In a bathroom fixture manufacturing company, the fire alarm sounded at around 2 p.m. after a biomass boiler had begun to overheat. The personnel were evacuated, and the following actions were carried out:

• shut down of the dust and chip extraction systems in the workshops;
• disconnection of the gas supply to the gas boilers located in the neighbouring premises;
• shutdown of boiler rooms (wood and gas).

The emergency rescue services were able to identify the hot spot using a thermal imaging camera. They stripped down and dismantled a chimney flue. After disassembly, no hot spots are detected in the boiler’s lining.

The production line was then restarted at around 4:30 p.m. Production losses were estimated at 2 hours. The two gas boilers were put back into service to supplement the shutdown of the wood-fired boiler while it was being cleaned and restored (restarted on 20/04, late in the morning).

A water outage was the origin of the event

The operator told the inspection authorities for classified facilities that the incident resulted from a water outage scheduled for 19/04 by the water utility. This water outage resulted in a drop in pressure within the wood boiler’s water network, causing it to enter failsafe mode. The failsafe mode stopped the discharge of heat from the boiler and caused the firebox to heat up. The fumes were then discharged through the fresh air ducts, causing the boiler’s outer walls to heat up.

The following corrective actions were implemented:

• shutdown of the wood-burning boiler in the event of a water outage;
• investigation as to the cause of the pressure drop on the hot water network.