Safety inspectors have examined more than 500 gas-fuelled buses after a second engine fire in two months on Saturday but Transport Minister Troy Buswell has again stopped short of suspending the fleet.
The driver of the bus, which caught fire on Adie Court in Bentley about 4pm, activated an isolation valve at the back of the vehicle to cut the gas supply, but not before passengers were forced to flee.
Mr Buswell yesterday detailed a "very proactive five-point plan" to "maximise safety" in response to the unexplained fires.
He ordered that all buses be examined before leaving depots this morning and said he would double inspections to twice a week and review fire-suppression systems.
The investigation into a blaze that engulfed a gas bus in Munster on December 14 would be expanded to include Saturday's incident and manufacturer Mercedes-Benz had been invited to help.
Public Transport Authority staff will meet the bus drivers' union today over safety concerns.
Mr Buswell said an investigation into the December fire had failed to pinpoint the cause but he expected this blaze to yield more answers.
"That bus was effectively reduced to molten metal and that's an issue," he said. "My understanding is yesterday's fire wasn't as catastrophic for the vehicle."
Wheelchair-bound Bentley resident Alma Fernihough, 82, saw the blaze from her home and said she would never ride another gas-fuelled bus. "It just went bang and the flames were shooting up to the powerlines," she said.
Mrs Fernihough said the driver had told her a bus ramp would still work if there was a fire. But she said the bus door had to stay closed until the ramp was extended, which would put everyone on board in danger.
"I'm afraid I'll never get on another gas one, I'll sit and wait for a diesel," she said.
Fires also destroyed a gas-fuelled bus in Yokine in 2009 and one at the Esplanade busport in 2008.