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.

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      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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