Failure Knowledge Database - 100 Selected Cases

Poison Gas Leakage from Chemical Plant in Bhopal, India【December 2nd, 1984

Bhopal, India.】

Mitsuo Kobayashi (Graduate School of New Frontier Sciences, University of Tokyo)
Masamitsu Tamura (Graduate School of New Frontier Sciences, University of Tokyo)

From mid night of December 2nd, 1984 to

the dawn of the 3rd, Bhopal, the state

capital of Madhya Pradesh in central India, was conta minated with toxic gas. An

enormous disaster resulted with over 2000

persons dying on the spot and 200,0 00 to

300,000 per sons injured. The final number offatalities was reported to be 14,41

0

persons. Th e toxi c gas was methyl isocyanate (MIC) that is used as a pesticide raw
material, an d it leaked from th e st orage tanks of Union C arbide Ind ia Co. (UC IL) inthe suburbs of Bhopal. MIC is used as araw material for organic s olvents and s oil

fumigants, etc. MIC is much more toxic th an even the famous phosgen e gas, and theaverage acc eptable conc entration of work envir onment p er eight hou rs in the USA is
0.02 ppm, which is 1/500 of the 10ppm limit that is allowed for cyanogen compounds.
The leakage accident began with the contamination of the water in the MIC storagetank. A n abnormal r eaction was caused , the p ressure rose, and MIC le aked from t hestorage tan k. Safety eq uipment th at had been left in und esirable c ondition d id notoperate, and MIC leaked outside of the factory. The leaked MIC spread to the city along
the ground by the northwest wind, and the citizens were exposed to the gas while t hey
were sleeping. As the accident occurred at midnight, proper public information was notmade availa ble, and the citizens were unabl e t o take refug e, causing t he damage tospread. The local p eople had not been infor med that d angerous M IC was being
manufactured and stored in thefactory. Furthermore, n either the administrative

authorities nor the medical personnel of the city had knowledge about t he cure for the
MIC p oison; this fact may also h

ave been a factor lead ing to theenormity of thedamage.
When th e background of this accident is

co nsidered, t he relation between t helifecycle of manufactured go ods an d the management poli cy of the enterprise can benoticed. UC IL was an I ndian subsidiary of Union Carbide and Carbon (UCC) in

the

USA. UCC possessed over 50% of the capital o f UCIL, and UCIL m anufactured MIC
and its final product, pesticide, using U CC technology. The MIC plant was constructed
in 1977. H owever, around the time of

accident, a cheaper and safer pesticide

manufactured by a different system went on the market, and the business of UCIL was

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Failure Knowledge Database - 100 Selected Cases

in a bad con dition. At the end of the fiscal year in 1982, the profit was z ero, and it was
forecasted that there w ould be a four million US dollar d eficit in 1984. Theref ore, themanagement of th e factory was rationalized, safety education was seldom carried out,
and safety of the facilities and operation was disregarded, and problems occurred often.
This chain of events is c onsidered to hav e caused the cata strophe. Thi s disaster w as
not only the problem of the local subsidiary that was operating the plant, but also t heproblem of the responsibility of the parent company.
1. Event
From midnight of December 2nd, 1984 to th e dawn of the 3rd, the deadly poisonous
MIC gas lea ked fr om th e st orage ta nk. MIC , w hich was an intermedia te in pestici demanufacture, was stored in thre e storage tanks of the pesticide factory in UCIL Co. at
Bhopal in c entral Ind ia. MIC evaporated as a r esult of a n abnor mal r eaction. The
northwest wind was blowing on that night, and the temperature was low, so the leakedgas spread silently to the southeast over the ground to cover an area of about 40 km2 inthe city. Because the accident occurred at mi dnight, the citi zens were not able t o takerefuge. The numberof victims was at least 200,000 persons, which

was over one

quarter of Bhopal’s population of 800,000,

a nd according to otherestimates, thenumber of victims was as much as 300,000

persons. The number of instant deaths

exceeded 2000, and the final number of fatalities was 14,410 persons.

2Failure Knowledge Database - 100 Selected Cases

The manufacturing plant had sto pped operation a fe w days before the day whe n theaccident occurred. For some days before the stopping, theoff-specification product,

which contained high concent ration chloro form, was r undown into one tank of thethree storage tanks. From the tank in whic h the off-specification product was stored,
MIC vapor was generat ed by a work error , and MIC gas leaked from t he tank bec ausesafety devices did not operated.
2. Course
The manufacturing plant had sto pped operating since October 23rd. However, in theoperation from 18th to 22nd, MIC containing 12 to 16% chloroform, which exceeded thespecified maximum content of 5%, was rundown, and that MIC was stored in a stora getank where the accident occurred.
MIC vapor was generated due to a n increa se i n te mperature and p ressure of theliquid, which was caused by an abnormal r eaction in the ta nk. In the a fternoon of t he
day of the a ccident, the water washing work of the vent piping of the tank was carriedout. In th e safety manual, the operation of “ins erting a bli nd plate” was sp ecified, but
the blind plate was not inserted. The water used for washi ng entered the tank by s eat
leakage from a valve or new piping that was mount ed ju st before th e accid ent. The
operators d iscovered a r ise in the t ank p ressure at 23:00 on the sameday, and th ey

tried to take s ome measures but w ere no t able t o reduce the pressu re. N ext, th ey
noticed MIC vapor leaka ge at 23:30, but they could not do anyt hing to stop it. At 00:45
on the next day, the leakage quantity of MIC increased, and the leaked gas broke someequipment and then sp read in the factory. The plant manager who wa s called reached
the factory at 02:30, and then h e notified the police. This was the only communication
with anyone outsid e of the facto ry. A t 03:30, the leak ed vapor d iffused outsid e t hefactory.
The management conditions of the MIC tanks are described below. For managementof MIC, which is very dangerous and has a low boiling point, threekinds of safety

devices had been p repared: a refrig eration unit for ke eping the tank te mperature at
0℃ or l ower because of the low boi ling po int of MIC, a scrubber for absorbing MIC
vapor by alkali, and a f lare st ack to burn leaked gas. How ever, th e ref rigeration u nit
was stop ped fro m July. As the t emperature alar m of the ta nk was n ot operating, t healarm did not ring whe n the temperature rose over 5℃. The scrubber was not effective
because the circulation pump of the absorber had been stopped from October 22nd. The
flare stack had also be en sto pped fo r piping wo rk. Therefore, the ge nerated MIC gas
diffused first outside of the plant and then outside of the factory.

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Failure Knowledge Database - 100 Selected Cases

As the wind directionthat night was from t he n orthwest, th e l eaked gas spreadtowards the city zone where the population was m ost dense. A large amount of humandamage was an inevitable result of high toxi city of MIC , of the large lea kage quantity
35 tons in total, of the time of the leakage that was midnight, and of a lack of publicity
activities and rescue operations.
The history of UCIL Co. is described below for reference.
The company was established as a dry cell manufacturing company in 1 934, and thefirm name was changed to UCC India instarted in 1969, and the1959. The compounding of insecticide

manufacturing of insecticide based on MIC

was

was started in

1977. The MIC manuf acturing plant where the disaster occurred was constructed in
1980. The disaster occurred in 1984, and the Bhopal factory was closed thereafter.
3. Cause
The causal chain of ev ents lead ing to the lea kage of MIC vap or is considered asfollows. The off-specification product that

contained much more chloroform than thespecification was distilled into a storage ta nk for a few days before the plant stooped
operation. A large am ount of water was contam inated in the tank. Hydrochloric aci d
was generated from t

he high temperatur e reaction of chloroform and water.

Hydrochloric acid corroded stainless steel of the tank material, dissolvi ng iron. With
the iron as a catalyst, a series of abnormal reactions were caused, which led t o leakageof MIC vapor. The series of abnormal reactions is shown below. MIC vapor leaked froma safety valve, and a p ressure r elief valve d ue to a p ressure rise cau sed by carbon
dioxide formation and MIC vaporization.
MIC reacts with water to form carbon dioxide and methylamine with the generationof heat. In addition, d ue to th e ris e in te mperature and the catalytic effecttrimers of MIC were formed with a largeof ir on,heat generation of 325kca l/kg-MIC. The

temperature became high due to the reaction, causing a runaway reaction to occur. The
reactions fr om th e ge neration of h ydrochloric acid to trim erization of MIC had be en
known.
The underlying cause of the accident was th e production of off-specification productduring on-stream operation. A little producti on of off-specification product might beinevitable, and it is not an important matte r. However, the off-specification operation
continued for four days. They had more than three years of operation experience, so thelong off-specification operation seems abn

ormal. Moreover , the contents of theoff-specification were a large amount of ch loroform, which, when combined with wa ter
contamination, is very dangerous. However, they did not seem t o take any particu lar

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Failure Knowledge Database - 100 Selected Cases

care regarding water contamination.
The direct trigger of the accident is water contamination in the tank, and the causes
appear to be a violation of work instru

ction i n the water washing operation andleakage of the valve. The manager had ordered the work, but he arrived at his post justbefore the accide nt, and he did no t know we ll t he details of technique. Actually, thework was regarded as unnecessary . Although the valve seemed to l eak, a seat leak of
the valve may occur sometimes. Therefore, the operation of “inserting the blind plate”
is specified in the work i nstructions. Considering the four d ays of successive rundownof off-specification prod uct and the violation of work instructions, the major causes of
the accident were lack of morals and insufficient education.

In addition, all three kinds of safety devices failed completely, and MIC gas spread tothe city . Three kinds of safety faci lities ha d b een pre pared, as is de scribed in the“Course” se ction above. Howev er, t he refrig eration unit had been stopped since July ,and the scrubbe r had also be en sto pped on October 22nd when the manufacturing
plant was sto pped, po ssibly be cause it was jud ged to be u nnecessary si nce it tr eatedthe process off-gas. Finally, the flare stack was stopped for piping work. B ecause of
these reasons, the lea

ked gas was discha

5rged out of

the facilities without any

Failure Knowledge Database - 100 Selected Cases

treatment. Although not directly related to the accident, there were some problems in
the processing capacity. The maximum processing capacity of the scrubber was equal toeight to ns of MIC . How ever, th ere was 40 tons of MIC in t he tank at t he tim e of t heaccident. The scrubber could

not handle th at much MIC . Fu rthermore, th ere weresome questions regarding whether or not the processing rate was sufficient. Althoug h
the scrubber ’s processi ng rate should be designed for the total

flow rate fromthepressure relief valve and safety valve, the actual processing rate might not be sufficient.
These issues indicate there were problems not only in the operation control but also inthe safety d esign of the plant itself. It wa s regulated that the tank t emperature must
be lower than 0 ℃ beca use the MIC boiling point is just 39.1

℃ and MIC is easily

vaporized, but the r efrigeration un it had been stop ped ov er six months befor e t heaccident to cut down el ectrical charges by a certain opinion. Although i t is not known
whether or not theoperation of the refrig eration unit could have p revented the

runaway reaction direct ly, there is no doubt that refrigerat ion would have lengthened
the time to the leakage.
The considerations above indicate thatproblems in operation management andprocess d esign were c onnected wit h the accid ent d irectly. Howev er t here was p oor
safety management ba sically. For example, there were three leak age accidents thatcaused the death of employees in December 1981, February 1982, and October 1982. In
May 1982, the parent company carried out a research study on operation safety , andthey indicated ten defective items i ncluding some fatal defects. How ever there was no
written report that described the countermeasures to be executed.
The matters mentioned above appear to be the resultof the abandonment of thesafety management. Th e final products of th e factory b ecame out of date and businessbecame depressed, for the rationalization of management, maintenance of facilities andemployee ed ucation was negl ected. Because of t his co mpetent engin eers quit wo rking
at the company.
Besides, ma ny factories and users of MIC but manufacturer of MIC h ad decreased
the st orage volu me of MIC beca use of its dangerousness. Gene rally, MIC is useddirectly as an intermediate in the next

process without storage. In

France, MIC isstored only in small, stainless steel drum cans.
The more i mportant p roblem is w hy the di saster b ecame so large. There was ntransmission of informationoregarding the d angerousness of MI C to the l ocal

government and inhabitants from the company. Therefore, emergency countermeasures
were completely ignored by everyone, incl

uding the l ocal government. There is n odoubt that t his fact resulted in the expans ion of the damage. In addition, information

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Failure Knowledge Database - 100 Selected Caseson th e tr eatment of M IC p oisoning was brou ght after th e accid ent from the U CC
headquarters and the U.S.A. disaster inform ation center, but the information could not
be transmitted to the doctors who were administering the medical treatment.
The maincauses of t he d isaster are1) that UCC de

cided to continue the

manufacturing and storage of a large quanti ty of MIC without sufficien t risk analysis
and 2) that both UCC and UCIL did not make sufficient safety countermeasures due toa heavy deficit.
In other words, the disaster was causedby an almost complete lack of safe

consciousness of the company. The technical capacity of UCIL was supposed to be much
lower than UCC, and UCC had the responsib ility for the plant construct ion. Guidanceand execution of the safety tech niques of a for eign subsidiary are duties of th e parent
company.
4. Process of cause elucidation
Although the most important point of the cause elucidation is “why the water leakinto the tank occurred”, there is no report that focused on that point. If MIC leaks andspreads to the city zone, human damage is inevitable considering the characteristics ofthe gas. It also became clear that t he scrubber of the plant and the refrigeration unit
for cooling had stopped from th e operation record. The p rogress of the d isaster can be
described if the watercontamination is p

roved. Fro m the rep orts of the partiesconcerned and info rmation about the works and the plant situations on and before theday when th e disaster occurred, the water contamination route seemed to be specified.
However, in the report by th e parent company, it is cl aimed that an operator

hadinjected water into the t ank intentionally through the n ozzle of the p ressure gauge at
the up per p art of the t ank where the accid ent occu rred, based on the fact that thewater hose was discovered nearby.
5. Immediate action
The leak was noticed by the shift leader, but he did not take any measures. Spraying
of water was started after the gas

accumulated near the t ank, but the water did notreach the re. The p olice wer e c ontacted after p ersons r esponsible for the accid ent
arrived. However, as shown above, appropri ate measures had not been taken atall,and nothing could have been done after the leak.
6. Countermeasure
Countermeasures to p revent the recurrence of the accid ent were n ot taken, becau se7

Failure Knowledge Database - 100 Selected Cases

the factory was closed. As a general rule,facilities manufacturing, usi ng or storing

poisonous gas should carry out suf ficient in vestigations and stud ies on the d anger ofthe poisonous gas in order to ensure the suffi cient safety of the facility and operation ,to prepare against an accident by making ap propriate c ontact with the l ocal

government and nearby inhabitants.
7. Knowledgea) This accident is a typical example involving

a company that is running a deficit.

Accidents will occur if minimum safety co untermeasures and safety education are
neglected, even wh en management must be i mproved. It has be en shown thatkeeping the safety is a minimum condition for the existence of a corporation.
b) There are many forms of toxic chemicals. Corporations that handle toxic chemicals
in large amounts must understand that a
result of j

ust one handling mistake, andmajor disaster can easily occur as athey must consid er ap propriate

countermeasures. Several milligrams or l ess of a toxic chemical may b e enough t okill a person, and the pollution of a large region may be caused if a large quantity of
the ch emical is rel eased. Safety

is an imp ortant d uty of the ex ecutive of acorporation, and it should not beleft to l ower-grade ma nagers and operators.

Although th ere are so metimes majo r accid ents related to t he energy i ndustries
including L PG or petr oleum refining, acci dents involving toxic chemicals can bemuch m ore seri ous with damaging wider ar

ea and causin g seri ous s equelae tomany persons, resulting in terrible disaster s next to a major nuclear accident suchas Chernobyl.
c) The accident was also a result of a problem of t he overseas expansion of a large
enterprise. The responsibility of the pare nt company for t he safety of a foreignsubsidiary in which the tech nology level is low is important. When the technology
adopted by the foreign subsidiary is the tech nology of the parent company, or it isdecided by the parent

company, t he fina l responsibility for the sa

fety of thetechnology belongs t o t he parent c ompany. In this acciden t, th e paren t company,
which was a stockhold er of over 50% of the foreign subsidiary, paid over 90% of thetotal reconciliation cost of 470 million US dollars, and the chairman was criminallyaccused. Although it is i mportant to respec t the individuality of the sub sidiaries in
the ad vancement ov erseas, a mi nimum safety manage ment is an

imp ortant

obligation of the parent company and headquarters.
d) Safety equipment, including monitors an d alarms for storage facilities, must not
be stop ped even if the

manufacturing p lant is shut down. Substitute measures8

Failure Knowledge Database - 100 Selected Cases

should be taken when the safety equipment is stopped, and the safety equipment
should be restored as rapidly as possible.
e) Safety equipment such as scrubbers should have a sufficient processing rate and acapacity for treating the estimated discharge rat e and quantity from saf ety valvesand so on. S ome buffer facilities are necessary to handle the situations where therate is extremely large and a scrubber of sufficient size cannot be constructed.
f) It is important to carry out safety education, especially that of managers. Th ewater washing of the piping, which might be unnecessary and was executed on the
instruction of a site manager who had been transferred ju st before, t riggered theaccident. Education regarding safety

and basic knowledge forsupervisors and op erators wo rking at the c hemical p lant was also

management
important,considering that they d id not insert the blind plate to the p lace where a leak may
occur and they did not think that a valve may leak sometimes.
8. Influence of failure
The number of instant d eaths just a fter the accident was estima ted to b e over 2000
persons, the final total of fatalities resulted from the accident was reported to be 14,410
at a reconciliation of the Su preme Court, and it was said th at by December 2004, over
20,000 persons had died as a result of theaccident. The total num ber of injuries wa s

estimated to b e 200,000 to 300,000 persons, including 20, 000 persons who could nolonger be employed and about 75,000 persons who were in pain with the sequelae.
As for the monetary loss to the corporatio n, the amount of the reconciliation payment
was 470 million US dollars, and the stock pr ice of UCC declined by 32%. Furthermore,
the enterpri se was forced to downsi ze, and the market sa les per year of 9 billion US
dollars dropped to 6.3 b illion US dollars. In addition, although th ere were some otherreasons involved, UCC was merged into another corporation.
9. On the side
A small violation of a discipline of a foreign subsidiary triggered the crisis of a large
global corporation, and now, we can not find the name of U CC in the world . From thestandpoint of the parent company , the subs idiary was insignificant in scale and theshare of th e sto ck was not s o lar ge. The ma nagers and emp loyees of th e p arent
company had to f eel that “What hap pened to our company?” The safety management,
especially the leakage control may need to be reconsidered in factories, particul arly
which handle toxic chemicals. As the reputation of a corpora tion in society will have alarge effect on th e c ontinuance of the enterprise in th e future, it is imp ortant to

9Failure Knowledge Database - 100 Selected Casesconsider an d execute countermeasures against accid ents and to ensure the essential
safety.
In essence, the disaster was a typical resu lt of a deficit company where safety was
the responsibility of the parent company. Fr om this point of view this disaster w ascompletely the same as the criticality accident of JCO in Japan.
10. SequelThis accident led t o a civil suit to de termine the co mpensation for damage in India
and USA. Furthermore, in India, a crimi

nal trial for a

ccidents homicide by tchairman of the parent company was cond ucted. In 1989, theheIndia Supreme Court

issued a reconciliation order that the company should pay a total amount of 470 million
US dollars as an indemnity to t he vict ims of the accident, and both the I

ndia

government and the p arent company co nsented to th e order. T he sto ck p rice of theparent company also plummeted by over 30% in the aftermath of this accident, and in
addition, a company about 1/10 in scale of U CC made a hostile TOB (take-over bid). As
self-defense m easures, UCC ne eded a hug e a mount of m oney, and a s a result, thecompany w as changed from selling the indust rial gas and petrochemical products of
the $ 9 billion sales a year to selling commod ity chemical products of the $ 63 hundred
million sales a year . When the 21 century comes, though there might be some otherreasons, UCC was merg ed into a m ajor chemical company, and at p resent there is nocompany existing with the name of UCC.
References
・ Ikuo Fuk uyama, “B hopal d isaster and th e influences”, SE s eries Lear n fr om
accidents 2nd ed.” P29-34 , Safety Engineering(1989)
・Association watching Bhopal disaster. “Bhopal - The death city” (1986)
・ Toshiyuki Miyake,“Bhopal accident”, J.

Japan Soc. for Safety Engineering,

26,346-352(1987)
・ Yoichi U ehara, T erushige Ogawa, “T echnical Hand book of Fir e and E xplosion
Protection”, p12-22(1998)
・Masamitsu T amura, Mitsuru Arai and Y oshiaki Akutsu. “Energetic materials andsafety”, p69-71, Asakura Shoten(1999)
・Koji Nishikawa, “How to obtain knowledge from accident case (2 ) ”, J.High-pressure
Gas Safety Institute of Japan, 32, 507-509 (1995)

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