Failure Knowledge Database / 100 Selected Cases

Fusion and Explosion of Oxygen Gas Containers
in The Filling Process
Mar. 25th, 1996, Kasuya, Fukuoka
AKATSUKA, Hirotaka (High Pressure Gas Safety Institute of Japan)
KOBAYASHI, Hideo (Tokyo Institute of Technology)(Summary)
On March 25th, 1996, the staf f members of a gas fi lling st ation in Fukuoka Prefect ure w ere fi lling
medical oxygen gas into s ix a luminum alloy c ontainers an d 2 0 st eel co ntainers at a g as fi lling station i nFukuoka Prefect ure.

When th e st aff members had completed fil ling t he containers w ith gas and w ere

closing the valves on the containers and the mount frames, one of the aluminum alloy containers suddenly
fused somewhere between the valve-fitting and the shoulder section, causing flames to sp out out.

In thisaccident, one staff member was killed, and another suffered severe burns.
The oil c ontent that w as m ixed i nto t he container during a c ontainer insp ection t est w as pr esumed t ohave settled on t he interior surfaces of the container and the valve. That oil was believed to have ignited
due to a temperature rise during the filling operation.
1. Event
One of the al uminum alloy containers that had been filled with oxygen gas, suddenly fused somewhere
between the valve-fitting and the shoulder section, causing flames to spout out.

(See Fig. 1)

Accordingto the results of the investigation, the origin of inflammation was in the end section of the container valve
where th e bra nch tube for filling was i nserted. The flames then s hot the m ain bo dy of the valve an ddirectly hit against the outer surface of the aluminum container to melt an opening.

The fused area of themain body looked as if it had been irradiated with an electron beam.
In the meantime, the flames melted the surface of the valve sheet and penetrated into the container while
propagating through the inlet of the container valve. The oxygen gas ignited in the check valve cartridgein the container valve.

The resulting flames fused down the foot part of the valve body toward the fillingside, and then directly hit and fused the outer s urface of the container at a n angle of 135° (se en clockwisewith the top face as 0°).

(See Fig. 2) Furthermore, the flames penetrated through the mouth of the valve

into the confined space on the valve sheet surface, fused the surfaces of the valve sheet (brass) and the seatpadding (nylon 66), and then reached the inner depth of the container while propagating through the inlet ofthe container valve. Both the fusion face caused by the irradiation of flames and the knife-edged fusion
face caused by the spout of flames were observed on the fractured area of the opening on the container.
Since th e dimensions of t he co ntainer re mained unchanged after t he acc ident, t he burst c ould not b e
attributed to a rise in t he i nner pressure , nor co uld it be attri buted to material or manufacturing defects
according to the results of mechanical and nondestructive tests on the container material.

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Failure Knowledge Database / 100 Selected Cases

2. Cause
When th e c ontainer was cut in ha lf i n the p ost-accident investigation, oil c ontent, iron p owders, an dother residual materials were identified on the surface of the packing and inside the branch tube for filling.
Fig.3 shows the inner surface condition of the burst container.

In addition, the two containers next to theburst container were cut in half and checked using ultraviolet ray anal ysis to see whether any oil content,iron p owders, or other s ubstances w ere a lso present i n the container.

As the res ult of t he UV analysis

showed a glowing star pattern, it was confirmed that oil traces were on the inner surface of the container.
It was also revealed that the lubricant applied to the crank shaft section of the hydraulic pump during acontainer recheck test had been mixed into the water used in a pressure expanding test.
the oil content had entered the container during the container recheck test.

It is presumed that

It is likely that the oil content

had settled on the inner surface of the valve as the gas was flowing. Also identified was iron powder dustthat resulted from the stripping of the threads when the valve was fitted. The stripping of the threads wasattributed to a slight mismatch between the threads of the screw cap and t he brass valve. A part of th e
main body of the container was manufactured in Australia, and the thread of the screw cap was machinedusing t he refe rence gauge i n A ustralia. However, t he threa d of the brass va lve was machined usin g t hereference gauge of a domestic manufacturer.
Incidentally, it was a general practice to use high speed filling for small 9.7 liter containers at the filling
station.

However, if a co ntainer is filled w ith compressed gas at a hig h sp eed, the g as temperature w illincrease due to adiabatic compression. As a result of a quantitative analysis, it was estimated that the gas
temperature could reach 140°C.

The post-accident investigation also revealed that the polymeric materialof the seat packing (nylon 6) would creep at a temperature of 140°C and lose the ability to seal gas againstleakage.

If a subtle gas l eak occurred in t he c ontainer va lve d ue to frict ion, t he tra pping o f foreig nmaterials in the seal, or some other mechanism after the gas had been filled, the small space (about 0.1 cc)
in the valve would quickly change to atmospheric pressure.

Since the sealing ability of the seat packing

had been l ost, the gas i n t he c ontainer would flow i nto the sm all space in t he val ve, increasing thetemperature further. As a result of the analysis, it is presumed that the tem perature could increase to ashigh as 3 10°C.

In t he presence of oxygen, g as w ould i gnite at a t emperature of 31 0°C because th e o ilcontent on t he sea t padding (ny lon 66) and t he s eat packing ( nylon 6) w ould s erve as t he m edium forinflammation.
(1) High speed fillingHigh speed filling triggered a rise in the gas temperature in the container, leading to gas ignition.
(2) Presence of oil content and iron powder dust
If neit her o il nor iro n p owder ha d b een present i n e ither the c ontainer va lve or t he c ontainer, the gas
could not have ignited even though the temperature might rise.
3. Countermeasure(1) When filling gas containers, adopt a procedure that can keep the gas temperature from increasing in2Failure Knowledge Database / 100 Selected Cases

the container.
(2) Conduct periodic checks to ensure that neither oil nor iron powder is present in the gas equipment.
4. Knowledge○Temperature rise caused by high speed filling
The gas temperature will increase if high-pressure gas is filled into a container at a high speed. Extra

care should be taken to prevent a rise in temperature in the atmosphere of high-pressure oxygen gas, where
the spontaneous inflammation temperature of substances could decrease.
under som e con ditions.

Aluminum could serve as a fuelAlso, th e barrel p late of an aluminum all oy cont ainer could m elt and i nflate

extraordinarily due to a temperature rise resulting from high speed filling.

Therefore, the measurement ofinflation deformation is essential in a container recheck test.
○Mixture of oil content into a high-pressure gas container
The oil content mixed into a high-pressure gas c ontainer could cause inflammation and combustion incontainers c ontaining h igh-pressure o xygen an d e ven in containers co ntaining h igh-pressure air.

The"Shippai Hyakusen" (A Selection of 100 Failure Cases) contains information titled "Compressed Air Tank
Explosion from Oil Mixture in 1995" for a case where this happened.
5. Information Source(1) Research Report on Fusion an d Burst of O xygen G as Con tainer ( Dec. 1 996): High Pressure G as
Safety Institute of Japan.
6. Primary Scenario
01. Poor Value Perception
02. Poor Safety Awareness03. Organizational Problems
04. Poor Management
05. Poor Equipment Management
06. Usage
07. Maintenance / Repair
08. Adhesion of Oil Content
09. Usage
10. Operation / Use
11. Stripping of Threads
12. Adhesion of Powder Dust
13. Usage
14. Operation / Use
15. High Speed Filling
16. Bad Event3

Failure Knowledge Database / 100 Selected Cases

17. Thermo-Fluid Phenomenon
18. Adiabatic Compression
19. Temperature Rise
20. Failure
21. Fracture / Damage
22. Fusion
23. Burst

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Failure Knowledge Database / 100 Selected Cases

A-A

B-B

Fig. 1 Valve.

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