| Case Name |
Explosion due to sparks of an electric grinder during repairing a wastewater treatment vessel with neutralization |
| Pictograph |
|
| Date |
June 24, 1996 |
| Place |
Aichi prefecture, Japan |
| Location |
Chemical factory |
| Overview |
An explosion occurred while hot work was underway on a walkway at an upper part of a waste water neutralization vessel in a chemical plant. Workers probably did not pay enough attention to the hazards of waste water. |
| Incident |
An electric grinder was used during repairing of a walkway at the upper part of a waste water neutralization vessel at a chemical plant. A combustible gas-air mixture in the vessel exploded due to sparks from the electric grinder. |
| Processing |
Manufacture |
| Individual Process |
Waste water and waste oil treatment |
| Substance |
Waste water |
| Organic solvent |
| Organic peroxide |
| Type of Accident |
Explosion, fire |
| Sequence |
While a waste water neutralization vessel was being operated, the upper walkway was repaired. Workers came to repair the walkway with tools in the morning. They got permission to use an electric grinder, and started repair work. First, they began to cut the old walkway with the electric grinder. An explosion occurred around the vessel and a fire broke out. |
| Cause |
As a measure to prevent sparks from falling was not taken when they used an electric grinder, sparks from the electric grinder ignited a combustible gas-air mixture in the waste water neutralization vessel and it exploded. |
| Countermeasures |
A prior check of a construction site should be carried out with safety measures. Thorough exchanges of information about the work environment should be enforced. |
| Knowledge Comment |
There are hazards in unexpected places.
Process waste water in a plant is not merely water. It has to be considered as a solution of chemical substances related to the process. |
| Background |
A combustible gas-air mixture was generated in the waste water neutralization vessel, but a person in charge of plant maintenance did not recognize it. It is important to be aware that waste water can be a hazardous solution. The structure of the vessel allowed suspended matter to easily separate and attach. In fact, nitrocellulose and organic peroxide attached. The substances dissolved into waste water were overlooked. |
| Sequel |
According to an analysis after the accident, in the gas on the surface of the waste water neutralization vessel, toluene and ethyl benzene were detected at the concentration of a combustible gas-air mixture. Nitrocellulose and organic peroxide were detected in the sludge attached to the wall surface of the vessel. Sludge is usually removed using scrapers once a month, but only water was sprayed on the wall surface on that day. |
| Incidental Discussion |
There are many fire accidents at waste water treatment facilities. Process waste water is a mixture containing organic substances related to the process. Especially when it comes in contact with light gas under a high pressure condition, it dissolves a large amount of gas, and diffuses the gas because it is mostly at atmospheric pressure in the waste water treatment facilities. It can become a very dangerous gas source. |
| Reason for Adding to DB |
Example of explosion of waste water treatmenthaving overlooked hazards |
| Scenario |
| Primary Scenario
|
Poor Value Perception, Poor Safety Awareness, Inadequate Risk Recognition, Organizational Problems, Inflexible Management Structure, Insufficient Education/Training, Ignorance, Insufficient Knowledge, Insuficient Study and Experience, Planning and Design, Poor Planning, Poor Planning of Repair, Usage, Maintenance/Repair, Hot Work, Bad Event, Chemical Phenomenon, Dispersion, Secondary Damage, External Damage, Explosion, Bodily Harm, Injury, 4 person injured
|
|
| Sources |
Japan Industrial Safety and Health Association, "Details of accident occurrence."
Japan Industrial Safety and Health Association. Information Center for Safety and Health, Labor accident case No.100129," "Explosion while repairing walkway at upper waste water neutralization vessel, Information Center of Safety and Health home page
|
| Number of Deaths |
0 |
| Number of Injuries |
4 |
| Physical Damage |
Damage to a waste water neutralization pit and shed, etc. |
| Financial Cost |
¥ 3 million (Japan Industrial Safety and Health Association) |
| 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)
|
