600/1-76-020
1976
Environmental Health Effects Research Series
CHLORINE AND HYDROGEN CHLORIDE
Health Effects Research Laboratory
Office of Research and Development
U.S. Environmental Protection Agency
Research Triangle Park, North Carolina 27711
-------
RESEARCH REPORTING SERIES
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.
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EPA-600/1-76-020
April 1976
CHLORINE AND HYDROGEN CHLORIDE
By
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
U.S. ENVIRONMENTAL PROTECTION AGENCY
OFFICE OF RESEARCH AND DEVELOPMENT
HEALTH EFFECTS RESEARCH LABORATORY
RESEARCH TRIANGLE PARK, N.C. 27711
-------
DISCLAIMER
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.
NOTICE
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.
11
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SUBCOMMITTEE ON CHLORINE AND HYDROGEN CHLORIDE
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
Jersey.
NORMAN LACASSE, Spring Mills, Pennsylvania.
WILBUR D. SHULTS, Oak Ridge National Laboratory, Oak Ridge, Tennessee.
Consultants
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.
iii
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COMMITTEE ON MEDICAL AND BIOLOGIC EFFECTS OF ENVIRONMENTAL POLLUTANTS
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,
Topeka.
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.
iv
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CHAPTER 1
INTRODUCTION
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 -
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CHAPTER 2
SOURCES OF CHLORINE AND HYDROGEN CHLORIDE
CHLORINE AND HYDROGEN CHLORIDE IN THE ENVIRONMENT
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.
81
capacity in 1972). Because the largest users of chlorine are the chemical
industry (approximately 70% of total consumption) and the pulp and paper
77
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.
-------
98
(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
234
rate of approximately 5-7%. In the United States, hydrogen chloride is
88
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
88
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
-3-
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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
gasoline.
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
355
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.
-4-
-------
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
356
humidity may allow it to exist as anhydrous hydrogen chloride. There
has been one report of hydrochloric acid aerosol concentrations in the
126
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
253
emission.
NATURAL SOURCES OF CHLORINE AND HYDROGEN CHLORIDE
276
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
46la
sodium chloride) and gastric juices at 0. 4-0. 5% (as hydrochloric acid).
-5-
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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-
36
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.
266
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
-6-
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ARTIFICIAL SOURCES OF CHLORINE AND HYDROGEN CHLORIDE
Manufacture
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-
319
nesium chloride fused with other chlorides, the electrolysis of hydro-
85
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
87
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
81
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;
87
and occasional equipment failure (especially compressor breakdown).
-7-
-------
TABLE 2-1
CHLORINE PLANTS IN THE UNITED STATES6
Location
Alabama
Le Moynec
Mclntoshc
Mobile0
Muscle Shoals
Arkansas
Pine Bluff6
California
Pittsburg0
Delaware
Delaware City**
Georgia
Augusta
Brunswick*3
-p
Brunswick '?
Illinois
East St. Louis"
Kansas
Wichita5
Kentucky
Calvert Cityc
j
Calvert City"
Louisiana
Baton RougeCj^
st
Baton Rouge
_ , C-
Producer
Stauffer Chemical
Company
Olin Corporation
Diamond Shamrock
Chemical Co.
Diamond Shamrock
Chemical Co.
U.S. government
The Dow Chemical
Company
Diamond Shamrock
Chemical Co.
Olin Corporation
Allied Chemical
Corp.
Brunswick Chemical
Co.
Monsanto Company
Vulcan Materials
Co.
B.F. Goodrich
Chemical Corp.
Pennwalt Corp .
Ethyl Corporation
Allied Chemical
Corp.
Year
Chlorine
Production
Began
1965
1952
1964
1952
1943
1917
1965
1965
1957
1967
1922
, 1952
1966
1953
1938
1937
Cells
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)
Containers
Filled*
SB
--SB
S -
--SB
- T S -
S -
S -
- - S -
_ _ _ _
- - S -
C T S -
_ _ _ _
--SB
S -
- - S -
BASF Wyandotte Corp. 1959
Diamond D3 (diaph.), Uhde 30 sq.
m. (mere.)('64), Hooker S4
(diaph.)('69)
--SB
-8-
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New York
Niagara Falls^
Falls'
d
TABLE 2-1
CHLORINE PLANTS IN THE UNITED STATESa - (Cont'd)
Location
Gramercy0
Lake Charles
Q
Plaquemine
St. Gabriel0
Taft°
Maine
Orrington
Michigan
Midland0
Montague0
Wyandottec
Q
Wyandotte
Mississippi,
Vicksburg"
Nevada
Henderson
New Jersey
Linden0
Newark0
Producer
Kaiser Aluminum &
Chemical Corp.
PPG Industries,
Inc.
The Dow Chemical
Company
Stauffer Chemical
Company
Hooker Chemical
Corp.
Sobin Chlor-Alkali
Inc.
The Dow Chemical
Company
Hooker Chemical
Corp. :
BASF Wyandotte
Corp.
Pennwalt Corp.
Vicksburg Chemical
Co.
Stauffer Chemical
Co. of Nevada
Inc.
Linden Chlorine
Products Inc .
Vulcan Materials
Year
Chlorine
Production
Began
1958
1947
1958
1970
1966
1967
1897
1954
1938
1898
1962
1942
1956
1961
Cells
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
(diaph.)
De Nora 24H5 (mere.)
Dow (diaph.)
Hooker HC-3 (diaph.)
Hooker S3B (diaph.)
Diamond D3 (diaph.) ('60)
None
Hooker S (diaph.)
BASF-Krebs ('69)
Hooker S (diaph.),
Containers
Filled*7
SB
- T S B
- - S -
SB
S -
- - S -
S -
S -
— — S —
C T S -
S -
- - S -
- T S -
S -
Co.
E.I. du Pont de
Nemours & Co.
Inc.
Hooker Chemical
Corp.
1898
1898
Hooker S4 ('68)
Downs (fused salt)
Hooker S,S3A, Gibbs
(modified diaph.)('61)
- T S -
-9-
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TABLE 2-1
CHLORINE PLANTS IN THE UNITED STATESa - (Cont'd)
Location
Niagara Falls^
Niagara Falls
Syracuse
North Carolina
Acmec
Q f
Canton jj
o f
Pisgah Forest ij
Ohio
Ashtabula5
Ashtabula^
Barberton
Painesvillec
Oregon •
Albany
Portland0
Tennessee
Charleston0
Memphis^
Producer
Hooker Sobin
Chemical
Olin Corporation
Allied Chemical
Corp.
Allied Chemical
Corp.
Champion Inter-
national Corp.
Olin, Ecusta
Operations
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
Year
Chlorine
Production
Began
1971
1897
1927
1963
1916
1947
1963
1949
1936
1928
1970
1947
1962
1958
Cells
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)
Containers
Filled"
- - S -
- - S -
>
?46),
- - S -
_
_
— — S —
S -
- T S -
C T S -
_
C T S B
SB
S -
Memphis
Texas ,
Cedar Bayou
Corpus Christic
Denver Cityc
Nemours & Co.
Inc.
Velsicol Chemical
Corp.
1943
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,
-10-
-------
West Virginia
Moundsville
New Martinsville
TABLE 2-1
CHLORINE PLANTS IN THE UNITED STATES'2 - (Cont'd)
Location
Houston^
Houston ,,
Houston3^
Point Comfort0
Port Neches
Snyder6"7'
Virginia
Hopewell
Washington ,?
Bellingham jj
of
Longview
x>
Tacoma
Tacoma
Producer
Ethyl Corporation
Shell Chemical Co.
Champion Inter-
national Corp.
Aluminum Co . of
America
Jefferson Chemical
Co . , Inc .
American Magnesium
Co.
Hercules , Inc .
Georgia-Pacific
Corp.
Weyerhaeuser
Company
Hooker Chemical
Corp.
Pennwalt Corp.
Year
Chlorine
Production
Began
1952
1966
1936
1966
1959
1969
1939
1965
1957
1929
1929
Cells
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.)
Containers
Filled*
- - S -
_ _ _ _
_ _ _ _
SB
_ _
_ _ _ _
S -
SB
S -
- T S B
C T S -
Allied Chemical 1953
Corp.
PPG Industries Inc. 1943
Solvay S60 (mere.)
Columbia N 1, N 3, N 6
(diaph.), Uhde 20 sq. m.
(mere.)('58)
SB
SB
So. Charleston
Wisconsin ,,
Green Bay J^
Port Edwards0
PUERTO RICO
— st
Guayanilla
FMC Corporation
1916
Fort Howard Paper 1968
Co.
BASF Wyandotte Corp. 1967
PPG Industries
(Caribe)
1971
Hooker S3B (diaph.)('57),
Hooker S4 (diaph.)('67)
Hooker S4 (diaph.)
De Nora 24H5 (mere.)
De Nora (mere.)
- T S B
-11-
-------
TABLE 2-1
CHLORINE PLANTS IN THE UNITED STATES - (Footnotes)
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.
Q
Not operating.
mill.
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.
•j
Electrolytic plant producing magnesium and chlorine from molten
magnesium chloride.
k
Electrolytic plant producing chlorine and hydrogen from hydrochloric
acid.
I
Includes both Texas and Oyster Creek divisions.
-12-
-------
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.
-13-
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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
87
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
87
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
87
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
87
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
87
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,
87
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-
480
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
87
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
87
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
-15-
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compressor. Carbon-ring reciprocal compressors usually have a double
stuffing box vented to a caustic scrubber or the suction of the compressor.
87
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
87
scrubber.
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
87
atmosphere.
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,
2
the elimination of packed joints in dogleg assemblies through improved de-
sign, and essentially complete draining of chlorine-containing brine from the
-16-
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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
87
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-
98
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.
-17-
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88
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.
2
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
-18-
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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.
88
The synthesis process accounted for 5. 6% of the hydrochloric acid
98
(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
201
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
-19-
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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-
88
tionnaries, and emission factors--pounds of hydrogen chloride emitted per
(Saurae")
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
2
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
process.
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
98
(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-
276
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,
88
poor design of absorption systems. In the Mannheim furnace operations,
losses of hydrogen chloride can also occur through leaks at the furnace and
201
through removal of hot salt cake. No quantitative data are available on
the magnitude of such losses to the atmosphere from the Hargreaves process.
-20-
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Combustion of Fuels
The combustion of fossil fuels, particularly coal, produces a major con-
307
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.
447
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
163
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
237
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.
-21-
-------
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
488
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
440
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
128
heating.
*,
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-
I
bustion gases, however, can be a significant problem because of their
-22-
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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
449
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
452
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
21
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
40
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,
-23-
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491
and composting. Another source has estimated sanitary landfill at 10% and
222
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
landfalls.
One incinerator emission that is generating a great deal of concern is
that of hydrogen chloride gas from the combustion of chlorine- and chloride-
261
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
-24-
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plastic materials involved, in that they generate hydrogen chloride on incinera-
261
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.
482
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
124
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
393
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
-25-
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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.
505
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).
505
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
102
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,
-26-
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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.
222
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
355a
Industrial Pollution Control Council, polyvinylchloride makes up less
than 0. 15% of all collected household, commercial, and industrial waste.
262
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
261
and Carotti list a 0. 50% chlorine content of a typical municipal refuse,
-27-
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226
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
505
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
161,446,447,492,493
in exhaust from any mode of transportation. In fact,
there is no evidence that such gaseous emission exists. Hydrogen chloride,
-28-
-------
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
33
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
9
1971 domestic gasoline consumption at 92, 953 million gallons. The aviation
gasoline volume was 751 million gallons, leaving 92, 202 million gallons. An
153
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
422,423
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
-29-
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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
494
of lead was used for production of antiknock compounds, but some of
459
the product was exported.
136
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
218,472
lead II bromide chloride (PbClBr), but other chlorine-containing solids
have also been identified, such as the ammonium lead II bromide chloride
218
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
-30-
-------
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
4
2NH Cl'PbClBr 7 0.513:1
4
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%
161
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.
-31-
-------
Some indication of this reduction can be obtained from Figure 2-1, dis-
362
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.
-32-
-------
0 -
10-
20 -
30-
o
tj 40-
I
c 50-
I
§ 60-
I
70-
80-
90 -
100
r 200
Lead Free Reductions Only
Lead Free
and Leaded
Reductions
73 74 75 76 77 78 79 80 81 82 83 84 85
Year
FIGURE 2-1. Projected reductions in lead emission resulting from EPA
lead regulations.
-33-
-------
A 1973 final environmental statement of NASA OSS launch vehicles and
propulsion programs indicates that environmental pollution by these vehicles
355
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
vehicles.
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.
-34-
-------
TABLE 2-2
Comparison of Emissions into the Lower Atmosphere*
6
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
(b)
Jet Aircraft 270 90
(a)
Based on first stage propellants, 1969-1971 average.
(b)
For 1966. Source: "The Federal R&D Plan For Air-Pollution Control By
Combustion-Process Modificaton", January , 1971, PB 198-066.
(c)
Estimates from Gerstle and Devitt, "Chlorine and Hydrogen Chloride
Emissions and Their Control", Paper No. 71-25, Air Pollution Control
Association, 1971.
(d)
Al 0 from solid propellants.
2 3
o c c
*R,eprlnted from National Aeronautics, and Space Administration,
-35-
-------
TABLE 2-3
Summary of Estimated Maximum Radius of Ground Level Effects for
Titan HIE/Centaur or Titan IIIC *
Event
Normal Launch
Cold Spill
On-pad Catastrophe
Low Level Destruct
Engine Test
Maximum Radius
at which Exposure
Exceeds Criteria
2.4km
6km
Criteria Not
Exceeded
Criteria Not
Exceeded
Criteria Not
Exceeded
Limiting
Pollutant
HC1
N O
2 4
HC1
HC1
CO
Criteria
**
Used
4ppm
2ppm
7ppm
7ppm
SOppm
*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
exposures.
-36-
-------
TABLE 2-4 - EXPOSURE CRITERIA FOR SOME COMBUSTION PRODUCTS AND PROPELLANTS
Controlled Populations'8' Uncontrolled Populations '^'
Substance
HC1
CO
Al203(mg/m3)
NO (N 0 )
L i*
Hydrazlne
UDMH
AlCl3(mg/m3)
TLV. 1C)
ppm
5
50
10
5
1
0.5
loOO
Short-Term Exposure from Emergency Plants
Emergency
10 min.
30
50<9)
30
30
100
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
Resistant
(1)
1000/1 (14)
ioo,ooo/-(50)(k)
—
1000/1 (1A)
-25/4<51>
_31/4(51)
and generally
tlally result
Animals
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
354
hydrogen from the combustion process.
EMISSION CONTROL
Chlorine
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
-38-
-------
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
a^
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
scrubber
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. . . .
-39-
-------
Table 2-6 summarizes present practices for the treatment of chlorine
in blow gas as reported in 24 questionnaire responses.
TABLE 2-6
a^
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
87
towers and to treat waste water before discharge.
^ 87
Derived from Cooperative Study Project. . . .
-40-
-------
TABLE 2-7
Emission and Operating Data from Chlor-Alkali
a^
Establishments using Blow-Gas Treatment
Plant number
28
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
wt
Liquor circulation rate, gal/min
Liquor temperature, °F
Scrubber pressure drop, in. H2O
Scrubber
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
56
30.5'
None; 4-in. standard
pipe launderer
Concrete sections
Blow gas, process
29
140
140
M
Two caustic-packed
towers in parallel
52C
6.83
2-in. Intalox saddles and
ceramic tiles
Titanium-lined steel
Blow gas. brine blowing.
btowdown, tank car ! process blowdown, tank
venting
Ca(OH),
17
550
N.M.h
2.5
N.M.
456
19.7
0.0009
N.M.
N.M.
99.9
1.16
0.314
80
car venting
NaOH
4 and 17
75
N.M.
2
N.M.
4,140i
0.325
N.D.k
N.M.
N.M.
>99.9
None
None
40
30
180b
ISO13
W&
Wff-
D
149=
149°
liy
119°
Packed-tower water absorbed under
pressure
42
29
Alternately stacked
1-and 1-1/2 in.
Intalox saddles
Rubber-lined steel
Blow gas only
115
52
3
191
17V
14.4
4.46'
18.0
19.6
72.5'
2.130
1.090
N.O."
H,O
112
75
4
184
15li
14.1
1.55
22.4
21.6
91.0
659
388
N.O.
112
75
4
163
127i
13.9
0.44
22.4
18.6
97.4
158
106
N.O.
31
316
316
M
Two milk-of-lime cascade
baffle towers in parallel
60
12'
None; 3-ft overlapping
baffles
Hetron, glass-matte rein-
forced
Blow gas,*1 cell end boxes.
tank car vents
Ca(OH),
3.2
112 200
75
109
3.5 2
139
106i
N.M.
1.1 201
13.1 ! 1.41
0.1
22.3
15.2m
99.4
29.6
24.9
N.O.
0.0008
N.D.
N.O.
>99.9
0.284
0.095
_n
•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.
87
-41-
-------
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
1
D»
240
4
D
BO*
5% NaOH ; 5% NaOH
25
60
21
120
21
30
17
2-in.
Raschig
rings
Rubber lined
steel
4
2
2
21
0
0
1,078
100
tons/day ; nil
Lb chlorine emitted solidus j
100 tons of liquid
chlorine
-
10
1
20
2
22
10
20
7
D
65
H,0
80
0
20
?
20
24
30
1-in.
Raschig
rings
Rubber-lined
steel
-60
0.1
0.1
-10
0
0
8
>99
<0.1
<400
1.5-in.
Intalox
saddles
Rubber-lined
steel
25
35
26
20
34.66
3
14.5
1
0
-
9
D
50
CalOHIj"
N.A.»
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
N.A.
35
35
7
10
M
230
Ca(OH),
2
0
30
150
30
72
32
Spray
tower
Concrete
20
0.5
9
25
0 : 0
0 * 0
180 ' 390
>99
100
j
N.A.
' N.D.
j'
1, -
12 13
M M
1 14
M
260 130 112
Ca(OH)] i Na(OH) | Waste
; alkali'
600
73 50
10 0 0
30
20
32
72
32
Raschig
rings
28 30
33
?
40 35
72 i 72
20
40
i
Chemical ! 8- x 12 in.
stoneware . clay
rings ; tile
Concrete Concrete Concrete
i
40 3 35 to 40
0.14 15
35
1 15 7
32 40 i 30 to 35
000
0 0 ! N.D.k
600 120
100 100
N.D.
N.D.
-
370
>99
N.D.
-
18
M
262
CCI,
17
0.01h
-18
9.4h
10
42'
29'
50 i
501
Plates1
1-in.
Raschig'
Steel
100
95
30
30
40
0
-
100
nil
-
22 25«
M
ISO1
-
-
-
-
-
-
38
20
3-in.
ceramic
partition
rings
Rubber-lined
steel
-10
5
5.2
20
0
0.5
510
90
0.4
<400
D
458"
H,O
550
0
32.2
1.23
32.2
48
20
2-in.
ceramic
Berl saddles
Rubber-lined
steel
-38
35
11
32.2
35.0
0.3'
202
97
0.084
54
•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.
hMole%.
'Stripper.
'Absorber.
kNot detectable by odor.
'Water absorber vented to caustic scrubber; chlorine emissions reported as zero.
87
(Reprinted from Cooperative Study Project. ... )
-42-
-------
TABLE 2-9
Questionnaire Data on Handling of Chlorine from Shipping-Container
Vents During Loading
Plant number
Rated capacity.
tons/day
Liquid capacity.
tons/day Cl,
Quantities of Clj.
trorn tank car
loading, tons/day
Frequency of tank
car loading,
no. /day
Tons of chlorine
evolved/55-ton
tank car loading
Tons of chlorine
evolved/ 100 tons
of chlorine
liquefied
Treaiment of tank
car waste chlorine:
Scrubber
In-plant
Vent
1
240
240
2
3
0.67
0.84
X
—
2
180
a
0.1
2»
0.35
0.055
-
X
3
150
a
0.1
*
0.1
0.067
x
4
50
50
0.2
1
0.2
0.4
X
_
6
70
a
<0.1
c
-
<0.14
X
—
7
65
69
<1.0
a
-
O.45
-
X
8 9
180 50
,
a a
2.0 0.25 to
0.50
a 1
0.25 to
0.50
1.1 0.5 to
1.0
- X
X X
10
230
230
0.2
d
-
0.087
X
-
11
79
a
1 to 2
e
1.3 to
2.5
-
. X
12
260
250
1
1
1.0
0.40
X
—
13
130
100
3.0
e
3.0
X
—
14
112
112
2.0
f
_
1.8
X
_
15
254
a
1.0
"
2
0.5
0.39
_
X
19
222
a
1.0
1
1.0
0.45
X
X
20
138
a
1.0
d
-
0.72
_
X
21
190
a
243
g
-
1.28
_
X
i
22
180
100
0.3
25
0.01
0.167
X
_
25
458
308
5.6
g
_
1.22
X
_
~
aUnknown.
bPer week.
cRare.
dlntermittent.
"8-hr day.
(6-hr day.
SDaily.
h 0.5% vented = 10 Ib/day.
'140 Ib/day vented.
87
(Reprinted from Cooperative Study Project. ... )
-43-
-------
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,
424
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
154
wide range of concentrations, if high temperature and low pH are avoided.
Seven of the 24 plants that responded to questionnaires in the cooperative
87
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.
-44-
-------
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
87
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
-45-
-------
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
224
with live steam. One such process is described in detail in a patent.
Two diaphragm-cell chlorine plants indicated use of water absorbers in
87
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.
366
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
82
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
87
questionnaire response indicated that chlorine recovery in the absorber is
-46-
-------
200
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
absorbent.
87
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
87
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
525
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
-47-
-------
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
2
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
-48-
-------
TABLE 2-10
Emissions from By-Product Hydrochloric Acid Manufacturing Plants^
Plant
number
BP-1
BP-2
BP-3
BP-4
BP-5
BP-6
BP-7
BP-8
BP-9
BP-tO
BP 11
BP-12
BP-13
BP-14
BP-15
BP-16
BP-17
BP-18b
Bp.19b
BP.JOk
BP-2ll>
Plant
capacity.
tons per day
115
40
30
IB
220
70
15
7
76
12
25
30
30
105
141.5
17.8
8.3
90
60
140
225
Acid
oonnontratlon.
°Ba
20
20
20
20
20
22
20
22
22
20
20
20
20
20
22
22
22
20
20
20
20
20
Exit gas conditto if
"Volume,
cfm
200
0
0
NA
2
180
NA
0
270
NA
0.01
leakage
only
10
315C
138C
NA
0.1-3.5
520
187
187
B.3
Temperature.
°r
180
60
NA
NA
100
50
NA
85
104
NA
GO
85
100
70
70
70
108
76
£7
40
60
Percent
HCI"
0
NA
NA
NA
0
0
0
0
NA
NA
0.01
NA
3
0
0
0
0
<0.001
0.024
0.160
1.95
0.0023
0.0019
0.0746
60.6
47.2
63.9
Control
equipment
Water jets on
storage tanks
Water scrubber
None
Caustic sciubber
None
None
None
Water scrubber
back up
Phosgene decom-
position towers
None
None
Fume jet
None
Closed system
Closed system
None
Na3COj scrubber
Caustic scrubber
Water scrubber
Water scrubber
None for HCI,
CCI, scrubber
for chlorine
Substances other
than HCI entering
atmosphere
Air, hydrogen, carbon
monoxide and dioxide
Trace Inerts
NA
NA
Air. carbon dioxide
Air, benzol
None
None
Nitrogen and Phosgene
NA
Water vapor
Chlorine
Air. organic]
Methane, nitrogen.
RCI
Chlorine, R Cl
Inerts
Chlorine
Nitrogen, traces of
aromatics
NA
Organics
Chlorine,
carbon dioxide
Pounds HCI .mined
per ton of 20° 84
acid produced"
None
None
None
Nrrne
None
None
None
None
None
None
None
None
1
None
None
None
None
<0.008
0.10
0.70
8.5
0.0044
0.0037
0.14
2.6
2.5
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
2
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
2
chloride absorber for final process emission control.
366
Oldershaw et a_L describe and give a flowsheet for a system designed
to make 32 wt % hydrogen chloride from gases containing chlorinated hydro-
carbons.
2
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
-50-
-------
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
88
upsets.
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
88
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
chloride.
-51-
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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-
go
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
88
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
-52-
-------
FRESH WATER IN
INERTS OUT
TO ATMOSPHERE
TAILS TOWER
(PACKED)
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.
88
-53-
-------
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-
276
absorber.
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
276
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
37
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%
232
recovery of hydrogen chloride.
-54-
-------
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
product.
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
88
no emission to the atmosphere, because the manufacturing systems are closed.
-55-
-------
CHAPTER 3
CONSUMPTION OF CHLORINE AND HYDROGEN CHLORIDE
CHLORINE
2
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.
Chemicals
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,
140
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-
2
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
-56-
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TABLE 3-1
Major Products from Chlorine
Required Production of Chlorine,
millions of pounds
Product
Carbon tetrachloride, CC1
4
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
3
Methylene chloride, CH Cl
2 2
Monochlorobenzene, C H Cl
6 5
Phosgene, COC1
2
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
I960
620
140
300
220
290
540
380
130
230
420
200
360
470
1970
1, 500
450
500
300
2, 140
900
260
550
610
490
400
820
1, 340
680
830
b
1980
3,420
1,460
850
350
7, 070
1, 550
440
2,000
1, 550
570
1, 650
2, 630
3, 580
2, 700
1, 820
2 3
Vinylchloride, C H Cl
2 3
Total
Total chlorine production
a
Derived from Air Pollution from
450
4, 750
9,280
Chlo rination
1,410
13, 180
19, 500
2
Processes.
4, 340
35, 980
45, 500
b
Estimated.
-57-
-------
TABLE 3-2
Minor Products from Chlorine-
Product
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)
2
Chloroparaffins, (C -C )C1
10 30
1, 2-Dichloropropane, C H Cl
36 2
Required
millions
I960
1,845
270
180
70
30
10
15
Monochloroacetic acid, C H O Cl 40
232
Pentachlorophenol, C Cl OH
6 5
Phosphorus trichloride, PCI
3
Sulfurylchloride, SOC 1
2
Vinylidene chloride, CH = CC1
2 2
Total
a_
Derived from Air Pollution from
50
--
--
--
2, 510
Production
of pounds
1970
— — _
140
170
100
20
70
80
60
100
120
80
940
of Chlorine,
b
1980
— - _
80
240
280
60
210
130
80
200
160
1,440
2
Chlorination Processes.
Estimated.
-58-
-------
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
example:
C H Cl 900 C CH =CHC1 -f HC1.
24 2 50 psig 2
-59-
-------
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 .
(air)
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
2
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
-60-
-------
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
442
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
-61-
-------
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,
372
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
372
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
372
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
-62-
-------
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,
348
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
401
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
294
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
512
of marine fouling organisms in seawater cooling circuits. White states
that:
1. All waters--fresh or salt--are capable of growing slime
on heat exchange surfaces.
-63-
-------
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
293
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.
-64-
-------
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
shutdown.
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.
HYDROCHLORIC ACID (100% BASIS)
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
Chemicals
Metals industry
Food -processing
Oil-well acidizing
Miscellaneous
Totals
Fraction
a
1965
51
21
9
7
12
100
of Total, %
b
1971
33
47
7
6
7
100
a. 140
Data from Faith et _a_l.
b 234
Data from Chemical Briefs.
-65-
-------
BIOLOGICAL FORMS
• SANITARY BACTERIA
• NUISANCE BACTERIA
• HIGHER MICRO-ORGANISMS
CHEMICAL SUBSTANCES
» AMMONIUM ION
t ORGANIC NITROGEN
AND SULFUR
COMPOUNDS
IRON fOUS)
MANGANESE (OUS)
NITRITE. NITROGEN
SULFUR
>. '''''''
TOXIC IT y
• DESTROYS PATHOGENS
• CONTROLS NUISANCES
• REDUCES TASTES t, ODORS
COMBINATION
• FORMS CHLORAMINES
• FORMS ORGANIC
CHLORAMiNES AND
CHLORO-ADDITION
AND SUBSTITUTION
PRODUCTS
OXIDATION
• IRON (1C)
• MANGANESE (1C)
• NITRATE NITROGEN
• SULFATE
FIGURE 3-1. Principles of water chlorination. (Reprinted with permission
JQA
from Laubusch. H)
SANITARY AND
INDUSTRIAL WASTES CHLORINATION
FOOO PROCESS/KG
EEfcT SUGAR
CANNERY
MEAT PRODUCTS
PACKING HOUSE
MILK PRODUCTS
METAL PROCESSING
CYANIDE
ELECTROPLATING
MISCELLANEOUS
TANNING
OIL INDUSTRY
PRINCIPLES
PRACTICES.
WASTE CONDITIONING
COOLING WATERS
PROCESS WATERS
REUSE
ASTE TREATMENT
PPETHEATMENT
IN-PLANT
STREAM CONTROL
CHEMICAL
CCXE PL.ANT
DYE MFC.
GAS MFG.
PHENOLS 1 S.P
RUBBER.OTHERS
PULP AND PAPER
WHITE WATER
TEXTILE
WOOL SCOURING
DYES
FIGURE 3-2. Typical applications of chlorine in waste treatment for resource
conservation and pollution abatement. (Reprinted with permission from
Laubusch.293)
-66-
-------
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
235
production figure for the corresponding year. In addition, actual production
of byproduct hydrochloric acid (100% basis) is considerably in excess of what is
235
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
-67-
-------
276
acid. The use of the aqueous acid has grown tremendously in the metal
2
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
235
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
276
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
276
over dilute acid (under 20%) may be considered negligible.
-68-
-------
CHAPTER 4
ATMOSPHERIC CHEMISTRY OF CHLORINE COMPOUNDS
ATMOSPHERIC CHEMISTRY OF NATURAL CHLORINE COMPOUNDS
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
source.
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
-69-
-------
and must also be considered. Thus, the best estimates are that the sea salt
12
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
9
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
9
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
507
igneous rocks of 0. 032% results in a chloride production estimate of
9
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-
9
duction from forest fires of only 1.5x10 kg/year.
Gases. There has been considerable controversy concerning the source
113
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
-70-
-------
TABLE 4-1
NATURAL SOURCES OF ATMOSPHERIC PARTICULATE CHLORIDE
Estimated Production Rate,
9
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-
68
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).
-71-
-------
526
These reactions were studied in detail by Yeatts and Taube, who found
134
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
527
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.
134
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:
-6.4
HC1 >HC1 ; K = 10 . (3)
(aq) (g)
The pressure of hydrogen chloride (pHCl) in equilibrium with the saline
droplets is given by
-6.4
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
-72-
-------
-9
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
254
particles. Junge has pointed out that the ammonia concentration in the
41
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
258
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.
398
On the basis of Junge1 s results, Robbins et a_L studied the following reac-
tions:
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
-73-
-------
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.
398
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
3
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.
380
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.
414a
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.
-74-
-------
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
258
aerosols. Junge found a mean atmospheric chloride:sodium ratio of
74
(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 -
324
cles in Puerto Rico by Martens et aL was (1. 57 +_ 0. 1 6): 1, suggesting
516
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
-75-
-------
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.
210
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.
170
Their arguments are supported by Gillette and Blifford's evidence of
increasing chloride: sodium ratio with altitude over the Pacific Ocean.
324
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
398
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.
324
In Puerto Rico, Martens et al. found a relatively constant chloride
loss from the sea salt particles, about 0.006 micromole/SCM. Assuming a
254
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
-76-
-------
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
495
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.
134
Eriksson estimated the total worldwide volcanic production of
9
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-
11
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.
-77-
-------
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
521
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
306
confirmed by Lodge in Puerto Rico. With improved collection techniques,
522
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/
-------
PARTICLE RADIUS AT INDICATED R.H
WIND FORCE NUM3ER OF
SAMPLING DAYS -
I I
4
22.1 <70%
55.0 91%
110.0 99%
10° 10
102 I03 I04 I05
WEIGHT OF SEA SALT PARTICLES
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
521
distribution points. (Derived from Woodcock. )
-79-
-------
389
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
118
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.
394
Reitan and Braham found only two such particles per standard cubic
418
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
484
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
116
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
-80-
-------
TABLE 4-2
Gaseous and Particulate Chloride in the Marine Atmosphere
Gaseous Chloride
concentration, pg/SCM
oo
i— •
Location
Florida, coastal258
255
Hawaii, coastal
Hawaii, coastal116* 350
North Atlantic,56
Mean
2.2
2.2
3.7
3.4
Range
?
1.0-3.4
0.3-6.5
1.6-11.6
No. samples
7
11
6
20
Particulate Chloride
concentration, yg/SCM
Mean
2.4
5.1
4.5
14.5
Range
?
2.5-12.3
2.3-7.0
2.6-43.8
No . samples
7
8
11
15
Gas: Par tide
Ratio
0.
0.
0.
0.
9:1
4:1
8:1
2:1
sea level
Hawaii, 3,000 m255
Hawaii, 3,500 m
116
1.0
2.0
0.8-1.4
0.8-3.1
6
3
MD.l
2
1
20:1
-------
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
254
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
116
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-
114,132,159,256,483,523
ty.
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.
-82-
-------
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
259,307
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-
307
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. ,
259
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
-83-
-------
1241
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).
-84-
-------
I
00
Ol
I
1.17
1.67
0.33
0.43
0.32
4.58
05.35
0.85 0.5199
<* 0.63
O 1.26
0.78
0.59
0.38
0.58
0.35
6.07
1.43
,3.71
FIGURE 4-3. Average chloride concentration in rainfall over the United States, in milligrams
per liter, 1960-1966. (Reprinted from Lodge et al.307)
-------
I
oo
1.22
0.97
0.83
1.4
FIGURE 4-4. Average chloride:sodium concentration ratios, 1960-1966. (Reprinted from Lodge et al.307)
-------
10
10V
10
CO
A
9k
o
C
•H
h
O
«-«
.C
ao
10
10
; I i r
10-
10'
f) "
10° «=
C'
r:
•—i
fi
.o
u
Pi
•o
r:
in-1 r-
ID —<
-.I
O
111)
i I
1
\
10
-2
10
-3
A B
D
F Tot. A
CI S
D
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)
-87-
-------
10
10
0
10
-1
M
10*
i—i—i—i—i—i r
r~i—i—i—r
Cr/Cl 1
I/C1
1 1
i
1 L
_L
_L
10
0
10"
10
-2
o
•o
0
O
o
10
A B C. D E F
B C D li F Tot.
CI
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)
-88-
-------
117
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
118
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
349
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,
420
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
-89-
-------
TABLE 4-3
Halogen-Compound Concentrations in the Natural Atmosphere
VO
(— 1
Location
Hawaii, sea
levelH6,225,349,350
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
<0.1
Bromide ,
Gaseous
46 + 13
7.9 + 2.
7.4 + 2.
ng/SCM
Particulate
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 +
.9
0.39
0.12
-------
62a
anthropogenic. This was also suggested by Cadle to explain the high
bromide:chloride ratios found in stratospheric aerosols.
349
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
3
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
350
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.
-91-
-------
350
Gaseous iodide -was also measured by Moyers and Duce and
118
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.
343
Laboratory studies by Miyake and Tsunogai and Martens and
323
Hariss with iodine-131 tracer have shown that gaseous iodine can be
released from seawater by photochemical oxidation of iodide in the sea.
419
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
350
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
apply.
419
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
350
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
117
perfect sink for atmospheric iodine. Duce et al. pointed out that the
iodine:chlorine ratio on sea salt particles was inversely proportional to particle
-92-
-------
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
135
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,
350
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
309
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
527
but little work has been done on this subject.
Quantitative estimates of the atmospheric residence time of gaseous
118
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-
67
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.
-93-
-------
515,516
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
516
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.
516
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
-94-
-------
8
atmosphere each year. This is equivalent to about 2-4x10 kg of fluoride
per year. Trichlorofluoromethane and sulfur hexafluoride have been measured
308
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.
ATMOSPHERIC CHEMISTRY OF ANTHROPOGENIC CHLORINE COMPOUNDS
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
296
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
-95-
-------
3
6.0
S.O
4.0
3.0
2.0
1.0
0.9
0.8
0.7
0.6
O.S
0.4
0.3
0.2
0.1
I I I I I I
III III
I I I I
FAIRFAX •
PHILADELPHIA.
CHICAGO
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
98
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)
-96-
-------
thought to be more prevalent than chlorine, except near special isolated
sources.
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
3
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
407
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
233
under atmospheric conditions, but Hutzinger _e_t al. have speculated about
reactions involving polychlorinated biphenyl compounds (PCB's).
-97-
-------
oo
i
TABLE 4-4
Concentration of Particulate Chloride in Urban Atmospheres
Location
Los Angeles
Pasadena
Chicago
Philadelphia
Fairfax, Ohio
San Francisco
Niles, Michigan
Date Concentration, yg/m3 Reference
1965
1969
1969
1969
1969
1970
1971
3
0.10
3.54
3.02
2.50
2.93
<1.2
•si n
Ludwig et al. u
P. K. Mueller et al. (in Miller
e_t al.341
JQf.
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
i
VD
VO
I
Concentration, ug/nr'
Location
Windsor, Ont.
Donora, Pa.
Cincinnati
Charleston
Baltimore
Niagara Falls,
New York
Japan
Berlin (near
incinerator —
1,500 m downwind)
Japan
Japan, Tokushima
Prefecture
Japan, Tokyo -
Chiba/lchihara.
Germany (near
potassium plant —
2,000 m downwind)
USSR
Global
Date
1950
1949
1946-1951
1950-1951
1950
1971-1973
1965
1970
1967
1970
1969
1972
1961
(estimated)
Average
145
109
50.4
24.5
56.6
85
536
—
—
1,500 (without
scrubbers)
150
Range
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
1-5
Reference
Katz269
Katz268
Glotko174
Seiio^l?
Lahmann and
Moeller288
Okita and Nakamura-'"-'
Matsuoka et
al.327
Environmental Sanitation
Center255
Kirsch275
Rjazanov395
Junge256
-------
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.
-100-
-------
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)
(1)
(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
reservoir)
(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)
-101-
-------
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
248
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
-102-
-------
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
unimportant.
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
aerosols.
Recently, considerable concern has been expressed about the
increasing ambient concentrations or organochlorine compounds, particularly
the chlorofluoromethanesC'Freons"). An extensive review of the problem
-103-
-------
405a
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
layer.
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.
-104-
-------
For conditions of heavy freeway traffic, where lead
o
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.
ATMOSPHERIC REMOVAL PROCESSES
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
208
processes have been described for other reactive trace gases by Hidy
-105-
-------
/* o ^o
atmosphere by fallout is 5.1 x 10~° yg/cm -sec, corresponding to 3.1 x 10
Particles
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
.-6
Mg
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
TOO
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.
Gases
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
-106-
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TABLE 4-6
Calculated Residence Times of Sea Salt Particles over the Ocean
I
I-J
o
I
Sea Salt
io-12
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
species.
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
-108-
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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.
INADVERTENT WEATHER MODIFICATION
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
--109-
-------
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
210
reported by Hidy et al., did not provide any evidence of this kind of
disturbance.
There appears to be no evidence of any influence of anthropogenic
chlorides on weather.
-110- '
-------
CHAPTER 5
EFFECTS OF CHLORINE AND HYDROGEN CHLORIDE ON MAN AND ANIMALS
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. '
PHYSICAL STATES OF CHLORINE AND ROUTES OF EXPOSURE
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.
MECHANISMS OF ACTION OF CHLORINE
Chlorine is a most reactive element and readily combines with a variety
of organic compounds and radicals well justifying its reputation of a general
-111-
-------
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
"^67
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
-112-
-------
duration of a few seconds (range, 1-120 sec). However, some bacteria (such as
Mycobacterium tuberculosis) and some fungi (such as Aspergillus niger) require
295
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
197
opinion of a recent reviewer.
EFFECTS OF CHLORINE ON NONMAMMALIAN SPECIES
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.
-113-
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EFFECTS OF CHLORINE ON MAMMALIAN SPECIES OTHER THAN MAN
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.
-114-
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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
o
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
o
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
508
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
3
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.
o
The animals exposed at 2,900 mg/m showed little early excitement.
There was dyspnea, lacrimation, and foaming secretion of the nostrils.
3
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,
-115-
-------
hemorrhagic fluid in the lungs, and some congestion of the liver at all chlorine
SDR
concentrations. Weedon et al. gave the Lt_-, that are shown in Table 5-1.
-- 50's
TABLE 5-1
o
Lt , for Chlorine Exposures of Various Species—
min
Chlorine concentration, mg/m-3
2,900 725 183 47
»960
Animals
Houseflies
Mice
Rats
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.
o
The lowest concentration, 730 mg/m , killed two of 20 animals. Values derived
from their graphs are shown in Table 5-4 .
-116-
-------
TABLE 5-2
o
Lt's for Various Percentages of Population Exposed to Chlorine—
Lt, min
Chlorine concentration,
Fraction
killed, %
1
16
30
50
84
99
Houseflies Mice
12
19
23
45 28
41
67
2,900 mg/nr Chlorine concentration, 725 mg/m3
Rats
14
28
36
48
78
155
Mice
261
364
409
467
598
834
Rats
207
327
384
460
648
1,024
—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
o
LCt's for Chlorine Exposures of Mice and Rats—
o
LCt, mg-min/m
Chlorine concentration, 2,900 mg/m3 Chlorine concentration 725 mg/m3
Fraction
killed, %
1
16
30
50
84
99
Mice
34,800
55,100
66,700
81,200
118,900
194,300
Rats
40,600
81,200
104,400
139,200
226,200
449,500
Mice
189,225
263,900
296,525
338,575
433,550
604,650
Rats
150,075
237,075
278,400
333,500
469,800
742,400
—Calculated from data of Weedon et
-117-
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TABLE 5-4
Dose-Response Regression Data for Lethality in Mice
Exposed to Chlorine for 10 Minutes3-
Dose-Response Regression Data
Miscellaneous Mice
Fraction
killed %
1
16
30
50
84
99
Chlorine Concen.
mg/m3 LCt,
600
1,120
1,310
1,520
1,900
2,430
o
mg-min/m
6,000
11,200
13,100
15,200
19,000
24,300
Selected
Chlorine Concen.
mg/m3
—
1,360
1,530
1,730
2,100
—
Mice
LCt , mg-min/m
—
13,600
15,300
17,300
21,000
— —
a 433
"Derived from Silver and McGrath.
434
In another investigation, Silver e± al. found an LCt _ of 19,600 + 1,900
o
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
3
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
508
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
-118-
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TABLE 5-5
Dose-Response Regression Data for Lethality in Mice
Exposed to Chlorine for 10 Minutes^-
Fraction
Killed, %
1
16
30
50
84
99
Dose-Response Regression Data
Chlorine Concentration, mg/m3
970
1,550
1,750
1,960
2,500
3,300
LCt, mg-min/m3
9,700
15,500
17,500
19,600
25,000
33,000
"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)
o
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
-119-
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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
animals.
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.
-120-
-------
TABLE 5-6
Acute Deaths (within 72 Hours) in Dogs Exposed to
Chlorine
Median
408
1,425
1,740
2,060
2,375
2,690
4,645
Chlorine
Concentration, mg/m3
Range
16- 800
1,270-1,580
1,580-1,900
1,900-2,220
2,220-2,530
2,530-2,850
2,850-6,340
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
-121-
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TABLE 5-8
Lethality of Single-Inhalation Exposures of Animals
Animals
Mice
Rats
Cats
Dogs
Not stated
Most animals
Most animals
Not stated
Not stated
Chlorine Concentration, mg/m3
1,800
1,520
1,730
1,960
1,820
2,900
725
2,900
725
—
2,220-2,530
2,500
3,000
2,900
40,000-60,000
5,600
5,600
to Chlorine
Exposure Time, min
10
10
10
10
—
28
467
48
460
—
30
30
30
Few
30-60
10
10
Ct, mg-min/m3
18,000
15,200
17,300
19,600
18,200
81,200
338,575
139,200
333,500
7,520
66,455
75,000
90,000
—
—
56,000
56,000
Toxicity Value
LCt 158
LCt5Q
LCt5Q433
TO 433
LCt5Q
LCt5Q434
TO 434
LCt5Q
T ft- JVO
^n
LCt5Q508~
T /-> f JvJo —
LL.CC- rt
LCt50508^
Mortality ,
product
LCt50486,487£
Mortality
product1**
Mortality ,
Product498d
Lethal for most'
Serious or
fatal242e.
Mortality
product502_
Mortality ,
242£
product-
-122-
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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 ,
product384—
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.
-123-
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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.
-124-
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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,
413
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,.
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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
oo
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
58
carbon dioxide tension and a slight reduction in bicarbonate concentration.
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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
edema.
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.
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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
reflexes.
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
518
constricted, with almost complete closure of the lumen. It has been
suggested that the constriction might have resulted from sectioning of the
lung.290
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
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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
sacrifice.
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
o
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.
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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
O
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
-130-
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organs. The incidence of malignant tumors was the same in control and
112
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.
EFFECTS OF CHLORINE ON MAN
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
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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. ^
299
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
395
adversely affected by the environment. Many western scientists disagree
with this interpretation and doubt the value of such studies.
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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.
blov/er—£•
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 )
-133-
-------
• 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
occur.395,456
• 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
-134-
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• 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,
395
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.
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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
results.1&5
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.
-136-
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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.
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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-
168
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,
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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
edema.108
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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.
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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
great.
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
-141-
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TABLE 5-9
Subjective Responses to Chlorine
Odor
None
Minimal
Easily Noticed
Strong
No.
Air
Samples
65
16
12
29
Chlorine Concentrati
in Air, ppm
Range
0.08-
1.1 -
1.9 -
2.9
2.7
3.5
2.2 -41
Average
1.2
1.6
2.5
8
Respiratory
Irritation
None
Minimal
Painful
Intolerable
No.
Air
Samples
81
7
11
23
Chlorine Concentration
in Air, ppm
Range
0.08- 2.9
1.95- 2.9
1.92- 4.23
2.6 -41
Average
1.3
2.6
3
9
Eye Irritation
None
Minimal
Painful
No.
Air
Samples
81
1
4
Chlorine Concentration
in Air, ppm
Range
0.08- 2.9
8.7-41
Average
1.3
7.7
20
•^Data from H. R. Hoyle, personal communication.
-142-
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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
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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
Q
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
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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.
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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
damage.228
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
£O
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
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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
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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
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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
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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.
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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.
PHYSICAL STATES OF HYDROGEN CHLORIDE AND ROUTES OF EXPOSURE
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,
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TABLE 5-10
Summary of Chlorine Thresholds and Limits
Chlorine Concentration,
ppm Remarks References
0.03-3.5
1.0
1.0
1-2
1-3
3
3
3
3-6
Range of reported odor thresholds
TLV, OSHA time-weighted average
Permissible concentration; 8-hr working
day
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,
95,
7,
246
206
528
377
7
528
299
490
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
a
"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
-152-
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Established Limits TABLE 5-11
Examples of Some Established Limits for
Chlorine Concentration
Reference
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)
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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
Sciences.357
-154-
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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)
a.
""Values are tentative. The PEL's are ceiling limits and are not to be
exceeded. Derived from National Academy of Sciences.
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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
MECHANISMS OF ACTION OF HYDROGEN CHLORIDE
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
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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
damage.101
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
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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
448
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.
EFFECTS OF HYDROGEN CHLORIDE ON MAMMALIAN SPECIES OTHER THAN MAN
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.
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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)
and
guinea
pigs 450 (300)
Rabbits 5,000 (3,400)
and
guinea
pigs
Time, min CT, mg-min/m^ Effects
Up to
360
75
360
90
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
exposure
—Data from Lehmann.
-159-
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TABLE 5-15
LC of Hydrogen Chloride Vapor and Aerosol in Rats and Mice3.
Animals
Vapor :
Rats
Mice
Aerosol:
Rats
Mice
JU'Jj . _ .
LC , mg/m3 (ppm)
50
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.
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TABLE 5-16
Lowest Concentrations of Hydrogen Chloride Vapor or Aerosol that Caused
a
Death in Experimental Rats and Mice-
Animals
Vapor:
Rats
Mice
Rats
Mice
Aerosol:
Rats
Mice
Rats
Mice
Exposure
Time, min
5
5
30
30
5
5
30
30
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)
No.
Deaths
1/10
1/10
1/10
2/15
1/10
3/10
1/10
2/10
~Data from Darmer et al.
—Lowest concentration tested.
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TABLE 5-17
Bliss Dose-Response Regression Data for Lethality of Hydrogen
Chloride Vapor and Aerosol in Mice and Rats-3-
Fraction
Killed, %
1
16
30
50
84
99
1
16
30
50
84
99
LCt, mg-min/m
Vapor
Mice
13,462
38,643
56,076
84,937
186,697
535,998
29,994
65,754
86,763
118,187
212,369
465,640
Rats
5-Min
192,307
250,596
275,136
305,361
372,105
484,883
30-Min
109,157
158,819
181,303
210,135
278,034
404,490
Aerosol
Mice
Exposures
44,089
63,645
72,451
83,723
110,133
158,990
Exposures
28,653
57,171
72,950
95,747
160,384
319,918
Rats
91,918
155,787
187,673
231,009
342,558
580,586
119,081
179,381
207,319
243,615
330,825
498,360
.—Data from Banner et al.
-162-
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CT.s....(mq Jrri ri/xu". in) '..
..TO..MICE FOLLOWING .TOTAUBODY.
DF:HYDROGEN..:CHLORID
MINUTES..
i-
.LIMITS:
.FOR...5
I ,000
50,1000
Ct (mg min/cu
100,000
m)
500,000
-163-
-------
r r ?
I I
FIGURE 5-:
O> «•* en
iiH!M '• r 1 ;
''LIMITS OF
.ETHAL
HYDROGEN! CHLOP,!DE"..TQ.;RATS; FQLLP>JING_1QTAL .BQDY..EXPOSURE.
20,000
50,000 100,000
Ct (mg 'min/cu m)
500,000
-164-
-------
r r
•4
LLOl
'LH
4J.!
99
84: _
c
Ol
if
Ol
o.
.50
30
15 -
-FIGURE'.5-4 .LTTHALXts- (nig! min/cu- rn'};:AN'd--9^
;-[.i.JO MICE FOLLOWING TOTAL-BODY1. E
CONF-IOENCE -LIMITS1 OF-
POSUREFOP 30-MINUTES.
I . i , . • . : .i I .
HYDROGEN CHLORIDE •*••
,000
50,000
Ct (mg
100,000
mln/cu m)
500,000
-165-
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: i III1'—!1 : !• I i
AND.. 95s:cwRiBtN'CEXxHlTs'idE4: YOROGEN: CHLOR
J_L I JJJl
' LP LL1 l
•T—r-~r -t-TT-:
FOLL'OWING-TOTAL BODy-fXPOfeUR^FOR :30 MINUTES!
10,000
50,000 100,000
Ct (mq min/cu m)
I
500,000
-166-
-------
99~i-
84 -
•-. 50 - -—
-------
O» -4 O» 10
! I ! !
99 -
84 - '--:--
.01
o
30
15 -
/&
CHLORIDEJAEROSOLS iTO. RATS FOLLOWING.
EXPOSURE-FOR-5 MINUTES.
50,000
1.0.0,000
Ct (mg min/cu m)
560,000
-168-
-------
99
_ • ! I ' i
^
AEROSOL}..TO.. MICE FOLLOWING TOTAL-BODY- EXPOSURE- FOR- 30 MINUTES.
3,000
min/cu m)
500,000
-169-
-------
LETHAL :CTs! (itg .mitr/cir m)--'AND;9i?iro'NFID!ENCE:bMlT.S:.O.U
CHLORIDE AEROSOLS
TOfRATS FOLLOWING TO
'- 30
AL BOD.Y...EXPOSURE
000
50,000 100,000
Ct (mg min/cu m)
I
500,000
-170-
-------
Mucociliary activity of excised rabbit trachea ceased permanently after
o
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
315
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
effects.
-171-
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TABLE 5-18
Summary of Toxicity of Single Exposures of Animals
to Hydrogen Chloride Vapor
Animals
Rabbits
and
guinea
pigs
Cats
and
rabbits
Rats
Mice
Hydrogen Chloride
Concentration.
mg/m-* (ppm)
5,000 (3,400)
1,000 (650)
6,500 (4,350)
450 (300)
2,000 (1,350)
5,500 (3,700)
Exposure
Time, min Ct, mg-min/m^
90
360
30
360
75
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)
450,000
360,000
195,000
162,000
150,000
27,500
<75,600
Effect
Reference
Deaths 148
100% deaths 315
100% deaths 315
Cloudy cornea 148
Respiratory
distress 148
No deaths 315
Running nose,
salivation
148
5
30
5
•
30
30
5
30
5
300,000
207,000
237,500
127,500
116,100
101,000
52,800
23,750
LL* t _
SO
LCt50
Lowest dose
causing
death
Lowest dose
causing
death
LCt
LCt50
Lowest dose
causing
death
Lowest dose
causing
death
101
101
101
101
101
101
101
101
-172-
-------
TABLE 5-19
Toxicity of Hydrogen Chloride Gas in Animals3-
Hydrogen Chloride
Concentration,
No. Rabbits No. Guinea Pigs mg/m^
3 3 6,500
3 3 1,000
3 3 5,500
33 100
3 3 50
(ppm)
(4,350)
(650)
(3,700)
(65)
(33)
Exposure:
Time, min
30
360
5
1,800
7,200
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.
Results
100% deaths
100% deaths
No deaths
b
No effects,
no patho-
logic
changes
-173-
-------
TABLE 5-20
Summary of Repeated Exposures of Animals to Hydrogen Chloride Vapor
Animals
Hydrogen Chloride
Concentration Exposure Daily
mg/nr* (ppm) Time, min Ct, mg-min/m-* Effect
Rabbits
guinea pigs 100 (65)
Rabbits,
guinea pigs,
and monkeys 50 (33)
Rabbits
guinea pigs,
and pigeons 150 (100)
Reference
l.SOQ3.
7,200^
18,00(£
36,000
18,000
54,000
Inflammatory reaction
in respiratory
tract 315
No effects, no
pathology
315
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.
-174-
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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
-175-
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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.
-176-
-------
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
503
the acid was said to spread the damage and to increase mortality in cats.
EFFECTS OF HYDROGEN CHLORIDE ON MAN
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
299
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
-177-
-------
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.
-178-
-------
TABLE 5-22
Subjective Response to Hydrogen Chloride^.
Response
None
Minimal
Easily noticed
Strong
No. Observations
6
4
5
5
Hydrogen Chloride Concentration, ppm
Average Range
0.4
0.7
4.17
13.37
0.06 - 1.8
0.07 - 2.17
1.9 - 8.6
5.6 -22.1
%)ata from H. R. Hoyle (personal communication).
-179-
-------
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.
-180-
-------
TABLE 5-23
Summary of Human Effects of Exposure to Hydrogen Chloride
Hydrogen Chloride
Concentration, ppm
1,300-2,000
1,000-1,300
1,000-2,000
50-100
50-100
35
10-50
35
10
10
10
5
1-5
0.402
0.335
0.26
0.134
0.13
Exposure
Time
Effects or Comments
Reference
Few minutes Lethal
30-60 min Dangerous
— Brief exposures dangerous
— Work impossible
60 min Intolerable
241, 449a
241
411
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
-181-
-------
TABLE 5-23 - continued
Hydrogen Chloride Exposure
Concentration, ppm Time
0.067-0.134
0.067-0.134
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
-182-
-------
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
457
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.
-183-
-------
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
-184-
-------
TABLE 5-25
Short-Term and Emergency Limits for Public Exposure to Hydrogen Chloride^
•3
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.
-185-
-------
CHAPTER 6
EFFECTS OF CHLORINE AND HYDROGEN CHLORIDE ON VEGETATION
EFFECTS OF CHLORINE ON VEGETATION
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
531
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.
195
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.
-186-
-------
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
fumigation.
509
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. ,
-187-
-------
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
477
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.
30
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.
-188-
-------
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.
531
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.
51
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
-189-
-------
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.
52
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
51
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.
-190-
-------
Sensitivity
30
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.
52
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.
30
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.
51
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
531
to reduce the sensitivity of tomato to chlorine gas. Zimmerman also reported
that water stress, even slight wilting, causes plants to become resistant.
-191-
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TABLE 6-1
Relative Sensitivity of Plants to Chlorine Gas
Intermediate
Resistant
Sensitivity
Alfalfa
Blackberry
Box elder
Chickweed
Crab apple
Globe -amaranth
Horse-chestnut
Mustard
Pin oak
Radish
Rose
Sugar maple
Sunflower
Sweetgum
Tobacco
Tree of heaven
Tulip tree
Virginia creeper
Wandering Jew
Zinnia
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
Buckwheat
Cheeseweed
Corn
Cucumber
Dahlia
Dandelion
Nasturtium
Nettle-leaf goosefoot
Onion
Petunia
Pinto bean
Scotia bean
Squash
Tomato
Azalea
Balsam fir
Begonia
Cactus
Chrysanthemum
Corn
Cowpea
Geranium
Kentucky bluegrass
Lamb's quarter
Mignonette
Myrtle
Oxalis
Pepper
Pigweed
Pine
Smartweed
-192-
-------
52
Brennan et al. reported that pine trees in a hardened condition
were less sensitive than those actively growing.
Accumulation of Chlorides
51
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.
52
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
395
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.
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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.
EFFECTS OF GASEOUS HYDROGEN CHLORIDE ON VEGETATION
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
195
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
3
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.
509
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
-194-
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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.
225
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.
11
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,
456
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
-195-
-------
gas was emitted through a stack 120 m high at 15 tons/day. The maximal ground-
3
level concentration of 34. 0 mg/m was measured 1, 000 m from the plant;
3
the maximal ground-level concentration at 3, 000 m was 17. 3 mg/m .
217
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.
520
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
46
chloride. Boettner and Weiss reported that hydrogen chloride gas accounts
for 58% of the weight loss in the low-temperature fraction of polyvinylchloride
combustion.
48
In 1969, Bohne reported hydrogen chloride gas damage to several
shrubs, trees, and flowers near a hospital incinerator.
-196-
-------
Symptomatology
195
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
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especially sensitive, particularly in chicory and cornflowers. The color change
i
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
195
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
520
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.
339
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
-198-
-------
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.
426
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,
-199-
-------
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.
175
Chronic fumigations of tomato (Bonny Best) were performed by Godish
177
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.
195
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.
-200-
-------
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
basis.
-201-
-------
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
4
based on unit chlorophyll content. At the highest light intensity (7. 6 x 10
2
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.
-202-
-------
175
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.
145
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
-203-
-------
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
experiments.
145
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
195
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
-204-
-------
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
443
resemble those described by Solberg and Adams for hydrogen fluoride; and
44
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
45
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.
-205-
-------
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
426
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.
-206-
-------
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
chrysanthemum.
Sensitivity
195
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
339
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
-207-
-------
suggest, however, that broadleaf plants are generally more sensitive than
476
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.
Accumulation
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.
-208-
-------
TABLE 6-2
Relative Sensitivity of Plants to Hydrogen Chloride
Sensitive
Intermediate
Resistant
Caespitose phlox
Columbine
Cornflower
Garden daisy
Oriental poppy
Tomato
Tuliptree
Black cherry
Chrysanthemum
European black alder
Norway maple
Pinto bean
Sugar maple
White pine
Adonis
Arborvitae
Austrian pine
Balsam fir
Douglas fir
Garden iris
Garden lupine
Garden peony
Goldenrod
Larkspur
Lily-of-the-valley
Norway spruce
Paniculate phlox
Pheasant's eye pink
Plantain lily
Red oak
Sweet William
a. 11 339
Data from Antipov and Means and Lacasse.
-209-
-------
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)
468
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
189
calcium chloride) used on high-ways for deicing. This symptom closely
resembles the marginal burning caused by hydrogen chloride gas.
-210-
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Appendix to Chapter 6
Common and Scientific Names of Plants
Common Name
Adonis
Alfalfa
Annual blue grass
Apple
Apricot
Arborvitae
Ash
Austrian pine
Azalea
Balsam fir
Basswood
Bean
Beech
Begonia
Bellflower
Birch
Blackberry
Black cherry
Bluets
Box elder
Bramble
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.
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Common Name
Buckwheat
Buffalo currant
Cactus
Caespitose phlox
Cheeseweed
Cherry
Chickweed
Chicory
Chinese holly
Chrysanthemum
Coleus
Columbine
Corn
Cornflower
Cosmos
Cowpea
Crab apple
Cucumber
Dahlia
Daisy
Dandelion
Dogwood
Douglas fir
Dragon tree
Scientific Name
Fagopyrum sagittaturn Gilib.
Ribes aureum Wendland f.
Cactaceae
sp.
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
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Common Name
Eggplant
Elm
European black alder
Fir
Garden daisy
Garden iris
Garden lupine
Garden peony
Geranium
Ginkgo
Globe-amaranth
Goldenrod
Hemlock
Horse-chestnut
Hybrid tea
Italian prune
Kentucky bluegrass
Lamb's quarter
Larch
Larkspur
Lettuce
Lilac
Lily-of-the-valley
Linden
Scientific Name
Solanum melongena L.
Ulmus sp. L.
Alnus glutinosa (L. ) Ga.ertn.
Abies
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.
Theaceae
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.
-213-
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Common Name
Loblolly pine
Maple
Meadow-grass
Mignonette
Mustard
Myrtle
Nasturtium
Nettle-leaf goosefoot
Norway maple
Norway spruce
Oak
Onion
Oregon grape
Oriental poppy
Osier
Oxalis
Paniculate phlox
Pea
Peach
Pear
Pepper
Petunia
Pheasant's eye pink
Phlox
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.
-214-
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Common Name
Scientific Name
Pigweed
Pine
Pin oak
Pinto bean
Plantain lily
Plum
Radish
Red beech
Redbud
Red clover
Red currant
Red oak
Rose
Rye
Scotia bean
Shortleaf pine
Silverbell-tree
Slash pine
Smartweed
Spruce
Squash
Strawberry
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.
-215-
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Common Name
Scientific Name
Sunflower
Sweetgum
Sweet william
Tobacco
Tomato
Tree of heaven
Tulip tree
Vibu rnum
Virginia creeper
Wandering Jew
Waterweed
White beech
White pine
White thorn
Zinnia
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.
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CHAPTER 7
PROPERTY DAMAGE AND PUBLIC NUISANCE
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.
HISTORICAL SURVEY OF AIR POLLUTION BY HYDROGEN CHLORIDE
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 >
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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,
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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.
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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.
473
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-
petual.147
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.
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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.
GENERALIZED CORROSION
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
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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"
rate.
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.
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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
T
OC1~ H+
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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
corrosion.
Hydrogen chloride dissolves in water to form hydrochloric acid, which is,
of course, no different from that formed when chlorine dissolves in water.
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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
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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
179
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.
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TABLE 7-1
Corrosion Rates of Various Metals Exposed to Chlorine
and Hydrogen Chloride in a Chlorine Plant—
Eip. No.
1
2
3
4
5 ...
6
7
8
9 ...
10
11
Corrosion Rates, Mils Per Year
Tl
0.002
0.005
0.01
0.004
0.004
Nil
Nil
0.0002
0.0003
0.0002
0.002
Zr | Nl
0.03
6> »
6>
42
0.02
0.04 •:
0.32
0.009
0.092
0.1
0.003
6" '
!.
0.05
0.02
0.2
0.003
0.8
0.3
0.03
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.
Monel
0.01
13
26
8'
0.1
0.1
0.9
0.03
1
0.4
0.05
Hast. C
0.001
0.001
0.01
Chlorlmet 3
0.006
0.2
0.01
Exposure
No.
1
2
3
4
5
6
7
8
9
10
11
304
7 -' '
103.6
32.6
0.4 i
2
0.004
0.2 i.4
316
0.0002
13'
83.«
43.9
0.05
0.3 *
12.5
6.62'
Al 6061
0.05'
33'
96
18
0.21
0.5
63
0.3
6
2
0.21
Environment
Moist
conta
Moist
Moist
Moist
Moist
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!
igCl-.-
igCh
CK-
Cls
Cls.'. ".'.'.'.'.
Cl2
Cla
'Copper
0.09
20 «
55«
2l«
0.2
2
2
0.09
1
0.8
0.6
Tem-
perature
Ambient
Ambient
Ambient
Ambient
Ambient
92 F
98 F
Ambient
Ambient
Ambient
120 K
Mlld Steel
3
38
90
58
8
6
7
4
141
30
3
Duration
of Test.
Days
166
118
92
137
166
214
214
195
19.5
195
166
Reprinted with permission from Gegner and Wilson.157
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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
177
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
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
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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.
OBNOXIOUS ODORS
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
matters.-*88
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.
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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.
DISCOMFORT
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.
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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.
TRAFFIC AND NAVIGATIONAL HAZARDS
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
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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.
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CHAPTER 8
SAFETY IN USE AND HANDLING OF CHLORINE AND ANHYDROUS HYDROGEN CHLORIDE
CHLORINE MANUFACTURE
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
States.
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.
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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.
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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.
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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.
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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:
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• 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
corrected.
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.
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Remote cell-circuit trip switches, automatic compressor controls., and so
forth are incorporated into plant design specifically for emergency situa-
tions.
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
personnel.
• 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.
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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.
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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-
centration.
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-
chloride.
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.
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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
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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.
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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.
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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-
leases.
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.
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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
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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 TRANSPORTATION
Containers
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.
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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
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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
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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
leaks:
• 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.
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• 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
containers.
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.
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Pipelines
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
ti
support structures should be promptly corrected.
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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 CONSUMPTION
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
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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-
sion.
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.
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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
washed.
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
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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
unattended.
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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.
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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.
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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.
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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
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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
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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
trichloride.
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.
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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
vaporizers.
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
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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.
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ANHYDROUS HYDROGEN CHLORIDE MANUFACTURE
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
satisfactory.
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.
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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.
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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.
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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
chapter.
ANHYDROUS HYDROGEN CHLORIDE TRANSPORTATION
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
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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.
Containers
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.
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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
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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.
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Pipelines
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.
INDUSTRIAL HYGIENE
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
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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.
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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.
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CHAPTER 9
SUMMARY AND CONCLUSIONS
ATMOSPHERIC SOURCES AND TECHNIQUES OF EMISSION CONTROL
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.
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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
sources.
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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
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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.
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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.
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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.
ATMOSPHERIC CHEMISTRY
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.
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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
n
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
moisture.
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
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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.
EFFECTS ON MAN AND ANIMALS
Chlorine
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.
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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.
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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,
etc.
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.
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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.
EFFECTS ON PLANTS
Chlorine
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
negligence.
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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.
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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.
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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
species.
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.
PROPERTY DAMAGE AND PUBLIC NUISANCE
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
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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
chloride.
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
public.
SAFETY IN USE AND HANDLING
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.
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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
area.
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CHAPTER 10
RECOMMENDATIONS
ATMOSPHERIC CONCENTRATIONS AND EMISSION CONTROL TECHNIQUES
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
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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
plants.
ATMOSPHERIC CHEMISTRY
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.
EFFECTS ON MAN
Chlorine
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.
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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.
EFFECTS ON VEGETATION
Chlorine
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.
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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.
PROPERTY DAMAGE AND PUBLIC NUISANCE
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—
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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.
SAFETY
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.
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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.
ANALYTIC TECHNIQUES
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.
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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
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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.
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APPENDIX: ANALYTIC DETERMINATION OF CHLORINE AND
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:
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"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.
PROPERTIES OF CHLORINE AND HYDROGEN CHLORIDE PERTINENT TO
CHEMICAL ANALYSIS
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
follows:
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Cl + HCO Cl +HOC1+CO
23. 2
In strong base, hypochlorite salts are formed. Hypochlorous acid itself
-8
is weakly ionized (K = 3. 7 x 10 ).
a
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~ — — -
-1.47
-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
follows:
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Acidic Medium
- -0-54
-1.06
-1.23
-1.20
Basic Medium
- -0-54 -0.45
-0.49
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
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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
111
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
15
for field use. Monochloramines and dichloroamines are much more stable.
SAMPLING
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.
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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
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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
344
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
3
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
chloride.
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
236
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.
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337
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
240
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.
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Continuous Monitoring
Chlorine and hydrogen chlorine have been monitored continuously both
electrochemically and spectrophotometrically.
125,462
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
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chlorine, but hypochlorite can be determined indirectly with an iodide-selective
369
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.
297
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-
53
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.
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-------
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
approach.
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.
ANALYSIS
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
467
for the Examination of Water and Wastewater and the Handbook of Chlorina-
514
tion. They have been thoroughly tested and evaluated by numerous workers.
361
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
304
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
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TABLE A-l
a
Common Analytic Methods for Chlorine~
Method
lodometric
titration
(I2 with S 03)
Amperometric
titration
(C12 with
phenylarsine
£ oxide)
o
DPD titration d
(C12 with Fe2+)-
_o-Tolidine;
colorimetry
o-Tolidine-
-arsenite
(OTA) ;
colorimetry
Stabilized
neutral _o-
tolidine
(SNORT)
b
Determination
TAG
FAC
CAC
TAG
FAC
CAC
TAG
FAC
CAC
TAG
FAC
CAC
FAC
CAC
Common Common
Concentration Interferences
Range
More than 1 Oxidants,
ppm (detec- reductants
tion limit,
40 ppb)
Less than Br2,I2,Cu,
2 ppm Ag, NCI2
cio2
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
Results
of ARS
Study^-
Not tested
Acceptable
for TAG
only
Acceptable
for
FAC and TAG
Not tested
Unaccep-
table for
FAC and TAG
Performed well;
acceptable
for FAC
and TAG
Relative Relative
Standard Error,
Deviation,
23-32 16-23
3.9;
12-42 8-25
4.5;
9-40 4-20
3.0;
31-65 20-42
28-52 14-49
3.7;
8-35 2-13
-------
TABLE A-l (continued)
Method Determination— Common
DPD; color imetry
Leuco crystal
violet ;
colorimetry
Methyl orange;
colorimetry
•%)ata from Bjorklund and 1
Taras,466 Taras e_t al. ,4<
Concentration
Range
FAC 0.1-2 ppb
CAC
FAC 10-2,000 ppb
TAG
FAC 100-2,000 ppb
TAG
38 304
Jand, Lishka and McFarren,
57 and White.514
b
•TTAC = free available chlorine; CAC = combined available
%ef. 304.
Common Results Relative Relative
Interferences of ARS Standard Error,
Study^- Deviation,
% %
Mn — 2.0
3+
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
-312-
-------
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
304
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
-313-
-------
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
-314-
-------
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
514
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
-315-
-------
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
38
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-
370
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
rapid.
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
-316-
-------
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
444
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
470
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.
-317-
-------
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
240
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
-318-
-------
spectrophotometric method for the determination of nitric and hydrochloric
318
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
sample.
The Intersociety Committee for a Manual of Methods of Air Sampling
and Analysis endorses a titrimetric procedure for determining the chloride
471
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
-319-
-------
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-
387
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.
285
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
-320-
-------
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
measurable.
501
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
65
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:
-321-
-------
_ _
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-
-5
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
369
should be mentioned. The determinations of FAC in water and of
297
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
-322-
-------
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
I
Putnam found gas-chromatographic conditions suitable for the determina-
352
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
measurements.
Both chlorine and hydrogen chloride were included in a broad chro.mato-
34
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
364
used. Obermiller and Charlier achieved quantitative separation of a
mixture of hydrogen sulfide, hydrogen chloride, and water at 90 C with. 5%
-323-
-------
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
188
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
406
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
-324-
-------
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
4
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
-325-
-------
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
3
concentrations of 0. 02-5. 6 Lug/m . Similar results for 17 other elements
382
were obtained simultaneously in this study.
-326-
-------
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;•'• American Conference of Governmental Industrial Hygienists. TLVs Threshold
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TECHNICAL REPORT DATA
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2.
LE AND SUBTITLE
CHLORINE AND HYDROGEN CHLORIDE
6. PERFORMING ORGANIZATION CODE
3. RECIPIENT'S ACCESSION'NO.
5. REPORT DATE
April 1976
7. AUTHOR(S)
Subcommittee on Chlorine and Hydrogen Chloride
8. PERFORMING ORGANIZATION REPORT NO.
9. PERFORMING ORGANIZATION NAME AND ADDRESS
National Academy of Sciences
National Research Council
Committee on Medical and Biologic Effects of
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14. SPONSORING AGENCY CODE
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15. SUPPLEMENTARY NOTES
16. ABSTRACT
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.
17.
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Hydrogen chloride
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(c) COSAT1 FIELD GROUP - Field and group assignments are to be taken from the 1965 COSATI Subject Category List. Since the ma-
jority of documents are multidisciplinary in nature, the Primary Field/Group assignment(s) will be specific discipline, area of human
endeavor, or type of physical object. The application(s) will be cross-referenced with secondary Field/Group assignments that will follow
the primary posting(s).
DISTRIBUTION STATEMENT
Denote reusability to the public or limitation for reasons other than security for example "Release Unlimited." Cite any availability to
the public, with address and price.
1 20. SECURITY CLASSIFICATION
DO NOT submit classified reports to the National Technical Information service.
NUMBER OF PAGES
Insert the total number of pages, including this one and unnumbered pages, but exclude distribution list, if any.
PRICE
Insert the price set by the National Technical Information Service or the Government Printing Office, if known.
•m 2220-1 (9-73) (Reverse)
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