Case Ditails

Case Name Explosion caused due to friction on manufacturing an air bag inflator
Date June 27, 1991
Place Ibogawa, Hyogo, Japan
Location Chemical factory
Overview Sodium azide and copper oxide were put into mixers to produce an air bag inflator, and mixing started. Fine powder of the mixture went into the clearance of the bearing in the mixer. The fine powder generated frictional heat. The mixture was ignited by the heat.
Incident At a factory manufacturing an air bag inflator, sodium azide and copper oxide were put into mixers, and an explosion occurred during mixing.
Processing Manufacture
Individual Process Mixing
Process Flow Fig2.Unit process flow
Substance Sodium azide, Fig3
Copper oxide, Fig4
Type of Accident Explosion
Sequence Ground sodium azide and copper oxide were put into a V blender at the proportion of 1:1, and mixing started. An explosion occurred during mixing.
Cause The V blender had a rotating shaft with a bearing inside, and fine powder of the mixture entered the clearance between gland packing and the driven part of the rotating shaft. The fine powder reached a high temperature due to frictional heat, and it ignited.
Response Fire extinguishing by the public fire brigade.
Countermeasures The mixer was changed to another type an internal bearing.
Knowledge Comment On using a mixer or an agitator in which a bearing comes in direct contact with internal substances, the substance usually enters the clearance of the bearing. In that case, countermeasures should be taken against heat generation if the substance generates friction.
Background A selection error of the mixer seemed to be a cause. It is considered that fine powder entered the clearance of an internal bearing. It is natural that it would be heated by friction at the bearing part if a foreign substance enters. The essential problem is that the actual movement in the blender during operation was not considered before use.
Reason for Adding to DB Example of explosion caused due to friction heat generated from a solid in a bearing clearance
Primary Scenario Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Insufficient Analysis or Research, Insufficient Practice, Effect of Machine Structure, Planning and Design, Poor Planning, Poor Design, Usage, Operation/Use, Operation/Drive of Machine, Bad Event, Mechanical Event, Contamination, Bad Event, Chemical Phenomenon, Abnormal Reaction, Secondary Damage, External Damage, Explosion, Loss to Organization, Economic Loss, Manetary Damage50 million yen
Sources Fire and Disaster Management Agency. Explosion of automobile air bag inflator. Accident cases of dangerous materials. 1991. pp.102-105.
National dangerous object safety association. Explosion caused by frictional heat when fabricating air bag inflator. One hundred cases of accidents at dangerous facilities. -No.2- p.15(1994).
Physical Damage 40 square meters of a reinforced concrete manufacturing building burned, 220 square meters of the external wall was damaged by an explosion. Debris was dispersed within a radius of 40m of the north-side of the building.
Financial Cost ¥ 50 million. (Fire and Disaster Management Agency)
Multimedia Files Fig3.Chemical formula
Fig4.Chemical formula
Field Chemicals and Plants
Author KOBAYASHI, Mitsuo (Office K)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)