Donald Ross, chief investigator for the Transportation Safety Board of Canada, said the insufficient brake force could have been due to mechanical problems with the handbrakes, or a problem with the way someone applied them.
"The train got out of control because it wasn't fully immobilized," said Transportation Safety Board investigator Ed Belkaloul. "The number of brakes (applied) is important, but the quality of the braking is also important."
An unattended Montreal, Maine & Atlantic Railway train was parked overnight on a rail line before it came loose, hurtling down a seven-mile (11-kilometer) incline on Jan. 6. The train derailed and ignited in Lac-Megantic, near the Maine border. All but one of its 73 cars was carrying crude oil, and at least five exploded, setting off massive explosions that devastated the small lakeside town of 6,000 people.
A spokesman for the agency said it has had a closer look at 25 tanker cars since gaining access to the blast site two days ago — and has taken pictures and samples.
The investigators said they are also analyzing the contents of the tanker cars that did not explode in the crash, looking for clues on why the crude oil in the other cars exploded so violently.
"We want a more in-depth chemical analysis of the goods. We want to make sure dangerous goods do not explode," said Belkaloul.
The agency says the investigation has already resulted in two safety advisories urging a revision of the Canadian Rail Operating rule governing the securing of parked trains.
