas.  However,

observations made on front-line troops exposed to it during World War I

led to its later use, at reduced concentrations, as a treatment for

respiratory tract infections.

     Although chlorine gas has a wide variety of current uses, none of

them results in the intentional exposure of mammals, including man.

Because the material is ubiquitous, however, acute and chronic inadvertent

exposures do occur.

     A wide variety of effects are reportedly associated with exposure to

chlorine gas, but those involving the respiratory system are considered

the most significant.  Chlorine has intermediate solubility in water and

therefore produces its irritant effects on both the upper and lower passages

of the respiratory system.  The physiologic response to exposures varies

from odor perception to pulmonary edema and death.  This response is in-

fluenced not only by concentration and duration of exposure, but also by

species and even individual variability.

     Odor threshold has been reported as low as 0.02 ppm and as high as

3.5 ppm.  Minimal mucous-membrane irritation shows similar variability:

0.2-16 ppm.  Part of this wide range can be attributed to biologic variability,

variation in individual tolerance and differences in test techniques or

methods of evaluation.  One researcher may use the lowest concentration

to elicit a response in the most sensitive subject as the threshold; another

may use the concentration that produces the same response from all members

of a panel of experts as the threshold.

     A single chlorine gas exposure can produce signs of acute obstructive

airway disease that usually resolves with symptomatic treatment by qualified

physicians.  Whether it resolves completely, whether intermittent significant

exposures cause permanent pulmonary changes, and whether chronic low-

concentration exposures result in pulmonary disease are still being debated.

Some researchers, on the basis of postexposure pulmonary-function studies,

believe that permanent pulmonary changes can occur as a result of single

or intermittent severe exposures.  Others, analyzing the same data, dis-

agree.  It should be noted that these are retrospective studies and that

no baseline pulmonary studies were available; therefore, "significant

changes" had to be inferred from "population norm."  There is another

problem in analyzing for the significance of chlorine gas exposures:

cigarette-smoking.  For the most part, the significance of cigarette-

smoking in the pathogenesis of pulmonary disease in victims of chlorine

gas exposure has been ignored.  Morbidity studies of personnel gassed in

World War 1, for example, seem to presume that all lung abnormalities were

a result of the gassing and completely disregarded other etiologies for

lung pathology.  Where cigarette-smoking has been considered, evidence

indicates that it is at least as significant as chlorine exposure in

the development of abnormalities of pulmonary function.


     Studies of workers chronically exposed in the work environment to low

concentrations of chlorine gas  (time-weighted averages of 0.006-1.42 ppm,

with a mean of 0.146 + 0.287 ppm) show no significant pulmonary changes,

in comparison with a control population matched for age, smoking history,


     This is not to say that similar low-concentration exposures would

be safe for the general population.  The industrial population is relatively

healthy and exposed to the material in an oscillating fashion (8 hr

"on," 16 hr "off," 5 days out of 7).  The general population potentially

could be continuously exposed to low concentrations.  Also, it contains

various subgroups that might be more susceptible to the adverse effects

of chlorine.  These subgroups may include the young, the old, and those

with acute and chronic respiratory problems, such as pneumonia, asthma,

and emphysema.   Additional populations at risk may be those with cardio-

vascular problems, heavy smokers, people with an ol antitrypsin deficiency

state, and even healthy people after heavy exercise.

Hydrogen Chloride

     Because of the chemical characteristics of hydrogen chloride, significant

biologic effects are limited to the teeth, the respiratory tract,  and, to

a lesser extent, the integument.  These very characteristics, however, pro-

vide hydrogen chloride with good warning properties and thus protect most

people from the harmful effects of acute exposures.  Although laryngeal

spasm, pulmonary edema, and death can occur from exposures to gaseous hydrogen

chloride, the effect is usually only a mild, transitory upper respiratory

tract irritation.  If able to do so, most people remove themselves voluntarily

from concentrations that are potentially hazardous.

     Minimal response has been noted at concentrations as low as 0.067 ppm,

and no response at concentrations as high as 35 ppm; however, most authors

agree that exposures become disagreeable at 5-10 ppm.  People who are

chronically exposed apparently can develop a tolerance to the material

and exhibit none of the symptoms of irritation or changes in pulmonary

function that are found in those acutely exposed to similar concentrations.

The only effect of chronic exposure to low concentrations of gaseous hydrogen

chloride appears to be erosion of the incisors.

     Although gaseous hydrogen chloride has not been reported to possess

any mutagenic, teratogenic, or carcinogenic potential, it has been recently

noted that high concentrations of hydrogen chloride and formaldehyde can

react under atmospheric conditions to form bis-chloromethylether, a material

of reported malignant potential.

     As for groups potentially at increased risk, most of the published

data deal with acute, subacute, or chronic exposures of laboratory aninals

or industrial workers—both relatively healthy subgroups of their populations.

The effects of exposure to gaseous hydrogen chloride on the young, the old,

and the infirm have not been explored; these may be the groups at hightsst

risk.  Ruminants, in light of the data on dental erosion, may also be at

increased risk of morbidity.



     There is a surprising amount of information available on chlorine

pollution in the air, despite the fact that it does not appear to be a

widespread or economically significant air pollutant.  The reports of field

damage indicate that injury from this pollutant is rather infrequent, and

that, when it does occur, it is usually as a result of an accident or



     Our knowledge of the comparative toxicity of chlorine gas to members

of the plant kingdom encompasses bacteria  and fungi, as well as higher

plants, but that knowledge appears to be very shallow.  There is little

or no information on several types of plants—for example, fruit and nut

crops, field and forage crops, and forest trees.

     Leaves of higher plants are more sensitive to chlorine than fungi,

bacteria, stems, seeds, and sclerotia.  The symptoms most often observed

on higher (broadleaf) plants are interveinal necrosis (usually close to

the margin and progressing toward the midrib), white to tan markings, and

an overall bleaching of leaves.  The characteristic response on conifers

is an orange to reddish-brown discoloration at the tip of the needles at

high concentrations, and bleaching at low concentrations.

     The sensitivity of plant species is modified by age, soil moisture,

water stress, and dormancy.

     Chlorides accumulate in plant tissues after fumigation, but the

accumulation does not appear to be related to exposure concentration or

to the amount of tissue damage.

     There seems to be a serious gap in our knowledge of chronic and

metabolic effects.   Reported episodes of plant damage from chlorine gas

have been accidental and have usually produced acute effects, and it is not

surprising that what research has been done on chlorine gas has reflected

the nature of the problem.   However, information on chronic and metabolic

effects should be obtained before considering establishment of standards.

Because chlorine is involved in photosynthesis,  it is important to determine

what chronic exposure to chlorine would do to yields of various crops.

Hydrogen Chloride

     The lack of detailed information on the effects of hydrogen chloride

gas on plants is probably a reflection of its unimportance as a generally

distributed phytotoxicant.  Because this gas can be easily scrubbed from

flue gases and because its major sources are point sources, there has not

been any urgency to mobilize research efforts in the descriptive pathologic

effects of this contaminant.  It is obvious from the minuscule amount of

research that has been done, however, that the gas can have serious effects

on plant life at very low concentrations.  Because of the increassed use of

halogen-bearing plastics in modern society and the disposal of such plastics

by incineration, hydrogen chloride gas may become a more common air con-

taminant.  In view of the limited available information, one can only con-

clude that the data base for the establishment of an air quality standard

for this gas is extremely narrow.

     Unfortunately, many of the conclusions derived from early experimental

work are no longer tenable, particularly those dealing with dose response,

because of improper fumigation methods.  The field observations, however,

are presumably still valid, although early researchers, seemed to be more

concerned about damage by hydrochloric acid than that by hydrogen chloride gas.

     One should be cautious in extrapolating results obtained under

rigidly controlled laboratory conditions to outdoor situations, because

of the problems associated with monitoring for hydrogen chloride and

because of the atmospheric reactions of hydrogen chloride.  Plants respond

differently to a gas and to an acid aerosol, so the determination of the

form of the chloride reaching the plant is as important as the degree of

exposure.  Future research with these two gases should reflect the expected

range of atmospheric conditions.

     Recent investigations indicate that chronic effects can be expected

at  0.40 ppm, and acute effects at a few parts per million  (3# 1-20 ppm),

depending on the species.  Perhaps the most significant conclusion to be

drawn from recent work is that relative humidity appears to be the governing

factor in plant response.  As opposed to the plant response to sulfur

dioxide in relation to relative humidity, which is essentially linear, there

appears to be a threshold of relative humidity above which plants will

incur twice as much damage at a given dose.  This phenomenon may be related

to the hygroscopicity of the gas, the mode of entry, and later injury

caused by the gas phase, as opposed to the acid phase.  The point is very

important to resolve, because it has such a crucial bearing on the estab-

lishment of a standard for this gas.

     Hydrogen chloride gas causes glazing on the lower surface of the leaf

similar to peroxyacetyl nitrate injury, and microscopic symptoms resemble

those caused by hydrogen fluoride, sulfur dioxide, and smog.  Only limited

information is  available on the relative  sensitivity of various  plant


     The physiology of uptake, distribution, and accumulation and the effects

of hydrogen chloride is still poorly known, although it has been studied to

a limited extent.   It appears that, at least in the gas phase, hydrogen

chloride enters through stomata and accumulates' as chlorides in the foliar

parts of the plant.  It is not known whether the injury is due to the acidity

of the gas, to the toxicity of the chloride, or both.


     The lack of data on atmospheric concentrations of chlorine and hydrogen

chloride or the acceleration of atmospheric corrosion caused by them prevents

firm conclusions at this point.  All that can be said is that hydrogen chloride

and chlorine in the atmosphere at some concentration will cause acceleration

of atmospheric corrosion.  Whenever there is a major release of chlorine or

hydrogen chloride, there will be a major increase in atmospheric corrosion,

which will depend heavily on meteorologic conditions, such as humidity,

temperature, and wind velocity.  It is not known how chlorine or hydrogen

chloride in combination with other pollutants would act.

     Obnoxious odors are poorly defined.  There is some disagreement with

respect to the olfactory threshold concentrations of chlorine and hydrogen


     Trace amounts of chlorinated organics produced in minute quantities

at chlorine plants are often identified as chlorine by the general public

when referring to the characteristic odor of a chlorine plant.

     Unquestionably, the threshold concentrations presented in this report

will cause human discomfort.  However, they will occur only when there are

substantial releases of chlorine or hydrogen chlorine.  Derivatives of

chlorine that are coincidentally produced in trace amounts on the premises

of chlorine plants are highly unlikely to cause any discomfort to the general



     Safe handling and emission control are on a solid base in the manufacture

and use of chlorine and anhydrous hydrogen chloride.  Engineering, operating,

and maintenance safeguards are well established for these materials.

     Exclusion of moisture from chlorine and anhydrous hydrogen chloride

equipment is the most important element in controlling corrosion.

     The high solubility of anhydrous hydrogen chloride in water provides

an effective method for controlling hydrogen chloride emission.  Water

cannot be used in controlling chlorine emission.

     The chlorine industry has developed standardized containers, emergency

devices for stopping container leaks, and emergency teams for response to

chlorine leaks.  These have been highly beneficial in controlling and

correcting leaks.

     The construction and use of anhydrous hydrogen chloride containers are

regulated by the Department of Transportation.  They are not standardized.

     The major factors in the proper response to a chlorine or hydrogen

chloride leak are prior establishment of an emergency plan, trained

personnel,  access to respiratory protective equipment, access to emergency

devices for stopping container leaks, coordination with local authorities,

and first-aid facilities and trained first-aid personnel.

     The response will vary with the type of leak, the equipment, the

location, etc., but the emergency plan should include provisions for stopping

the leak, minimizing the gas emission, and protecting persons in the affected


                               CHAPTER 10



     Surveys should be conducted by the EPA or other governmental agencies

or nongovernmental associations or organizations, to determine the concen-

tration of gaseous and particulate chlorine compounds in the atmosphere in

selected urban and nonurban areas and their sources.  Survey results from

areas that have a heavy concentration of chlorine-producing or -using

plants should be compared with survey results from industrial areas that

have few potential chlorine emission sources; this would contribute to

an understanding of the magnitude of an atmospheric chlorine concentration

problem and thereby assist in the development of whatever chlorine emission

guidelines or standards are deemed necessary.

     Emission gas that contains chlorine should be alkaline-scrubbed before

being emitted to the atmosphere.

     All cell-room chlorine header seals in electrolytic process plants

that manufacture chlorine should be piped to a lime or caustic scrubber

for absorption of cell chlorine when seals blow owing to backpressure.

     If hydrochloric acid is air-blown to remove traces of organics, this

should be done in a vessel equipped with a water scrubber or ejector for

emission control.

     New or modernized public incinerators in the United States should

be equipped with wet-scrubbing systems for control of emission of particles,

sulfur dioxide, hydrogen chloride, and organic acids.

     No attempt was made to estimate the maximal potential hydrogen chloride

emission from the combustion of fuel oils, because little information was

 available on the average chlorine content of fuel oils.  Inasmuch as fuel

 oil amounted to 16% of the total fuel used in 1970, the chlorine content

 of fuel oils should be determined.

     Further research and development work is needed in the design and

 selection of materials of construction for public incinerator internal

 components, to minimize corrosion problems and to ensure the proper feeding

 and complete combustion of refuse.

     Continued research and development work is urgently needed on

 commercially useful systems for control of emission of sulfur dioxide,

 nitrogen oxides, and hydrogen chloride from large stationary fossil-fuel

 (particularly coal) industrial heating plants and electric generating



     The chemical forms of gaseous chlorine in nonurban and urban air

 should be determined.

     The major reactions of gaseous chlorine compounds with other

 atmospheric constituents should be studied, with particular attention

 to photochemical interactions.

     The major sinks and the mean residence time for atmospheric gaseous

 and particulate chlorine should be determined,  with special emphasis in

 cities on building surfaces and vegetation.



     Physicians experienced in the handling of  cases of chlorine inhalation,

 under the auspices of the Chlorine Institute, have put together a set of

recommendations for the medical evaluation of patients suffering from

chlorine exposures. Thetr recommendations should be distributed to and followed

 by all physicians likely to treat patients exposed to chlorine.


     Prospective studies of the effects of chronic exposure to low concen-

trations of chlorine should be conducted, so that the debate as to the

significance of such exposure can be concluded.

Hydrogen Chloride

     Further studies should be conducted on population subgroups potentially

at increased risk.  The problem of the spontaneous reaction of gaseous

hydrogen chloride with other atmospheric contaminants to produce carcinogens

should be evaluated in detail.



     Studies should be undertaken to determine the injury threshold

concentrations of chlorine gas.  Such studies should be done on a wide

variety of plants representing several classes.

     Diagnostic methods should be developed to aid in field identification

of air pollution damage.  If a suitable chemical method for tissue analysis

cannot be developed to determine positively whether damage was caused by

chlorine gas, then it will be necessary to determine the entire spectrum

of response, and symptom expression will have to be studied in detail.

Hydrogen Chloride

     There is need to expand knowledge further on the sensitivity of plant

species to hydrogen chloride gas.  A number of species representing different

classes of plants should be tested to determine the exposure to the gas

that can be tolerated without injury.  There is a need to standardize fumigation

methods, to fill gaps in the knowledge of plant response and to permit com-

parison of results from various researchers.

     Additional information is needed on synergistic effects of hydrogen

 chloride with other common air pollutants on a number of plant species.

 Nothing is known of the effects of this gas on yield impairment, flowering,

 and community or ecologic effects.  And nothing is known of the effects on

 soil and soil microbes or of the fate of the chloride once it enters the

 food chain.

     Diagnostic methods for field evaluation of symptoms are needed.

 Because the symptoms caused by hydrogen chloride can be easily mistaken

 for those caused by other agents, reliable sampling techniques and laboratory

 procedures need to be developed.


     The concentrations of chlorine and hydrogen chloride should be de-

 termined at the perimeter of property that contains emitting sources or

 potential emitting sources, such as plants that produce or use chlorine

 or hydrogen chloride (paper mills, chlorinated organics plants, water

 treatment plants, etc.).  Similar measurements should be made at coal-

 burning power plants and incinerators.  Such a program would determine

whether a pollution problem exists and, if so, define its extent.

     Because there is some indication that chlorine and hydrogen chloride

 contribute to atmospheric corrosion,  it is important to determine whether

 the contribution is significant.  This can be done by establishing a program

 in which specimens of various materials—such as painted and unpainted

metals, fabrics, and limestone—are placed where chlorine or hydrogen

chloride is known to be present in the atmosphere.   In such a program,

analyses should be carried out to determine the concentration of sulfur

oxides, nitrogen oxides, and other species that are known or suspected to

contribute to accelerated atmospheric corrosion.   Meteorologic conditions—

such as hours of sunlight, humidity, temperature, and wind velocity and

direction—should also be closely monitored.  Besides providing insight

into the influence of hydrogen chloride and chlorine on accelerated

atmospheric corrosion, it would yield information on the influence of other

chemical species on atmospheric corrosion and their interactions.  Tesl:

specimens would then be examined to determine corrosion products, as well

as changes in appearance, physical properties, and weight.

     Additional research is required to determine what constitutes an

obnoxious odor.  It is also necessary to develop an unambiguous, quantitative

method of determining odors.  The extent to which chlorine and hydrogen

chloride interact with other odorous species, which might be present in

the atmosphere, to produce an increased odor must also be established.

     The development of a method for identifying the trace quantities of

chlorinated organics that impart the characteristic odor to chlorine plants

might be considered, as well as techniques to control their release.


     Producers and repackagers of chlorine and anhydrous hydrogen chloride

should continue to conduct safety seminars and film and slide presentations

and to supply technical bulletins, etc., to users, transporters, and others

involved in handling these materials.

     Training geared to responding to emergency situations involving chlorine

and hydrogen chloride containers should be made available to local emergency

teams, firemen, etc.  Although not directly involved with chlorine handling,

these groups will get the first call in some leak situations and should be

trained in the proper response.

      The need for container standardization and emergency devices for

 container  leaks should be evaluated for anhydrous hydrogen chloride

 transportation.  The past record, the use of water with hydrogen

 chloride for emission control, etc., should be considered.

      Chlorine and anhydrous hydrogen chloride producers should continue

 to strive  to use fail-safe systems in the manufacturing plants.


      Several titrimetric and colorimetric methods are commonly used for

 the determination of elemental (available) chlorine.  These have been

 evaluated by individual investigators and by interlaboratory comparisons.

 In general, the methods are adequate when evaluated under carefully con-

 trolled laboratory conditions, but they yield marginally acceptable results

when  evaluated under round-robin (interlaboratory) conditions.  Many of

 these procedures can be used to determine elemental chlorine in air by

 collecting the chlorine in absorbing solutions.  The continued use of all

 these methods does not appear to be warranted.  The use of o-tolidine

methods should be discouraged, because the reagent itself is allegedly

 hazardous and because the methods are inferior to other methods.  The

use of N, N-diethyl-p_-phenylenediamine (DPD) methods should be encouraged,

because both titrimetric and colorimetric procedures for them exist,

they have few interferences, and they are simple to use.  The methyl orange

colorimetric procedure is also attractive, particularly for analyzing

absorbed impinger solutions.  In recommending the adoption of these pro-

cedures, however,  there is a danger that other—possibly superior—methods

will not be given proper consideration.   The leuco crystal violet procedure,

for example, appears to be nearly ideal and should be evaluated thoroughly.

Similarly,  the barbituric acid procedure appears to perform well and should

be studied further to establish its true utility.


     In 1966, Gilbert suggested a means for flame-photometric determination

of total chlorine.  He modified a Van der Smissen burner to include indium,

rather than copper, in its construction, so that the indium chloride spiectral

band would be emitted from the flame.  The indium chloride band, which

occurs at 359.9 nm, proved to be both selective and sensitive.  For example,

Gilbert estimated that about 0.001 ug of chlorine could be detected in 1

liter of air.  The problem is that the detector would not be specific for

chlorine or hydrogen chloride; it would respond to chlorine from any source.

Nevertheless, the idea is intriguing and should be pursued as a possible

means for source (and perhaps ambient) air and water monitoring.

     Colorimetric procedures specific for hydrogen chloride are non-

existent.  Electrochemical and gas-chromatographic methods have been

studied, but have not gained wide popularity.  Methods for determining

hydrogen chloride, as opposed to total acidity or total chloride, are

                                                            I       1—
sorely needed.  Electrochemical techniques that respond to H  and Cl

already exist; they should be investigated jointly as a possible hydrogen

chloride detector.  Gas-chromatographic techniques are also known to work,

but not satisfactorily enough to meet current needs.  Research into in-

creased inertness in chromatographic columns and into more sensitive and

reliable detector systems is warranted.  It has recently been reported

that hydrogen chloride can be selectively and quantitatively absorbed

from the gas phase by the phosphates of cadmium, zinc, mercury(II),

and silver.  This suggests the possibility of quantitatively collecting

and concentrating hydrogen chloride specifically from the atmosphere

before analysis.  The use of a solid reactant as an absorber has obvious

advantages over liquid absorbers.  It might be combined with chromatographic

or electrochemical measurement techniques to provide both specificity and

 extreme  sensitivity.  Research is warranted to understand and implement

 this phenomenon.

     Simple tests that are reliable and reasonable in cost are needed.

 The development of simple and inexpensive monitoring instruments,

 particularly of the probe type, is needed.  This is especially true of

 chlorine, because its samples are not stable over a long period.  Research

 into the development of a chlorine-specific electrode is warranted.  In

 fact, electrochemical monitoring devices of several types have been touted

 for some time, for both oxidizing and acidic constituents in water and

 air.  Heretofore, instrumentation for these types of devices has been

 rather complex and expensive.  Recent developments in instrumentation

 should allow inexpensive, compact, and simple electrochemical instrumentation

 to be developed for monitoring purposes.  Modern electronic components and

 construction techniques should be  used for air monitoring purposes for

 both chlorine and hydrogen chloride.

     Methodology for generating standard gas mixtures containing known

 amounts of hydrogen chloride is needed for calibration purposes.  Chlorine

 can be prepared in precisely known amounts by electrolysis and with permeation

 tubes,  but these techniques are not suitable for preparation of gaseous

mixtures of hydrogen chloride.  Saltzman established that pure hydrogen

chloride at 470 ppm could be swept reliably from 1:1 hydrochloric acid

 solution under carefully controlled conditions.   This technique, although

workable, is not suitable for general calibration purposes.   New approaches

 to this difficult problem are needed.


                          HYDROGEN CHLORIDE

     This appendix deals with the analytic determination of elemental chlorine

and vapor-phase hydrogen chloride.  It is not concerned with the determination

of total chlorine--i. e. , with methods for  determining total chloride ion--ex-

cept for a few methods of particular interest because of their environmental

utility or promise.

     There are many more methods for determining molecular chlorine than

there are for determining vapor-phase hydrogen chloride.  Most methods for

chlorine are based on its oxidative properties, -whereas those for hydrogen

chloride are based on its acidity.  Accordingly, the two will be treated sepa-

rately in the following discussion,  except where it is particularly appropriate

to discuss  them together. Determinations of chlorine and hydrogen chloride

in both aqueous and gaseous media are discussed in the following sections.

The  discussion is not oriented toward specific applications,  but is oriented

toward the analytic techniques and problems themselves.  Many final measure-

ments are  common to both types of samples; only the sampling techniques differ.

     The determination of chlorine in water is extremely important.  It is used

widely, both in the field and in the laboratory. A word about the terminology

characteristic  of this analysis is desirable.  Chlorine in water is normally

referred to as  "available" or "active"  chlorine.  "Available" denotes avail-

ability for  sterilization purposes; but for  analytic purposes, it expresses

iodine equivalency.   Iodine equivalency is not necessarily analogous with

ability to kill a particular species.   Chlorine  that is bound tightly in some

organic compounds may not contribute to  "available" chlorine.  More im-

portantly,  chlorine in water may be  combined with ammonia or other nitro-

genous materials that also have  oxidizing power, or it may be present as

hypochlorite, OC1 .  The currently accepted terminology is as follows:


"Free available chlorine" (FAC), or "free available chlorine residual, " refers

to elemental chlorine, hypochlorous acid,  hypochlorite ion, or all those acting

jointly.  "Combined available chlorine" (CAC),  or "combined available chlorine

residual," refers to the derivatives of ammonia or other nitrogenous compounds

that have the capacity to  combine -with chlorine  or hypochlorous acid so as to

modify its rate of bactericidal action.  Analytic procedures may distinguish FAC,

CAC, and "total available chlorine" (TAG).  Some procedures are even more

selective and distinguish different species  that fall within the category of CAC.

Note that both free and combined available chlorine may be present simultaneously;

they then constitute TAG.

       In this appendix,  "hydrogen chloride" will be used to refer to vapor-phase

hydrogen chloride, and "hydrochloric acid" will be used to refer to hydrogen

chloride in solution.


       When dissolved in water,  chlorine undergoes a small but measurable

hydrolysis (disproportionation),  according to the following  reaction:

                                          +                -4
            Cl   + H OZZZC1  + HOC1+ H  ;   K = 4. 66 x 10   .
               2    2  ^

This reaction is rapid at the pH  of natural waters.  Only a  low pH and at high

chlorine concentrations does a measurable amount of molecular chlorine exist;

hence methods  for determining FAC actually determine both molecular chlorine

and hypochlorite.   The reaction  can be made to go to virtual completion by adding
a species that reacts with H  or Cl  or both.  For example, bicarbonate is  too

weak a base to react with hypochlorous acid, so its reaction with chlorine is as


                  Cl   + HCO       Cl  +HOC1+CO
                     23.                    2

In strong base,  hypochlorite salts are formed.  Hypochlorous acid itself
is weakly ionized (K   = 3. 7 x  10   ).

       Aqueous oxidation potentials for the several chloro species are

shown below:

                                     -1.27  CIO-   -1.15
   Acidic Medium                     -    *   - 1
                                    [ -
                            -1.64   I     -1.
                            - HC5C1   —
         - -1.36 _,   -1.63 TW1, -1.64        -1.21         -1.19
           - C12  - HOC1 - HC5C12  — -  C1X>3~  — — -
                                     -1.16  C102  -0.50
Basic Medium -                        "   "
                                          ["  "        ~~|
       el" 13-36 ci2 12-40 clo-   10.66  QQ -  12.33 ciC^'=^ CIO,

         	-0.88	  	-0.50	
Hence,  in acidic solution, hypochlorous acid and chlorous acid are

thermodynamically unstable with respect to disproportionation, and

chlorine and perchlorate are capable of oxidizing water.  In basic

solution, the only reaction that proceeds rapidly is the alkaline

decomposition of chlorine.  The standard aqueous oxidation potentials

for iodinated species are also important, because of the role that

iodine plays in the analytic chemistry of chlorine.  They are as


                  Acidic Medium
                   - -0-54
                  Basic Medium
                   - -0-54    -0.45

       At least thermodynamically, elemental chlorine and all positive

oxidation states of chlorine can be quantitatively reduced by excess iodide.

This is the basis of several analytic procedures.  Note, however, that

                                               2+         2-        -      4+
many other oxidants react with iodide (e. g. , Cu   ,  Cr O    ,  MnO    ,  Ce   ),
                                                      27          4
                                                            2+      2-
and many reducing agents can be oxidized by iodine  (e. g. , Sn  , SO    , H  AsO
                                                                   3      33

Moreover, chlorine itself reacts with iron, manganous manganese, nitrite,

hydrogen sulfide,  and a variety of organic  materials.   Accordingly,  analytic

procedures must be judiciously designed and carefully performed if accuracy

is to be ensured.

       In water that contains ammonia, a. series of chlorine substitution reactions

occur to form monochlorinated,  dichlorinated, and trichlorinated species.

These  reactions deactivate chlorine, converting it ultimately to chloride,  the

products and rate depending heavily on pH.  These reactions form  the basis of

the "breakpoint" chlorination procedure: chlorine is added to water that  contains

ammonia until the ammonia is consumed.  Continued addition of chlorine after

ammonia and amines are consumed yields "free"  chlorine.  This occurs after

3 moles  of hypochlorous acid are added for each mole of ammonia.  This ex-

plains the need for analytic procedures that distinguish different "forms" of

chlorine.  The situation is  complicated from the analytic point  of view, however,

in that organic materials in water may react with chlorine slowly and may form

tightly bound chlorinated derivatives that are not reactive or partially or slowly

reactive to iodide.   Thus,  analytic results .often are more empirical than the

procedure might indicate.

     Hypochlorous acid and hypochlorite are both unstable,  especially :Ln the
presence of sunlight.  Draley      reports that in sunlight it takes about 31 sec

to reduce the concentration of free chlorine from  0. 5 to 0. 01 pprn.  In -the dark,

an equal decrease may require 30 min to several hours.   This  susceptibility

to light is especially important in  designing sampling procedures; and methods
for field use.  Monochloramines and dichloroamines are much  more stable.


     Chlorine in aqueous solution  is not stable,  and the  chlorine content of

samples or solutions, particularly weak solutions, decreases  rapidly.  Ex-

posure to sunlight or other strong light or agitation accelerates the reduction

of chlorine in such solutions.  Therefore,  it is mandatory that  chlorine content

be determined as soon as possible after sampling and that excessive light and

agitation be avoided.  Samples to be analyzed for  chlorine should not be stored.

     All glassware used for the determination of chlorine residual should be

exposed  to water containing residual chlorine at at least  10 ppm for 3 hr  or more

and then rinsed with chlorine-demand-free water  before use.  Owing to the

rapidity  with which this water may absorb some laboratory fumes,  it should

be examined for  nitrites, chlorine, and reducing agents immediately before its

use for determining chlorine  at very low concentrations.


      Chlorine-demand-free water is prepared by adding sufficient chlorine to

distilled water to destroy ammonia.   (The amount required will be about 10

times the amount of ammonia nitrogen present; an initial chlorine residual of

more than 1 ppm is mandatory. )  The chlorinated distilled water  is allowed to

stand overnight or  longer; it is then exposed to direct sunlight until all residual

chlorine is discharged.  Irradiation with a bare ultraviolet light source is  some-

times used.  Alternatively,  chlorine-demand-free water can be prepared by ion

exchange.  A 3-ft (91.4-cm) column approximately 2. 5-5 cm in diameter con-

taining both strongly acid cation-exchange and strongly basic anion-exchange

resins is used.  Distilled water is passed through this mixed-bed column at

a relatively low rate  and collected in a scrupulously clean receiver that is

arranged to protect the treated water  from exposure  to the  atmosphere.  A

sulfuric  acid or calcium chloride trap on the air inlet to a stoppered storage

bottle must be used.  The water is withdrawn by glass siphon through the same

stopper.  Unless such precautions are taken,  the water may very quickly absorb

ammonia from the  atmosphere.  In using ion-exchange columns, care must be

taken to  ensure  that all organic materials are washed from the resins before

use, because even  trace amounts of methylamine could destroy the integrity

of chlorine-demand-free water.  Because water used for preparation and

dilution of samples and for  rinsing glassware must also be  free of elemental

chlorine, the water should be checked for the absence of chlorine before use.

Collection of Air Samples

     Air samples for chlorine and hydrogen chloride  are collected either in

absorber or impinger trains or in evacuated  sampling bulbs (i.e., "grab"

samples).  Numerous arrangements have  been devised to meet specific

requirements.   Typical sampling procedures and equipment are described
           87, 88
eisewhere.         The usual sampling train consists of two to four impingers

or absorption vessels,  a gas drying tube, a pump,  and a flowmeter.  Heated

(250 C) sampling probes are included for stack sampling applications. All-

glass construction minimizes corrosion  and absorption losses.   The usual

grab sampler is a Pyrex bulb of known volume (e. g. ,  2 liters) fitted with a

coarse probe-filter  to remove particulate matter.

     Absorption columns (bubblers) are  preferred for longer-term (about 24-

hr) sampling.  The compact sampler developed for the National Air Sampling
Network has proved to be reliable and easy to operate and maintain.     It

consists of a bubbler connected through a filter and critical orifice to a pump.

The in-line  filter protects the  critical orifice;  a membrane prefilter removes

particulate matter.  Polypropylene centrifuge cones serve as absorption vessels,

and plastic and Teflon components and fittings  are incorporated for ruggedness.

These trains are designed to operate from a manifold that accommodates five

sampling units in parallel.  The temperature of the samplers can be controlled
at 35  C.  Air flow typically is  150-200 cm   /min at a vacuum of 16-20 :.n. Hg

(406-508 mm Hg).  These units were designed  for sulfur dioxide and nitrogen

dioxide measurements, but should be equally effective  for chlorine and hydrogen


     Several different absorber solutions are  commonly used for chlorine and

hydrogen chloride, depending on the particular application.  Water or, prefer-

ably,  dilute sodium  hydroxide  solution is used  for hydrogen chloride.  The solu-

tion can then be analyzed for acidity  or for chloride content.  Chlorine is com-

monly absorbed in standard sodium arsenite solution or in excess  potas.sium
iodide solution.      The solution can then be analyzed  by determining excess

arsenite or  iodide or perhaps liberated iodine.

     When both chlorine and hydrogen chloride are present,  two analyses are

required (chlorine and total chloride),  so that hydrogen chloride can be determined

by difference.

     Meador and Bethea     compared the standard bubbler technique with

 glass- and polypropylene-syringe gas sampling techniques and found that the

 polypropylene syringe technique was superior for both chlorine and hydrogen

 chloride analysis in polluted air.  They used disposable 50-ml polypropylene

 syringes that had been preconditioned by cleaning with acetone and then over-

 night exposure to the gas at several thousand parts per million.  For chlorine

 determination, a minimal amount of liquid (3 ml) was placed in the  syringe to

 absorb free chlorine from a 47-ml gas sample.   The liquid, contained o_-tolidine

 at a concentration of 0. 005 g/liter in 10% hydrogen chloride.  Under these con-

 ditions, the lowest detectable concentration of chlorine was 0. 12 ppm in air.

 The syringe was held above and nearly perpendicular to the gas sample line,

 so that chlorine bubbled through the £>-tolidine reagent in the syringe and was

 immediately absorbed.  Contact of free chlorine with the syringe walls was  thus

minimized.   This was necessary, because free chlorine apparently was absorb-

 ed on the walls of the plastic syringe.  Reproducibility was also enhanced by

 thoroughly rinsing the syringes with fresh reagent between samples. The rela-

 tive error using the above technique was 3. 4% at 4. 0 ppm.  Reproducibility was

 poorer when glass syringes were used.

     The syringe technique was also used for determining hydrogen chloride in
 air. The colorimetric method of Iwasaki et al.     was  used.  This method

measures total chloride,  in that it is based on the reaction of chloride and

mercuric thiocyanate and measurement of the reddish-orange color of ferric

 thiocyanate.  Although the method was  optimized for use with syringe sampling,

 Beer's law was not obeyed; thus, the calibration curves  were nonlinear and  of

 low slope.  Hence,  the relative errors for analysis of  samples in this concen-

 tration region were high:  24. 7% with hydrogen chloride  at 30 ppm in air,  10%

at 12 ppm, and 8% at 0-5 ppm.  The lower detection limit of this method was

found experimentally to be 0. 5 ppm in air.


Continuous Monitoring

     Chlorine and hydrogen chlorine have been monitored continuously both

electrochemically and spectrophotometrically.
     Chlorine in water has been monitored continuously by "coulometry. "

In this approach, ferrous ions are generated electrolytically in an electro-

lytic cell.  Any oxidant (such as chlorine) that enters the cell and reacts* with

ferrous ion is monitored by following the electrolytic current required to main-

tain a preselected ferrous concentration.  Because electrolytic current is moni-

tored,  the  technique is not truly coulometric, but rather is amperometric.

The progress of the reaction  is followed potentiometrically with a platinum-

calomel electrode pair.  If any difference develops between the detected potential

and the preselected potential,  then a current is generated that restores the  system

to its steady-state  value.  Such devices have been used for many years.  They

are characterized by accuracy (+_ 1% is typical) and by lack of specificity.  Simi-

lar systems have been devised for several gaseous air  pollutants, including

chlorine.   For example, the Detectachlor chlorine-gas leak detector, marketed

by Fischer & Porter  Co. ,  is  based on continuous amperometric monitoring of

the ferrous-ferric  couple in a solution saturated with sample air.  The  Chlorine

Detector, marketed by Wallace & Tiernan Division of the Pennwalt Corporation,

is similar, except  that the iodide--iodine electrolytic couple is monitored,  rather

than the ferrous-ferric couple.  Such instruments can detect chlorine in air at

1 ppm  or above, so they are useful primarily as warning devices -where  release

of chlorine gas  is a possibility.

     A simpler and more recent approach uses so-called ion-selective  electrodes

for measuring  or monitoring  chlorine in water.  These are potentiometric devices

that respond  semilogarithmically to the concentration (i. e. , activity) of  the species

being measured. No electrode is available that responds directly to molecular

 chlorine, but hypochlorite can be determined indirectly with an iodide-selective
 electrode.      This approach can be used for discrete samples  or for continuous

 monitoring.   The concentration range for good performance (+_ 10% accuracy) is

 0. 1-100 ppm, with a lower detection limit of 0. 05 ppm.  Response time of the

 monitoring system is 8-10 min (99% response to a  stepped concentration change

 at the inlet).  A marriage between this aqueous monitoring system and an ab-

 sorbing sampler for gaseous samples seems attractive.
      Potentiometric monitoring of gaseous constituents is not new.   Lee

 devised a continuous monitoring system for hydrogen chloride in gaseous

 mixtures that was based on the response of a chloride-selective  electrode.

 The problem is that total chloride is not necessarily analogous to hydrogen

 chloride.  More specificity could be achieved by monitoring both hydrogen ion

 and  chloride potentiometrically in the absorber solution, using a pH electrode

 in parallel with a chloride electrode.

     A somewhat similar approach for continuously monitoring hydrogen chlor-
 ide in gaseous mixtures was recently reported by Brittan, Hanf,  and Liebenberg.

 They used an  automatic (volumetric) titrator to neutralize hydrogen  chloride con-

 tinuously as it was absorbed from the gas stream,  and  titrant  flow was recorded

 as a function of time.   A glass-calomel electrode pair was the sensing system,

 with the selected pH set at 5, to avoid carbonate  ion interference.   Chlorides

 were trapped  out of the heated sampling probe.  The technique was suitable

 for determining gases that contained hydrogen chloride at 10 ppm to  20%.

     A number of laboratory and continuous monitoring  systems  are marketed,

 all of -which are based on spectral detection and measurement.  The  Technicon

AutoAnalyzer is the most widely used automated  system for wet  chemical

analysis. Most conventional wet chemical procedures are adaptable to the

 Technicon system,  and they  can be implemented  for monitoring water or air.

The determination of chloride by indirect formation of ferric thiocyanai:e has

been modified for AutoAnalyzer use for aqueous samples.  Most of the

spectrophotometric methods described in the following  section could aliso

be adapted for automated or continuous  operation via the AutoAnalyzer


     Finally, it should be mentioned that there are physicochemical monitoring

devices on the market that are not based on wet chemistry.  Beckman Instruments,

Inc. ,  includes chlorine and hydrogen chloride monitors in its line  of nondispersive

analyzer systems. Chlorine is measured in the ultraviolet region; hydrogen

chloride is determined in the infrared region.  Both are sensitive  enough (about

10 ppm) for monitoring for  episodal situations, but insufficiently sensitive for

ambient monitoring.  This is true  of chlorine  and hydrogen chloride monitors in

general.  It points to a need for research into monitoring systems that cifford

roughly a thousandfold increase  in sensitivity over existing devices.


     Almost all analyses for chlorine in aqueous samples are titrimetric or

colorimetric.   The most common methods are listed in Table A-l.  Mout of

the methods in Table A-l are discussed in some detail  in Standard Methods
for the  Examination of Water and Wastewater     and the Handbook of Chlorina-
tion.      They have  been thoroughly tested and evaluated by numerous workers.
The critique by Nicolson    is particularly thorough:  three titrimetric and

nine  colorimetric methods are included.  Table A-l includes relative standard

deviations and relative error values resulting from extensive testing of known

samples by  about 30 laboratories,  as  reported in Standard Methods.  A larger
study by the Analytical Reference Service     has also been  conducted on a

number of the methods in Table A-l,  and the recommendations resulting from

that study are listed as a separate entry--"ARS Study." It is clear from these

Common Analytic Methods for Chlorine~


(I2 with S 03)

(C12 with
£ oxide)
DPD titration d
(C12 with Fe2+)-


(OTA) ;
neutral _o-





Common Common
Concentration Interferences
More than 1 Oxidants,
ppm (detec- reductants
tion limit,
40 ppb)
Less than Br2,I2,Cu,
2 ppm Ag, NCI2

4 ppm Br2, I2, Mn,
NCI3, C102

10-10,000 ppb Fe, Mn, N02,
C102, Br2,
I2, 03
10-10,000 ppb

10-6,000 ppb

of ARS
Not tested

for TAG

Not tested

table for

Performed well;
for FAC
and TAG

Relative Relative
Standard Error,
23-32 16-23

12-42 8-25

9-40 4-20

31-65 20-42

28-52 14-49

8-35 2-13

                                                   TABLE A-l (continued)
Method Determination— Common

DPD; color imetry
Leuco crystal
violet ;
Methyl orange;
•%)ata from Bjorklund and 1
Taras,466 Taras e_t al. ,4<
FAC 0.1-2 ppb
FAC 10-2,000 ppb
FAC 100-2,000 ppb
38 304
Jand, Lishka and McFarren,
57 and White.514
•TTAC = free available chlorine; CAC = combined available
%ef. 304.

Common Results Relative Relative
Interferences of ARS Standard Error,
Study^- Deviation,
% %
Mn — 2.0
Mn Excellent; 1.8
Acceptable 32 1-18
for FAC
and TAG
Mn + , Br Acceptable 20-43 7-22
for FAC
and TAG
361 370 444
Nicolson, Palin, Sollo and Larson,
chlorine; TAG = total available chlorine.

—DPD = N, N-diethyl-p-phenylenediamine.

data that the methods are inherently precise and accurate enough for most

environmental needs, but in actual practice their performance is at best

marginal.  An important advantage of automated or continuous methods is

that they minimize the human contribution.

Titrimetric and Colorimetric Techniques

     The iodometric titrimetric method is considered the standard by which

other methods are judged or  on which they are based.  Chlorine will liberate

free iodine from potassium iodide solutions when their pH is 8 or less.  The

liberated iodine is titrated with standard sodium thiosulfate solution, usually

using starch as the indicator. The reaction is preferably carried out at

pH 3-4.  This method provides the means for standardizing chlorine water used

in preparing temporary standards for other methods. It is also suitable for the

determination of high chlorine residuals.  The iodometric method is generally

more precise than colorimetric methods when the residual chlorine concentration

exceeds  1 mg/liter,  but it is  not accurate at lower concentrations or in the pres-

ence of interferences.  This procedure is particularly susceptible to interferences,

inasmuch as both oxidants and reductants can cause errors.  The standard poten-

tial of the iodide-iodine couple is such that many common species either oxidize

iodide or are oxidized by iodine.

     The amperometric titration method is largely unaffected by the presence

of common oxidizing agents,  temperature variations, turbidity, and color.

The method is not as simple as colorimetric procedures and requires greater

operational skill to obtain its inherent accuracy.  In  this method, FAC  is

titrated at a pH of 6. 5-7. 5 with standard phenylarsine oxide solution, and

the progress of the titration is monitored amperometrically.  This means

that the titration is carried out in an electrolytic cell that is fitted with a

platinum indicator electrode and a reference electrode,  and the voltammetric

current between these two electrodes is monitored.   The voltammetrlc

current acts as a null-point indicator, being large when the chlorine residual

is high and decreasing to a minimum when the chlorine residual disappears.

The end point is recognized when no further decrease in current

can be obtained by adding more phenylarsine oxide.   CAC can be determined

by this procedure if potassium iodide is added and the titration repeated at
a pH of 3. 5-4. 5.  The Analytical Reference Service study     found the

amperometric titration procedure to be acceptable only for the determination

of TAG.  The unacceptability of  this procedure for determining FAC may be

attributable to its need for  strict pH control.  It may also be  due to the fact

that stirring can lead to loss  of chlorine via volatilization. It is noteworthy

that other halogens (bromine  and iodine) are titrated exactly like chlorine

in this procedure.  Copper and silver have also been identified as  interferences.

However, manganese, nitrite, and iron do not interfere,  although  they can be

serious interferences in most of the other procedures listed in Table A-l.

   The jD-tolidine methods have gained wide acceptance for the routine

measurement of residual chlorine in water, both industrially and in the field.

The £-tolidine-arsenite  (OTA) method permits  the differentiation of FAC and

CAC in the presence of color from common interfering substances.  The OTA

modification is satisfactory for routine control with properly calibrated  photo-

meters,  visual color disks, or permanent color standards.  The Analytical

Reference Service study found the OTA method to be unacceptable  for FAC

and TAG.  But the stabilized  neutral £-tolidine (SNORT) modification performed

well and was considered acceptable for both FAC and TAG.

   ^-Tolidine methods are based  on the formation of the characteristic  yellow

halogen derivative that results from the reaction between  chlorine and ^-tolidine.

Correct  color development with  chlorine is  obtained when the  solution pH is 1. 3

or lower, the ratio by weight of £-tolidine to chlorine is at least 3:1,  and the

chlorine concentration does not exceed 10 ppm.   The reaction time and temperature

are critical in this procedure and must be controlled carefully to minimize

loss of color by fading or increase of color due  to interfering oxidizing agents.

Such interferences include  ferric and manganic  ions and nitrites.  The yellow

holoquinone color obeys Beer's law over a considerable chlorine  range.

Samples that contain predominantly free chlorine are characterized by maxi-

mal color development almost instantly, and then the color begins to fade.

Samples that contain combined chlorine develop the maximal color at a rate

that depends largely on temperature:  at 20 C, maximal color is developed

in about 3 min.  About 5 min after maximal color development, a slight fading

begins.   Therefore, samples containing combined chlorine should be  read

within about 5 min; color development preferably goes on in the dark.  It must

be emphasized that the precision of the  results depends on strict adherence

to the  recommended  intervals and the temperature of the sample.

    The OTA method is designed for use whenever interferences--such

as ferric and manganic ions, nitrites,  and organoirpn compounds--are

suspected.  However, according to the Analytical Reference Service  study,

the OTA procedure is unacceptable for FAC and TAG measurements.   Because

of the  critical dependence on technique, this method is very likely to be in the

category of methods that can be used satisfactorily by experienced personnel

and can be disastrous in the hands  of inexperienced personnel.

    The SNORT modification performed well in the ARS study and is considered

acceptable for FAC and TAG measurements.  ^-Tolidine has classically been

used at a pH of 1. 3 or lower, because the stability of the oxidized form de-

creases as the pH increases. As the pH increases,  however, the rates of

reaction of ^-tolidine with combined chlorine, iron,  and nitrite become lower;

their interfence essentially disappears at pH  7.  The SNORT procedure capital-

izes on this fact.  Anionic surface-active agents stabilize the  color developed

by free chlorine and ^-tolidine at a pH of 7.  To ensure correct: color de-

velopment and minimal interference,  a pH of 6. 5-7. 5 is specified and a

ratio of (3-tolidine to  free chlorine of at least 8:1  is used.  The sample

must be added to the  reagents.  The reaction time and temperature are

relatively unimportant in this procedure,  compared with other procedures.

Complete mixing of the sample and the reagents and reading of the absiorbance

are usually  accomplished within  2 min. Potential interferences include bromine,

chlorine dioxide, iodine,  manganic compounds, and ozone.  The reduced forms

of these compounds do not interfere.  It is to be emphasized that reducing agents

like  ferrous compounds, hydrogen sulfide, and oxidizable  organic matter do not

form an interference in the analytic method,  but may interfere by reducing  the

chlorine residual by reaction with elemental chlorine.  Although the SNORT

method is still considered tentative in Standard Methods,  it is clearly superior

among the ^-tolidine  procedures.  The use of permanent chlorine standards

based on the color  of carefully prepared chromate-dichromate solutions is

advantageous.  The use of standards based on the formation of the holoquinone

derivative itself is problematic,  because the color  is not stable.

    Because ^-tolidine is regarded as a potential cause of tumors in the urinary
tract, its use has  been abandoned in the British Isles.      The only colorimetrtic

method in use there is the N, N-diethyl-p_-phenylenediamine (DPD) method.  FAC

reacts instantly with  DPD to produce a red color.  This reaction is the: basis of

both titrimetric and colorimetric procedures.  In the titrimetric procedure, the

FAC is titrated with standard ferrous ammonium sulfate solution to  the disappear-

ance of red.  The  decolorization is instantaneous.  In the colorimetric version

of this method,  standard  colors are prepared with a standard potassium per-

manganate solution and compared with colors formed by the reaction with free

elemental chlorine.  The colors  are stable, few reagents are required., and a

 full response in neutral solution is obtained from dichloroamine.  The only

 interfering substance likely to be  encountered in water is manganic manganese.

 This can be corrected for by including  sodium arsenite in the test portion.  The

 DPD colorimetric procedure has been studied extensively by Bjorklund and
 Rand.     The titrimetric procedure also was included in the Analytical Reference

 Service  study and found to be  acceptable for both FAC and TAG.  A.  T. Palin,

 to whom this method is attributed, has  also published a modification of the pro-
 cedure that is of particular utility for field use.      In this modification, the

 reagents are available in table form; hence, the procedure is both  simple and


    The  compound 4, 4', 4"-methylidyne-tris (N, N-dimethylaniline),  also known

 as leuco crystal  violet,  reacts instantaneously with free  chlorine to form a

 bluish color.  If  this reaction is carried out in a buffered medium at a pH of

 3. 6-4. 3, if the ratio of leuco  crystal violet to chlorine is at least 30:1, and

 if the color is measured within 5 min, the reaction can be the basis of a

 colorimetric method for both  FAC and TAG.  No significant interference from

 GAG occurs when the free chlorine content is determined within 5 min after

 indicator addition.   The one interference that deserves attention in the determina-

 tion of free residual chlorine is manganic ion, and it may be overcome by addition

 of arsenite, as in the OTA method.  TAG is measured by reacting both free and

 combined chlorine with iodide ion  to produce hypoiodous  acid, which in turn re-

acts instantaneously with leuco crystal violet to form  the dye crystal violet.   *

The color is stable for days and follows  Beer's law over a wide range of  total

 chlorine  values.  Semipermanent color  standards for  TAG determination can

be prepared from the crystal violet itself.   The minimal detectable concentra-

tions are 10 ppb for FAC and  5 ppb for TAG.  The  Analytical Reference Service

study found this method to be excellent and  acceptable for FAC and TAG,  but

its findings were qualified by the fact that relatively few laboratories par-

ticipating in the study used this procedure.  The leuco crystal -violet method

has almost ideal characteristics; its use should increase.

   At a pH below 3, methyl orange is red and has an absorption spectrum

that exhibits a maximum at 510 nm.  Chlorine bleaches that color quanti-

tatively.   Accordingly,  if the change in absorption is measured,  the con-

centration of free chlorine in a solution added to a known amount of methyl

orange may be  established.  At a pH of 2 or greater, the rate of reaction

of chloroamines with methyl orange is very low; but in the presence o:: ex-

cess bromide ion, chloroamines also bleach methyl orange rapidly.  There-

fore,  sodium bromide may be added to the  sample after  the free chlorine

concentration is determined,  and the additional decrease in absorption will

be due to chloroamines.  This method was  found to be acceptable for FAC

and TAG in the Analytical Reference Service study,  and  it has also been
evaluated thoroughly by Sollo and Larson.      The methyl orange method

has been adopted as a "tentative" method by the Intersociety Committee for

a Manual of Methods of Air Sampling and Analysis for determining free chlorine
in the atmosphere.      The method has some advantages:  it is simple and

quick and can be run visually; the reagent serves as its own standard and

so can be used  for both routine and occasional use; manganic manganese  is

the  only  interference,  and it can be removed by the arsenite modification;

the method is sensitive to chlorine at 100 ppb; and it is  independent of sample

temperature.  The major disadvantage is that the method is based on bleach-

ing,  rather than formation, of a color.  This means that precise addition of

reagents is required, and it also lends something of a credibility gap 1:o the

procedure:  one always wonders whether the bleaching is truly due to 1:he

reactant of interest.

    A method that is not commonly used in the United States, but performed
                                   361                               13
 especially well in Nicolson's study,     is the barbituric acid method.

 It is based on the formation of a red-violet complex when an  aqueous chlorine -

 potassium cyanide solution is mixed with an aqueous solution containing

 pyridine and barbituric acid.  At the absorption maximum of 578 nm, Beer's

 law is obeyed over a wide concentration range--1-2, 500 ppb.  This method is

 not as simple to perform as most other colorimetric methods for FAC,  and

 in time it responds  to combined chlorine; the latter probably accounts for its

 disfavor in the United States.  It was,  however, rated by Nicolson as the

 best method for determining  FAC.

    There are no colorimetric procedures that determine hydrogen chloride
 as such.  The Iwasaki et aL method     was developed originally to meet the

 need for a procedure for measuring small quantities of chloride in natural

 waters.  The method is  based on the reaction  of chloride ion with mercuric

 thiocyanate to form mercuric chloride, tetrachloromercurate-II, and thiocyanate.

 The orange color of ferric thiocyanate is measured at 490 nm as an indirect

 indication of  chloride.  When dioxane is included in the test portion,  the

 absorbance-concentration relationship obeys Beer's law and can be used over

 the chloride concentration range of 0. 05-80 ppm.   The problem with this pro-

 cedure is that any substance that reacts with mercuric thiocyanate to liberate

 thiocyanate will falsely indicate  chloride.  Sulfide is a prime example of

 interference  for environmental applications.  Turbidimetric and nephelometric

methods that are based directly  or indirectly on the formation of silver chloride

have a similar disadvantage.  Again,  these methods determine chloride, not

hydrogen chloride.

    The other approach to colorimetric analysis for hydrogen chloride utilizes

hydrogen ion response.  Manita  and Melekhina,  for example, have reported a

spectrophotometric method for the determination of nitric and hydrochloric

acids in the  atmosphere.        Their procedure is  simple; it is based on the

color of an ethanolic  solution of methyl red when it contacts dilute hydro-

chloric acid  solution.   The maximal wavelength for this measurement is

530 nm, with distilled water as the  blank.  Under the proper conditions,

there is a linear relationship between absorbance and acid concentration

at 0. 18-1. 83 ppm.  For the determination of acids in atmospheric air,  a

sample of air was passed through 5 ml of distilled  water at  1 liter/miii;

samples  of 10-20 liters were collected and measured spectrophotometrically.

These workers showed experimentally that, under  their conditions  of sampling,

carbon dioxide and sulfur dioxide in  the air did not interfere with the spectro-

photometric  determination  of hydrochloric or nitric acid. However,  c-ther

acidic and basic  constituents do interfere in this procedure.  The standardiza-

tion for this  method was based on the use of hydrochloric acid solutions,  so

the method conceivably could be used for measuring dilute aqueous samples

of hydrogen chloride; but the method obviously has little  specificity and would

be subject to great interferences from acidic  and basic constituents in  the


   The Intersociety Committee for a Manual  of Methods of Air Sampling

and Analysis endorses  a titrimetric  procedure for  determining the  chloride

content of the atmosphere.      It is based on the formation  of mercuric

chloride; chloride in  an absorber or impinger solution is titrated with

mercuric nitrate, with diphenylcarbazone as the indicator.  A blue-violet

color is developed  as soon  as  excess mercuric ion is added. Steps are

taken to circumvent interference from chromates,  ferric iron, sulfite,, and

sulfide; but iodide, bromide,  cyanide,  and thiocyanate are titrated  and  re-

ported as chloride.  The procedure is designed to determine 0. 1 mg of

chloride in 50 ml of solution (2 ppm), with an error of up to 0. 1 ppm or

2%, whichever is greater.

Electrochemical Techniques

    The determination of chlorine in water and sewage samples has been

studied briefly by conventional voltammetric techniques with a silicone-
graphite electrode.      The supporting electrolyte used  in these studies

was 0. 1 N sulfuric acid.  The electrode reaction in unstirred solution

gave an exemplary waveform for an irreversible process at a stationary

electrode, with the peak potential occurring at about+0. 3 V vs.  the

saturated calomel electrode (SCE).   Although the electrode reaction was

shown to be irreversible,  it was useful for the determination of  chlorine
     -3    -2
at 10   -10  M.  Peak height was measured and found to be linearly re-

lated to concentration over that range.  With stirred solutions, satisfactory
                                      -4    -3
calibration curves were obtained at  10   -10   M.

   Work  at the Oak Ridge National Laboratory has shown that the reversi-

bility of the chloride-chlorine  couple depends strongly on sulfuric acid con-

centration. The couple becomes reversible at sulfuric acid concentrations

of about 6 M and above.   This  means that chlorine  can be determined by

electrolytic reduction,  and chloride  can be determined by electrolytic

oxidation  in 6 M  sulfuric  acid at a platinum working electrode.  The formal

potential under these conditions is about+ 1.0 V vs. SCE. This  approach is

being developed specifically for air monitoring.  It could easily  be developed

for water monitoring.
   Kuempel and Shults     studied the use of  a mercury  pool electrode for

measuring chlorine  in air.   They used a thin-layer cell configuration and

two techniques of measurement: a controlled-potential experiment in which

molecular chlorine was reduced to chloride with 100%  current efficiency,  the

electrolytic current being monitored, and electrolytic accumulation of solid

mercurous chloride at the mercury solution interface followed by stripping

of the accumulate calomel voltammetrically.   The amount of electric charge

transferred during the voltammetric stripping (i. e. , the area under the

cur rent-voltage curve) was related to the amount of chlorine in the  air during

the accumulation step.  Concentrations of chlorine  in air  of 100-200 ppb were

   J. Waolavik and Waszak     studied a galvanic  system for measuring

chlorine in air.  It used a gold electrode paired against an active silver

electrode in a closed  system.   A supporting electrolyte composed of potassium

chloride solution acidified with hydrochloric acid was circulated in  a closed

system.  The determination of chlorine  bubbling through this  electrolyte was

based on the reduction of chlorine to chloride at the gold electrode; the  silver

electrode •was oxidized to  silver chloride.  The galvanic current was measured

directly without amplification,  and its magnitude  reflected the presence of

chlorine and was proportional to its concentration.  This  approach is simple

and allows rapid determination of  small quantities of chlorine iri gases.  The

technique allowed the  determination of chlorine at 1.5 ppm with an accuracy

of 0. 02 ppm.

   In contrast with these methods, which require complete dissolution  of the

active gas in water containing a suitable supporting electrolyte before the
electroanalytic measurement is made,  Cante et al.   reported file detection

and determination of acid  vapors at partially exposed platinum electrodes.

The principal feature  of their  cell is a partially exposed sensing electrode

that permits the  gaseous sample to react without prior dissolution of the

vapor in the bulk electrolyte.  This absorption-induced  electrode-potential

approach was used to  detect acidic vapors via  the reaction:

                          _      _
                       IO    + 51 + 6H  —> 31  + 3H  0.
                         3                     22

 This reaction does not take place in neutral  or alkaline medium, and it is

 very sensitive to hydrogen ion concentration.  Hence,  the electrolytic cell

 is set up as follows:  Pt (exposed blade)Iodate,  lodide/Pt (immersed wire).

 Acidic vapors are injected into a nitrogen stream that flows continuously

 through  the cell.  On entering the cell, the vapor is absorbed into the

 electrolyte meniscus at the exposed electrode, where active  components

 react  chemically with the  electrolyte to produce iodine.  The  cell functions

 amperometrically, with the magnitude of the current  response being propor-

 tional to the concentration  of iodine  (depolarizer) in the cell electrolyte.

 The current is proportional to iodine and hence to hydrogen ion, because

 the two are related stoichiometrically. A linear relationship between the

 limiting  current for iodine and moles of hydrochloric  acid injected was ob-
 served over the acid concentration of 1-7 x 10   M.   This approach, al-

 though interesting, does not offer selectivity:  it would respond to both strong

 and weak acids in the air stream.

    Finally, potentiometric measurements with ion-selective electrodes
 should be mentioned.  The determinations of FAC in water     and of
 chloride in gas streams    by this approach were mentioned earlier.

 Because of their simplicity and rather selective  response,  ion-selective

 electrodes appear to offer promise of environmental analysis for chlorine

 and chloride.  This promise is just beginning to  be developed.  It  is likely

 that an electrode could be  designed that responds to chlorine,  and perhaps

 to hydrogen chloride, directly.  Research in this area is warranted.

 Chromatographic Techniques

    In  view of the success  that gas chromatography has had in the  deter-

mination of some constituents (e. g. ,  sulfur dioxide) in air, it is surprising


that there have been so few reports of the application of this technique to

the determination of chlorine and hydrogen chloride in air.  Myers and
Putnam found gas-chromatographic conditions suitable  for the determina-
tion of hydrogen chloride in their study of chloroboranes and diboranes.

They were able,  by use of Teflon, Fluorolube,  and silicone columns and by

operating under subambient conditions,  to separate hydrogen chloride from

other constituents in their samples.  Their procedure was not extremely

sensitive--they were detecting mole percentages of hydrogen chloride but it

did suggest the potential of this technique for monitoring air.  The most suc-

cessful design used a 10-ft (3-M) length of 1/4-in.  (0. 635-cm) OD copper

tubing  filled with 42-60 mesh uncoated Teflon powder.  Hydrogen chloride

values in  the range of 0. 01-5. 0 mole % were determined by peak height


    Both chlorine and hydrogen chloride were included in a broad chro.mato-
graphic study of Bethea and Meador.     This work was a study of chromato-

graphic conditions  suitable for use with  many reactive gases.  They found

suitable conditions for separating and detecting chlorine and hydrogen

chloride,  but their work was  qualitative, rather than quantitative.  The

lower detection limit of 0. 3 ppm for chlorine in air was reported when 1-ml

samples and an electron-capture  detector was used.  The relative analysis

error was +_ 10%  for chlorine at 10 ppm  under these conditions.
              71                  -12
    Ceiplinski    found that 3  x  10  .  g of chlorine  could be detected

in a 50-^il air sample with a  1-m  column packed with 20 wt % silicone

fluid DC-200 on 60-80 mesh  Chromosorb W at 50 C.  The carrier gas

in this case was  1% methane in argon and an electron-capture detector was
used.  Obermiller  and Charlier    achieved quantitative separation of a

mixture of hydrogen sulfide,  hydrogen chloride, and water at 90 C with. 5%

 Carbowax 20 M on a Fluoropak support.   The lower detection limit for

 hydrogen chloride -was 0. 1% with a  1-ml sample.  Helium was the carrier

 gas.  It was necessary to precondition this column with 5 ml of hydrogen

 chloride before analysis  of any samples; otherwise, results were invariably
 low.  Hamlin,  Iveson,  and  Phillips     used a 14-ft (4. 3-m) column packed

 with 16. 7% Kel-F 40 oil on Kel-F 300 low-density molding powder at 90 C

 for the separation of chlorine and hydrogen chloride in the presence of re-

 active inorganic fluorides.  Nitrogen carrier gas was  used at a flow rate

 of 10 ml min.

    Perhaps the most successful  chromatographic analysis for chlorine and
 hydrogen chloride in air was reported by Ruthven and  Kenney.      They

 used a tritolylphosphate column supported on Celite.  This stationary phase

 was advantageous,  in that the normal order of elution  is reversed--!, e. ,

 chlorine is  eluted before  hydrogen chloride.  The chlorine peak was there-

 fore unaffected by tailing in the hydrogen chloride peak.  The column was

 as follows:   220 cm of 3-mm ID PTFE tubing packed with 60-80 mesh acid-

 washed  Celite having a liquid loading of 4% by weight of tritolylphosphate.

 The column was operated at room temperature.   Chlorine gave sharp peaks

with very little tailing, and the  calibration proved to be linear with peak

height.  The relative accuracy and reproducibility for chlorine were esti-

mated to be within 0. 25%.  However, the hydrogen chloride peak exhibited

 considerable tailing, especially when traces of moisture were present.

 Calibration with peak heights was nonlinear,  but calibration based on peak

 area was  found to be close  to linear.  Even so, hydrogen chloride could not

be determined  to the same degree of accuracy as chlorine: the minimal

 amount that could be detected was about 2%, and the accuracy was within

 1-2%.  Again,  a column conditioning preface was mandatory for determining


hydrogen chloride by this procedure.  The time required for a complete

analysis in this particular case was 1-2 min.

    It is  evident that gas chroma tog raphy has never gained acceptance

as a routine analytic technique for chlorine or hydrogen chloride.  The

compounds can be separated and detected  without sophisticated equipment,

such as temperature programers or even  heated columns.  Unfortunately,

the approach is thus far limited in sensitivity and in ease of quantitation.

The attractiveness of this technique has not decreased, however; it re:-

sponds to the molecular species themselves and hence offers  specificity.

In view of this and the fact that new materials and equipment are con-

tinually appearing, further  research in the gas chromatography  of

chlorine and hydrogen chloride specifically is warranted.

Other Analytic Techniques

    In much environmental -work,  there is a need for measuring  total

chlorine content by means other than wet-chemical techniques.   Biologic

materials, for example, may lose some or all of their chlorine  by thermal

ashing above 400 C.  The same is true when  tissues are ashed at low tempera-

ture with active oxygen.  Analytic procedures that use fresh or dry tissue are

required.  Similarly, nondestructive analysis of particulate matter is desirable.

X-ray fluorescence and neutron-activation analysis have been used for this type

of application.  These are expensive and sophisticated analytic techniques that

provide multielement results.  It is this multielement capability that makes

them competitive  for environmental applications.

    X-ray fluorescence has been used for  determining total chlorine content
of biologic materials.    The tissues were lyophilized, ground to a fine

powder,  and mounted for excitation and measurement of the chlorine K.%

radiation.  Approximately 20 mg  of sample is required: the calibration curve


covers 0.4-5% chlorine.  The results obtained by this technique were re-

producible to +_ 4%,  with irradiations of only 3 min.  Current x-ray fluor-

escence techniques  offer the possibility of improving the sensitivity of

this analysis  by at least a factor of 100.

    Neutron-activation analysis  provides a direct method for the analysis

of trace elements in airborne particulate material collected on  filters, as
                           271, 382
well as biologic materials.           The technique  is characterized by

extreme sensitivity and, when combined with y-ray spectrometry, pro-

vides results for a number of elements simultaneously, without resort

to chemical separation procedures.   Computer interpretation of the y-ray

spectra makes the method suitable for  routine application.  Chlorine is
                   37        38
determined via the   Cl(n,y)   Cl reaction, using particulate matter col-

lected directly on filter paper as the  specimen.  The chlorine-38 decays

with a characteristic half-life of 37. 3 min,  yielding prominent y rays of

1. 64 and 2. 17 MeV.  This procedure has been used to measure  chlorine
concentrations of 0. 02-5. 6 Lug/m  .  Similar results for 17 other elements
were obtained simultaneously in this  study.


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                                   TECHNICAL REPORT DATA
                            (Please read Instructions on the reverse before completing)
                                                       6. PERFORMING ORGANIZATION CODE
                                                            3. RECIPIENT'S ACCESSION'NO.
                                                       5. REPORT DATE
                                                         April 1976

   Subcommittee on Chlorine  and Hydrogen Chloride
                                                            8. PERFORMING ORGANIZATION REPORT NO.
  National Academy of  Sciences
  National Research Council
  Committee on Medical and Biologic Effects of
  Environmental Pollutants, Washington. D.C.
                                                       10. PROGRAM ELEMENT NO.
                                                       11. CONTRACT/GRANT NO.

   Health Effects Research Laboratory
   Office of Research and Development
   U.S.  Environmental Protection Agency
   Research Triangle Park. N.C. 27711
                                                       13. TYPE OF REPORT AND PERIOD COVERED
                                                       14. SPONSORING AGENCY CODE

        The  purpose of this report  is  to discuss the medical,  biologic, and
   environmental effects of chlorine pollution in the lower  atmosphere.  The first
   three chapters discuss the natural  and anthropogenic  sources of pollution by
   chlorine  and hydrogen chloride,  the varied industrial and other usages of chlorine
   and hydrogen chloride and the  quantities consumed, the atmospheric chemistry of
   their transformation and transport  processes, and their spatial distribution.

        Later  chapters deal with  the effects of chlorine and hydrogen chloride on man,
   animals,  vegetation, and materials.   Chapters 9 and 10 present the summary and
   conclusions and offer recommendations for consideration in  future studies.  Methods
   of monitoring and analyzing aqueous,  gaseous, and biologic  samples for chlorine
   and hydrogen chloride are discussed in the Appendix.
                                KEY WORDS AND DOCUMENT ANALYSIS
                                              b.IDENTIFIERS/OPEN ENDED TERMS
                                                                    c. COSATI Field/Group
  Hydrogen chloride
  Air pollution
  Atmospheric  corrosion
                                                                      06, F, T
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 Insert the total number of pages, including this one and  unnumbered pages, but exclude distribution list, if any.

 Insert the price set by the National Technical Information  Service or the Government Printing Office, if known.
•m 2220-1 (9-73) (Reverse)