Failure Knowledge Database - 100 Selected Cases

Explosion of Resin Factory in Osaka【August 20th, 1982

Sakai, Osaka, Japan】.

Haruhiko Itagaki.
Mitsuo Kobayashi(National Institute of Industrial Safety)(Graduate School of Frontier Science，University of Tokyo)

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

This acci dent is an interesting

example for considering the safety o f a chemica lplant and the ways of establishing effective countermeasures after the occurrence of an
accident.
At midnight on August 20th, 1982, there was a relatively small explosion at a resin
manufacturing p lant of Daicel

Chemical I ndustries, Co., Ltd . at the Sakai

manufacturing complex in Saka i, Osaka, and the order to stop the plant was issued.
During the shutdown procedure of the plant, gas leaked from a monomer mixing drum
that contained two kinds of monomers as raw materials and a catalyst. The occurrenceof the leak was informed to the meeting of the managing staff who were discussing thecountermeasures to be taken to the first explosion. When all of the members attending
the meeting rushed to the leakage site, the second large explosion suddenly occurred.
This second explosion resulted in six fatalit ies, nine seriously injured, and 198 sligh tly
injured persons. 178 of the 198 persons who we re slightly injured were inhabitants of
the nearby area. Furthermore, the number of houses damaged in the accident was over
1700.
Before th e first exp losion, agitation of

the polym erization re actor and supply o flukewarm water to the cooling jacket had st opped due to a po wer failure . In orde r to
keep the reactor c ool, cold co oling water was used inste ad of the lukewarm w ater
immediately. Howev er, the reacti on le d toa runaway reaction,and monomers

evaporated. The evap orated gas by passed the combustion deodorization furnac e t hat
had been designed on the assump tion of usual exhaust gas proces

sing, and the

explosion occurred at the inlet of th e stack. H owever, this first exp losion did not cause
any human damage or large physical damage.
The shutdown procedure of the plant was executed in the s ettlement of the accident,
and at the same ti

me, the managing

staff held a meeting

countermeasures to b e taken. The next

to discuss theday , the shutdo wn pro cedure and t hecountermeasure meeting were continued. In the evening, a gas leakage occurred from amonomer mixing drum, which contained the monomers with which the reactor will be

1Failure Knowledge Database - 100 Selected Cases

charged. The gas leakage gradually increased, and no body co uld ge t ne ar the le akage
place. On hearing the news, all of the members who were attending the meeting cameto the leakage site. At that moment, a large explosion occurred. All human damage andlarge physical damage occurred in this second explosion.
While a liquid mixture of acryloni

trile, st yrene and a p olymerization catalyst oforganic peroxide was lef t in the monomer mixi ng drum fo r 42 hours, a polymerization
reaction started and let toa runaway reaction as a resu

lt of heat accumulati on.

Therefore, the p ressure inc reased, and co mbustible gas leakedout. Th e gas

accumulated in the factory and wa s ignited by a spark from th e electric devices t hat
were installed outside the dangerous facility zone. Staff members of the manufacturingsection had thought at t hat time that a po lymerization rea ction would not occur at a
low temperature of 27℃. However, it appeared that the polymerization reaction started
by the delay of the monomer charge to the reactor that resulted from the first accident.
When the plant was shutdown, there was st ill about 3800 kg of liquid in the monomer
mixing drum.
1.

Event
At this plant, AS resin (a co-polymer

resin (a tresin of acrylonitri le and styrene) and AB S

hree-component system co-polyacrylonitrile) were ma

mer resin of styrennufactured, and th

ere were fiv

e, butadien e ande r eactors for AS resinpolymerization. On th e day of the f irst exp losion, two r eactors named C and G we rebeing used for polymerization.

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Failure Knowledge Database - 100 Selected Cases

The 400V power supply of the polymerization section failed at around midnight. The
agitators and pumps for cooling water of the C and G po lymerization reactors stopped,
so cooling of the reactors stopped. In order to continue cooling, lukewarm supply w ater
was switched to cold water manually. One t on of cold water was a dded to each reactor
to cool them. Some time after, the polymerization reaction in the two reactors became arunaway reaction, and white smoky gas spouted from the manhole of the C reactor. The
alarm of the deodorizing furnace rang, and the safet y valveof the furna ce

automatically operated, redirecting the gas directly to the stack for combustion tail gas
bypassing t he furnace. At that time, the concentration of the co mbustible gas at the
furnace inlet was 35% of the lower explosion limit, and the temperature in the furnace
exceeded 830 ℃. Th e fir st exp losion occur red i n the exha ust gas d uct, and d amage
occurred only in the furnace system.
The reason why a large amount of gas flowed i nto th e furn ace syst em i s explained
below. The l iquid in the C and G reactors

separated into two la yers, a polymer lay er

and a monomer layer, because agitation in the reactors stopped. Furthermore, since theheat of reaction was not being removed, a rapid polymerization reaction occurred, andthe liquid t emperature reached the boiling point as a result of heat generated by t heexothermic reaction. Th e re mained mon omer evaporated, and a combustible gas w as
formed. The combustible gas flowed from the pressure regulating valve via the vent gas
collector t o the furnace system. The furnace system diagram is shown in

Fig.2.

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Failure Knowledge Database - 100 Selected Cases

The furnace had the foll owing instrumentation system installed for safety: when t he
combustible gas comp osition exce eds 50% of the lower explosion limit, or the furna ce
temperature is over 830 ℃, the gas is redirected through bypass piping and led to thestack which discharges the gas

after itis burned. I n this ac cident case,theinstrumentation system worked as designed.
After the fir st exp losion, a stop ord er of th e facilities was given by the fire fighting
authorities. Ther efore, the e mployees of the factory ca rried out only

the ne cessary

protection work such as drawing off the r emaining material in the r eactors in order tostop the plant in safe. The next day, thirteen managers of the factory had a preliminary
meeting for the accident investigation commi ttee at the same time as the shutdow

nprocedure w as being ex ecuted. In t he evening, gas began leaking fro m the m onomer
mixing d rum of th e C series. An o perator wh o found th e l eakage t ried to enter t hebuilding in order to confirm the sit uation, but he could not enter the building because
the leak had increased. Some of the operators left the site to take refuge. One of theminformed th e manage rs at the meeting of the leak. All the members
meeting rushed to theattending thesite. Th e s econd hug e exp losion occurred w hen they w ere

preparing to cool the mixing drum by spraying water on it with fireplugs.
2.

Course2.1. Course of the first explosion
At around 23:52 on August 19th, abnormal

behavior of the agitators of thepolymerization reactors was n otified, and an op erator i n the electric d evice r oom
checked the causes. While he was c hecking, an electromagnetic switch burned out. He
cut the pow er supply after he informed the in cident to th e manufacturing secti on. At
that moment, although two reactors were operating, the agitators and the warm water
circulation pumps for removing the reaction heat through thermal jackets stopped. The
cooling water was switched to cold water manually in order to continue the cooling.
At around 00:10 on August 20th, gas began

to le ak from the packing part o f the

manhole of the C reactor. The alarm of the furnace rang at 00:15. The bypass valve of
the furnace opened, and the combustible gas before combustion was directly discharged
into the stack for burnt tail gas. The temperature inside the furnace exceeded 830℃ atthat time.
At around 00:20, the gas detector

in th e building operated. At around 00:25, one

operator h eard the sou nd of the first exp losion. The op erators tried to extinguish thefire with the outdoor fireplugs and reported the explosion to the related parties.
At 00:28, the public fire brigade turned out, and the fire was extinguished at 00:31.

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Failure Knowledge Database - 100 Selected Cases

2.2.

Course of the second explosion

As the fire extinguishment was reported, from around 00:30 on August 20th, thefactory members start ed to ch eck the facto ry. The

check and c onfirmation wo rk

continued d uring a wh ole day. The check work was executed mainly around the tw oreactors. The managing staff memb ers w ere busy grasping the situation, explaining
the situation to the fire fighters and to th e pol ice, and rep orting the s ituation to theheadquarters.
At 13:00 on August 21st, the preliminary

meeting was started by the factory st aff

members for preparing for the accident cause investigation committee at headquarters.
This meeting continued until after 17:00.
At 17:12, a whistling sound was heard from the ro om where the reacto rs were

installed. When an operator looked into the room to check, he found a white gas coming
out from the G reactor. Another operator contacted the managers at the meeting. All of
the me mbers of the me eting hurrie d to the site. The white gas flowed from th e ro om
towards the north-sid e center road . A t around 17:25, the memb ers o f the me eting
gathered ar ound two firep lugs, an d while preparing to spray the site with water,ahuge explosion occurred.
3.

Cause

3.1. Cause of the first explosion
Stopping of the agitat or by a power failu re ca used a runaway reaction in the tworeactors an d the m onomers (styrene, ac rylonitrile) in the react ors evaporated. T heevaporated gas was int roduced int o the fu rnace system of the vent sys tem where t hecapacity was assumed t o b e d esigned for th e normal op eration, and th e furna ce w as
bypassed, since the temperature in the furnace became higher than the furnace designtemperature. The monomer vapor was ignited by some ign ition sauce, and it exp lodedin the duct of the furnace syst em. Theref ore, a pow er failure and the subseq uent
runaway reaction are the direct causes of the explosion.
The occur rence of thepower failure may

be a cause of the accident, but power

failures can occur anywhere. The problem is why a runaway reaction occurred after the
power failur e and why t he explosion oc curred after the ru naway react ion. The plant
was not designed for sa fety in the event of a power failure and the operation manual
did no t co ntain appro priate o peration pr ocedures for a p
mentioned above must be true causes.

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ower failure. Two items

Failure Knowledge Database - 100 Selected Cases

To begin with, theeffect of th e ag itation stop is d iscussed. The p roblem can b e

considered from tw o as pects. Th e fi rst is heat t ransfer. W hen agitation stop s in a big
vessel with a diameter of 2 met ers, it is no t possible to cool the liquid in the vessel.

Agitation makes a lami nar film on the heat transfer su rface thinn er, decreasing h eattransfer resistance, equalizing the t emperature of the content liquid, and thus coolingis carrie d out. Co nsidering the size o f the agitation drum, which is on an indust rial
scale, it is apparent tha t effective heat tran sfer is not possible, if the agitation stops.
Furthermore, th e p olymer in th e react or is p revented from sep arating from themonomer by agitation, causing the reaction to advance at a moderate rate. The polymer,
which is sol id and has a high density , separates from the l ow density monomer, if theagitation stops. The monomer layer with no polymer has

high reaction potential. As

agitation stopped, heat coul d not be re moved from the m onomer layer, and a hot spo t
was easily formed. The polymerization in the monomer layer advanced, and a runaway
reaction occurred. A s a resultof the te mperature ri se, it se ems to havebeen

unavoidable that the m onomer eva porated, its pressure r ose, and th e v ent gas of t hemonomer increased.
The n ext aspect is the small capacity of th e fu rnace. A s only two out of five resi nreactors we re in operation at the ti me of the p ower failure, a bypass was inevitable.
The combustible gas-air mixture th at was redi rected to the stack did not burn for t hat
reason, and the exp losion occurred as a result. The exact reason why t he combustible
gas-air mixture was formed is unknown, but th ere seemed to be som e problems in the
deodorization system of the vent gas. It

can be supposed that there were someproblems in the v ent g as system t hat might cause an exp losion under th e conditions
resulting from a power failure.

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Failure Knowledge Database - 100 Selected Cases

At present, more safety mechanisms for a power failure can be designed, as shown in
Fig.5. For instance, a large blowdown drum with diluents or coolants can be installe dfor r eceiving the reactor c ontents or an inhibitor drum can be installed with ahigh-pressure inert gas cylinder to add thepolymerization inhibitor to the react or.

Fig.1 shows that p iping to th e emergency d ischarge p it is mo unted fr om th e d raw-off
nozzle at the react or bottom. Although the co ntents of the discharge pit are unkno wn,
the piping seems to be emergency piping through which the slurry and the liquid in thereactor could be discha rged t o a s afety ve ssel when a runaway react ion occurred or
predicted to occur. If this case, it is a question why the piping was not used.

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Failure Knowledge Database - 100 Selected Cases

3.2.

Cause of the second explosion
The caus e of the se cond exp losion is though t to be as

follows. Since therawmaterial th at had been p repared befor e th e fir st exp losion was l eft fo r h ours in t hemonomer mixing drum, a polymerization reaction was caused in th e drum. Therefore,
the te mperature rose, and a gas le akage was c aused by th e asso ciated p ressure rise.
The p repared raw material was a mixtureof about 3.8 tons ofhighly reactive

acrylonitrile and styrene with initiator added.
Originally, the prepared raw material woul d have been tra nsferred to the reactor
one hour after preparation and it would have reacted by controlling the temperature in
the batch. However, since the raw material was left in the monomer mixing drum for
42 hours be cause of th e first exp losion, a runaw ay reaction occurred. The temperature

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Failure Knowledge Database - 100 Selected Cases

after the preparation was 27 ℃, and it may ha ve been th ought that no reaction would
occur at tha t low t emperature. Furthermore, from the equipment aspect, the preparedraw material in the monom er mixi ng drum had to be transferre d and re acted in thereactor.
Therefore, the true causes of the accident appeared to be one of the following three;insufficient study of safe storage ofthe prepared raw mat erial on th e R&D stage,

insufficient p rocess d esign for the prepared raw material, and the fact that all thefactory members did not pay attention to indispensable material for the sake of u rgent
countermeasures to the explosion.
The h uman damage resulting from the semembers at the meeting went to the site tocond exp losion was huge . A ll of th egether without sufficient confirmation ofsafety. This action appears to be one of the causes that increased the human damage. It
is necessary to construct a system th at gives sufficient information so t hat the director
can make an accurate judgment in the event of an emergency.
4.

Process of cause elucidation
The cause o f the first e xplosion can be easily u nderstood fr om a se ries of events

after a p ower failur e, o peration r ecords and th e t estimonies of th e p arties c oncerned.
Most of th e official a ccident inv estigation report was concern ed with the second
explosion and ther e w as no d escription of th e elucidation of the ca use of th e f irst
explosion.

Regarding the sec ond explosion, the blast center was d etermined almost perfectlyfrom t estimony of witn ess and on-site stud y. The so urce of the lea ked vap or was

9Failure Knowledge Database - 100 Selected Cases

confirmed according t o the order b elow; 1) To specify the vessel wh ere the sufficientquantity of the gas remained, 2) T o clarify th e reason why the gas lea ked fro m th evessel. The monomer mixing drum and the reactor were assumed the vessel where thegas might l eak. The quantity of monomers that remained in the reactor was too small
for the size of the second explosion. In the monomer mixing drum, there was about 3.8
tons of raw material monomers which was a sufficient quantity to cause the explosion.
After careful experiments, it was confirmed that the monomers in the mixing drum
had begun to react at a relatively low temperature and thus the gas leakage occurred.
Since th e s ize and for ce of th e explosion c ould be exp lained if lea kage fr om themonomer mixing drum was assumed, it was concluded that the gas leakage was caused
by a rise in pressure due to a polymerization reaction that had occurred during the longhours of storage in the drum.
5.

Immediate action
In the first explosion, four employees of the resin factory carried out the emergency

notification by an alarm and an office phone. In addition, they used outdoor fireplugs toextinguish the fire. One fire engin e of the facto ry turned out, and careful preparations
were made in front of the resin factory.
At the time of the s econd exp losion, the company memb ers wer e sp raying waterfrom one firep lug on t he site and p reparing to use oth er firep lugs. The f ollowing
activities were carried out after th e exp losion: notice to t he fire fight ing authorit ies,
rescue of th e victims , a nd emergen cy rescue re quests to the fire fighting authoriti es.
After the municipal fire fighting team a rrived, th e company’ s fire fighting t
executed rescue activiti es and cont inued to sp ray water on the siteeamusing outdoor

fireplugs under the supervision of the municipal fire fighting team. After extinguishing
the fire, they continued to cool the tank yard by spraying water on it for three days.
6.

Countermeasure
The futu re countermeasures, which cover as much as 14 pages, are described in

the acciden t investigation report. I n orde r to assure countermeasures for c omplete
safety, man y items ar e d escribed from man y aspects such as managementofenvironmental problems in the neighboring regions, a system for long-distance security
and fire p revention, establishment of organi zations for d isaster p revention, ed ucationand so on.
Here, the basic stance of the technical aspect is described.
1. Safety design of the plant: installation of adequate safety s ystems in the plant

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Failure Knowledge Database - 100 Selected Cases

is imp ortant to p revent the oc currence of large -scale d isasters by mini mizing
the effect of a s mall ac cident, failu re or dam age in the plant. Base d on thisviewpoint, redundancy , automatization andsystem should bemechanization of thecontrolconsidered. Also, in terlocks and depressurizing

devicesshould be p repared fo r emergent si tuations. At the p lant where th e a ccident
occurred, there seemed to be a lack of study of the cap acity of the furna ce andof consideration of countermeasures when the furnace is by-passed.
2.

Improvement of the facilities: it is natural to sufficiently consid

er thestructure and arrangement of the plant. In particular , the plant should beequipped with an early detection method devices and safe shutdown system for
emergencies. In addition, if the supply of the utilities fails, prolonged operationof the plant is not possible. The st eady supply of the utilities must be assured.
Utilities include el ectric power, steam, and cooling water, which are necessary
for plant operation. For example, isolation and duplication of the power supply,and spare diesel driven pumps for cooling water should be considered.
3. Related to chemical reactions: the characteristics of the reactions in the process
must be sufficiently understood, and fa cilities and handling methods should beestablished according to the charact eristics. At the plant where the accident
occurred, it would have been effecti ve to have an agitation method of injecting
nitrogen ga s to maintain the cooling e ffect when agitation stops and t o have
blowdown facilities.
4. Thoroughness of op eration stand ards and education: ev en the best safety
design and the best

construction of the p lant are us eless if they are n ot

reflected in operations. It is important to prepare operation standards based on
the c onsideration of t he characteristics, d angers of th e reacti ons and thematerials, the characteristics of th e plant, and to ed ucate the operators basedon the operation standards.
7. Knowledge
1) In abnormal situations, unusual phenomena may occur that cannot be imagine dunder n ormal operation cond itions. It is important to

prepare faci lities andoperation methods considering for utility failures because utilities are the lifelineof the plant.
2) Chemicals may have to be retained for an unexpectedly long period of time o r at
unpredicted temp eratures. It is n ecessary t o carry out pr ior examinations ofthese cases.

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Failure Knowledge Database - 100 Selected Cases

3) In the case of an

emergency, it i s d angerous for all of t he m embers to take th esame action and/or the same way of thinking. It is necessary to organize a system
for allotting the rol es of investigation, total management, and so on to eachmember.
4) Process design and operational control based on sufficient c onsideration of what
can happen when agitation stops are n ecessary. It is also n ecessary to consider
the way of education in an emergency.
8. Influence of failure
All of the human d amage caused b y the second exp losion was the d eaths of six
persons and the injured of 207 persons. Among the injured the number of inhabitantsof the neighboring area was 178.

The physical damage was as follows; 1733 buildings of 2812 households in the area
within the average radius of 1400m were da

maged. As the factoryin the densely

populated area, considerable damage was caused to the neighboring area.
In the factory, many facilities were burned and were damaged by a blast.
The direct monetary damage has

been ca lculated to beabout one billion yen.

However, the total damage including compen sation, indemnities, restoration expenses

12Failure Knowledge Database - 100 Selected Cases

and the cost of not operating the plant must be far more.
9. On the side
An exp losion of a ch emical p lant in an ov erpopulated region is un expectedly
common. A benzoyl peroxide explosion in It abashi Ward of Tokyo, and a hydroxylamine
explosion al ong th e nat ional road r oute 17 in Gunma Pr efecture are the examples.
These cases are also included in “Selected 100 accidents”. These accidents resulted incatastrophic damage, a nd made an excessively strong impact on s ociety. Someti mes,
isolation of the factory from the overpopulated region ma y be only o ne meth od foravoiding disastrous dam age caused by an accident that occu rred at a ch emical factory.
Furthermore, this accid ent was caused by a problem related to agit ation. Stopping or
restarting a gitation is one of the most im portant situation changes at a plant. One
example of an accident that wascaused by stopping of agitationis "Fire during

Ethylidenenorbornene Manufacturing" which occurred at a factory in Kawasaki and isincluded in “Selected 10 0 A ccidents”. Th ere are also som e examples of accidents th atoccurred du ring restart of agitation in syst

ems such as a reactionof concentrat ed

sulfuric acid and toluene. What w ill happe n when the b asic conditions are changed
such as in these examples is a basic p roblem at chemi cal p lants, and these examples
must be learned as a basis of safety engineering.
References
・Yoichi Uehara, “Outline of the AS resin plant explosion. Fire and explosion examples”,
J. Japan Soc. for Safety Engineering, 41, 97-111 (2002)
・The fire fighting union in Sakai City & Takaishi City, “Accident investigation report of
explosion a nd fire at the r esin p lant in Sakai factory ,Da icel C hemical Ind ustries
Ltd. ” (1983)
・ Ikuo Fukuyama, “Explosion by

the runawa y reaction” , SE series, “Learn fr om

accidents” pp. 20-23 Safety Engineering (1987)

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