Failure Knowledge Database - 100 Selected Cases

Explosion of Warehouse during Storage of Expanded Polystyrene Beads【August 23rd, 1982

Yokkaichi, Mie, Japan】

Yuji Wada (National Institute of Advanced Industrial Science and Technology）
Mitsuo Kobayashi (Graduate School of New Frontier Sciences, University of Tokyo)
Masamitsu Tamura (Graduate School of New Frontier Sciences, University of Tokyo)

At the dawn of August 23rd, 1982, th e Namakawa W arehouse in Y okkaichi, Mie

Prefecture which stored petrochemical products, exploded and burned down. The soundof the explosion was h eard throughout the city area. The warehouse and the ad joining
building were burned down, and the third ware house and the office bui lding were also
partially destroyed. The ware house was located in a zone w here factories and hous ing
were int ermingled, and seve ral p etrochemical factorie s and other p lants of theYokkaichi petrochemical complex a djoined the Namakawa Warehouse on the east. The
north side was a densely housed a rea, an d the explosion damaged over 330 buildi ngs
within a 1km radius the warehouse. Th e damage did no t re ach the pe trochemicalcomplex, because a machinery factory betw een the warehouse and the complex played
the roll of a shield. The human damage was of 24 p ersons injured. The warehouse did
not store any dangerous materials that could self-ignite and explode, but it is assume dthat some li ght hydroca rbon gas su ch as propane and butane that was impregnatedinto exp anded p olystyrene (PS) be ads was released , for med a co mbustible gas air
mixture, and was ignited by some electrical spark.
The exp anded PS bea d is a raw material for making expanded p olystyrene that isused for packaging material and heat insulating material, such as containers of the cupnoodles. Lig ht hydrocarbons such a s prop ane and butane are im pregnated into thebeads as a foaming agent at about 6wt% by pressurizing when styren e is polymerized.
This light combustible gas was gradually re leased d uring storage. A t the wareh ouse
where the accident occurre d, the storage area was required to

be kept below 5℃.

However, the switch of the refrigeration unit, which was mounted inside the warehouse,was not of an explosionproof type, so the fire s eemed to be caused by an ele ctric spark
due to electric discharge.
Until the year of the accident, 1982, many years had already passed since the use of
the expanded polystyrene started. Didn’t the manufacturer give any information about
the danger of expanded PS beads or take some countermeasures during this period?

Ifthe exp anded PS bead s were d istributed in the market wit hout any information, t he1

Failure Knowledge Database - 100 Selected Cases

main problem leading t o this accident woul d be the mass-distribution of the material
with a possibility of generating a combustibl e gas or vapor to the market without a ny
consciousness of danger.
1. Event
At dawn on August 23rd, 1982, a large explosion occurred at a warehouse, which
had stored synthetic resin, at Yokkaichi in Mie P refecture, Japan. Two out of the thr eewarehouses collapsed completely, and the other warehouse as well as an office building
was parti ally destroyed. A large amount of d amage was also caused to the nearbybuildings, since the re were a larg e numbe r o f p rivate houses nearby . T wenty-four
persons were injured in the explosion.
At first, some combustible gases s uch as butane and pentane were released fromexpanded PS beads stored in the warehouse. Then, the combustible gas was ignited bya sp ark of electric d ischarge of the refrigeration unit, resu lting in the exp losion. The
expanded PS, which is synthetic resin used as packing ma terial or molding material
after foaming, was impregna ted with a foaming agent at manufacturing. Combustible
petroleum g ases such as p ropane, butane, and pentane are used as foaming agents.
These gases were released into the atmosphere gradually after manufacturing, and thequantity of thereleased gas d ecreased with time. However, the foaming agentremained, even after a l ong time passed, because the foami ng agent was necessary inorder to foam. Light ga s of the f oaming agent kept being released accumulated in thebuilding, and caused a large gas explosion. Therefore, the accident like this may occur
at anytime and any pl ace if the counterme asures against the re leased gas are nottaken at all.

Although there were many kinds of expanded resins used in those days, including

2Failure Knowledge Database - 100 Selected Casesa cop olymer of styr ene, only fo r expanded PS beads, co mbustible gas was used as afoaming agent.
2. Course
In the Namakawa Warehouse, 30 tons of t he expanded PS bead s were sto red in
100kg drum cans, and 120 tons of PS beads we re received in 500kg flexible containers
on August 19th and 20th.
At 17:00 on A ugust 21st, the war ehouse was opened once, and after that time th ewarehouse was subject to only, remote supervision by the s ecurity company; there wasno personnel at the site.
Sometime after 03:10 on August 23rd, an ex plosion occurred in the war ehouse, andthe explosion shifted to the fire. After a short interval at 03:12, the display at the off iceof the se curity company showed the breaking of wire betwe en the ware house and theoffice. It may be considered by the accident.
At 13:54 on August 23rd, extinguishment of the fire was confirmed.
3.

Cause
At the end of 1980, the warehouse wher e the accident occurred started being used

as a constant temperature gr ocery warehouse. In June

1981, the stored goods werechanged to petrochemical pro ducts. At that time, the t emperature f or the cons tanttemperature storage was changed from 15℃ to 5℃.
Butane and p entane, which were released fro m the exp anded PS bead s that werestored in the warehouse, formed a combustible gas-air mixture d ue to the insufficientventilation in the warehouse. The switch p anel of the refrigeration uni t for

maintaining the constant temperature of 5℃ was mounted inside the w arehouse, butthe panel was not explosionproof, a nd it was estimated that a spark w as caused by theelectric d ischarge fr om the switch p anel. Wh en th e usa ge of the warehouse waschanged, th e te mperature s etting of therefrigeration unit was changed, but theinstallation location wa s not changed and the switch panel was not changed to anexplosionproof type. Similarly, no consideration was paid giving to ventilation.
The staff o f the Namakawa Warehouse d id n ot seem t o realize that a c ombustible
gas was released from the exp anded PS be ads. The manuf acturer knew it, so usu allythe beads are stor ed in the wareho use of the manufacturer right afte r the p roduction,
when a considerable amount of gas i s released. This is called "ripening". After that theripening, t he bead s a re s hipped or st ored in public warehouses. In thepublicwarehouse, for quality maintenance, th e bead s are stored at a constant temperature.

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Failure Knowledge Database - 100 Selected Cases

Due to a ce rtain report, some manufactures considered that there was n o gas releas ed
from the b eads if the beads were kept at

5℃ or less. However , by experi ments

conducted after the acci dent, it was confirm ed that the rele ase of the c ombustible gas
continued, although th e rate d ecreased ev en if the bead s wer e k ept at 5 ℃ or less.
Besides, it i s not k nown whether the beads that caused the accident had been ripened
or not.
Another report indicated that changing the storage c ontainer from a dr um can to aflexible container was a probl

em. Fl exible containers can handle

a much larger

quantity at one time, ca n be used more eas ily and easily kept clean, compared w ith
drum cans or p aper bags. The refore, p resently in Jap an, synthetic r esin p ellets aremainly handled using

flexible containers.

However, by changing to this flexible

container, t he possibility that rel eased ga s diffuses into the warehouse increased

incomparison with the time when drum cans were used.
Another r eport suggest ed that though the te mperature in t he wareh ouse was 5 ℃,
the c ontents of the flex ible contain ers br ought from outsi de in the s ummertime andthose of p aper bags that wer e p iled up could n ot co oled d own so easily, the refore t hetemperature remained high and release of the gas continued.
There is a r eport that claims that the accid ent was due to insufficient m anagement
and preliminary survey of th e warehouse owner, but this s eems to be an unreasonable
demand for the wareh ouse owner. Warehouse owners can not h elp d epending on theinformation from manufacturer about materi als, especially about chemical products,
thus the st ored mat erials will be handled in the way indicated by manufacturer.

Moreover, in case of chemical materials handled for the first time at the warehouse, it
is difficult for the warehouse owner to obtain more information than tha t was provided
by the manufacturer.
Considering the p oints that have been mentioned abov e, the main cause of th e
accident is themanagement responsibility of the ma nufacturer who could notunderstand well the c haracteristic of the in-h ouse p roduct. The s econdary cause w as
insufficient stud y of the wareh ouse own er at the tim e when the warehouse wasremodeled in order to handle the chemical products, for example a lack of considerationof the location, the structure of the electrical items and ventilation.
There was not any regulation though the products wer e d istributed in large

quantity. Why was it? Ten years bef ore this accident, there was an accident in which apolyethylene she et exploded d uring rep lacement work of fr eight cars a t the A omoristation. If the gov ernment regarded the expl osion of p olyethylene sheet as imp ortant,and some regulations were carried out, has the situation changed? From the view point

4Failure Knowledge Database - 100 Selected Casesof the auth or, it is

off the p oint to expect t he ad ministration t o carry out su chregulations. In such a s ituation, a person who actually handles the materials cannot
obtain as much knowledge and information as the manufacturer . It is necessary t hat
the primary responsibili ty be taken by the ma nufacturer and that the manufacturer
itself considers the d angers and countermeasures. It seems that a nonofficial rule thata manufacturer independently offers informat ion to person s who handle the materials
such as warehouse owners should be established.
4. Process of cause elucidation
The typ e of the exp losion was immed iately jud ged to be a gas exp losion. The n ext
step in the cause elucid ation was to d etermine the co mposition of the g as that caused
the explosion. The following materials were considered as causative agents: CFC of therefrigeration unit and unknown ga s that was not included in the reg istration to theauthorities. As a result of the field insp ection, CFC was ruled out based on the fac ts
that almost all of the CFC was recovered

and the exist ence of unknow n gas was als oruled out because any materials but PS beads were not stored in the warehouse. It w as
known that the expanded PS bead s were impregnated with a combusti ble gas. It wasalso confirmed by the investigation committee that the gas was released

ev en attemperatures below 5℃ by the experiment on the change with the lapse of time of theweight of th e exp anded PS bead s. Testing at the National Research In stitute of Fi reand Disaster verified this result. The results of the experiment are shown in Fig.2. As aresult, the explosion th reshold was calculated to be 27.5 ℃ as the t otal quantity ofbutane and pentane.

5Failure Knowledge Database - 100 Selected Cases

5. Immediate action
Since the explosion occurred suddenly in an unmanned warehouse, no action wastaken.
6. Countermeasure
After receiving the resea rch results from the accident investigation committee, thevice president of th e Fire and Disaster Management Agency sent a notification to theeach prefectural governor showing the countermeasures.
The main contents of t he c ountermeasures are as follow s: a fixed gas d etector
should be installed in warehouses of expanded PS beads in order to detect combustible
gas and an alarm should be sound if the c oncentration bec omes over 1/4 of thecombustion threshold, ventilation facilit

ies should be installed

for large scalewarehouses or ventilating openings should be installed for small warehouses t o assure
sufficient ventilation, and electric devices of the explosionproof type must be used.

6Failure Knowledge Database - 100 Selected Cases

The measures d escribed above we re ad opted based on th e approval of c ombustible
gas being generated, as it is impossi ble to compel the use of containers that will neverleak or never will be damaged when the gas released, since a large amount of expanded
PS beads have already been distributed in the market.
Although these c ountermeasures m ight be inev itable as they wer e tak en after theaccident, th ey were not fundamental countermeasures for p reventing the sim ilar

accident. B asically, onl y manufact urers can know th e p roperties of their p roducts
sufficiently, so adequate safety measures for ha ndling and storing the products should
be taken by the manufacturers. M oreover, manufacturers have a responsibility to offer
the information they have to users and warehoused operators.
7. Knowledge
The real situation is not known until the accident occurs. However, the main cause ofthis accid ent ap peared t o be th e res ult of sufficient examination of d anger in sp ite of
the knowledge about the generation of combustible gas. It is necessary t o maintain anacute sense of danger and sense of how-to-act against the danger. Why didn’t the actual
condition become clear in spite of a large distribution of the products? It is too late after
the accident occurred.
8. Influence of failure
Twenty-four pers ons were in jured in the accident. The p hysical damage included
the complete destruction of tw o warehouses and partial damage to one warehouse andone office building.
Since the warehouse was located close to a residential district, a total of 341 buildings
were damaged and 170 telephone lines became out-of-service. According to one report,
the total monetary damage including the d amage to t he neighbo rhood was 13.3

hundred million yen.
9. On the side
Accidents related to chemical factor ies that occ ur near a r esidential district cause
damage to many inhabitants who do not have any relation with the factories. Becauseof a high density of Jap anese cities, it is not easy to regulate the location of chemical
facilities, which are oft en older tha n the re sidential buildings nearby. So, the chemical
facilities that are locat ed close t o residential areas must be operated with far more
attention and knowledge compared t o the fac ilities in an industrial district, which arefar from p rivate hous es. How ever, i n fact, the opposite p henomenon s eems to oc cur7

Failure Knowledge Database - 100 Selected Cases

often.
One of the causes of this explosion was insufficient ventilation. Although it is an oldstory, th ere was an airc raft carrie r named “Oot ori (B ig bird )” that exp loded and w as
sunk by th e hit of only on e t orpedo in the World W ar Second. Thi s exp losion also
appeared to have been caused by the accumulation of gasoline vapor due to insufficientventilation. Considering these two a ccidents, there is a c ommon cause of the accid ent,
which is "insufficient ventilation", independent of the time and the place.
References
・ Fire-Defense Headquarter of

Yokkaichi City, “Outline of Fireon Namakawa

Warehouse”, Kindai Shobo, 242, 55-59(1982)
・National Dangerous Materials Safe Associ ation, “Fir e o f storage warehous e fo r
synthetic resin”, “Accidents examples of dangerous facilities 1”, p 8-10(1983)
・Fire Infor mation R es. C enter, “W arehouse explosion and fire-Fir e of Namakawa
warehouse (Yokkaichi)”, “Regional disaster prevention data overview”, p 88 (1986)
・Hiroshi Koseki, “Warehouse fire of the Yokkaichi City”, Fire fighting report, 36, 25-29(1982)
・Keiho Namba, “Namakawa Warehouse fire accident”, Kindai Shobo, 247, 17(1983)

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