Perth commuters could be left without bus services early next year after the union representing drivers threatened industrial action over an investigation into a bus fire in Munster two weeks ago.

Transport Workers Union bus industry organiser Kevin Starr said drivers might need to follow the actions of their Sydney counterparts - who went on strike after one of their Mercedes Benz gas buses caught fire at a depot in July last year - if they were not kept informed of the investigation.

"If they think we are going to continue waiting, they've got another think coming," Mr Starr said.

"Should the first or second of January arrive and we're still no wiser as to what's happened, we may well follow Sydney's path . . . they can find someone else to drive the buses."

The 530 bus from Fremantle to Cockburn was travelling along Rockingham Road in Munster about 6.30am on December 14 when it caught alight.

Nearby residents' windows were shattered by the force of the incident.

Public Transport Authority spokesman David Hynes said a report from the investigation was expected at the end of next month.

"We have retained an independent expert investigator," he said.

"The scope has been agreed and some preliminary work undertaken before the Christmas-New Year break," Mr Hynes said.

Approximately 550 buses, or close to half of Transperth's bus fleet, are gas-fuelled.

Officials from Mercedes Benz's German headquarters were flown to Perth in 2009 to help determine the cause of two similar incidents near the Esplanade Busport in 2008 and on a Yokine road in 2009.

In both cases, the buses were gutted by fire but no one was injured.

Fire suppression equipment was retrofitted to about 500 Mercedes gas buses as a result of that five-month investigation.

Mr Starr said the union had also requested cut-off switches be installed but that was rejected.

Mr Starr and Mr Hynes attribute explosion noises heard by witnesses at the Munster incident to the tyres on the bus bursting.

Mr Starr said drivers were "certainly concerned" by this month's bus fire and their patience was wearing thin because of the PTA's lack of action.

"The safety of the drivers and the passengers is paramount, the bus is their office," he said.

The West Australian

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