VANCOUVER – Calgary Transit is reviewing its fleet of nearly 350 natural gas-powered buses after the tragic chain-reaction crash that claimed three lives and injured more than a dozen others.
The second bus involved, powered by compressed natural gas (CNG) was on fire before an explosion occurred, according to Calgary police. Three passengers on the bus were killed.
Investigators have not yet determined what caused the crash, which has sparked concern about the safety of CNG buses in service across Canada, including in Hamilton, Ont., Metro Vancouver, and Victoria.
Gordon McTaggart-Cowan, a professor in the School of Sustainable Energy Engineering at Simon Fraser University, does not believe the Calgary tragedy, on its own, provides a reason to reconsider CNG bus fleets across Canada.
“There’s a lot of time and effort that’s gone into trying to make them as safe as a conventional bus,” said McTaggart-Cowan. Unlike conventional gasoline and diesel buses, CNG buses store their fuel in high-pressure cylinders.
The gas must be compressed to reduce the amount of space it needs, allowing the bus to carry enough fuel to travel a useful distance, McTaggart-Cowan explained.
He noted that the storage cylinders undergo extensive testing. “They go through drop tests, they go through puncture tests, they sort of shoot things at them. They do all sorts of tests to make sure that they’re going to withstand extreme events,” McTaggart-Cowan told CTV News.
The tanks are also equipped with pressure-release safety valves designed to release gas if a cylinder becomes dangerously hot. When ignited, the venting gas can appear as a torch-like flame shooting from the vehicle.
That appears to be what is taking place in videos from the Calgary crash that show flames shooting from the roof of the bus, although McTaggart-Cowan cautioned that he had not examined the crash scene and could not confirm what was happening.
The pressure release system is intended to reduce the risk of a cylinder rupturing, which can have serious consequences, including explosions.
Jim McMenemy, a former Transportation Safety Board of Canada investigator, said the Calgary crash will need to be examined from multiple angles.
That includes the design of the vehicles, their operation, driver training, and maintenance.
“You can’t leave any stone unturned,” McMenemy said.
McMenemy said a preliminary report could typically be released within about 6-8 weeks, although a complex investigation could take close to a year.
