Case Ditails

Case Name Explosion and fire of highly-concentrated hydroxylamine at a re-distillation unit
Date June 10, 2000
Place Ojima, Gunma, Japan
Location Chemical factory
Overview A re-distillation column (reduced-pressure distillation, the operation temperature 50°C) for a 50% aqueous solution of hydroxyamine exploded, and a fire occurred. The re-distillation column blew up leaving no traces, and there was blast damage to surrounding houses in a 1.5 km radius. The factory was completely destroyed. Damage outside the factory was also great. The traffic on a nearby national road was stopped temporarily by smoke and harmful gas generated by the fire. The cause was as follows. Hydroxylamine concentrated to 80-85 wt% was circulated in the column from the column bottom. A ferrous ion that had accumulated in emergency blow-down piping from circulation piping reacted with the high-density hydroxylamine.
Incident At a re-distillation unit of a hydroxylamine manufacturing plant, detonation of a highly concentrated hydroxylamine aqueous solution (concentration over 80% in weight.) occurred. It became a major accident in which the blast affected the factory and nearby buildings, as well as inhabitants, and there was a large number of casualties.
Re-distillation unit: A crude hydroxylamine aqueous solution of 50% concentration contains impurities, mainly iron, of more than 10 ppb. A high-purity hydroxylamine aqueous solution contains very small quantities of impurities such as 1 ppb or less of iron and sodium each. The plant that conducts this refinement process at the facilities was called a re-distillation unit. A re-distillation column for partial evaporation was the main part of it.
Processing Manufacture
Individual Process Distillation
Substance Hydroxylamine, Fig2
Type of Accident Explosion
Sequence Detonation occurred at the re-distillation column of a hydroxylamine manufacturing plant on-stream. Extensive damage was inflicted on surrounding facilities and nearby private houses. The fire generated a large volume of gas and smoke.
Cause A highly concentrated hydroxylamine aqueous solution causes explosive decomposition by itself or by reacting with a ferrous ion. At the re-distillation column bottom, hydroxylamine was concentrated to 80-85%, and was circulated in the middle of the column. A crude 50% solution of hydroxylamine was charged into the circulating high-concentration hydroxylamine. Then the hydroxylamine solution was heated to evaporate some part of the hydroxylamine. Next, in the column, 50% hydroxylamine vapor went to the top of the column and a 80% hydroxylamine solution dropped to the bottom. As a ferrous ion contained in feedstock at about 50 ppb is reduced to 1 ppb or less in the product, part of the circulation liquid was drawn out from the bottom circulation line. Emergency blow-down piping was installed at the underside of the bottom circulation piping to draw out column fluid in an emergency, and a block valve was installed just apart from the branching point. Very short piping from the branch to the block valve was dead-end piping. The major cause is as follows;
A very small amount of ferrous ions in the circulation liquid dropped to
the dead-end piping, and accumulated gradually. The accumulated iron
caused exothermic decomposition, and detonation was propagated from the re-distillation column bottom.
Countermeasures The factory was closed. If the plant is reconstructed or newly constructed, all facilities and the way of handling require very careful attention to the hazards of a high-density hydroxylamine solution as shown in the "Knowledge" column.
Knowledge Comment As highly concentrated hydroxylamine is very hazardous, it is used or transported after being diluted. It is not designated as a dangerous material under the fire protection law if the concentration is 15% or less.
When hazardous facilities are constructed, regulations that are the same as those for explosives are needed of protective barriers, a safety distance, open spaces, etc., and they should be constructed in a safe place.
Background It had been proven that hydroxylamine was dangerous, and the factory prepared countermeasures such as an underground water tank and piping in which total drawing-off in an emergency was possible. However, such a hazardous material was handled thoughtlessly. (The factory staff might not have considered it carefully because the regulation under law was not sufficient).
1) Reference was not made to other examples of accidents. There were 11 accident reports over 20 years.
2) A hazard of dead-end piping was not sufficiently recognized.
3) Sufficient study was not made of an explosion hazard and explosive power.
It was an error of management judgment to consider the hazard of hydroxylamine to be small.
Incidental Discussion 1. There occurred a hydroxylamine explosion in the U.S.A. in February, 1999, which killed five workers. However, it is doubtful whether this was kept in mind and used for safety activities. If a person checked the plant thoroughly based on the USA accident, this accident might have been prevented. Generally, it is very difficult to obtain information from overseas.
2. Hydroxylamine containing a very small amount of ferrous ions is used in the semiconductor industry, although it is also used as a raw material of nylon. Demand for semiconductors has rapidly increased because of the rapid development of the IT industry and a ban on the use of Freon due to environmental problems. As a result, the operation of the plant was carried out also on weekends. This might be an indirect cause of the accident.
Reason for Adding to DB There occurred a similar accident in the U.S.A. The Fire Protection Law was revised after the accident, and the material is regulated as a dangerous material.
Primary Scenario Organizational Problems, Poor Management, Slackness of Management, Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Planning and Design, Poor Planning, Poor Process Engineering, Bad Event, Chemical Phenomenon, Detonation in the Column, Secondary Damage, External Damage, Fire, Secondary Damage, Damage to Environment, Very Large Damage in the Neighbourhood, Bodily Harm, Death, 4 person died, Bodily Harm, Injury, 59 Persons injured, Loss to Organization, Social Loss, Abolish of the Factory
Sources Assoc. for safety techniques on dangerous materials, Accident investigation report on explosion and fire of hydroxylamine in a chemical plant in Gunma Prefecture. (2001)
Masamitsu Tamura, Safety countermeasures studied from a recent accident in a chemical plant. Dangerous material accident case seminar. pp.1-17 (2001).
Sakae Kajima (Ota district fire fighting union Fire-Defense Headquarters) Fire extinguishing and rescue operation at explosion and fire of N Co. Dangerous material accident case seminar. pp.19-39 (2001)
Number of Deaths 4
Number of Injuries 58
Physical Damage Factory: four buildings were destroyed by fire, nine buildings collapsed, two buildings partially collapsed. Outside factory: two buildings collapsed, five buildings partially collapsed, 286 buildings were damaged. 55 vehicles and machines were damaged. A high-voltage line was disconnected for several hours. A telephone line was damaged.
Consequences A blast from the explosion damaged buildings located within a 1.5 km radius. It also damaged buildings of the Ojima town office including windows and fixtures.
Multimedia Files Fig2.Chemical formula
Notes Hydroxylamine was designated as a hazardous material in the fire service law attached table, which was revised after this accident. In the United Nations dangerous materials oil bath recommendation, it has been designated as a corrosive substance (class 8). It is necessary to be revised to a combustible solid (class 4.1) in the future.
Field Chemicals and Plants
Author KOSEKI, Hirosi (National Research Institute of Fire and Disaster)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)