United States
                  Environmental Protection
                  Agency     	
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
                  Research and Development
EPA/600/S8-87/034m Sept. 1989
&EPA         Project  Summary
                   Prevention  Reference Manual:
                   Chemical Specific, Volume 13:
                   Control of Accidental
                   Releases of Methyl  Isocyanate

                   D. S. Davis, G. B. DeWolf, R. A. Nash, J. D. Quass, and J. S. Stelling
                    Interest In reducing the probability
                  and consequences of accidental tox-
                  ic chemical releases that might harm
                  workers within a process facility and
                  people in the surrounding community
                  has prompted  preparation  of  this
                  manual and a series of companion
                  manuals on the control of accidental
                  releases of toxic chemicals.  The
                  manual on methyl isocyanate (MIC) is
                  one of several chemical-specific pre-
                  vention reference manuals. This man-
                  ual  summarizes  Information  to  help
                  regulators  and  Industry personnel
                  identify and control release  hazards
                  associated with MIC.
                    To reduce the  risk associated with
                  an accidental release  of MIC, the
                  potential causes  of accidental releas-
                  es in process facilities that handle
                  and store MIC must be identified. The
                  MIC manual provides examples of
                  such causes, as  well as of measures
                  that may be taken to reduce the acci-
                  dental  release risk. Such measures
                  include recommendations on  plant
                  design; prevention, protection,  and
                  mitigation technologies; and opera-
                  tion and maintenance practices.
                    This  Project Summary was devel-
                  oped by EPA's Air and  Energy Engi-
                  neering Research Laboratory,  Re-
                  search Triangle Park, NC, to announce
                  key  findings of the research project
                  that Is fully documented In a separate
                  report of the same title (see Project
                  Report ordering information at back).
Introduction
  Increasing  concern about  the
potentially disastrous consequences of
accidental releases of toxic chemicals
resulted from the accident in  Bhopal,
India, in  1984, that killed approximately
2,300  people and injured 30,000 to
40,000 more. A  toxic cloud of methyl
isocyanate (MIC) was released from  a
storage tank at a Union Carbide of India
pesticide  plant.  In another incident in
New York in 1984, a pump failure at FMC
Corporation led to the release of 45 gal.
(170 L) of MIC. Nearby areas, including a
school, had to be evacuated. Nine  chil-
dren and  two adults were treated for eye
irritation at a local hospital. Such acci-
dents have increased interest in reducing
the probability of accidental releases and
prompted preparation of a series of
manuals  for regulators  and  industry
personnel on the prevention of accidental
releases of toxic chemicals. The manual
on is one of several chemical-specific
manuals that address issues associated
with the storage, handling, and process
operations involving toxic chemicals as
they are used in the U.S.

  MIC is  a small volume chemical. Total
production in 1994 was estimated to be
30-35 x 106 Ib  (14-16 x 1Q6 kg). Over
95% of MIC produced is used to man-
ufacture pesticides and herbicides. Since
the Bhopal release  and tightening of
transportation regulations,  MIC is  no
longer shipped by rail car or in drums.

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  MIC, which is primarily made from the
reaction of methylamine and phosgene is
an  intermediate  in the  manufacture  of
pesticides  such  as  carbaryl  (Sevin),
aldicarb (Tenik),  carbofuran  (Furadan),
and methamyl (Lannate).
Potential Causes of Releases
  MIC is  a  highly  volatile  liquid at
ambient conditions. It is a colorless liquid
with a  sharp odor  at  concentrations
greater than 2 ppm. Liquid MIC is slightly
less dense than water. Since the gaseous
form is twice  as dense as air, it tends to
stay close to the ground if released in still
air.  It is highly flammable  and reactive,
particularly  with  compounds  containing
active hydrogen atoms.   Since it is an
unstable compound, extreme care should
be  taken to avoid conditions that could
result in fires, explosions,  and runaway
reactions.  MIC is usually stored  and
handled  in  dedicated  stainless steel,
nickel, and  glass-lined equipment. Other
materials could catalyze  an undesirable
reaction that  might lead  to overpressure
releases.  In  some  cases,   the  heat
generated  by a water/MIC reaction is
sufficient to  initiate  self-polymerization.
Tanks and reactors should not be filled to
capacity to allow for possible  expansion
of the contents. Because MIC might react
with water  vapor in  air, tank contents
should be protected by a blanket of dry
nitrogen. Also, MIC can react with itself in
the presence of a catalyst to  form
trimethyl isocyanate. This reaction is also
exothermic  and could result in a violent
runaway reaction.
  The two basic causes  of MIC releases
are: uncontrolled chemical reactions, and
spills and/or leaks that may occur during
normal operation  such as routine
maintenance  and cleaning of equipment.
Uncontrolled  chemical reactions  of MIC,
such as the one in Bhopal, are extremely
dangerous. While the quantities  of  MIC
likely  to be spilled or leaked are not as
great  as those released  because of an
uncontrolled  chemical  reaction,  the
probability of spills and leaks occurring is
much higher. Most of such MIC releases
in the U.S. were the result of equipment
failure. Failures leading to accidental MIC
releases can be due to  process, equip-
ment, or operational problems.
  Process causes are related to  the fun-
damentals of process chemistry, control,
and general operation.  Possible  process
causes include:
• Contamination of  MIC with  rust from
  the nitrogen supply line, resulting in a
  runaway reaction;
• Contamination of MIC with a backflow
  of caustic solution  from a  scrubber,
  resulting in a runaway reaction;
• Contamination of MIC with brine used
  as a cooling  fluid, resulting in  a run-
  away reaction;
• Insufficient temperature  and  pressure
  monitoring equipment to  detect  pro-
  cess upsets or failure of instruments;
• Improper  design of control devices
  (flare,  scrubber)  to neutralize  MIC
  emissions caused by process upsets or
  failure of control systems; and
• Insufficient cooling capacity to  control
  MIC  storage  temperature  or failure of
  cooling system.
  Equipment causes of accidental  releas-
es result from hardware failure such as:
• Improper  materials of   construction
  operating  as  catalysts  of highly  exo-
  thermic reactions;
• Improper materials of construction that
  dissolve in MIC;
• Failure of equipment, and  no backup
  system;
• Excessive mechanical stress because
  of improper fabrication, construction, or
  installation; and
• Mechanical fatigue.
  Operational  causes of accidental
releases  result  from  incorrect operating
and maintenance procedures  or  human
errors,  including overfilling  of storage
vessels,  neglecting  to purge process
lines with nitrogen before making repairs,
incomplete disaster  plans, and  inade-
quate maintenance in general.


Release Prevention and Control
  To develop a thorough release preven-
tion plan, control must be  maintained
over the following areas:
• Process design;
• Physical plant design;
• Protective systems; and
• Operating and maintenance practices.
  Process  design  involves the  basic
chemistry of a  process  and how this
chemistry is affected by the variables of
flow, pressure, temperature, and compo-
sition.  The first concern  in process
design is understanding  how deviations
from expected  conditions  could result in
an  accidental  release. Any aspect of a
process may be modified to enhance the
integrity of the  system. For example, the
quantities of materials used, the pressure
and temperature conditions, the type and
sequence  of  unit  operations, contro
strategies, and the instrumentation used.
  After the Bhopal release, for example, c
joint Federal/State Task Force investigat
ed the potential for a MIC release at the
Institute, West Virginia, MIC unit.  The
major  areas  measured for this  stud)
were:
• Whether the process design preventec
  the likelihood of MIC concentration;
• Whether there was sufficient cooling o
  MIC in process  vessels;
• Whether MIC inventory was minimized
  and
• Whether sufficient instrumentation ant
  monitoring  were  provided for  earh
  detection of  possible process upsets.
  Physical  plant  design involve;
equipment,  siting  and  layout,  am
transfer/transport  facilities.  Because o
the extreme reactivity of MIC it shouk
always  be  handled  and  stored  in i
protective  environment.  Many metals
such as carbon steel, iron, tin, and  alumi
num, are commonly used by the  chem
ical industry, but  could  act to catalyze
dangerously rapid trimerization  of MIC
UCAPCO  (formally  Union  Carbide)  re
commends storing and handling MIC onl
in  stainless steel, types 304 and  316
nickel;  and glass-lined equipment.  Glass
lined steel should be free of pinholes.
  Of  the  four  companies  current!
producing  MIC in the U.S., DuPont an
Sandoz in Texas  consume  MIC a
quickly  as  it is produced, making  layoi
of the  site less critical.  The use c
underground storage tanks  at UCAPO
was considered in the Task  Force stud
and found to  be adequate  with existin
controls.  The  siting and   layout  of
particular MIC facility is complex, requi
ing careful  consideration of factors ir
eluding: other processes in  the vicinit
the proximity  of population  centers, pr<
vailing  winds, local terrain, and the potei
tial for flooding and other natural event
Generally,  large  inventories  of  Ml
should be kept away from sources of fii
or explosion.  Vehicular traffic near  Ml
process or storage  facilities  should t
minimized.  MIC  piping should  not t
located adjacent  to other  piping  undi
high pressure or  temperature or  th
carries flammable  materials.  Storac
facilities should  be segregated  from tf
main process.  During  an  emergenc
there should be multiple means of acce:
for emergency crews. Since all bulk shii
ments   of  MIC in the  U.S. have  be<
eliminated,  loading  and  unloadir
facilities are no longer potential accide
areas.

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  Protection technologies for the  con-
 ainment  and  neutralization  of  MIC
 iclude enclosures, scrubbers, flares, and
other  secondary  control  systems. En-
closures are containment  structures that
capture any MIC  spilled  or vented  from
storage or process equipment,  thereby
preventing  immediate discharge  of the
chemical  to the environment.  Enclosures
contain the spilled liquid  or gas until  it
can be transferred to  other containment,
discharged at a controlled rate, or trans-
ferred at a controlled rate to scrubbers for
neutralization. UCAPCO has  an  under-
ground enclosure capable of  collecting
42,000 gal. (159,000 L).
  Scrubbers can be used  to control MIC
released  from process vents and pres-
sure relief  discharges from storage and
process  equipment,  Because  of its
extreme reactivity with caustics,  MIC is
destroyed  rather than  absorbed by  a
scrubber. Scrubbers used to control  MIC
emissions are designed to convert  any
emissions associated with the processing
of MIC and to neutralize  MIC emissions
in case of a catastrophic release.
  Flares are routinely used in the chem-
ical processes to dispose of intermittent
or emergency emissions of flammable
waste gases. Flares used to control  MIC
emissions serve  as  a secondary or back-
up control; they should  be designed to
operate effectively during the course  of a
worst-case  event such  as the  failure of
the primary control device (scrubber).
  Other control  techniques currently in
service for  reducing possible releases of
MIC include carbon adsorption and vapor
incineration.
  If an accidental release occurs, mitiga-
tion technologies can reduce the conse-
quences. Such  measures include phys-
ical  barriers,  water sprays  and steam
curtains, activated carbon for liquid spills,
and  evacuation.  The purpose of  a
mitigation  technique  is to divert, limit, or
disperse the spilled or released chemical.
  Since accidental  releases  of toxic
materials result not only from inadequate
process design or equipment failure, but
also  from  deficiencies in  operation  and
maintenance, the safe operation of plants
processing MIC requires competent  and
experienced  managers end  staff. Em-
ployees should  be  fully trained  in  the
important  aspects of handling MIC, in
potential hazards,  and  in  cleanup  and
emergency  procedures.  Well-defined
procedures can  decrease  the possibility
of a hazardous  release and  reduce the
magnitude of any release that occurs.

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D. S.  Daws, G. B.  DeWolf, R. A. Nash, J.  D.  Quass, and J.  S. Stalling are with
  Radian Corp., Austin, TX 78766.
T. Kelly Janes is the EPA Project Officer (see below).
The complete report, entitled "Prevention Reference Manual: Chemical Specific,
  Volume 13: Control of Accidental Releases of Methyl Isocyanate," (Order No. PB
  89-1161 483/AS; Cost: $15.95, 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
Official Business
Penalty for Private Use $300

EPA/600/S8-87/034m
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