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TEXT FOR SLIDES
SEMINAR ON THE BHOPAL DISASTER: A CASE HISTORY
Prepared by
Ronald J. Willey
Department of Chemical Engineering
Northeastern University
©AICHE NEW YORK, NEW YORK 1998, 2009
Abbreviations and Nomenclature:
BP Boiling Point
LC50 Lethal Concentration at which 50% of the population dies
LFL Lower flammable limit
MIC Methyl isocyanate
ppm parts per million (volume)
PVH Process vent header
RVVH Relief valve vent header
VGS Vent-gas scrubber system
Introduction:
This slide package is a summation of events that led to and concluded
with one of the most significant toxic releases that has occurred to date within the
chemical process industry. It is intended for the education of chemical engineering
students, and focuses on the chemical processes involved. It is best used in a course
devoted to process safety; however, it can be used in courses dealing with kinetics and
runaway reactions, or courses related to mass transfer and dispersion modeling.
The material sources were numerous and a partial listing of articles that
have appeared about the incident are given in the appendix. A major source for
technical descriptions of the accident came from a paper prepared by Ashok Kalelkar
of Arthur D. Little Inc. under contract to Union Carbide.
Chemical Engineering News has devoted numerous articles to the
incident including the February 11, 1985, December 2, 1985, and December 19, 1994
issues. These articles served as major references to the crisis and several portions of
this module are extracted from these sources. Also, Dr. Paul Shrivastava’s book
Bhopal: Anatomy of a Crisis 2nd Ed. 1992 published by Paul Chapman Publishing
Ltd, London, and Frank P. Lees’ case history section in Loss Prevention in the Process
Industries: Hazard Identification, 2nd Ed. 1993 published by Butterworth-Heinemann,
Oxford, England, served as other significant references for this case history.
Slide 2. The incident
At about 12:45 A.M. on Monday, December 3, 1984, an event occurred in Bhopal, India, that changed the way chemical process safety is practiced throughout the world. On that morning, 41 metric tons of a toxic gas, mainly consisting of methyl isocyanate, entered into the atmosphere from a Union Carbide India Limited (UCIL) pesticide plant. The release traveled with the prevailing wind into heavily populated areas located near the plant. Although accurate figures reflecting deaths and injuries do not exist, it is known that more than 1,000 people were killed and thousands more were injured or affected. Panic prevailed in the city of 900,000 inhabitants.1 In terms of loss of life, this is the largest chemical plant disaster recorded to date.
A personal account is provided by Mr. Rajat Vaish age 10 at the time.2 “These people that were running through the streets were some of the people that actually made it past their sleep... many people never woke up.” Mr. Vaish was at his uncle’s house at the time of the accident. When the warning went off, Mr. Vaish fled. His uncle, for some reason, stayed. His uncle became sickened and later passed away.
Image drawn by Daniel Willey, Sept 2009, all rights reserved.
1. NY Times, 8 Dec 1984 p 7.
2. As presented by a friend, Ms. Kokila Katyal, in a Professional Practice course, Univ. Pitts, 1998.
Slide 3. A trigger question for the information that follows.
Slide 4. Location
The disaster begins in the center of India in a region called
Madhya Pradesh. Bhopal was established by a Hindu king named Raja Bhoj
around 1010 A.D. In the early 1700’s, Rani (Queen) Kamlavati ruled Bhopal
under the protection of the emperor of India. After the emperor’s death, she
invited Dost Mohammed Khan, a Muslim chieftain, to be the territory’s
protector. After her death Dost Mohammed Khan annexed Bhopal to be his
own kingdom -- thus a change in rulers from Hindus to Muslim occurred. In
1956, Bhopal was named the capital of the state of Madhya Pradesh. The city
grew rapidly during the 60's to 80’s (and it continues to grow today). The
population in 1961 was 102,000. By 1981 the population had increased to
895,815.3 Much of this growth came by migration from rural areas
surrounding Bhopal. City housing could not be afforded by many of these
migrants, and they thus became squatters, creating slums and shantytowns.
By 1984, Bhopal had 156 slum colonies.4
3. 1981 Census cited in the NY Times 22 Dec 1984 p 4.
4. P. Shrivastava, “Bhopal Anatomy of a Crisis,” 2nd Edition, Paul Chapman
Publishing Ltd. London, 1992, pp 48 to 49.
Slide 5 Slum locations - Jaya Prakash Nagar and Kenchi Chola
Two slums were located very near the Union Carbide chemical
plant in an area not zoned for residential use. The huts were small, constructed
of mud walls and tin roofs. No water or sewage facilities existed. The
residents were illiterate. They consisted of very poor people who had migrated
from rural areas surrounding Bhopal several years earlier. Often these slums
were controlled by illegal landlords who exploited residents for protection.
The Union Carbide fence line is shown in the upper right hand quadrant of the
above figure.
Slide 6. Photograph of Bhopal
Bhopal was a developing city. At the time of the accident, only
10,000 phone lines existed for a city of nearly 900,000 residents. Four major
hospitals existed with 1,800 beds and 300 doctors. Electricity supply was
sporadic. Even with these shortcomings, the city offered more than most
towns and cities in Madhya Pradesh. The Indian and local governments had a
strong desire to industrialize cities like Bhopal.
Photograph by R.J.Willey, Photograph taken Dec 2004, all rights reserved.
Slide 7. Union Carbide Corporation Interest
The Union Carbide plant located in Bhopal was owned by
Union Carbide (India) Ltd. Union Carbide Corporation held 50.9% of the
shares of the UCIL.5 The remaining shares were held among 24,000
shareholders, including the government of India, which owned approximately
25% of the UCIL shares. The largest division of UCIL was the Battery
Product Division accounting for about 60% of the 1983 sales. The
Agricultural Products Division of UCIL controlled the Bhopal plant, which
manufactured agricultural products including fungicides, miticides, herbicides,
and insecticides. Just over 8% of the sales of UCIL came from this plant.
5. NY Times 8 Dec 1984 p 1.
Slide 8. History of the Bhopal UCIL plant
UCIL entered the pesticide market in the early 1960’s. The
Agricultural Products Division began operating the Bhopal plant in 1969. The
manufacturing facility was located 2 miles north of the Bhopal railway station.
Initially, the plant was used only for formulation blending of pesticides. In
1974, UCIL was granted permission to manufacture pesticides and gradually
the plant was “backward integrated” so that by 19786 methyl isocyanate (MIC)
production began at the plant. In order to conserve foreign exchange and
promote the local pesticide market, the Indian government required the facility
to be “backward integrated,” which forced the manufacture of all intermediate
chemicals, such as MIC and phosgene, on site, rather than importing the raw
materials. The plant had a capacity of 5,250 metric tons per year of MIC.
[Photograph reprinted with permission from Chem. Eng. News, January 4,
1988, 66
(6), p 8. Copyright 1988 American Chemical Society]
6. Lees, A 5/2.
Slide 9. Plant siting
When the UCIL plant was originally built in the late 1960’s, it
was situated in an industrial area 2 miles north of the main railway station that
served Bhopal. At that time no residential areas were close by. As the plant
“backward integrated,” municipal authorities in Bhopal objected to the
continued use of the UCIL plant at its original location. 7 The city’s
development plan had designated the plant site for commercial or light
industrial use, but not for hazardous industries. The local authorities were
overruled by central and state authorities. As time continued, tens of
thousands of people migrated to Bhopal from rural areas. Housing in the city
was insufficient. As shantytowns developed near the UCIL plant property,
UCIL drew the government’s attention to them and requested that a
“greenbelt” be established around the plant, but to no avail. Instead, the
government granted ownership rights in the land to the occupants. Map
captured from Google Maps, searching on “India” August 31, 2009, © 2009
Google –Map data © 2009 Europa Technologies.
7. P. Shrivastava, p 35. Originally referenced from Town and Country
Planning Department, Bhopal Development Plan (Bhopal Municipal
Corporation, 1975)
Slide 10. Chemical production at the plant
The UCIL plant manufactured Sevin®, a Union Carbide trade name for a
pesticide, whose active ingredient is 1-napthyl-N-methylcarbamate8 or the
generic name carbaryl. The reaction involved two reactants, methyl
isocyanate and alpha naphthol:
8. C&EN 11 Feb 1985 pp 30-31.
Slide 11. Another trigger question for the slides that follow.
Slide 12. Methyl isocyanate (MIC): an extreme toxin
“Methyl isocyanate (MIC) is reactive, toxic, volatile, and flammable.” So begins the first page of the Union Carbide pamphlet.9 Let us first focus on the toxic effects. The maximum exposure during an 8 hour period is 0.02 ppm (20 parts per billion). This level is called the TLV (threshold limit value)-TWA (time weighted average). By comparison, phosgene, another extremely toxic gas, is 0.1 ppm.10
Individuals begin to experience severe irritation of the nose and throat at exposures of MIC above 21 ppm. The LC50 for rats exposed for 4 hours is 5 ppm.11 LC50 is the lethal concentration in which 50% of the population dies when exposed at this level.
In humans, exposure to high concentrations can cause enough fluid accumulation in the lungs to cause drowning.12 At lower levels of exposure, the gas affects the eyes and lungs. It acts as a corrosive agent, eating away at moist vulnerable tissue, such as mucous membranes and eye surfaces. Because the MIC is soluble in water and degrades rapidly, acute effects are short term.13
Long term effects do exist. Although no accurate figures exist, it is generally believed that, of the many thousands of people exposed, a significant number suffered permanent injuries. 14
9. C&EN 11 Feb 1985, p 27 as quoted from a Union Carbide pamphlet on MIC.
10. C&EN 11 Feb 1985 p 38.
11. NY Times 4 Dec 1984 p A8.
12. Ibid
13. NY Times 15 Dec 1984 p 4.
14. C&EN 19 Dec 1994 p. 12.
Slide 13. Other critical physical properties of MIC (BP & density as a vapor)
Methyl isocyanate has a boiling point of 39.1C and a vapor pressure of 348
mm Hg at 20C. As such, it is quite volatile and it will easily enter into the
surroundings at very high concentrations. Its molecular weight is 57. Thus, it
has a molecular weight about 2 times that of air and as a vapor, it will have a
higher density compared to air. It will tend to travel along the ground and
lower areas as a vapor when initially released into the atmosphere. However,
dilute mixtures in air will follow the predominant flow pattern of air. Dilute
mixtures still can be very toxic as this case proves.
Slide 14. Reactivity of Methyl isocyanate -- the adjacent double bond system.
Methyl isocyanate, which is of the isocyanate family, is a very reactive
molecule because of the cumulative unsaturation system of R-N=C=O where
the effect of the adjacent double bonds adds to the instability of the
molecule.15.
15. C&EN 11 Feb 1985 p 27.
Slide 15. The potential products of MIC reaction in the presence of water or a
catalyst
In the presence of small amounts of water, MIC reacts to form 1,3,5 trimethyl
biuret and CO2. In the presence of excess water, MIC reacts to form
methylamine that reacts with additional MIC to form 1,3 dimethylurea and
carbon dioxide.16. The overall reactions are exothermic and thus energy is
released. The initial amount of energy release is around 585 BTU per lb of
MIC or 3700 BTU per lb of water reacted. 17 A trace of acid or base will
catalyze the reactions. This energy, if not removed properly, will heat the
mixture, eventually bringing the mixture to its boiling point.
16. Ibid
17. C&EN 11 Feb 1985 p 28.
Slide 16. MIC can react with itself exothermally to form a trimer.
In the presence of a basic catalyst, MIC can react with itself to form trimethyl
isocyanurate. Energy release for this reaction is about 540 BTU per lb of MIC.
Additional catalysts include iron, copper, tin and zinc.18.
18. C&EN 11 Feb 1985 p 29.
Slide 17. Another trigger question for the slides that follow.
Slide 18. A runaway reaction -- An exothermic reaction in a closed system.
As additional energy is released, in a closed system, both temperature and
pressure will increase approximately following the vapor-liquid equilibrium
line of the mixture, which includes CO2, a gaseous product. In closed systems,
the pressure continues to rise to the thermodynamically fixed maximum or it is
relieved.
Additional heat can be formed by secondary reactions involving
methylamine and MIC to give additional products.
Slide 19. The production of MIC
The MIC required at the Bhopal facility was produced in batches every two to three months and stored in three cylindrical tanks. The last batch of MIC was made between October 7 and October 22, 1984. On October 22, the MIC unit was shut down for routine maintenance of the equipment, and the tanks were isolated. The process involves the following series of reactions done at the Bhopal site:
Formation of phosgene
2 C + O2 ---> 2 CO
CO + Cl2 ---> COCl2
phosgene
Next, methylamine was reacted with excess phosgene in the vapor phase to form methylcarbamoyl chloride and hydrogen chloride.19
heat
COCl2 + CH3NH2 ---> CH3NHCOCl + HCl
phosgene methylamine methylcarbamoyl
chloride
After the reaction, the reaction products were quenched in chloroform. The unreacted phosgene was separated by distillation from the quench liquid and recycled back to the
phosgene/methylamine reactor. The hydrogen chloride was removed and the remaining material, methylcarbamoyl went to a pyrolysis unit where the following reaction occurred:
heat
CH3NHCOCl ---> CH3NCO + HCl
methylcarbamoyl methyl
chloride isocyanate
The HCl produced was sent to an absorber.20 Crude MIC from the pyrolysis unit went to a refining still where the top product was sent to the MIC storage tanks and the bottom product recycled back to the pyrolysis unit.
19. Adapted from Lees, A5/2.
20. C&EN 11 Feb 1985 p 32.
Slide 20. The storage tanks
Three storage tanks existed for MIC produced at the site. Normally, two tanks
held production while a third was available for emergency use. The storage
tanks were constructed of 304 and 316 stainless steel. They were partially
submerged into the ground and the remaining exposed area was covered by an
earth mound upon which was placed a concrete barrier. Their dimensions
were 8 feet in diameter and 40 feet in length. Each tank’s volume was about
56,500 liters or 15,000 gals.21 Their pressure rating ranged from full vacuum
to 40 psig (2.72 bar) at 121 C. Each tank could hold about 45 tons of MIC,
which is sufficient for about 15 days of pesticide production. [Figure adapted
from Chemical Week/November 26, 1986 p 8. Original Source: Union
Carbide.]
21. Chemical Engineering 24 Dec 1984 p 17.
Slide 21. Photograph of Storage Tanks
This is a photograph showing the pipe racks and storage tanks. The storage
tanks are located near the center of the photograph towards the right side.22
22. Courtesy, Mr. Wil Lepkowski, Senior Correspondent C & E News.
Slide 22. Storage tanks continued, with process piping detailed
The process side of the storage tanks is shown in this slide. Material flowed
through a feed pipe opening located in the tank sump into one of two pumps.
One pump served as a circulation pump for a refrigeration unit. The other
pump served as the Derivatives Unit transfer pump that supplied MIC to the
Derivatives Unit. Two return lines existed -- one for the return from the
refrigeration unit and the other from the Derivatives Unit supply pump outlet.
Refrigeration was provided, in part, because surrounding temperatures in the
region could reach as high as 48 C (120 F) in the summer, is above the boiling
point of MIC at atmospheric pressure. Also, MIC is quite volatile even at
room temperature as Slide 11 pointed out. [Figure adapted from P. Shrivastava,
Bhopal: Anatomy of a Crisis, 2nd Ed. 1992 p 38. Original Source: Bhopal
Methyl Isocyanate Incident Investigation Team Report, Union Carbide
Corporation, March 1985.]
Slide 23. Storage tanks continued, with nitrogen header added.
Nitrogen was supplied to the storage tanks for three reasons. First, bone dry,
high purity nitrogen was used at the Bhopal plant to reduce the risk of
contamination, especially from trace amounts of water. Secondly, MIC is a
fuel and thus can burn -- so contact with oxygen is avoided. MIC’s flash point
is -18C, and its LFL (lower flammability limit) is 6% in air. Thus nitrogen
“padded” the flammable contents of the tank. This is also called nitrogen
blanketing or nitrogen purging. Nitrogen or inert padding is commonly used
in tanks holding volatile fuels or reactive chemicals. Thirdly, the nitrogen pad
provided a positive head of 15 to 20 psig within the tank so that material could
be forced through the feed pipe to the transfer pumps. Nitrogen supply
pressure was controlled by control valve labeled N2 in this figure. [Slides 20
through 23 were adapted from Ashok S. Kalelkar (ASK), "Investigation of
Large-Magnitude Incidents: Bhopal as a Case Study," in I. Chem.E.
Symposium Series No. 110 The Institution of Chemical Engineers 1988, p 575,
Figure 7.]
Slide 24. Storage tanks continued with process vent header
To the left of the nitrogen purge line existed a process vent header with a
control valve labeled “Valve 15” in this figure. Normally, Valve 15 was closed
except on vent line purging or control of moderate over pressure during filling.
The process vent header is used to vent normal process vents from various
parts of the unit to scrubbers or flares, so that they can be neutralized before
they reach the environment. Both the nitrogen pad line and the process vent
header line shared the same entry point to the storage tank through Valve 16.
Process vent lines are a common safety feature used for the processing of
hazardous chemicals. Finally, note the pressure gauge labeled “10” and the
valve directly below it. More details about this later.
Slide 25. Storage tanks continued with relief valve vent header added
Relief systems are required on closed storage and reaction vessels. They serve
to protect the equipment and personnel from an explosion that may occur if the
vessel over pressurizes and to provide a mechanism to transfer and neutralize
material vented through the safety valves. If an over pressurization event
occurs, relief systems “trip” at some design pressure “relieving” the unit of the
excess pressure and preventing failure of the vessel. The relief system is
labeled as “11” and “2” in this diagram. In this case, the design involved a
rupture disk in series with a relief valve. This is common practice with highly
corrosive and toxic materials. The rupture disk isolates the stored material
from the relief valve, preventing damage to the relief valve during normal
service. Note the pressure gauge on the line. This gauge can indicate pin hole
leaks that may develop in the rupture disk over time.
Slide 26. One last detail about the relief valve vent header
Note that the process vent header (PVH, #3) was connected to the relief valve
vent header (RVVH, #2) by a temporary jumper connection to permit routine
maintenance to be performed on the PVH, while the MIC unit was shut down.
One explanation of how the incident occurred is based on this connection
having these headers interconnected through open valves.
Slide 27. Downstream of the relief valve -- the vent gas scrubber system
The relief valve vent header (RVVH) and process vent header (PVH) went
separately to a flare tower or a vent-gas scrubber system (VGS). This is good
engineering practice to prevent uncontrolled releases. In an unrelated incident
at a ICMESA plant in Seveso, Italy, an uncontrolled toxic release of dioxin
went straight into the surroundings. It resulted in the dispersion of about 2 kg
of dioxin throughout a 16 km2 area and forced the relocation of 700 inhabitants
in the most severely contaminated zones.23
At the Bhopal plant, the vent-gas scrubber system was a packed
column with three sections. The upper section was a 1.65 m diameter, 5.54 m
high section that held ceramic Berl saddles.24 A middle section, 1.65 m in
diameter and 2.1 m in height, separated the upper section from the bottom
section. The bottom section, 3.6 m in diameter and 6.9 m in height, was the
accumulator with a capacity of about 80,000 liters that held a 10% caustic soda
solution. Caustic soda neutralizes MIC before it releases to the atmosphere
through a 100-foot stack.
Piping and valving existed so that the RVVH and PVH lines
could also be routed to a flare tower. The primary function of the flare was to
burn vent gases from the carbon monoxide unit and the monomethylamine
vaporizer safety valve. The flare also at times burned normal vents from the MIC
storage tanks (which could be routed to the VGS or directly to the flare), the VGS and
the MIC Refining Still. The vent gas scrubber system was part of an integrated
system designed to prevent, detect, and handle contamination, and was capable of
handling all reasonably foreseeable conditions.
23. See Seminar on Seveso Release Accident Case History, by Ronald J. Willey,
SACHE Slide Package 1994, AICHE.
24. A.Ritchie, “The Bhopal Disaster -A Critical Study” 3rd Year Report, University
of Nottingham, Dept. Of Chem. Eng. March 1988, p 10.
Slide 28. Proper safety systems were in place
This part of the plant, built in 1981, had acceptable safety systems in place at
the time to prevent a release of MIC from reaching the environment. A visit
by a Union Carbide Safety team was made in 1982 and 10 safety concerns
were brought forth at that time, one of which included the potential for release
of toxic materials due to equipment failure, operating problems, or
maintenance problems. Corrective actions were taken, including replacement
of corroded valves on the MIC unit. So what else happened?
Slide 29. Operating conditions prior to the disaster:
1. The refrigeration unit was shut down in June of 1984. The refrigerant was
drained and used elsewhere within the plant. Thus, MIC was stored without
the benefit of cooling, and, if an overheating event should occur, no cooling
was available.
2. Several weeks before the incident, after the MIC unit was
shut down, a corroded portion of the PVH line leading to the flare was taken
out of service for maintenance. During this time, the process vents could no
longer be routed to the flare, and were rerouted directly to the VGS.25
3. The scrubber was turned off and put in stand-by mode
because the MIC production unit was not operating. At the time of the
incident, however, the MIC unit operators were able to turn the scrubber on.
25. Information provided by Union Carbide to author, Mar 1998.
Slide 30. All were operations management decisions
It is likely that the decision to alter and by-pass established safety systems
were all management decisions. Typically these decisions are made by line
supervisors, and managers at the plant level. Although the reasons behind the
decisions are not fully known, the decision makers could not have foreseen the
catastrophe that ultimately occurred.
Slide 31. Another trigger question for the slides that follow.
Slide 32. Management of change: Guidelines now exist
Be cautious about decisions related to changing systems and procedures that
were originally installed for safety. Federal guidelines now govern major
changes in the chemical process industry (noted as “Management of Change”),
and a SACHE module is devoted to this issue.26 The potential consequences
of those decisions must be carefully considered.
26. Robert M. Bethea, Slide Package Chemical Process Safety Management
Flixborough and Pasadena (TX) Explosions Miscellaneous Case Studies 1994.
Slide 33. Sequence of events that directly lead to the event
Given below is the sequence of events that led directly to the release of MIC
into the environment.
Slide 34. Storage tank schematic
Two storage tanks, E610 and E611, contained MIC at the time of the incident.
Tank E610 had about 41 metric tons of MIC and Tank E611 had about 21
metric tons of MIC. During the month of November 1984, both tanks had
periods of low pressure. Tank E610 could not be used at the time of the
incident. Its pressure registered 2 psig instead of the normal 20 psig at
pressure gauge 10. Corrective maintenance work was performed on Tanks 610
and 611 on December 1 to correct the low pressure situation. Although the
plant personnel were able to correct the problem with 611, they were unable to
pressurize Tank 610. No work was done on either Tank 610 or 611 on
December 2 (two days before the event).
It is speculated that Tank E610 could not hold pressure because
normally closed Valve 15 was leaking.
Slide 35. Reactivity
As previously mentioned, water and MIC react exothermally; therefore, efforts
were made continuously to keep water and MIC apart. However, as part of the
normal operating procedure, transfer lines had to be periodically flushed with
water because MIC can self react to form a polymeric species along pipe walls
that eventually lead to blockages.
Slide 36. Two major explanations
Two major explanations have evolved to explain this event. Both explanations
agree that water entered into the MIC storage tank and runaway reactions
ensued. One explanation, referred to as the water washing theory, is based on
plant employee testimony and was issued by the authorities commissioned by
the Indian Government.27 The second, or sabotage theory, is based on
independent research conducted by Arthur D. Little, Inc., on behalf of Union
Carbide.28 We will begin with the first explanation. However, some details
about the second explanation will be included to assist in the understanding of
both explanations.
27. S. Varadarajan et al. “Report on Scientific Studies in the Factors Related to
Bhopal Toxic Gas Leakage (New Delhi: Council of Scientific and Industrial
Research, Dec 1985).
28. Ashok S. Kalelkar (ASK), “Investigation of Large-Magnitude Incidents:
Bhopal as a Case Study,” in I.Chem.E. Symposium Series No. 110 The
Institution of Chemical Engineers 1988, p 561.
Slide 37. The order to clean the lines29
On December 3 at about 9:30 P.M. that evening, the second shift production superintendent ordered the MIC plant supervisor to flush out a 2-inch filter pressure safety valve line near the process filters in the production unit, over 600 feet away (by pipe) from the MIC storage tanks. The relief valve vent header (RVVH) is tied to the filter pressure safety valve line through Valve 19. Valve 19 is normally closed. Plant maintenance records dated 29 Nov 1984 support this contention, and Valve 19 was tagged as closed.30 Valve 19 was tested in July 1985 and was determined to be leak tight.31
Part of the normal operating procedure included the insertion of a blind on the line leading to the RVVH to prevent water from accidentally entering this line. This procedure was normally carried out by maintenance personnel. It is assumed that the blind was not inserted. Flushing began by operating personnel shortly after 9:30 P.M.32 The proponents of the water washing theory contend that the water leaked by Valve 19 and entered the RVVH. This means that water had to have at least a hydraulic head of 10.4 feet to reach the RVVH line, filling a 6-inch header pipe to reach the 8-inch RVVH pipe. Then, the proponents hypothesize that water flowed through 65 feet of the 8-inch pipe, followed through another 340 feet of 4-inch pipe around the jumper pipe into the process vent header (PVH). Before the water finally reached the Tank E610, water had to have filled an additional 340 feet
of 2-inch PVH lines with several drops before entering the tank. Calculations showed that 540 gallons of water were required to fill all of the dead spaces in the pipe line before reaching the storage tanks.33 The lines could conceivably fill with water in 1.8 hours at 5 gallons per minute.
29. Diagram is from ASK Fig 4.
30. Ashok S. Kalelkar (ASK), “Investigation of Large-Magnitude Incidents: Bhopal as a Case Study,” in I.Chem.E. Symposium Series No. 110 The Institution of Chemical Engineers 1988, p 561.
31. ASK p 561.
32. P. Shrivastava, p 39.
33. ASK p 561.
Slide 38. What went in, didn’t come out
As presented in Shrivastava’s book,34 the operator who was in charge of
flushing noticed that water wasn’t exiting all of the bleeder lines (the proper
exit for the flushing operation). He ceased the flushing operation until the
MIC plant supervisor ordered him to resume the process. As will be presented
below in the alternative explanation, the argument goes that 3 of the 4 bleeder
lines labeled 18 in Slide 37 were open; therefore, insufficient back pressure
existed to force water back through the closed Valve 19.
34. P. Shrivastava, p 39. From International Confederation of Free Trade
Unions, The Trade Union Report on Bhopal (Geneva: International
Confedieration of Free Trade Unions, July 1985).
Slide 39. The path of the water flow
The proponents of the water washing theory speculate that water flowed from
the water washing area to the MIC storage tanks. It appears that the reason
that the tank E610 didn’t pressurize might have been that Valve 15 was faulty,
as it allowed water to enter Tank E610. About 500 kg of water entered the
tank and began to react exothermally with MIC. [Adapted from Ashok S.
Kalelkar (ASK), "Investigation of Large-Magnitude Incidents: Bhopal as a
Case Study," in I. Chem.E. Symposium Series No. 110 The Institution of
Chemical Engineers 1988, p 571, Figure 3.]
Slide 40. Exothermic Reactions begin
Although widely contradictory accounts of the events have been given by the
operators, the proponents of the water wash theory believe that the following
occurred. At 10:20 P.M. the pressure within Tank E610 was reported at 2 psig.
At 11:00 P.M. the pressure was 10 psig as noted by another worker who had
come in on a shift change. He did not consider this abnormal at the time since
operating pressure was about 15 psig. By 12:15 A.M. this same worker noticed
that pressure had risen to between 25 and 30 psig. Within another 15 minutes
the pressure had exceeded 55 psig, and the worker ran to the tank. There he
found the tank with loud rumbling and screeching noises. Around 12:45 A.M.,
the relief system opened.35 As time continued, temperature within the tank
exceeded 200C. Average pressure within the tank exceeded 180 psig during
the release. The relief valve vent header system directed a stream of MIC to
the vent gas scrubber/flare system stack.
35. ASK p 559.
Slide 41. Toxic Gas Release
The plant superintendent sounded the toxic gas alarm for the surrounding
community for a period of about 5 minutes and suspended operation of the
pesticide plant. Operators began futile efforts to spray water on the vent gas
stack (100 ft high); however, the water pressure was too low to reach the
emitting gases. The total release continued for two hours.
Slide 42. The dispersion of the gas
Because of the slums built up around the plant, many thousands of people were exposed to MIC. Recall that the density of MIC as a vapor is two times that of air, thus it initially flowed towards ground level. As the MIC continued to be dispersed into the air the molecular weight of the mixture approached that of air and the MIC moved along with the prevalent air currents diffusing and dispersing into the surrounding environment. Even though the concentrations were very low (in the ppm levels), the mixture was still quite toxic as it moved across the UCIL property line. Secondly, this was a release during night time. At night the atmosphere is much calmer and sometimes inversions exist. Dispersion and mixing (dilution to concentrations below the threshold level) were hindered by the lack of atmospheric turbulence that normally occurs during daylight hours. The release blanketed an area of many square kilometers.36 Although accurate figures do not exist, more than 1,000 people were killed, and thousands more suffered injury. Hospitals and dispensaries were unable to cope with the flow of victims. The tragedy was profound. The toxic-gas alarm that was sounded for 5 minutes wasn’t heard by most. Further, many who heard the alarm didn’t understand its implication.
Instructors note the shape of some of estimates of the dispersion, circular in this case. Many dispersion models predict a long cigar shape. You may want to discuss dispersion modeling.
36. C&EN 10 Dec 1984 p 6.
Slide 43. Findings after the accident
After the accident, the remaining contents of Tank E610 were determined. The
investigation concluded that 512 kg of water had entered the tank. This was
enough water to create enough temperature rise to promote additional catalytic
reactions including that of MIC to its trimer (a total of 6,938 kg remained).
Additional materials found included 2,660 kg of dimethyl isocyanate, 390 kg
of cyclic dione, (Slide 40) 195 kg of trimethylurea, 423 kg of trimethylamine,
240 kg of dimethylamine and small percentages of trimethylbiuret,
monomethylamine, dimethylurea, and salts of sodium, iron, chromium, and
nickel.37 (Tables 1 & 2 provide more detail). The presence of the iron, most
likely coming from corrosion inside the tank (metal analysis showed the
composition matched the tank walls),38 or less likely from back flushing water,
promoted the trimerization reaction. This reaction, being exothermic, heated
the tank contents to 200C, which caused high pressures to build and finally
the opening of the relief valve system and the release of MIC into the relief
valve vent header. After the pressure had subsided, the relief valve did
reseat.39
37. C&EN 6 Jan 1986, p 6.
38. Information provided by Union Carbide to author, Mar 1998.
39. C&EN 10 Dec 1984, p 6.
Slide 45. An alternative explanation --“a deliberate act”
As discussed above, the point of water entry for the filter process was 600 feet
away and had elevation points 10 feet above the addition point. After an
extensive investigation, Union Carbide has rejected the water wash theory as
scientifically untenable,40 contending the addition of water to the MIC tank
was “a deliberate act”. 41
40. C&EN 6 Jan 1986, p 6.
41. Chemical Week 26 Nov p 8.
Slide 46. Points made against the filter line cleaning explanation
Ashok S. Kalelkar of Arthur D. Little, Inc. Cambridge, Mass., presented a paper in London in May of 1988 regarding the cause of the Bhopal incident.42 Three strong arguments against the water-washing theory were presented.
1. Bleeder Valve Hydraulics:
With 3 of the 4 bleeder valves functioning, backpressure before the valves could not exceed 0.7 foot of hydraulic head. A minimum of 10.4 feet was required to reach the RVVH.
2. Closed Intermediate Valve:
As explained above, all evidence points to Valve 19 being closed and leak tight at the time of the incident.
3. Dry Header Piping:
If the header piping system, RVVH and PVH, had entirely filled with water (as would be required if water entered from the wash station), then water should have been observed in any low points located through this piping arrangement. When these lines were inspected no water whatsoever was found. On Feb. 8, 1985, the Superintendent of Police of the Indian Central Bureau of Investigation ordered a hole drilled at the lowest point in the PVH line (the line that supposedly filled from the water washing). This point was well away from the MIC tanks and far enough away from the RVVH (which would have emptied upon the release) so it would have been unaffected by heat. The line was found to be bone dry.
42. ASK pp 553 to 575.
Slide 47. Water entered by direct connection.
Union Carbide’s investigation team found compelling evidence that water was deliberately introduced into the tank. First, a witness, an instrument supervisor, who reported that the pressure gauge labeled 10 was missing on the morning after the incident and the line was unplugged. He also testified that a hose with running water was near.
Deliberate acts of mischief by workers in industrial plants are not uncommon and had, in fact, occurred previously in the Bhopal plant. The investigation team identified an employee of the plant, working on the third shift that night, who was keenly disgruntled. Immediately prior to the incident, his supervisors demoted him and he openly expressed resentment against management. Investigators found he confessed to being near the tank at about the time water would have been introduced and had the motive, the means, and the opportunity to commit sabotage. The investigators found that he introduced the water during the shift change by removing the pressure indicator and temporarily opening Valve 16. He likely believed he would only spoil a tank of MIC. Although the accounts given by plant personnel are wildly contradictory, the investigation team concluded that at 11:30 to 11:45 P.M., workers on the plant floor detected minor MIC leaks and the source was incorrectly identified near the scrubber flare tower. The incorrect source was wetted down with a fire hose spray. After tea time (around 12:00 midnight), several operators noted the high pressure on Tank E610. Workers ran to the tank and discovered the hose attached. Several solutions were discussed including the transfer of material from Tank E610 in hopes of getting the water out before anything else occurred. The release happened around this time. There is evidence that those involved in the discussion of the transfer decided to a cover-up.
Slide 48. Another trigger question for the slides that follow.
Slide 49. Lessons learned (Three Slides)
1) Have contingency plans available for dealing with major accidents.
Currently, in the United States, emergency response exercises
for training purposes are required on a frequent basis. It is not unusual in large
plants to have staged minor events monthly and larger events every six
months. Larger events can include fire drills that shut down a major chemical
line.
2) Public involvement in risk management and acceptance is now recognized
as a critical element of chemical manufacturing. Public involvement in risk
management programs are required under “Right to Know” laws and other
initiatives that exist across the U.S.A. New chemical industry programs were
implemented to better manage health, safety, and environmental risks and
encourage more public involvement, such as the Chemical Manufacturers
Association establishment of Community Action Emergency Response
(CAER), and Responsible Care programs.
Slide 50. Lessons Learned: Reduce the inventory of the hazardous chemicals
3) Another lesson to be learned from this incident is consideration of inventory reduction for process intermediates. What you don’t have, can’t leak, catch on fire, or cause any other problems.43
Could the process be designed that kept the amount of MIC to a minimum? This would require integrating the MIC production unit with the carbaryl production unit, such that when production of carbaryl was required, the MIC unit would begin production and produce only a small amount of the intermediate. A present design exists in which the maximum inventory of MIC is 10 kg.
Process safety analysis should be done early in the design stages. You need to ask the question: if hazardous intermediates are involved, can they be eliminated by alternative methods (see in the next slide) or, if possible, can these be minimized? Inherently safer plants would be toward the total elimination of the hazardous intermediate like MIC. For a SACHE lecture on inherently safer plants, see Kubias.44
43. T. Kletz, “Lesson from Disaster” Institution of Chemical Engineers, Rugby, Warwickshire CV21 3HQ, UK, 1993, p 83.
44. O. Kubias, “Inherently Safer Plants,” SACHE-AIChE 1996.
Slide 51. Alternatives
Another possibility is to look at an alternative route to carbaryl that involves
less hazardous intermediates. One such route is the direct reaction of alpha
naphthol with phosgene to form alpha naphthol chloroformate. Alpha
naphthol chloroformate can then be reacted with methyl amine to give the
desired product carbaryl.45
45. C&EN 11 Feb 1985 p 30.
Slide 52. Siting of the plant
The plant was originally designed to formulate pesticides. As it “backward
integrated,” it became more hazardous. Hazardous plants should be sited away
from populated areas and “green belts” established around them.
Slide 53. Release mitigation
Release mitigation involves methods to lessen the effects of any release event
that may impact the surroundings.
1. Conduct toxic release modeling based on a potential release
scenarios.
2. Evaluate measures to mitigate, such as reduction of
inventory, spill containment, proper maintenance, detection by sensors, and
water sprays as a few examples.46
3. Emergency and safety training of operators.
4. Emergency response exercises with local community
services.
46. R.W. Prugh and R.W.Johnson, Guidelines for Vapor Release Mitigation
AICHE, New York: 1988.
Slide 54. Maintaining the integrity of safety systems
Safety systems, such as flares, scrubbers, refrigeration systems, relief devices,
or emergency shutdown devices, are critical to the safe operation of the
processes in which they are employed. Any changes affecting the integrity of
these systems must be managed carefully. Management of change procedures
are now required through regulation in the US.
Slide 55. Risk management overseas
Another important concept is that risks must be managed in a consistent way
no matter where the plant is located around the world. U.S.-based
corporations must hold their U.S. locations to the same standard as those
outside the country. This applies both to the design and the operation of these
facilities.
Slide 56. Employee threats of violence programs
Acts of violence and mischief in the workplace have increased in prevalence in
recent years. As a result, many companies have instituted programs to detect
disgruntled or potentially violent employees. Companies should adapt threat
of violence programs that include training and education, procedures to
recognize early indicators and procedures to manage threats once they have
occur. In recognition of the problem, OSHA has begun work on a workplace
violence standard.47
47. For more details see the following web sites that were active in 1998:
“http://www.osha-slc.gov/SLTC/WorkplaceViolence/index.html” and
“http://www.osha-slc.gov/workplace_violence/wrkplaceViolence.Table.html”
Slide 57. Other outcomes after the incident
As news of the incident spread, several events occurred. The chairman of Union Carbide, Warren M. Anderson, traveled to Bhopal. He was arrested by the Madhya Pradesh authorities; then released at the end of the day. He then returned to New Delhi.48 Within in a week of the incident, Union Carbide set up a $1 million fund to assist in direct aid at Bhopal. The remaining MIC located in Tank E611 was converted to pesticide two weeks later under very careful precautionary means that included a helicopter spraying water on the plant.49 The Indian Government termed the processing “Operation Faith”.50 Before the disposal, tens of thousands of remaining Bhopal residents fled the city in fear of another release from the plant. In the ensuing months, Union Carbide gave another $5 million to the Indian Red Cross and donated additional millions of dollars to other relief organizations for humanitarian work in Bhopal.
Union Carbide settled with the Indian government for $470 million in 1989 and contributed an additional $20 million for the construction and operation of a new hospital. In the fall of 1994, Union Carbide sold its share in UCIL, and about $74 million from the sale went into the hospital’s trust fund.
48. NY Times 8 Dec 1984 p 1.
49. NY Times 17 Dec 1984, p A 8.
50. ASK p 556.
Slide 58. U.S. legislative initiatives.
A number of U.S. legislative initiatives were instituted and aim at prevention
of such an incident in the future. These include Process Safety Management
Standard, OSHA 29CFR1910.119, and EPA’s Risk Management Program Rule,
40CFR68.
Slide 59. Additional Initiatives
Slide 60. Acknowledgments
This slide module was prepared from materials originally referenced by Dr.
Walt Howard. The author is thankful to have had this list and this listing is
presented in a portion of the index for those who wish to read further. The
author acknowledges: Ms. Cristy Godoy de Urruela for collecting the many
citations related to the incident and creating the tables that are attached as an
appendix to this module; Mr. Wilbert C. Lepkowski, Senior Correspondent,
Chemical & Engineering News, for several original photographs used in this
work; and Mr. Bob G. Perry for a copy of the Arthur D. Little paper presented
in 1988 that assisted in understanding the plant process properly. Finally, the
author acknowledges the SACHE committee whose reviews of text and slides
are gratefully accepted.