Ignition Source
Either hot clinker or sparks from chisel

An explosion occurred in a 90-ton-per-day incinerator at a municipal refuse incineration facility. Three workers were seriously burned by high-temperature gas that spouted from the inspection door, and one of them died 10 days later. The accident happened during inspection and repair of the furnace ash chute damper. The workers injected water to remove some blockage, and the water reacted with incinerated aluminum ash to form hydrogen, which caused the explosion.

Workers noticed that the post-combustion zone was full of ash and the ash pusher was not working properly, so they tried to remove the ash from the inspection door with a shovel. They discovered a solid layer of "clinker", which is formed by solidification of molten material such as aluminum. The explosion occurred inside the ash chute while the operators were trying to crush the clinker with a chisel and intermittently injecting water.

Incident Date
Jul 06, 1995
  • Hand Tools
  • Chisel
  • Heating Equipment
  • Refuse Incinerator
When Incident Discovered
Lessons Learned

The investigation determined that hydrogen was formed by the reaction of hot aluminum and water, air was admitted via the inspection door, and the mixture was ignited by the hot clinker or sparks from the chisel. Aluminum should have been separated from the refuse prior to feeding it to the incinerator, and this incident could have been avoided. Specific lessons learned included:

Incineration of crushed material with a high aluminum content was stopped.
Nitrogen should be used for purging combustible gas generated when blockage is removed.
Sufficient cooling time and safety confirmation steps must be completed prior to removing any blockage.
Water injection is no longer allowed. - An industrial camera and thermometer were installed for early detection of blockage.
The capacity of the ash pusher was increased.
Standard operating procedures were prepared for employees to follow.
A warning was issued to the public emphasizing the need for complete separation of combustibles and non-combustibles from their refuse.