United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S8-87/034f Feb. 1988
Project Summary
Prevention Reference Manual:
Chemical Specific, Volume 6:
Control of Accidental Releases of
Carbon Tetrachloride (SCAQMD)
D. S. Davis, G. B. DeWolf, and J. D. Quass
The South Coast Air Quality Manage-
ment District (SCAQMD) of California
has been considering a strategy for
reducing the risk of a major accidental
air release of toxic chemicals. The
strategy, which will serve as a guide to
industry and communities, includes
monitoring activities associated with
the storage, handling, and use of certain
chemicals. This manual summarizes
information that will aid in identifying
and controlling carbon-tetrachloride-
associated release hazards specific to
the SCAQMD.
Carbon tetrachloride has an immedi-
ately dangerous to life and health (IDLH)
concentration of 300 ppm, making it a
moderate acute toxic hazard.
To reduce the risk associated with an
accidental release of carbon tetrachlo-
ride, the potential causes of releases
from processes using carbon tetrachlo-
ride in the SCAQMD must be identified.
Such measures include recommenda-
tions on: plant design practices; pre-
vention, protection, and mitigation
technologies; and operation and main-
tenance practices. Conceptual costs of
possible prevention, protection, and
mitigation measures are estimated.
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
The South Coast Air Quality Manage-
ment District (SCAQMD) conducted a
study in 1985 to determine the presence,
quantities, and uses of hazardous chemi-
cals in the SCAQMD, which comprises
Los Angeles, Orange, San Bernandino,
and Riverside Counties. This study cul-
minated in a 1985 report, "South Coast
Air Basin Accidental Toxic Air Emissions
Study," which outlined an overall strategy
for reducing the potential for a major
toxic chemical release.
The strategy involves monitoring in-
dustry activities associated with the
storage, handling, and use of certain
chemicals to minimize the potential for
accidental releases and the consequences
of any releases that might occur.
This volume of the manual discusses
process operations and practices relating
to the prevention of accidental releases
of carbon tetrachloride as it is used in the
SCAQMD.
Carbon tetrachloride is manufactured
commercially by chlorinating carbon
disulfide or hydrocarbons at pyrolytic
temperatures. Its primary current appli-
cations include chlorofluorocarbon pro-
duction, grain fumigation, and use as a
reaction medium. In the SCAQMD, carbon
tetrachloride is used primarily as a
reactant in chlorofluorocarbon manufac-
ture and as a solvent in the chlorination
of paraffins.
Potential Causes of Releases
Carbon tetrachloride can be used safely
in appropriate processing and storage
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equipment; however, there are many
possible sources of a hazardous release.
Large-scale releases could result from
leaks or ruptures of large storage vessels
or from the failure of process machinery
such as pumps. Failures leading to ac-
cidental releases may be caused by pro-
cess, equipment, or operational problems.
Possible process causes of a carbon
tetrachloride release include: (1) backflow
of chlorofluorocarbon process reactants
to a carbon tetrachloride feed tank; (2)
inadequate water removal from carbon
tetrachloride and hydrocarbon feedstock
feed in the chlorofluorocarbon process,
leading to possible corrosion; (3) excessive
feeds in any part of the system, leading to
overfilling or overpressuring of equip-
ment; (4) loss of condenser cooling to
distillation units; and (5) overheating in
reactors or distillation units.
A carbon tetrachloride release can also
be caused by: the failure of vessels at
normal operating conditions brought on
by excessive stress, corrosion, or external
loadings; mechanical fatigue and shock
in any equipment; or thermal fatigue and
shock in reaction vessels, heat ex-
changers, and distillation columns. Brittle
fracture of equipment can occur, as well
as creep failure in high temperature
equipment subjected to extreme opera-
tional upsets.
Operational causes of accidental re-
leases result from incorrect procedures
and human error, including overfilled
vessels, improper process system opera-
tion, errors in loading and unloading,
inadequate maintenance (especially of
water removal units and pressure relief
systems), and lack of inspection and
nondestructive testing of vessels and
piping to detect corrosion weakening.
Hazard Prevention and Control
Prevention of accidental releases of
carbon tetrachloride relies on the proper
design, construction, and operation of
facilities where the chemical is stored
and used and on the protective systems
that guard against accidental release.
The most important process design
considerations are preventing moisture
from entering the process and preventing
the overheating of systems containing
carbon tetrachloride. Wide temperature
fluctuations can significantly decrease
the life span of construction materials.
Monitoring of the moisture content will
prevent the decomposition of carbon
tetrachloride and the formation of highly
corrosive hydrogen chloride.
Equipment used in carbon tetrachloride
service must be constructed of materials
chosen to minimize the possible de-
composition of carbon tetrachloride. When
dry, carbon tetrachloride can be stored in
contact with many metal surfaces, but it
does react, sometimes explosively, with
aluminum and its alloys. Nickel and
nickel-copper alloys are used at critical
points of processing plants to minimize
and control thermal decomposition of
carbon tetrachloride.
Pressure vessels (including storage
tanks, tank trucks, and rail cars) are
usually protected by pressure relief valves
and/or rupture disks. Relief piping must
be sized for adequate flow. To avoid direct
discharge to the environment, an overflow
tank might be provided for overpressurized
liquid. Carbon tetrachloride pipework
design must also reflect the pressure,
temperature, and corrosion concerns
associated with the chemical. As with
other hazardous chemicals, the number
of pipe joints and connections should be
minimized. Valve placement should en-
sure isolation of leaking pipes and
equipment.
Siting and layout facilities and equip-
ment should be designed to reduce per-
sonnel exposure to a possible carbon
tetrachloride release. There should be a
good distance between large inventories
and sensitive receptors and ready ingress
and egress in the event of an emergency.
Vehicular traffic near carbon tetrachloride
process or storage areas should be kept
to a minimum, and carbon tetrachloride
piping should not be located adjacent to
other piping that is under pressure or
that carries flammable materials. Storage
facilities should be segregated from the
main process if possible. Carbon tetra-
chloride equipment, piping, and vessels
should be protected from heat sources,
and storage should be located away from
control rooms, offices, utilities, and
laboratory areas.
Storage vessel shutoff valves should
be easily accessible. Containment for
liquid storage tanks can be provided by
diking. When possible, the carbon tetra-
chloride should be transferred using fixed
rigid piping. Vapor balance systems con-
sisting of a pipeline between the vapor
spaces of an unloading vessel and a
carbon tetrachloride storage tank can be
used to create a closed system that
minimizes releases of carbon tetrachloride
vapor.
Three protection technologies for con-
taining and/or neutralizing releases of
carbon tetrachloride are enclosures, vapor
recovery systems, and incinerators. En-
closures, which can provide secondary
containment of a released chemical,
should be equipped with continuous
monitoring equipment and alarms. An
enclosure for carbon tetrachloride could
be a building or bunker constructed of
concrete blocks or sheets. It should be
gastight and have a ventilation system to
draw air in when the building is vented to
a vapor recovery or incinerator system.
Vapor recovery systems recover toxic
materials from process streams. Carbon
tetrachloride discharges are commonly
sent to a refrigerated vapor recovery unit
or to a carbon absorption unit.
Incineration, another method of de-
stroying toxic vapor from process streams,
can be used to control releases from
vents and pressure relief discharges from
process equipment or from secondary
containment enclosures.
Mitigation techniques are those that
reduce the consequences of an accidental
release of a hazardous chemical. Such
measures include physical barriers, water
sprays and fogs, and foams where ap-
propriate. These techniques can divert,
limit, or disperse the chemical that has
been spilled or released into the atmo-
sphere to reduce the concentration and
the area affected by the chemical.
Secondary containment systems (e.g.,
impounding basins, dikes, and flotation
devices and foams) reduce the evaporation
rate of a spilled chemical.
Since accidental releases of toxic
materials result not only from design
deficiencies but also from operational
deficiencies, safe operation of plants using
carbon tetrachloride requires competent
and experienced managers and staff.
Proper maintenance and modification
programs should be incorporated into
plant design and operation to prevent
possible hazardous releases of the
chemical.
-------
D. S. Davis. G. B. DeWolf, andJ. D. Quass 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 6: Control of Accidental Releases of Carbon Tetrachloride (SCAQMD),"
(Order No. PB 87-234 514/AS; Cost: $13.95, 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 Project Officer can be contacted at:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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