An explosion that fired a boiler room door across a school playing field highlights how risks can escalate – with broad lessons for the use of safety equipment like hazardous area heaters in any explosive atmosphere.

The incident occurred at a Halifax primary school in September 2011, just one day before the children were due to return for the new academic year.

A build-up of rust and debris in the boiler room itself had led to poor circulation of gas around the appliances, and this in turn allowed unburned gas to accumulate to an unsafe level.

Ultimately it caught light and exploded, blowing out the door, which was sent flying towards the school playing field.

HSE inspector Jackie Ferguson said: “It was pure luck no children were around at the time as the boiler house was close to the school playing field and access routes for staff and pupils alike.

“On the wider issue, all companies who carry out gas work must comply with their legal duties and responsibilities.”

The incident highlights how knock-on effects can escalate a situation even beyond the risks of the initial explosion – and why hazardous area heaters are so important in locations with a risk of explosion.