Failure Knowledge Database / 100 Selected Cases

Filling Station Explosion due to LP Gas Discharge
from an Overfilled Container
May 17th, 1986, Yokkaichi, Mie Pref.
AKATSUKA, Hirotaka (High Pressure Gas Safety Institute of Japan)
KOBAYASHI, Hideo (Tokyo Institute of Technology)(Summary)
On May 17th, 1986, staff members at an LP gas filling station in Yokkaichi City were filling LP gas into
a 20 kg container.

Noticing that the container had overfilled halfway, the s taff member opened the valve

to discharge t he overfilled gas, w hich t hen i gnited causing a fire.

Heated by t he flam es of the fire, t hesafety valv es of th e su rrounding co ntainers op erated an d di scharged more gas, w hich caused t he f ire tospread through the filling station. As a r esult, containers of various sizes burst one after another, and thehorizontal propane and butane gas tanks went up in flames, resulting in the filling station itself exploding.
This case example demonstrated the importance of taking appropriate measures to prevent the spread of afire in order to avoid escalation to a major disaster.
1. EventAt th e LP (Li quefied Petro leum) gas fil ling s tation, the staf f m embers w ere fil ling gas into a 20 k g
container and a 50 kg container (see Fig. 1) using a filling machine. Noticing halfway through the processthat th e gas meter w as not prop erly set on th e 2 0 k g co ntainer, t hey che cked and fo und o ut tha t th econtainer was overfilled with gas.

They turned the overfilled container sideways near the filling machineand opened the valve (see Fig. 2) to start discharging liquid-state gas directly into the air.
was disch arged in to the air, the gas i gnited a nd developed into a fir e.

The moment it

The ran ge of fire w as cont ained

initially, b ut it so on s pread across the ar ea of th e fi lling s tation. Because the valve of t he overfilledcontainer was left open after the initial inflammation, gas continued to come out fr om the open valve andfueled the fire, which in turn heated the surrounding containers so intensely that their safety valves released
and discharged gas, causing the fire to spread through the filling station (See Fi g. 3).

As a resul t, the 20kg, 50 kg, and 500 kg containers exploded one after another. One 20 ton horizontal propane tank and one
15 ton horizontal butane tank in the station burst into flames as w ell.

The inflammation source was thesparks that occurred between the electrostatically-charged gas from the overfilled container and a numberof ele ctrical conductors nearby (incl uding other containers).

This accident not only dem onstrated theimportance of taking appropriate measures to prevent the spread of a fi re in an accident, but it also taught
us a number of other important lessons discussed below.
The figure below shows the results of a fault tree analysis.
Fig. 4: Fault tree diagram with a focus on mode, mechanism, and process of fracture
The first i gnition oc curred the m oment that the li quid LP g as was disch arged from the ove rfilledcontainer.

This ignition w as tri ggered by spark discharge.
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The L P gas d ischarged from the con tainer

Failure Knowledge Database / 100 Selected Cases

was charged with static electricity and reacted with a number of electrical conductors nearby such as othe rcompressed-gas cylinders.

When rele ased from a narrow nozz le, a gas ca n be come char ged w ith st atic

electricity and generate sparks through reaction with other electrical conductors.
At the early stage of the fire, on ly the LP gas coming out of the overfi lled co ntainer was burning.
However, because the valve of the overfilled container was left open after the initial inflammation, the firecontinued to grow. As a result, the pressure in the small containers around the area increased, causing theirsafety va lves to operate and rele ase L P gas.

This gas int ensified t he sc ale of t he fire, wh ich eventually

spread th roughout the entire fi lling st ation.

Presumably, som e of t he c ontainers exploded a nd s catteredbroken pieces around aft er being exposed directly to the flames of the LP gas spewing out from the safe ty
valves of the other containers.
There were also large-sized 500kg containers on the filling platform.

Just as with the small containers,

the safety valves of some of th e 500kg containers operated and released LP gas, which also ignited.

It isbelieved that the resulting flames heated the barrelheads of the other 500kg containers so intensely that they
burst and scattered broken pieces around.

Tthe explosion of these containers was followed by a firebal labout 50m in width and 63m in height.
The filling station was also equipped with one 20ton horizontal propane tank and one 15 ton horizontal
butane tank.

The flames of the fire bur nt out the seats of the block valves that were attached to the gas

release pipes of thes e ta nks.

As a result, gas als o spewed from t hese t anks, a nd t he t anks burst i ntoflames.
The figure below shows the results of an event tree analysis.
Fig. 5: Event tree diagram of filling station explosion
Because the LP gas was di scharged in a liquid state fro m the overfille d container, the LP gas becam e
charged with static electricity and re acted with t he electrical conductors nearby to generate sparks, which
triggered the inflammation of the discharged gas.

Because the valve of the overfilled container was l eft

open after t he i nflammation, the f ire grew lar ge e nough to c ause the safe ty v alves of the s urrounding
containers to operate, causing the range of the fire to enlarge.

In this process, some of the containers burst,

and the valve seats of the tanks burnt out, releasing gas which in turn ignited.
2. Course
At the fil ling station, on e st aff member had start ed fil ling g as in to a 20 k g co ntainer usin g th e N o.1
filling m achine a nd was m aking pre parations to fil l gas i nto a 50 kg co ntainer using the No .2 fi llingmachine.

In the meantime, another staff member checked the No.1 filling machine and noticed that thegas meter was not properly set on the 20kg container.

He then removed the 20kg container to check it,

and found that it was overfilled with gas. He moved the overfilled container a short distance away and set
another 20 kg container on the filling machine.
The staf f m embers turned the o verfilled 20k g co ntainer sideway s n ear the No. 1 filling m achine andopened the v alve t o st art discharging the liquid-state L P gas (th is operation w as n ot uncommon in t hosedays.)

Immediately after that, the discharged LP gas ignited and caused a fire. At this time, both of the2Failure Knowledge Database / 100 Selected Cases

safety manager and the safety foreman were not at the filling station.
Two minutes after the fire broke out, a staff member called the fire department. A fire en gine arrived
at th e sce ne five m inutes later.

When the fire e ngine arrive d, o nly the co ntainers aroun d t he filli ng

machines were burning on the filling platform, and the containers along the outer edge of the platform werenot. A bout five m inutes after th e fire eng ine arriv ed, the grow ing fire eventually trig gered sev eral
explosions over the next t hree minutes. In the m eantime, the valve seats on the gas release pipes of thetanks burnt out, causing the gas to leak out from the tank and ignite.
3. Cause(1) Incorrect handling of the overfilled container
There are three ways to handle the gas in an overfilled container:○ allow the gas in the overfilled container to va porize and c ollect the vaporized gas into a storagetank using a gas compressor;○ refill (i.e. transfer) the gas from the overfilled container into another container; and○ dispose of the gas by diffusing it (i.e. to gradually discharge the gas into the air in an airy location
at least 8 m away fro m areas wh ere combustible or flammable objects or m aterials may be
handled or stored).
It probable that at the filling station in question, the staff members would customarily discharge a large
amount of liquid g as directly in to t he air fro m the c ontainers t hat were p laced n ear t he f illing machines.
They did not have any specific manual as to h ow to handle overfilled containers or how to t ake adequate
measures.
(2) Inadequate measures to prevent the expansion of a fire
The fire would not have spread throughout the filling station if the valve of the overfilled container had
been closed immediately after the initial inflammation of gas.

Not only was this operation neglected, butalso there were no signs that any of the emergency shutoff valves of the storage tanks were operated.
did the sprinkler system function although an attempt was made to operate it.

NorAll these facts suggest thatthe people at the filling station did not have sufficient safety awareness and had not been trained adequately
to handle accidents that could lead to a disaster.
4. Immediate Action
If a fire occurs at a gas filling station, highest priority should be given to controlling the fire at an earlystage.

To c ontrol t he fire at a n e arly st age, stoppi ng the bl owout and lea kage of gas is most effective,

because the leaking gas would otherwise serve as the medium for inflammation. The blowout or leakageof gas must be stopped by closing the source valve.

In most cases, the source valve can be accessed andclosed safely, because the direction and the scale of a fire generally remain constant at the early stages.

To

prevent the spread of a fire, it is also important to ensure that sprinklers and emergency shutoff valves willoperate.
In this accident, the valve of the overfilled container that triggered the fire was left open.
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Not only that,

Failure Knowledge Database / 100 Selected Cases

the emergency shutoff valves were not operated and the sprinkler system did not work because it was not
maintained regularly.

The important lesson is that the regular training of staff and the proper maintenanceof safety cont rol equipment are e ssential for the succes sful implementation of the a bove-mentioned safetymeasures in the case of an accident or a disaster.
5. CountermeasureWith this event as a turning point, the following amendments were made to the supplementary standards
for ministerial ordinance (June 22nd, 1987):(1) Emergency sh utoff valves, sprinklers, or oth er safety s ystems shall be a ccessible from at least twolocations, one of which shall be in an office or such other building.
(2) Filling platforms and thelocations wh ere tan k tr ucks are sto pped shal l a lso be eq uipped withsprinklers or other safety systems.
(3) The electrical power supply shall be reinforced to ensure that the pump will opera te for sprin klers orother safety systems.
(4) Discharging liquid-state gas from containers shall be banned.
6. Knowledge○ Never cut corners when handling a potential disaster.
This accident is an outstanding example of the importance of taking appropriate measures to prevent theexpansion of a disaster. The regular training of st aff, as well as t he proper maintenance of safe ty control
equipment, are essential for the successful implementation of appropriate measures against the expansionof a disaster.

On the other hand, the training for the prevention of disaster does not make any sense if it

ends in a mere formality that people view without any sense of urgency and that does not ensure that thepeople involved wil l ta ke a ppropriate a ction in the case that a re al accident or a disaster oc curs.

Anytechnical staff that may handle hazardous substances should reconsider the meaning of the training for theprevention of disaster and use it on a regular basis.
7. On the Side
○ Fireball
A fireball is often seen accompanying a huge explosion in a wide open space.

The name "fireball" isderived from the appearance of a globular mass of flames that an explosion forms in the air.
8. Information Source(1) Report of th e Revi ew Com mittee for A ccidents a nd C ountermeasures at LP G as Instit utions (N ov.
1986): Industrial Location and Pollution Bureau, Ministry of International Trade and Industry.
9. Primary Scenario
01. Carelessness
4Failure Knowledge Database / 100 Selected Cases

02. Insufficient Precaution
03. Overfilling
04. Organizational Problems
05. Poor Management
06. Poor Manual
07. Lack of Practical Training
08. Stultification of Training
09. Usage
10. Disposal
11. Discharge of Liquid-state LP Gas
12. Bad Event
13. Chemical Phenomenon
14. Static Electrification of LP Gas
15. Spark Discharge
16. Inflammation
17. Fire
18. Non-Regular Action
19. Inaction
20. Failure to Close Container Valve
21. Gas Blowout
22. Failure
23. Fracture/Damage24. Container Rupture
25. Fire
26. Secondary Damage
27. External Damage
28. Explosion of Filling Station

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Failure Knowledge Database / 100 Selected Cases(with a siphon pipe)

Fig. 1 Gas container.

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Failure Knowledge Database / 100 Selected Cases

Fig. 2 Valve

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Failure Knowledge Database / 100 Selected Cases

Blowout

Filling machine

Containers

Filling machine

Fig. 3 The scene of an accident.

8Failure Knowledge Database / 100 Selected Cases

Multiple explosions of containers
Or gateRapid fracture (time-independent fracture)

Starting point (time-dependent fracture)Or gate
Ductile fracture

Brittle fracture
Or gateBurst by external force

Elastic collapse by excessive pressure
Or gatePressure rise over time

Sharp pressure rise
Or gateVapor explosion

Unusual temperature rise with fire expansion
And gate

LP gas blowout from nearby containers
And gate
Fire

Failure to close container valve
And gate
Discharge of LP gas

Spark discharge
And gate
Electrical conductors

Overfilling

Static electrification of LP gas

Fig. 4 FTA.

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Failure Knowledge Database / 100 Selected Cases

Overfilled Container

Discharge of LP gas

Ignition

Close container valve

Nearby containersFire burnt out the seatsof block valve
Yes

Explosion +Fire of Tans

Yes
NoExplosion

NoNoFire

Yes
Yes

FireYesNo

LP gas blowout

NoHealthinessFig. 5 ETA.

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