Fire and Rescue NSW (FRNSW) has determined a faulty electrical appliance caused a fire in a mobile phone repair shop at Maroubra, in Sydney's east.
The blaze broke out inside the business, on the ground level of an eight-storey building on Anzac Parade, near Wise Street, just before 6:45am, 29 March 2023.
More than 100 people in apartments above the shopfront were evacuated as firefighters began to attack the flames.
FRNSW crews also used a thermal imaging camera to ensure the fire had not spread into the upper levels or to neighbouring buildings.
It was contained and extinguished in less than an hour.
Experts from FRNSW's Fire Investigation and Research Unit (FIRU) have attended the scene to establish the cause of the fire.
While it was initially suspected a lithium-ion battery sparked the blaze, investigations revealed it was instead caused by a malfunctioning heat gun.
Heat guns are a handheld device used to emit a stream of hot air, and are commonly used in phone repair shops to fix or alter a device's circuit board.
In this case, FIRU investigators established the heat gun was left plugged into a power board overnight, and an automated 'kill switch', meant to force a shutdown of the device when it overheats, didn't activate.
The extent of the damage was reduced by a nearby door being left shut, and the activation of a building smoke detector which quickly alerted firefighters.