Failure Knowledge Database - 100 Selected Cases

Explosion and Fire of Dibenzoyl Peroxide Factory【May 26th, 1990

Itabashi, Tokyo, Japan】

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

At around 10:40 on May 26th, 1990, a large explosion occurred at the chemical plan tof Daiichi Chemical industry Co., Ltd.

The plant was located in the area wh

erefactories and houses exist together in the north of the 23 wards of Tokyo. Eight persons
were killed, 18 persons were injured, nine of the twenty factory buildings burned down,
and 33 buildings in the surrounding area were damaged.
The larg e e xplosion started with a small exp

losion of d ibenzoyl p eroxide (B PO),

which the company ma nufactured, in the su bdivision room. The explosion spread t oeach workshop at different buildings. Several explosions occurred at intervals of one or
two minutes after the first explosion. BPO

that caused the first explosion was ahigh-density p roduct t hat exce eded 98% p urity. This high-density p roduct was
manufactured at only this factory in Japan( there were six manufacturers of t his

product in Japan). Since manufacturing of this high-density product is very dangerous,
the U .S.A. a nd Jap an were the only count ries where this p roduct was manufactured.
BPO is known as a dan gerous material, and it is designated as a self-reactive material,
dangerous material ty pe 5, in the fire p rotection law. The c ompany that caused theaccident had recogniz ed sufficiently the danger and th e re gulations of the fireprotection law. However, at sit e inspections by the fire fighting authorities, in order tohide the fact that the s tock of BPO had ex tensively ex ceeded the permitted quantity ,the company repeatedly conduc ted t he illegal actions, such as covering the fiber ca ns
containing BPO with a sheet

or putting empt y fiber cans on the upper partof t hemultistage pile. Furthermore, th e company ha d caused ac cidents thr ee tim es in t hepast.
As a result of this accid ent, the problems related to the l ocation of a factory that
handled dangerous materials, where existed adjacent to p rivate residences in the ar ea
where factories and houses exist together, were recognized.
BPO: abbreviation ofdibenzoyl p

C6H5-CO-O-O-CO-C6H5. It iseroxide.

The chemical form

ula isorganic p eroxide wh ere t wo benz oyl gro ups ar e

combined at the O-O. The O-O bond iseasy to bre ak, and the drie d pro duct can

1Failure Knowledge Database - 100 Selected Cases

explode by friction, imp act, or heati ng. F or a l ong tim e, it has been us ed for th e
bleaching fats, oils and flour . M ore rec ently, w ith the rise of the p etrochemicalindustry, it is used as a catalyst for manufacturing resin.
1.

Event
In the area where factories and houses exist together of Itabashi Ward in Tokyo, an

explosion occurred at a chemical plant at around 10:40

on May 26th, 1990. The

material ca using the explosion wa s organi c p eroxide B PO. B PO ha s been us ed formany years for bleachi ng of fats, oils andflour . With th e rise of th e p etrochemicalindustry, it i s now used as a catalys t for manufacturing resin. For ch emical use, t hreegrades of B PO products ar e produced: 100%, 75% and 50 %. The 100% grade product,
which means the p roduct with ov er 98% purity, was manufactured at only this factory
among six BPO manufacturing comp anies in Japan, and only the USA and Japan werethe countries manufacturing the 100% grad e product in the world. The 100% grade
product is designated as a self-reactive substance by the Fire Protection Law.
The factory at which the explosion occurred manufactured each of the three gradesof product: 100%, 75% and 50%. The product f orms were also varied, including crystal ,granular, wetted, and po wder. Various processes were placed in a complicated manner
within a small area of the factory in Tokyo, an d each stage of wo rk w as frequentl ychanged in p roportion to the fluctu ation of the demand for the product. Furthermore,manufacturing and han dling opera tions were often d ifferent fr om th ose p ermitted
under the fire p rotection law, and it was re peatedly co ncealed during site inspe ctions
by the fire fighting authorities and so on.
The accident occurred when the op erators were subdividin g 100% grade products
into 5 kg p olyethylene bags from a fiber can t hat contained 40 kg us ing a polyvinyl
chloride scoop and anelectronic balance on a dolly . The 100% grade products a reproduced by refining th e 75% g rade p roducts and finally by drying using methanol.
The explosion happened during the subdivisio n work in the subdivision room by somecauses. An operator, who was passing by the subdivision room, saw flames spouting out
before the explosion from under the part o f the east door of the subdivision room. Somebuildings where low-density products were manufactured or stored exploded one after
another, because the flames scattered with fragments of a slate roof and so on.
This explosion and fire resulted in a large disaster. Eight persons were killed, 18
persons w ere inj ured, and nine of the buildings in the factory burned down.

Furthermore, 33 p rivate hous es a djacent to the factory were d amaged, inclu dingbroken windowpanes and so on.

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Failure Knowledge Database - 100 Selected Cases

According to the newspaper, the illegal situ ation of the fact ory was as f ollows: thedaily output was six ti mes larger t han the permitted quantity, an d the stockpile also
greatly exceeded the permitted quantity . Th e methods of illegalities and the cover -up
were report ed in newsp apers and other mass media after the accident. For example,
they hid the cans containing BPO by piling empty cans above and beside the filled cans,and they p repared the count ermeasure man ual which ind icated the r oles of t heemployees in hiding the illegality at the site inspections, etc.
2.

CourseThe work on May 26th, 1990 started at 8: 30. The subdivision staff removed dust

and other materials manually from the dried product, and then they carried dried BPO
from the d rying ro om t o th e subd ivision r oom. The subdivision wo rk started at 9:30.
The floor was wetted with water before the work to prevent static electricity.
At 10:40, a f ire occurred in the subdivis ion room with spouti ng a small scale flamefrom the room, and a large exp losion followed in the ro om soon after . The c ourse of
events was guessed as follows, regarding the start of the fire as 0 seconds.
0 second:

A small fire occurred.

A few secon ds later: An explosion occurred in the room, an d a funnel state holewas generated in the room.
12-15 seconds later:

The subdivision r oom burned down, and block fen ces andso on, fell down. The fire spread to the adjacent buildings.

BPO

in the drying process at the adjacent building exploded twice.
After this, explosions occurred one after another, causing the fire to expand.
3.

Cause

3.1. First small fire and explosion in the subdivision room
A combusti ble gas–air mixture was gen erated by evaporation of methanol thatremained in the BPO product cont ained in the fiber drum.
mixture was thought to have been ignited b

The combustible gas-air

y electrosta tic discharge of subdividing

operators. Then the fire spread to BPO powder that was in a floating state in the fiber
drum, and next, it was estimatedthat the B PO p owder exploded. In ad dition, theexplosion spread to other BPO in the subdivision room. An operator saw the first fire.
Another possible cause of the explosion was that BPO dust or BPO decomposed gasthat was generated by friction filled the room a nd was igni ted by an el ectrical spark
due to brea kage of a fluores cent la mp. Ther e i s a possibili ty that some BPO spill ed
while being transported to the subdivision room and that the BPO got into the bearings

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Failure Knowledge Database - 100 Selected Casesof the d olly, where it w as decomposed by friction. How ever, the d amage of fluor escentlamps that was observed after the accident might have been a result of the explosion.
Although matters mentioned

above were triggers that directly

caused the

explosion, the true cause of th e explosion was t he company’s characteristics itself t hat
had caused many accidents, had stored

BPO extre mely exce eding the p ermitted

quantity and had hidden the illegality for a long period.

3.2 .

Cause of the spread of the damage extension
1)

The burning speed of the 100% BPO product is very high, and it is a material
that burns intensely. Therefore, the explosion spread to the adjacent building
and the fire occurred in an instant.

2)

There was a lot of BPO stored in the places where the explosions spread.

3)

The fire th at was caused by the e xplosion in the subdivision room sp readrapidly and caused explosions one after another because the buildings where
BPO was handled were close each other.

4)

The distance from the factory gate to the area of the subdivision room was far,and evacuation was not easy.

5)

Storage and production that exceeded the permitted quantity had been done.

The cause s mentioned above are no t the tr ue causes, just as th e cau ses of th e
explosion in the subdivision room. Although it might have been an ine vitable result of

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Failure Knowledge Database - 100 Selected Cases

the econ omic situation, the main problem was t hat the operation was continued a t asite without room f or expansion, which wa s located in an area crowded with privat e
residences.

4. Process of cause elucidation
Since all fo ur p ersons who w ere working in the subdivision room died and thesubdivision room was destroye d without leaving any traces by the explosion, the causeof the expl osion was confirmed th rough va rious experi ments design ed to t est t heconceivable hyp otheses based on interviews wi th the p ersons co ncerned and slighttraces that remained at the site.
1) It was shown that the explosion was a condensed phase explosion caused by some
explosives, not a gas explosion, because a funnel hole remained in the subdivision
room was in a typ ical shap e of a cond ensed p hase exp losion. The explosion was
therefore determined to have been generated by BPO in the subdivision room.
2) The four p ersons wo rking in the su bdivision ro om d ied outside the r oom, whichmeans they escaped fro m the r oom and d ied. From this fac t, it was shown thatthe fire occurred first, and then the explosion followed.
3) The hypothesis that the fire had occurred as a result of the contamination of BPO
itself was rejected based on the examination of the National Institute of Fire andDisaster.

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Failure Knowledge Database - 100 Selected Cases

4) The possibility that the explosi on was caused by a cigarette or direct sunlight
was also ex amined. T he cigar ette hypothesis was rej ected by the te stimony ofother employees, and the possibility of direct sunlight was also reject ed based on
the consideration of the building structure and working condition.
5) The existence of methanol was sufficiently possible after drying for obt aining the
100% grade BPO product. It was also

possible that static electricity was

generated in the subd ivision work. If the el ectrostatic charge prevention method
was insufficient, for instance only wetting of fl oor by water spraying was done,
and then the prevention effect would be lost when ventilation was carried out.
Incidentally, the BPO pro duct m ay no t have be en drie d p erfectly during drying
operation. Also, it is certain that static electricity is generated when work is done.
5. Immediate action
The factory staff tried to extinguish the fire by using the fire p ump at the site in
the initial s tage of the explosion. However the power line of the pump was cut by t heinfluence of the explosion.
6. Countermeasure
After rec eiving the sur vey result of the investigation committee, the Ministry ofLabor demanded the concerning group as take countermeasures as follows;
1) Change to a safe BPO product, for example, a conversion to a lower purity grade.
2) Ensuring the safety of BPO handling facilities.
3) Paying more attention to the ti me and ventilation conditions for t he drying of
BPO.
4) Ensuring the safety of the subdivision room (four items).
5) Ensuring the safety of the subdivisio n work; wearing the anti-static electri city
clothes and decreasing of BPO quan tity in the subdivision room, and so on (fiveitems).
6) Providing complete safety education, preparation of work standards, and so on.
The guidance and advice mentioned above are reasonable. However, the essential
problem remains unsol ved if the safety cons ciousness of the manager s and executives
is not imp roved. Furthermore, n o solution wa s given fo r the locatio n p roblem of thefactory where factories and houses exist together.
7.

Knowledge
This case is an example of an accident

in which the largest problems lies in the6Failure Knowledge Database - 100 Selected Cases

attitude an d conscious ness of the manageme nt staff. An y difficult t echniques wererequired for operating t he facilities in safety. This accident would not have occurred if
the company had operated the factory with c ommon care about safety that is required
for nor mal chemi cal p lants. If they were aware of the ddoing, they should have taken the basic sa

anger of th e work they werefety measures such as static electricity

countermeasures and confirmation of drying.
8.

Influence of failure
As the human damage, eightpers ons were killed and 18

persons were injured.

Furthermore, some of the nearby residents were treated temporarily for eye pains andother minor problems. As for the physic al damage, nine buildings with a floor area of
970m2 burned d own in the factor y, wind owpanes of 38

private resi dences in t heneighborhood broke, and 19 cars w ere damaged. The monetary damage was estimatedto be about 150 millio

n yen, and 700 millio n yen was paid

as indemnities to thebereaved family members.
The biggest damage would be a loss of the social confidence in the enterprise.
9.

On the side
Many accidents had occurr

ed at the fact

ory before thi s accid ent. The list ofprevious accidents is as follows.
1) In September 1975 , a small explosionof a piece of

metal adherent to BPO

occurred wh en a small p iece of a metal was thrown fro m the sec ond floor of th e
factory and hit the metal adherent to BPO on the first floor.
2) In July 1978, 170 kg of BPO, which was stopped shipping, was ignited by the heatof sunlight, and the fire spread to the warehouse. Twelve persons were injured.
3) In March 1990, a b atch of BPO product, in which alkalinity of sodium hydroxide
remained a s a resultof insufficient water w ashing during the

manufacturing

process, exploded und er storage d ue to a sp ontaneous chemical r eaction, and th e
external wall and glass of the factory were damaged.
In this accident, the damage to the neighb orhood was small, because t he explosions
had occurr ed at a time when c hildren w ere not playing outside. The

damage woul dhave been much greater if the time of the explosions had been different.
Although the factory was surrounded by houses at that time of the accident, it islikely that there had been only a few r esidences n earby when thi s factory w as
established. It appears that houses wereconstructed around the factory s ome t ime

after the factory had been built. Considering such a time course, it can be seen that the7Failure Knowledge Database - 100 Selected Cases

problem here is equival ent to the p roblem that "an old building that fulfilled the laws
and rules in that days becomes illegal in to day’s laws and r ules” which is mentioned
related to the earthquakes. The idea of th e management should be changed according
to the environment changes, or danger will be generated.

References
・Ministry of Labor sp ecial investi gation comm ittee for D aiichi Kasei Kogyo Co. Ltd.
“Investigation report on Daiichi Kasei Kogyo Co., Ltd. explosion accident” (1991)
・ Yoichi Uehara, T erushige Ogawa, “T echnical Hand book for Fir e and E xplosion
Protection”, p.49-51 (1998)
・Fire and Disaster Management Agency, “Exp losion and Fir e of th e che mical p lant
manufacturing dibenzoyl peroxide, etc.”, “Acci dent case of t he d angerous material”,
p. 66-67(1990)
・Research secti on of Fire Pr evention Div. Tokyo Fire De p. “Outline of investigat ion
report of ex plosion and fire occur red at No1 f actory, Daiichi Kasei Kogyo”, Kindai
Shobo, 470, 95-101 (2000)
・Yasuda Fire and Marine Co., Ltd. “Chemical plant exploded in the thickly housed are
and 8 person died”, Urgent Techno Report (1990)

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