Failure Knowledge Database / 100 Selected Cases

Explosion of Liquefied Nitrogen Storage Tank
by Closing Shutoff Valve for Safety ValveAug. 28th, 1992: Ishikari-county, Hokkaido
KOBAYASHI, Hideo (Tokyo Institute of Technology)(Summary)
In a foo d f actory l ocated al ong a national r oad, the l iquefied ni trogen stora ge t ank for t he c oldevaporator (CE) exploded at a mid-night, causing the destruction of the upper half of the factory as well assome extent of damage to other factories and structures in a circle with radius of 400m. The sh utoff valve
for the safety valve had been closed manually, causing the tank to close totally. The pressure of the tankincreased gradually as a re sult of heat penetration, leading to the explosion which occurred more than one
month later.
1. Component
A schematic diagram of the liquefied nitrogen storage tank (CE, cold evaporator) is shown in Figure 1.
The cold evaporator is a n ap paratus w hich se nds pr essurized gases, su ch as oxygen, n itrogen, argon,carbonic acid gas, etc., to users, after eva porating the stocked super cold gases by using the pressurizing
evaporator, t he se nding gas ev aporator, and o ther a ttached equi pments. "Super high tem perature" a nd
"extremely cold temperature" are used generally as terms describing extreme temperature, but in this field,"super cold" is used instead of "extremely cold".
A double shell, vacuum insulated tank maintains thermal insulation by evacuating the insulator chamberpacked w ith pearlite between i nner vess el w all, m ade of stai nless s teel, a nd outer vessel w all, made ofcarbon steel. The degree of thermal insulation, therefore, depends on the degree of vacuum.
2. Event
In a food factory located along a national road, a liquefied nitrogen storage tank exploded and dispersed
at mid-night, causing the destruction of the upper half of the factory as well as damaging other factories andstructures par tially, i ncluding t he o uter w alls, w indow glass, an d shutt ers of 25 b uildings, 39 par ked
vehicles c onsisting of busses, truc ks a nd cars, a nd electric p oles i n a circl e w ith r adius of 400m (Figure2~4). Th e tank w as a vertical ty pe, double sh ell, vacuum insula ting vessel (m odel CE-7 500), an d it isshown in Figure 1, with its attachments. Exploded circumstances of the in ner and outer vessels are shownin Figure 5 and 6, respectively. The piece of the vessel that flew the furthest was the top dish plate of theouter vess el, 1.5m in diam eter a nd 8mm in thi ckness tha t reac hed a distance of 35 0m. The insu lator
composed of pearlite sca ttered over circular are a wi th a radius of 100 m. The appe arance of the top dishplate is shown in Figure 7. The direct cost of the damage was estimated to be about 440 million yen.

1

Failure Knowledge Database / 100 Selected Cases

3. Course
The st orage t ank w as fa bricated by N issan K ogyo Co . in Se ptember 197 3, and it w as set u p i n t heIshikari Factory of Suzuki Sogo Food Co. in September 1988. After being set up, the first, second, and third
annual inspections were conducted by Hokusan Engineering Co. each September in 1989, 1990, and 1991,
respectively. Daily inspections at start up, shut down, etc. by Suzuki Sogo Food Co. were not conducted atall, nor was any safety training conducted.
The tank was charged with nitrogen gas on June 26th, 1992, and the gas was used on June 27th and 28th.
After that, a lorry of T omakomai Distribution Center, Hokusan Co. charged the tank with 2000m3 of gas
equivalent to 2800m3 when converted under standard atmospheric pressure and temperature. The tank had
not been used for 61 days when the accident occurred.
The M inistry for Interna tional T rade a nd In dustry or ganized t he Research C ommittee o n L iquefied
Nitrogen Storage Tank Explosion Accident, chaired by Prof. H. Kobayashi, in the High Pressure Institute ofJapan on September 1st, 1992, because of the importance of the accident in society. The total number of theliquefied nitrogen storage tanks in all of Japan had reached 9000.
4. Cause
The results of analyzing the cause of the accident are as follows;(1) The exact time of the accident was not determined, but the safety valve with spring had been actuatedor the shutoff valve for t he safety valve had been closed manually without actuating some time after
the last annual inspection in September 1991. After that, even though the time was also not determined
strictly, the rupture plate was estimated to explode so as to close the shutoff valve manually. The stock
tank, therefore, became totally closed.
(2) The pressure of the liquefied nitrogen in the stock tank increased gradually through the penetration of
external heat under the completely closed condition, eventually exceeding the rupture pressure of theinner vessel ( about 7 MPa) . Th e period of t ime requ ired r each this condition w as est imated t o be
between 50 and 80 days.
(3) Because of the i ncreased pressure, the outer ve ssel exploded fo llowing th e ex plosion o f th e i nnervessel, causing the dispersion of pieces of the v essel including the attachments. The rupture pressureof the out er vessel was also about 7 MPa , estimated from the fly ing distance of th e broken pieces of
the inner and outer vessels. The fault tree diagram showing the fracture morphology, mechanism, andprocess is shown in Figure 8. The event-tree diagram is also shown in Figure 9.
5. Immediate Action
Liquefied inert gas (ni trogen, argon, car bonic ac id, et c.) stor age ta nks are w idely used f or v arious
purposes such as freezing, gas replacement. They regarded as relatively safe equipments so that some of theregulations are relax ed compared with other production equipments. Liquefied inert gas stora ge tank can,however, ca use serio us pro blems under t he w rong o perating c onditions. A ll persons w ho are concernedwith s uch e quipment shoul d, t herefore, c hange t he conventional rec ognitions t hat t he i nert gas is always
safe, and adopt the safest and wisest measures for preserving maintenance.
2Failure Knowledge Database / 100 Selected Cases

6. Countermeasure(1) Increasing the awareness of the importance of safety maintenanceClosing both the s pring ty pe safety va lve and the shu toff val ve w as con ducted b y em ployees of thefactory who do not have enough awareness of the importance of safety maintenance, and who did not havethe basic knowledge that the shutoff valve for the safety valve must always be kept open. There was also
the serious problem that the managers of the factory lacked sufficient awareness of the importance of safety
maintenance s o t hat t hey did n ot or der daily i nspections by the em ployees, a nd t hey als o entrusted t heannual shutdown maintenance to some outside maintenance companies.
(2) Improving manuals and arrangement of valves
The manuals for operation of safety valves and for communications with gas suppliers were incomplete.
The arrangement of valves was also complicated and difficult to operate.
(3) Support by gas suppliers
Gas suppliers should support user companies in achieving items (1) and (2) mentioned above.
7. Knowledge
The bas ic k nowledge that the s hutoff valve f or t he sa fety valv e m ust al ways b e kept op en sh ould be
reaffirmed. The common sense notion in society that the shutoff valve of gas in homes must be kept closed
and that the electric breaker must be turned off before leaving for long time, is not appropriate for factories.
Those w ho do ha ve the b asic knowledge a bout s afety val ves have th e m isunderstanding that a c losed
shutoff valve i s sa fer than op en one. Cold ev aporators a re used so wid ely i n so ciety re cently t hat theaffirmation of this basic knowledge must be reconsidered.
8. Social Impact
The following items were mentioned as being strong influences to society,(1) The distance over whic h pieces of t he t ank were dispersed was large c ompared to that of past
incidents.
(2) The same type of cold evaporator is used in about 9000 sites all over Japan.
(3) The same type of cold evaporator for liquefied oxygen is used for medical purpose in hospitals.
(4) Other evaporators of same type have a similar possibility to cause accidents.
(5) Cold e vaporators be long to a cl ass of e quipment tha t can be use d w ith only no tice. Th is c lass ofequipment is used by t he seco nd cl ass manufacturers, w ho have no le gal o bligations of s afety
maintenance and periodical voluntary inspections.
9. Information Source(1) Report of Research Comm ittee for Accident of L iquefied Nitrogen Storage Tank, The High Pressure
Gas Safety Institute of Japan, August, 1993.
(2) Hideo K obayashi, Takao Nagasaki, H ideo O htani, Y uji W ada, Teruo Yoshioka, an d A kio Hori:
Analysis for accident of liquefied Nitrogen S torage Tank (CE), J ournal of T he Ja pan Soci ety ofMechanical Engineers (A Edition), 60-572(1994), 1100-1107.
3

Failure Knowledge Database / 100 Selected Cases

10. Primary Scenario
01. Ignorance
02. Insufficient Knowledge
03. Too Presumptive
04. Misjudgment
05. Narrow Outlook
06. Inexperienced/Not habituated
07. Regular Operation
08. Erroneous Operation
09. Incorrect Operation
10. Close the Shutoff Valve for Safety Valve
11. Usage
12. Operation/Use
13. Use of Equipments/Materials
14. Liquefied Nitrogen Storage Tank
15. Bad Event
16. Thermo-Fluid Event
17. Thermal Event
18. Penetrated Heat
19. Pressure Increase of Liquefied Nitrogen
20. Failure
21. Large-Scale Damage
22. Rupture
23. Secondary Damage
24. External Damage
25. Scatter of Broken Pieces4

Spring type safety valve

Rupture discFailure Knowledge Database / 100 Selected Cases

Pressurizing
Vacuum insulation

Liquefied nitrogen(at charging)

LiquefiednitrogenTo users
Evaporator for pressurizing gas
Fig. 1

Schematic diagram of storage tank.

5

Failure Knowledge Database / 100 Selected Cases

Fig. 2

Appearance of damage (Part 1).

Fig. 3

Appearance of damage (Part 2).

6

Failure Knowledge Database / 100 Selected Cases

Fig. 4

Appearance of damage (Part 3).

7

Failure Knowledge Database / 100 Selected Cases

Weld bonded at recovery time( Unit : mm )Fig. 5

Exploded circumstances of inner vessel (Stainless steel).

8

Failure Knowledge Database / 100 Selected Cases

Weld bonded at recovery time
( Unit : mm )Supporting leg set position
Perforation hole for piping

Fig. 6

Exploded circumstances of outer vessel (Carbon steel).

9Failure Knowledge Database / 100 Selected Cases( Unit : mm )Fig. 7 Crushed piece of top dish plate of outer vessel.

10Failure Knowledge Database / 100 Selected Cases

Rupture of storage tankor GateRapid fracture(Time independent type fracture)

Initiation point(Time dependent type fracture)

or GateBrittle fracture

Ductile fractureor Gate

Plastic fracture by over pressure

Fracture by outer force

or GateRapid increase of pressure

Time dependent increase of pressure
or GateDegradation ofinsulating performance

Penetrated heat from outside
or GateReleasing shutoff valve
for safety valve

Fig. 8

Closing shutoff valve
for safety valve

Fault tree diagram noticing morphology, mechanism, and process of fracture.

11Failure Knowledge Database / 100 Selected Cases

Liquefiednitrogen

Closing shutoff Penetrated heat Time dependent
valve forfrom outside increase of pressure
safety valve

Not actuation ofsafety valve

Fracture ofstorage tank
Yes

ResultRupture

Yes
NoYes
Yes

Yes

NoNoNoSoundness

Soundness

Soundness

NoFig. 9

Soundness

Soundness

Event-tree diagram for explosion of storage tank.

12