Failure Knowledge Database - 100 Selected Cases

Explosion and Fire of Hydroxylamine【June 10th, 2000
Hiroshi Koseki.

Ojima Town, Gunma, Japan】(National Research Institute of Fire and Disaster)

Mitsuo Kobayashi (Graduate School of New Frontier Sciences, University of Tokyo)
Masamitsu Tamura (Graduate School of New Frontier Sciences, University of Tokyo)
In Oji ma Town, locat ed in the southwest area of Gunma Pref. near the b oundarywith Saitama Pref. a large expl

osion ofhydroxylamine occurred a t the Niss hin

Chemical Industry Co. Ltd Gunma factory , wh ich is next to the national road No.17and No.354. The explosion power of hydroxylamine is almost equivalent to the famous
explosive TNT.
After 18:00 on Saturday June 10th, 2000,

the explosion occurred suddenly at there-distillation column resulting in a fire. A pillar of flames like a flash spouted out fromthe factory at the moment of the explosion. The damage involved the housing area thatadjoined the factory . Four persons were

killed and 58 persons w ere injured in theaccident. 54 persons of injured persons wer e residents living near the factory . The
re-distillation column disintegrated without leaving any t race, and t he factory wasseverely damaged. Damage outside of the factory included the complete collapse of twobuildings, severe damage to five buildings and partially damage to 285 buildings.

The plant where the accident occurred was manufacturing a 50% aqueous solution ofhydroxylamine, which contained nearly zero level impurities such as a ferrous i on. The1

Failure Knowledge Database - 100 Selected Cases

high purity hydroxyla mine has recently b een used as s emiconductor removers andmetal surface tr eatment agents. The fe ed stock of 50% hyd roxylamine that wascontaminated with about 40 to 50 ppb ferrous

ion was f ed into the bott om circulationline in the c olumn whe re the 50% h ydroxylamine was evap orated, in or der to obtai nproducts with under 1

ppb ferrous ion. The concentration of the bot tom ci rculation

liquid reached 80 to 85% as a result of concentration of the 50% feed stock. A part of thesolution was drawn off from the circulation line in order to prevent the concentration ofa ferrous ion from the dangerous zone.
This accident seemed

to be caused by an explosion of the80 to 85%

high-concentration hydroxylamine aqueous solution at the bottom of the column and in
the botto m circulation l ine, and th e exp losion exp anded to the near by equip ment.
High-concentration hydroxylamine has a dangerous tendency to decompose explosively
at high te mperatures, and it may explode even at ambient temperature if th e ferrous
ion concentration increases. It was not possible to p erfectly elucidate the cause of theexplosion, because the area around the re-distillation column was completely destroyed,
and all the operators w ere killed. Since the emergency draw-off line branched from thebottom circulation line and a valve was mount ed at the li ne, the pa rt of the draw-offline from the branch point to the valve became dead-end piping. There is a p ossibility
that the ferrous ion concentrat ion in the de ad-end piping had be come high and it isregarded as one of the cause of the accident.
At least eleven examp les have bee n reported as accid ents caused by hyd roxylaminein the past twenty years. Although the company was sufficiently aware of the danger,and appeared to have ta ken appropriate co untermeasures against the d anger, still t heaccident occurred. After the a ccident, the company stopped manufacturing of the 50%
aqueous solution of hydroxylamine.
The cause was notcomplet ely clarifie d, as described above. Furtherm ore,hydroxylamine was not designated as a d angerous material und er the fire p rotection
law at the time of the a ccident. However, after the accident, both the hydroxylamineaqueous solution and salt were d esignated as self-reactive materials in the No .5 groupof the fire protection law’s classification of dangerous materials. However, regardless ofthe designation in thelaw, it is necessary for

manufacturing plants and processi ng

facilities that treat hi

gh-concentration hy droxylamine t o prepare a dequate safety

countermeasures, considering both its explosion power and handling volume.
1.

Event
The company that caused the accident had been manufacturing and selling2

Failure Knowledge Database - 100 Selected Cases

hydroxylamine use d for me dicine and pe sticides. In additi on, from 19 82 they also
manufactured and sold a 50% aqueous solution

with a very low l evel of contami nantnearly equal to zero under the trade name of “Free hydroxylamine”, which was used forsemiconductor removers and meta l surface t reatment. “F ree hyd roxylamine” wasmanufactured from a 50% aqueous solution by decreasing the ferrous ion concentrationfrom 40 to 6 0ppb in the 50% solution to be low 1 ppb using re-distillatio n column. The
50% hydroxylamine aqueous solution was obtained by concentrating a low

concentration of hydroxylamine made by two kinds of manufacturing processes.
The method of re-distillation w

as as follows. Alarg e amountof 80-85%

hydroxylamine aque ous solution wa s circulated at the b ottom of th e c olumn. A fe ed
stock 50% hydroxylamine was fed to the circulating liquid , and the whol e cir culating
liquid was heated and partially evaporated, and then charged to the column. The

column was operated at a vacuum of 20 to 30torr, and the te mperature was controlled
so that the vapor conc entration sho uld be the s ame with t he 50% feed stock. A s thevapor p ressure of a fer rous i on is almost zer o, ferr ous ion s remain ed at the botto ms
without being entrained, and were accumulated in the bottom circulation. The vapor at
the top of t he column was totally condens ed, and after adjusting concentration, it wasshipped as “Free hydroxylamine”. The flow of the Re-distillation column is shown inFig. 2.
A part of the bottom circulation was continuously drawn off so that the ferrous i onconcentration would not exc eed the danger thre shold. A bout 4% of the feedstock wasdrawn off i n o rder to keep th e co ncentration at 3p pm o r less .

An emergency l ine

branched from the bottom circulation line for emergency evacuation of the circulating
liquid at the column bottom into the underground vessel for cooling and diluting, whena temp erature rise was detected. Th ere wa s about 70 to 80 mm of a dead-end pi pingbetween the stop valve and the bra nch p oint. The valv e ha d neve r bee n op ened af ter
the initial start-up.
On the day of the accident, the oil of the vacuum pump of the column became dirty,
and after stop ping the operation of the c olumn and exchanging the oil, operation wasrestarted at around 17:30. The

start-up began by starting of the bott om cir culation,next the feedstock supply, and then the vacuum pump. Finally the steam supply to t hevaporizer started. After about 39-40 minutes from the re-start, the explosion occurredsuddenly at 18:08.

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Failure Knowledge Database - 100 Selected Cases

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Failure Knowledge Database - 100 Selected Cases

2. Course
1.1.

Progress on the dayAt 13:30, sh utdown work of the re-distilla tion column started, and the shutdown

work finish ed at 14:00. The exchange of th e oil of the vac uum p ump, which was thecause of the stop, was carried out.
At 15:45, the preparations

for r e-starting op eration bega n, and the operation

restarted from 17:20 to 17:30.
An explosion occurred at 18:08, and a large sound was heard from around thecooler nearby the vacuum pump.
At 18:11, the fire fighti ng team turned ou t, and the traffic of the national roadnext to the plant was restrained at the same time.
At 23:10, the extinguishment of the fire was confirmed.
1.2. History of the company
The compa ny was established in 1953, and manufacture andsale ofhydroxylamine hydrochloride was started. A new factory was established in1960 at thesite where t he accident occurred. The hydr oxylamine sulfate manufacturing facilities
were constructed in 1977, and t

he hydr oxylamine hydrochloride

facilities were established in 1980. The sale5

manufacturingof “Free hydroxylamine” started in 1982 ,Failure Knowledge Database - 100 Selected Cases

and the ma nufacturing capacity of “Free hydroxylamine” increas ed to 8000 tones per
year in 1988.
2.

Cause
All four op erators d ied, and th e operation r ecord was d estroyed. Fu rthermore,

the re-distillation column was also completely disintegrated, and so investigation into
the causes of the accid ent was ver y d ifficult. The caus e was estimated from sta tus
investigations, interviews of the related part ies, characteristics of hydroxylamine, andso on . Th ough the caus e co uld not be mad e p erfectly cl ear, it was estimated to be asfollow.
The mate rial that exp loded was 80 to 85% hyd roxylamine a t the botto m of thecolumn and in the bottom circulation line, which was estimated from the fact that thedetonation position wa s in the c olumn, that theexplosion had

occurred at t hecirculation line or near the heater, and that the only flammable material that existed
in the column was the 80-85% aqu eous solution. It was confirmed that the d etonationof 80 to 85% hyd roxylamine aque ous s olution was p ossible fr om exp eriments on theexplosive properties and calculations.
As for the cause of the accident, following three possibilities were considered; 1) arise in theferrous i on concentration, 2) a rise in the temperature of the aqueo us

solution, and 3) a rise i n the aqueous soluti on concentration. As a result, it was shownthat the ca use was the "partially rise in

the concentration of a f errous ion that had

accumulated in the dead-end piping in the emergency piping ".
3.

Process of cause elucidation
At first, the p lace wh ere th e acci dent occu rred and material that caused

explosion w ere estimat ed. Intervi ews and examination

theof the situ ation after theexplosion showed that the explosion had occurred at the l ower section of the column orat the circu lation system of th e bottom liq uid. Only the 80 to 85% hydroxylamineaqueous solution existed in thoseplaces, and the solution had thepossibility ofdetonation. Therefore, t he 80 to 85% con centration hyd roxylamine aqueous s olution
was concluded to be the material causing the explosion.
Three p ossibilities for t he cause of the acci dent were given, as described in the“cause” section above. First, the possibility of a t emperature rise was rejected from theconsideration of the temperature control system and the fac t that the temperature rise
alarm did not ring. The possibility of atemp erature rise by the dest ruction of t hevacuum sys tem was also considered to below, because only the lower secti on w as

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Failure Knowledge Database - 100 Selected Cases

destroyed severely. A rise in the concentration of the circulation liquid was also rejected,because 1) t he ar ea of s evere d estruction was limited to t he low er p art, and , 2) t hetemperature at which d ecomposition starts is a bout 130 ℃, is not lowered, even if t heconcentration rises, and the outlet temperature of the evaporator was only about 50℃.
Therefore, only a rise in the ferrous ion concentration remained. The p ossibility of an
insufficient quantity of chelate of t he inhi bitor was also rejected b ecause the sample
taken on the previous day was normal and the feedstock of the day of the accident wasfrom the same lot as that of the previous da y. There is no possibility that ferrous ions
could have been supplied by rapid dissolution, because stainless steel was used as thematerial of the colu mn and p iping. So by theprocess of e limination, the cause w as

estimated to be an increase in the ferrous ion concentration at the downward dead-end
piping lo cated in the em ergency li ne whi ch ha d been accu mulated ov er th e l ong-term
operation.
4.

Immediate action
There is no record of im mediate actions cond ucted. It is estimated that no actions

could be taken immediately because the explosion was too rapid and large.
5.

Countermeasure
No concrete countermeasur es wer e taken, be cause themanufacture of “Fr eehydroxylamine” was sto pped. Furtherm ore, n o concrete co untermeasures have b een
shown in the report of previous accidents that have occurred overseas.
6.

Knowledge
1) Even if previous acciden ts have occu rred in foreign countries, the information is
not useful, i f there is n o detailed report of the cause and countermeasures of th e
accident and/or if the receiver has insufficient ability to understand the report.
2) It is desirable that factories that handle dangerous materials are located far awayfrom the p laces wher e a lot of p eople gather or wher e a large numb er of theprivate residences are located.
3) There are a lot of examples of accidents that have been caused by dead-end piping.
Although t he ap pearance of each accid ent is different, t he accident s can bedivided into two types.

One pattern is th e acci dent that occurs at th e contact

position of a flow part and no flow part, and the other is that occurs because of noflow.

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Failure Knowledge Database - 100 Selected Cases

7. Influence of failure
The factory was near th e intersection of two national r oads. Th e p lace was a key
point of th e traffic, and there were many stores and private houses along the natio nalroads. The Ishidagawa River was flowing ne arby. Th e exp losion caused d amage in a
1500m radius of the factory.
As for the human damage, four persons died and 58 persons were injured including
54 persons living in the area outside the factory.
As fo r the physical damage, the co lumn whe re the explo sion occurred wascompletely disintegrated and many buildings in the factory site were damaged. Outsideof th e facto ry, two bui ldings were c ompletely destroyed, five buildings were half
destroyed and 285 buildings were damaged partially, and 47 cars were damaged.
As for the social damage, the local traffic was regulated, the power was cut for 249
households, telephone s ervice was interrup ted f or 47 lines, and using city water wasprohibited in the east d istrict of the p refecture d ue t o the d eath of fish in theIshidagawa River near the place of accident.
8. On the side
There s eems no d omestic manufac turer any more, sinc e it is to o d angerous atpresent. As shown in the “Cause” section, the only one possibility, which remained as
the caus e of the explosion, is the e mergency blowd own p iping. If the c ause is c orrect,
the piping, which was mounted for preparation for very rare troubles, was the cause. Itis very unf ortunate. Although it ha s not be en specified in the reports, probably thepiping branched off from the lower part of the main piping. If the piping had branche doff from the upper part, the remained possibility might be also rejected. There are someaccidents that are caused by a mistake inthe direction of t he branch p iping. Carefulattention and adequate consideration are necessary even in the design of simple piping.

8Failure Knowledge Database - 100 Selected Cases

References
・ Dangerous Material Safety T

echnique A ssociation, “Investigation Report onhydroxylamine explosion and fire accident occurred at th e chemical plant in Gun maPrefecture” (2001)
・ Masamitsu T amura, “Safety countermeasu re learn ed from r ecent accidents atchemical plant”, Seminar on accident cases due to hazardous materials, 1-17 (2001)
・ Sakae Kajima, Fire-Defense Headquarters,

Ota District FireFighting Uni on,“Situation of explosion and fire accident occurred in Nisshin Chemical Industries andextinguishing and rescue operation with to ugh and difficult y”, Sem inar o n accide nt
case due to hazardous materials, 19-39 (2001)
・ Terushige Ogawaet all, “Hydroxylamine

32,233-242(2001)

9explosion”, Saigai no Kenkyu,