United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034b Sept. 1987
<&ERA Project Summary
Prevention Reference Manual:
Chemical Specific, Volume 2:
Control of Accidental Releases of
Chlorine (SCAQMD)
D. S. Davis, G. B. DeWolf, J. D. Quass, and K. P. Wert
The South Coast Air Quality Manage-
ment District (SCAQMD) of southern
California is developing a strategy for
reducing the risk of a major accidental
air release of toxic chemicals. The
strategy, aimed at guiding industry and
communities, includes monitoring
activities associated with the storage,
handling, and use of certain chemicals.
Its purpose is to aid in identifying and
controlling release hazards associated
with certain toxic chemicals. This
manual presents information on the uses
and hazards of chlorine specific to the
SCAQMD.
Chlorine is a highly reactive and cor-
rosive liquid that boils at room tem-
perature. It has an IDLH (immediately
dangerous to life and health) concentra-
tion of 25 ppm, making it an acute
toxic hazard. Examples of potential
causes of accidental releases of chlorine
are identified, and specific measures
that can be taken to reduce the risk of
such releases are listed. Such measures
involve design practices; prevention,
protection, and mitigation technologies;
and operation and maintenance prac-
tices. Conceptual cost estimates of
these measures applied to some example
systems are also provided.
This Project Summary was developed
by EPA's Air and Energy Engineering
Research Laboratory, Research Triangle
Park, NC, to announce key findings of
the research project that Is fully docu-
mented In a separate report of the same
title (see Project Report ordering In-
formation at back).
Introduction
In 1985, the South Coast Air Quality
Management District (SCAQMD) con-
ducted a study to determine the presence,
quantities, and uses of hazardous chemi-
cals in the SCAQMD, which comprises
Los Angeles, Orange, San Bernardino,
and Riverside Counties. The study re-
sulted in a report, "South Coast Air Basin
Accidental Toxic Air Emissions Study,"
outlining an overall strategy for reducing
the potential for a major toxic chemical
release incident. The strategy includes
monitoring industry activities associated
with the storage, handling, and use of
certain chemicals in the SCAQMD and
obtaining technical information that will
guide industry and communities in re-
ducing the potential for accidental re-
leases and the consequences of any
releases that occur. This manual provides
some technical information on the pre-
vention of accidental releases of chlorine
as it is used in the SCAQMD.
Chlorine is a major commodity chemical
in industry. The major industrial uses of
chlorine in the SCAQMD include chemical
synthesis of chlorinated chemicals, and
disinfection of drinking water and waste-
water. Other uses include cooling tower
water treatment, bleach manufacture,
chemical synthesis, and repackaging.
Though chlorine is not manufactured in
the SCAQMD, its uses there require the
storage of large quantities of the chemical.
In the SCAQMD, chlorine is stored in
small cylinders, 1 -ton cylinders, railroad
tank cars, and bulk storage tanks.
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Another concern is the backflow of "
material into a storage vessel. When
chlorine is being mixed with a liquid, it is
possible for the liquid to be drawn back
into the chlorine container. Such backflow
can be prevented by a vacuum-breaking
device, or a barometric leg, check valves,
and positive-displacement pumps.
A chief concern in liquid chlorine pipe
domes and valves is overpressure caused
by thermal expansion of the chlorine, or
pressure pulses caused by rapid valve
closure. These pressures can rupture
pipes. An expansion chamber, consisting
of a rupture disc and a receiver chamber,
can be installed to prevent thermal ex-
pansion ruptures. Pressure pulses can be
avoided by selecting valves that do not
close abruptly. Ball and plug valves should
be designed so that excess pressure in
the body cavity will relieve spontaneously
toward the high pressure side. Pipes,
valves, and process machinery such as
pumps and compressors must be con-
structed of materials resistant to chlorine
at operating temperatures and pressures.
Facilities and equipment should be sited
to minimize personnel exposure in the
event of a release. Large inventories of
chlorine should be kept away from
sources of fire or explosion hazard. If
possible, chlorine piping should not be
located next to other piping under high
pressure or temperature. Storage facilities
should be segregated from the main
process and away from control rooms,
offices, utilities, and laboratories.
Protection technologies for facilities
that use or manufacture chlorine include
enclosures and scrubbers. While enclo-
sures for secondary containment of
chlorine spills or releases do not seem to
be widely used, they can be considered
for areas near especially sensitive re-
ceptors. Enclosures capture and contain
any chlorine spilled or vented from storage
or process equipment, preventing im-
mediate discharge of the chemical to the
environment. If enclosures are used, they
should be equipped with continuous
monitoring equipment and alarms. For
chlorine, concrete block or concrete sheet
buildings or bunkers are most suitable.
Scrubbers, which absorb toxic gases
from process streams, can be used to
control chlorine releases from vents and
pressure relief discharges from storage
equipment, process equipment, or secon-
dary containment enclosures. Spray
towers, packed bed scrubbers, and ven-
turis are appropriate for chlorine dis-
charges. An alkaline solution is needed
to achieve effective absorption because
Potential Causes of Releases
Potential chlorine releases may be in
the form of either liquid or vapor. Liquid
spills can occur when chlorine is released
at or below its boiling point of -34°C
(29.3°F), or when a sudden release of
chlorine at temperatures above -34°C
results in vapor flashing. Direct releases
of vapor gas can also occur.
Chlorine is frequently stored in 68 kg
(150-lb) cylinders and 1-ton containers.
These containers are equipped with
fusible plugs as a form of pressure relief.
Although fire is not the most frequent
hazard, it may be the most serious, since
fire can melt the fusible plug of a con-
tainer at 70°C (158°F), allowing most of
the chlorine in the container to escape.
Defective fusible plugs have also failed to
melt, allowing a fire to rupture the con-
tainer. Corrosion or poor bonding between
the lead alloy plug and the plug retainer
allows moisture to accumulate, causing
corrosion at the connection and leading
to the chlorine leak. One frequent cause
of chlorine emissions is failure of the
copper tubes commonly used to connect
cylinders and 1 -ton containers to process
equipment.
Possible process causes of a chlorine
release include:
• Excessively high chlorine feed rate
to a bleach reactor leading to exces-
sive exothermic reaction, combined
with failure of the cooling system;
• Backflow of chlorination water to a
chlorine cylinder;
• Loss of agitation in batch reactor
systems;
• Excess chlorine feed leading to over-
filling or overpressuring equipment;
• Photo-lamp failure in photochemical
reactor; and
• Overpressure of a chlorine storage
vessel caused by overheating from
reactions.
Equipment causes of accidental re-
leases result from hardware failures such
as excessive stress caused by improper
construction or installation, mechanical
fatigue and shock, thermal fatigue and
shock in bleach reactors, brittle fracture
(especially in carbon steel equipment),
creep failure in equipment subjected to
extreme operational upsets, and corrosion.
Operational causes of accidental
chlorine releases involve incorrect oper-
ating or maintenance procedures, or
operator error. Examples are overfilled
storage tanks, errors in loading and un-
loading procedures, inadequate main-
tenance, and lack of inspection and non-
destructive testing of vessels and piping
to detect corrosion weakening.
Hazard Prevention and Control
The prevention of accidental releases
relies on a combination of technological,
administrative, and operational practices
applied to the design, construction, and
operation of facilities where chlorine is
stored and used.
The most important process design
considerations are aimed at preventing
overheating and overpressuring systems
containing chlorine. Temperature moni-
toring is important, not only because of
potential overpressure or equipment
weakening caused by overheating, but
also because chlorine can react with
many metals above a certain activation
temperature. Chlorine can also cool itself
while off-gasing and potentially reach
temperatures below the safe operating
range of some metals.
Physical plant design considerations
include equipment, siting and layout, and
transfer/transport facilities. Equipment
construction materials must be chosen to
prevent deterioration or product con-
tamination. Steel, cast iron, wrought iron,
copper alloys, nickel alloys, some varieties
of stainless steel, and lead are common
construction materials in chlorine pro-
cesses. On vessels, relief devices provide
overpressure protection against cata-
strophic rupture or explosion by allowing
a controlled release of the overpressured
contents. Vessels larger than cylinders or
1-ton containers are usually equipped
with pressure relief valves and rupture
disks. Even with these devices, however,
a catastrophic sudden release could oc-
cur. Further protection can be gained if
the relief device is routed to a caustic
scrubber.
Overfilling can be prevented by using
level sensing devices, pressure relief
devices, and adequately trained person-
nel. Relief devices for chlorine overfilling
may be the same as or similar to those
used for gas pressure relief.
According to guidelines developed by
the Chlorine Institute, chlorine tanks,
usually constructed of normalized carbon
steel, should be designed to accept a tank
car dome assembly. In addition to venting
provisions, containers should have valve
arrangements that allow the vessel to be
isolated from the process to which the
chlorine is being fed. As a protection
against corrosion, moisture must be ex-
cluded from the tank, and it should not be
situated in standing water or exposed to
moist air.
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absorption rates with water atone would
require unreasonably high liquid-to-gas
ratios. In an emergency, however, water
scrubbing could be used in a makeshift
scrubber if an alkaline solution were not
available.
If a chlorine release occurs in spite of
all precautions, the consequences of the
release may be reduced by employing
mitigation measures such as physical
barriers, water sprays, fogs, and foams,
where applicable. The purpose of a
mitigation technique is to divert, limit, or
disperse the chemical that has been
spilled or released to the atmosphere.
The choice of a mitigation technology for
a particular chemical depends on that
chemical's specific properties (flam-
mability, toxicity, reactivity), as well as its
dispersion characteristics in the atmo-
sphere. Secondary containment systems,
such as impounding basins and dikes,
reduce the evaporation rate of a released
liquified gas, as do flotation devices and
foams. However, even when measures
such as these are employed after a
chlorine release, a hazardous vapor cloud
will probably form. The primary means of
dispersing as well as removing chlorine
from the air is with water sprays or fogs.
The effectivensss of water sprays depends
on wind direction, on the distance of the
nozzles from the point of release, on the
fog pattern, and on nozzle capacity, pres-
sure, and rotation. If the right strategy is
followed, a "capture zone" can be created
downwind of the release into which the
chlorine vapor will drift and be partially
absorbed. In some cases, it may be possible
to use fans and blowers to disperse a vapor
cloud.
Operation and maintenance practices
that can reduce the probability of a large
chlorine release include training em-
ployees in proper handling and storage
procedures. To prevent corrosion, chlorine
should be analyzed for water several
times a week, and pH readings of cooling
water and condensate can be taken
several times a day to detect internal
leaks.
D. S. Davis, G. B. DeWolf, J. D. Quass. and K. P. Wert are with Radian
Corporation, Austin, TX 78766.
T. Kelly Janes is the EPA Project Officer (see below).
The complete report, entitled "Prevention Reference Manual: Chemical
Specific—Volume 2: Control of Accidental Releases of Chlorine (SCAQMDj,"
(Order No. PB 87-227 054/AS; Cost: $18.95, subject to change) will be
available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
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United States
Environmental Protection
Agency
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