When operations began at 7 a.m. on a Monday, the staff at a hazardous waste storage facility noticed the smell of melted plastic in the storage area designated for big bags pending stabilisation. Big bags filled with biomass ash from two different boiler rooms had been smouldering over the weekend. Ten big bags had been delivered 12 days earlier, and 28 big bags had arrived five days earlier. The packages had completely burnt out, and the ashes were still hot when the staff arrived.

It was estimated that 6.84 t of ash had been involved in the accident.

Plant personnel had not detected anything at the end of the shift on the previous Friday. The site is closed on weekends, and the waste storage area is not equipped with fire detection. The heating phenomenon likely occurred during the day on Saturday or Sunday.

The big bags containing the ashes were stored for several days without any heating phenomenon being observed. They were to be allowed to stabilise four days before burial. The treatment had to be postponed because part of the staff had been mobilised to replace tiles and cladding damaged during the storm five days earlier.

This batch of waste had not been stabilised immediately upon receipt, but this type of waste had never before caused problems during the interim storage period. The need to process the waste as soon as possible upon receipt had not been identified.

Furthermore, this incident highlighted the lack of temperature detection in the storage area for waste awaiting stabilisation.

The operator has considered implementing the following improvements:

• if the waste cannot be processed on the day it is received, a thermal camera is used to check its temperature at the end of the day. This waste is stored in an area that is isolated from other waste;
• installation of a thermographic camera to detect temperature increases on waste awaiting stabilisation.