Date of incident: May 2024
Notice of incident number: 2024198000006
Employers: Retail property management company; HVAC services company

Incident summary
A boiler inside a boiler room in a shopping centre exploded, causing damage to the ceiling and the interior and exterior walls. No workers were injured.

Investigation conclusions

Cause

• Plugged heat exchanger caused gas buildup. The deposits on the external fins of the water tubes inside the heat exchanger (one of the main components of the boiler) restricted the flow of flue (exhaust) gases, which caused pressure to build up inside the combustion chamber. The high exhaust back-pressure switch, which was designed to stop boiler operation if the pressure within the combustion chamber exceeded the allowable amount, did not function due to deposits that had clogged the inlet to the switch. With the boiler operating in this state, unburnt fuel, carbon monoxide, and air from the combustion chamber leaked out of the combustion fan inlet and into the boiler room. The unburnt fuel accumulated inside the room and an unknown ignition source caused the explosion, resulting in damage to the vent piping and interior drywall and ceiling.

Contributing factors

• Boiler not maintained according to manufacturer’s instructions. The manufacturer recommended that the boiler be maintained on a daily, weekly, monthly, semi-annual, and annual basis. The retail property management company and the heating, ventilation, and air conditioning (HVAC) services company that it had hired to perform monthly and annual maintenance on various pieces of equipment did not ensure that regular preventive maintenance was performed on the boiler. The boiler had only been maintained on two separate occasions in the 10 months prior to the incident.

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