Failure Knowledge Database / 100 Selected Cases

Tank Explosion at the LP Gas Filling Station
Sept. 14th, 1964, Ibaraki, Osaka
AKATSUKA, Hirotaka (High Pressure Gas Safety Institute of Japan)
KOBAYASHI, Hideo (Tokyo Institute of Technology)(Summary)
In November 1964, there was a great tank explosion disaster that resulted in three deaths and 61 injuries
at an LP g as filling st ation i n Osa ka. At t he fill ing sta tion, LP g as l eaked a nd was ignited during a n
attempt to fill containers with LP gas using the pump from a tank truck.

Heated by the flames of the fire,the LP gas conta iners and the 10 t on horizontal tank at the s tation exploded one after another. With thisevent as a t urning point, nationwide training and guidance were provided to the management and working
staff at LP gas filling stations across the country in order to establish an assured safety management systemand ensure the proper maintenance and checks of equipment.
1. Event
At the LP (Liquefied Petroleum) gas filling station, an attempt was made to fill a 10 kg container and a
50 kg container with LP gas using the pump of th e tank truck instead of the compressor and pump of th e
station, which were out of order, but this attempt failed and was abandoned. (See Figs 1 and 2.)
About 30 minutes after the attempt was suspended, white fumes suddenly spouted out with a hiss fromsomewhere in the l ine connecting the tank truck and the containers and completely filled the area.
then ca me, a nd th e ex plosion oc curred a fter t hat.

There

Heated by the resulting flames, the LP gas containers

and the horizontal tank burst one after other, resulting in a catastrophic explosion disaster with three deaths
and 6 1 minor an d serious injuries.

According to the investigation carried out af ter the accident, LP gas

was presumed to ha ve blown out due to either the ru pture of a det eriorated hose or the breakage of so me
coupling caused by the movement of the tank truck.
The figure below shows the results of a fault tree analysis.
Fig. 3: Fault tree diagram with a focus on mode, mechanism, and process of fracture
LP g as b lew out so rap idly that i t t ook on ly a bout 20 s econds t o fil l the are a a nd f low over t heconcrete-block wall that surrounded the site of the filling station.

It is estimated that the total volume ofwhite fumes and the rate at which the gas blew out immediately before the explosion were m ore than 600
m3 and about 360 liters per minute, respectively.
The horizontal ta nk rup tured d ue to a ductile frac ture in the l ongitudinal direction of the b arrel p late.
The barrel p late (6 0 kg c lass hi gh stre ngth st eel) w as h eated to t he r ecrystallization t emperature, a nd it spressure strength at 650°C was 20.7 kg/cm2.

The operating pressure of the safety valve was 29.8 kg/cm2,

which w as higher t han t he pressure stre ngth of the barrel pl ate. This su ggests tha t a ru pture ho le hadformed on the barrel plate due to a longitudinal ductile fracture before the safety valve could operate.
The inner s urface of t he burst horizontal t ank left a clear mark of dis coloration that showed the1Failure Knowledge Database / 100 Selected Cases

boundary surf ace of the gas li quid.

From this fact, i t is pres umed t hat a bout si x tons of l iquid w as

contained in the horizontal tank immediately before the explosion.

Furthermore, the safety valve had been

operating n ormally unt il j ust before t he e xplosion. Th ese fa cts demonstrate that t he LP g as i n thehorizontal tank was not above the critical temperature. As a result of the investigation, the explosion was
believed to occur as follows.

A large volume of LP gas was released from a rupture hole that had formedon the barrel plate due to a rise in the inner pressure, and so the inner pressure dropped suddenly. A quick
drop in the i nner press ure disturbs t he gas-liquid e quilibrium, causi ng t he liquid to b oil i ntensely in an
overheated condition. As a consequence, a large volume of gas evaporated instantaneously, resulting in a
powerful impact pressure e xerted o n t he tan k.

This series of e vents -- know n as a steam explosi on --caused the entire horizontal tank t o break into pieces starting from the rupt ure hole formed on t he barrel
plate.
The figure below shows the results of an event tree analysis.
Fig. 5: Event tree diagram of horizontal tank explosion
2. Course
At the LP gas filling station, there was one 10 t on horizontal tank unit, from which LP gas was fille dinto 1 0 kg a nd 5 0 k g c ontainers.

The monthly sal es at t he fi lling stati on w as a bout 100 t ons, an d t hehorizontal tank was refilled with LP gas from two 4.8 ton tank trucks every three days.
On the date of the accident, the manager of the filling station made a phone call to cancel the dispatch of
the tank truck that had been reserved because there still was a sufficient volume of LP gas left in the tank,
but the tank truck had already left at t hat time.

In the meantime, the staff members of the fill ing station

were transferr ing LP gas i nto containers without usi ng th e pump be cause t he pump and th e c ompressor
were out of order.
The tank truck arrived at the station in the afternoon, but the driver of the truck was asked to wait until
enough of the LP gas in the horizontal tank was used so that the gas contained in the tank was at a level low
enough to accept the LP gas from the tank truck.

While watching the inefficient operation of transferring

LP gas m anually, the driver suggested filling the gas into the containers using the pump of th e tank truck.
He con nected the pressure equ alizing line b etween t he h orizontal tan k a nd the ta nk truck and tried
operating the pump.

However, the plan did not work and the idea was abandoned.

About 3 0 m inutes aft er th e dri ver's plan w as ab andoned, w hite fu mes sudde nly spo uted o ut with ahissing sound and completely filling the area impairing visibility.
had started the gas ignited.

About 20 seconds after the gas blowout

Heated by the resulting flames, the LP gas containers ruptured, and gas blew

out i ntermittently from the safety valve of th e horizontal ta nk. About 18 m inutes after ignition, th ehorizontal tank exploded, and its broken pieces scattered into the surrounding area.
The post-accident investigation revealed no trace of any fracture from the m ain body of the tank truck
through the pump to the hose joint and that the horizontal tank was not connected to the tank truck and thefilling zone. (See Fig. 4.) Therefore, the origin of the blowout of the large amount of LP gas must havebeen somewhere in the connection hose, including the couplings, between the tank truck and the horizontal

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Failure Knowledge Database / 100 Selected Cases

tank.

A det eriorated LP gas hose could rupt ure ev en within t he operat ing press ure range, a lthough its

normal burst pressure is 90 kg/cm2.
In addition, the tank truck had moved back 2 m from its origi nal position to a p osition where the hose
did not fully reach the rec eption port of the tank. The roll-off section of the thread of the coupling on theliquid feed line was stripped, and the coupling on the pressure equalizing line was removed with its thread
stripped. The roll-off section of t he thread was stripped easily when the tank truck moved, since it w as
only 2 mm in thickness and about 0.8 tons in bending strength.
3. Cause(1) Unfamiliar operation by inexperienced staff
The root cause of th e LP gas blowout was the attempted filling operation using the pump of the t ank
truck.

Although this is not an uncommon operation, it was t he first attempt at th is station and was done

when the operation supervisor was not present.
Additionally, no whe el st oppers were use d to prevent t he t ank truc k from moving accidentally. The
tank truck was customarily parked with its rear wheels on the sleeper wood in order to balance itself on the
inclined surface of the site.

Furthermore, the pressurized hose was left connected to t he pump even after

the attempt was abandoned.

All of t hese observa tions sug gest that the staff a t t he fi lling s tation lacked

sufficient safety awareness.
(2) Li mited space
The filling station had only a very limited space and was crowded with individual installations. As aresult, although the firefighting crews rushed to the site only three minutes after the initial ignition, the LP
gas containers burst one after another and the horizontal tank exploded while the firefighting crews wereextinguishing the flames from the containers.

Also, because of the close proximity of the horizontal tankand the firewall combined with the short height of the firewall, flames were co ncentrated intensely on t heupper half of the horizontal tank, thus causing the tank to burst.
4. Immediate Action
If a fire occ urs at a g as fil ling sta tion, h ighest priority sho uld be given to s topping t he blowout a nd
leakage of gas even at the early stage of the fire.

In general, the blowout or leakage of gas can be stopped

by accessing the stop valve or other control values from a safe direction, because the direction and the scaleof a fire usually remains constant for a while after an initial explosion has occurred.
However, if LP gas blows out in a liquid state as in this case, the concentration of LP gas could become
higher t han t he e xplosion limit in th e r ange of wh ite fu mes that r esult fro m evapora tion and coo ling.
Therefore, one should avoid entering the area containing white fumes except when it is confirmed that there
is no possibility of ignition.
5. CountermeasureWith this event as a turning point, countermeasures were implemented, including regulations to:(1) Provide sufficient space or install a barrier between individual equipment;
3

Failure Knowledge Database / 100 Selected Cases(2) Install a sprinkler system and a level gauge to the LP gas tank;(3) Apply improvements to the tank truck, including the inspection of e xcess flow valves, the protectionof protruded parts, and the standardization of hose and coupling structures/dimensions;(4) Encourage the drivers of ta nk trucks to pull the handbrake and apply wheel stoppers when parking atank truck;(5) Improve the management's awareness of autonomous safety;(6) Provide practical training to the w orking staff at the gas filling station (including the drivers of tanktrucks); and(7) Promote a qu alitative improvement of th e equipment at the gas fi lling station by ensuring that every
staff member is aware of and adheres to the autonomous safety standards.
6. Knowledge○ Build a high level of safety awarenessThis accident could have been prevented if the m anagement and t he staff had m aintained a suf ficientlevel of safety awareness a nd had perfor med proper m aintenance on a regular basis.

The m anagement

should be well aware of the potential risks of what they are handling and take all possible safety measuresat all times. (See Fig. 6.)○ Potential risks of an LP gas tank in the case of a fireIf heate d by t he flames of a fire, an LP gas ta nk c ould poss ibly b urst due t o a n incre ase i n th e in ner
pressure of t he tank even w ithin the range of the operating pressure of the safe ty valve. Needless to say,
LP gas would leak even if the safety valve operates correctly.

Therefore, it is very difficult to address thisproblem technically.
7. BackgroundAt the time of the a ccident, th e LP g as business w as developing at a rapi d pace, and th e l ayouts a ndscales of filling stations were chan ging year by year .

In t he e arly days of the L P gas i ndustry, the s taff

members at th e gas f illing stations were s till inexperienced, and the safety management system there waslacking.
8. SequelWith this event as a turning point, nationwide training and guidance were provided to the management
and working staff at filling stations across the country in order to establish an assured safety management
system and ensure the proper maintenance and checks of equipment.
9. Social Impact
The interested parties in t he LP gas i ndustry were greatly shocked by the fac t that an LP gas tank had
exploded even if the safety valve operated. This event disproved the general assumption that LP gas tanks
were free from the risks of explosion in a general fire.

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Failure Knowledge Database / 100 Selected Cases

10. Information Source(1) Research Report on th e Accident and Countermeasures at LP Gas Filling Station: Extra Issue of High
Pressure Gas Safety Institute of Japan Report, Jan. 1965.
11. Primary Scenario
01. Organizational Problems
02. Poor Management
03. Poor Maintenance
04. Compressor / Pump Failure
05. Misjudgment
06. Narrow Outlook
07. Insufficient Experience / Skills
08. Non-regular Operation
09. Change in Operation
10. Filling LP Gas with the Pump of Tank Truck
11. Leaving Hoses as Connected
12. Movement
13. Careless Movement
14. Movement of Tank Truck
15. Failure
16. Fracture / Damage
17. Chipping of Coupling
18. Damage
19. External Damage
20. Leakage
21. Fire
22. Failure
23. Degradation
24. Drop in High-temperature Strength of Horizontal Tank
25. Failure
26. Fracture / Damage
27. Burst of Horizontal Tank
28. Release of LP Gas
29. Bad Event
30. Thermo-Fluid Phenomenon
31. Thermal Phenomenon
32. Inner Pressure Drop
33. Secondary Damage

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Failure Knowledge Database / 100 Selected Cases

34. External Damage
35. Steam Explosion
36. Burst of Horizontal Tank

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Failure Knowledge Database / 100 Selected Cases

Fig. 1 The scene of an accident.

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Failure Knowledge Database / 100 Selected Cases

Fig. 2 Arrangement machinery.

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Failure Knowledge Database / 100 Selected Cases

Tank Explosion
orFast fracture (time independent)

Fracture from Origin (time dependent fracture)or
Ductile fracture

Brittle fractureorElastic fracture by high pressure

Fracture by the force outsideor
Steam Explosion

Combustion inside tankorPressure drop suddenly

Overheating

Rupture holeandPartial determination of strength

Sharp pressure riseorFatigueandTemperature rise by flames

No actuation of safety valve

andOrigin of ignition

LP gas leakor

Many solves
Coupling breakage

Fig. 3

Deterioration of hose

Fault tree diagram with a focus on mode, mechanism, and process of fracture.

9Failure Knowledge Database / 100 Selected Cases

LP gasLeak

Ignition Combustion

Safety valve
troubleRisepressure

Fallstrength

Explosion

Fallpressure

Large amountof LP gas
Yes

Yes
No

Yes
No

Yes
No

Yes
No

Yes
No

Yes

Explosion
Fire
Fire
Fire

Fire

No

Yes

Vapor
explosion

Fire

No

Yes

Result

Leak

No

Leak

No

HealthinessFig. 4 Event tree diagram of horizontal tank explosion.

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