While the STM figures out how a city bus caught fire while driving on the Ville Marie Expressway, wheelchair users are worried about what would have happened if someone with limited mobility had been on board.

On Thursday afternoon a 485 bus from Pierrefonds to Lionel Groulx metro station caught fire while approaching the Atwater exit off the Ville Marie Expressway.

All the passengers and the driver managed to get out safely.

The STM has yet to determine how people escaped, but witnesses have told CTV that most passengers used emergency windows on the left side of the bus, since the driver had parked very close to the median.

Lauren Fagen said she managed to get out the bus door before someone opened the window.

The bus caught fire soon afterward and was destroyed by flames.

The incident has people with limited mobility upset, with RAPLIQ saying there is no way someone in a wheelchair could have escaped the bus before it caught fire.

Laurent Morissette of the Regroupemont Activistes Pour L'Inclusion Quebec said the ramps used on STM buses often fail -- sometimes after a passenger has boarded.

Morissette said he knows that bus drivers are trained in emergency procedures, but he is not certain their training is up-to-date.

"We the users, we don't know about the training that they receive and seeing the way that the bus driver is using the ramps on a not-so-daily basis, and sometimes they lose their training. I wonder - do they keep this kind of training current?" said Morisette.

The STM said it has examined the type of portable, foldable ramps that RAPLIQ would like to use, and said they cannot be used on everyday buses because they are bulky and unwieldy.

"The problem with removable ramps, we can not let them in the buses because of security reasons, so it would have to be in a Chief of Operations vehicle, and it would take some time for a Chief of Operations to arrive on site, so it would not be optimal," said Amelie Regis.

After Thursday's fire the bus was towed to an STM garage for the beginning of a lengthy investigation to determine how the fire started. There are reports the NovaBus model used was recently subject to a recall notice because of a problem with the alternator.