| Case Name |
Explosion of hydrogen gas due to a backflow during a turnaround shutdown at a hydrogen producing unit. |
| Pictograph |
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| Date |
May 24, 1996 |
| Place |
Yokkaichi, Mie, Japan |
| Location |
Refinery |
| Overview |
A solution of potassium carbonate was being drawn off to an inventory tank for turnaround shutdown maintenance at a hydrogen producing unit in a refinery. The tank exploded. As the solution level in the tower was not checked, the gas flowed into the tank. The direct cause was that workers neglected to check the level of the tower. However, it is questionable whether the inflow of hydrogen gas to the inventory tank was assumed beforehand or not. |
| Incident |
Explosion occurred due to a backflow of hydrogen gas while a solution of potassium carbonate was being drawn off to an inventory tank for turnaround shutdown maintenance at a hydrogen producing unit in a refinery. |
| Processing |
Manufacture |
| Individual Process |
Maintenance |
| Substance |
Hydrogen, Fig2 |
| Type of Accident |
Explosion |
| Sequence |
On May 23rd, 1996: operation was stopped.
7:05 on 24th; the shift changed
7:30; a meeting about turnaround shutdown maintenance was held.
About 8:00; the meeting finished and operators in charge of solution draw-off read out and collated an operation manual for twenty minutes.
About 8:10; a potassium carbonate water solution started to be drawn off into an inventory tank. As a pump cavitation occurred, a delivery valve was adjusted, but it continued, so the pump was stopped and draw-off work was also suspended. After a few minutes, the tank exploded. Its roof was scattered around the sites of neighboring offices, and office buildings and vehicles were damaged by a blast. |
| Cause |
When a water solution in an absorption tower for carbonic acid gas is drawn off, the water level of the solution drops. The level drop of the solution was ignored and the pump cavitated. As the pump and a transfer valve were not shut down immediately, hydrogen in the absorption tower flowed into the tank for carbonic acid. The force of the flow blew off scales, coarse particulates, and solution in the tank, and they settled having been electrically charged. Then, it is assumed that they sparked at the wall surface or the solution surface. |
| Countermeasures |
Draw-off operations should be improved. The operation manual should be reviewed. Education on compliance with the operation manual should be carried out. |
| Knowledge Comment |
Hazardous factors should be eliminated reasonably in the aspect of facilities rather than depending on human efforts such as following a manual. |
| Background |
The absorption tower for carbonic acid gas where residual hydrogen gas remains was not substituted with nitrogen gas before turnaround shutdown maintenance. There was a mistake in directions for the operation procedure. There was also a problem with operations including poor handling of pump cavitation. |
| Sequel |
On reading out and collating the operation manual, workers reconfirmed that the tower level should be checked, the draw-off adjusting valve should be slightly opened, and the block valve should be throttled beforehand. |
| Incidental Discussion |
The reason why the pump cavitated during the draw-off operation was because the solution level fell. Therefore, when the pump started to cavitate, it should have been stopped. It is questionable why workers did not pay attention to this point. |
| Reason for Adding to DB |
Example of explosion caused due to removal of process hazards factors |
| Scenario |
| Primary Scenario
|
Organizational Problems, Poor Management, Slackness of Management, Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Misjudgment, Misjudgment of Situation, Continueing Thoughtless Liquid Draw-off, Malicious Act, Rule Violation, Safety Rule Violation, Planning and Design, Poor Planning, Poor Shutdown Planning, Secondary Damage, External Damage, Explosion, Loss to Organization, Economic Loss, Manetary Damage8 million nyen
|
|
| Sources |
Japan Industrial Safety and Health Association. Information Center for Safety and Health, "Roudou Saigai Jirei No.100128," "Explosion of hydrogen gas during periodic maintenance in hydrogen producing plant," Japan Industrial Safety and Health Association's Web-site
Fire and Disaster Management Agency, Explosion in storage tank for collecting carbonic acid gas absorption solution, Accident cases of dangerous materials.1996, pp.80-81
Japan Industrial Safety and Health Association, "Details of accident occurrence"
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| Physical Damage |
A tank roof and the upper part of the side wall were deformed. Damage to windows of nine buildings, their contents, and 15 vehicles. |
| Financial Cost |
¥ 8 million (Fire and Disaster Management Agency) |
| Multimedia Files |
Fig2.Chemical formula
|
| Field |
Chemicals and Plants
|
| Author |
WADA, Yuji (National Institute of Advanced Industrial Science and Technology)
TAMURA, Masamitsu (Center for Risk Management and Safety Sciences, Yokohama National University)
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