Insufficient brake force was applied before an oil train came barrelling out of nowhere in the middle of the night and slammed into a small town in Canada, killing 47 people, officials say.
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 11-kilometre incline on July 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.
It says the rule is not specific enough because it does not spell out how many handbrakes to apply for various weights and types of cargo. It also said that the standard, so-called "push-pull test" does not always accurately show whether the brakes have been adequately applied.
"Rule 112 says you need a sufficient number of brakes. What does that mean, sufficient? Because if you have a locomotive of 120 rail cars, that is the problem, a train engineer has to decide how many of those elements to take into account and that is the problem," said Belkaloul.
The board has also advised Transport Canada that dangerous goods should not be left unattended on a main track and, also, that rail equipment be properly secured.
Ross said there are similarities between the Lac-Megantic accident and previous ones, including an incident near Sept-Iles, Quebec, in December 2011 that had to do with securing trains. In that case, air brakes on the train were released and it started to move because an insufficient number of hand brakes were applied.
Ross said they are also looking at official documents, like shipping documents and rail journals.
"We are interested in the one-man train operation that existed here as well as the railways' safety management system plan," Ross said.
The transportation watchdog's advisory comes a week after Edward Burkhardt, president and CEO of the railway's U.S.-based parent company, Rail World, blamed the train's engineer for the accident. Burkhardt questioned whether he had properly set enough hand brakes and said the engineer had been suspended without pay.
The board said that while the investigation is expected to take quite some time, it won't wait to send safety warnings.
Transport Minister Lisa Raitt's office said Friday that the department has been directed to review the board's recommendations on an expedited basis.
Canada's two largest railways announced earlier this week that they are strengthening their own safety procedures in the wake of the Lac-Megantic disaster. Canadian Pacific Railway and Canadian National Railway said the tragedy prompted them to review their policies, including brake-setting procedures.
Montreal, Maine & Atlantic railway has also said it is reviewing its safety procedures.
Meanwhile, emergency officials continue to comb through the wreckage, searching for bodies amid intense heat and hazardous conditions.
Authorities have recovered the remains of 42 bodies, five bodies remain missing. Initially officials estimated 50 people died in the disaster but have revised that figure to 47.