OTTAWA - A Grade 12 student killed in a freak explosion at an Ottawa high school was being mourned by thousands of fellow students, teachers and parents.

By Friday afternoon, more than 13,000 people had joined a Facebook memorial page to 18-year-old Eric Leighton, who died in hospital late Thursday after being critically injured in shop class when a empty oil drum ignited and blew up.

Their posts ranged from the simple condolences of strangers touched by Leighton's untimely death to the deeply personal eulogies of friends and family.

"My heart broke last night when I saw you. My heart broke when you were gone. My heart broke when seeing our family feel so much loss. My heart smiled when I saw how many people you touched who came out last night to say goodbye," wrote Perry Brown.

"You weren't just a cousin, but a friend. RIP Eric :'("

But with the grieving came concern and anxiety from parents with their own school-aged children. There were questions about how such an accident could have occurred in the first place.

Those questions won't be answered until the city Fire Marshal's Office finishes its investigation.

In the meantime, the Canada Safety Council is telling parents not to worry about sending their kids to school.

"Schools are about 99.9 per cent safe," spokeswoman Valerie Powell said.

"There's a lot of regulations with them, and they do follow all the safety procedures that you need to. This event that happened in Ottawa is just really unfortunate. It is an isolated incident, and you don't hear of this happening very often."

Police say students and a 33-year-old teacher at Mother Teresa Catholic High School in the city's southwest end were apparently building barbecues in the auto shop when vapours from an empty 55-gallon drum ignited and blew up.

The mid-morning blast rattled desks throughout the school and sent a total of six people to hospital.

The five others, including the male teacher, had minor injuries but were sent to hospital as a precaution because of the concussive effects of the blast.

It is believed the drum contained peppermint oil, but that is still under investigation.

Richard Smythe, a forensic scientist and analytical chemist who has investigated fires and explosions, said peppermint oil is an organic liquid that can give off vapour.

Smythe speculated that if a steel drum contained a bit of oil vapour and some oxygen, the mix would be just enough to create an explosion if it was ignited. The students at the school were building barbecues, and might possibly have been trying to cut into drums with torches or saws.

"If that drum was left, and only a bit of vapour came off and it mixed with the air inside, you have a potential bomb," said Smythe, who stressed he did not have all the details of the accident.

"Because when you put the torch to that metal drum and sparks get inside, there's already a pre-mixed mixture of fuel and oxygen, and it's in a steel drum -- you've got a bomb."

Julian Hanlon, the director of education at the Ottawa Catholic School Board, said students at the school used a similar drum to build a barbecue last week and were attempting to do it again Thursday.

"There was only one drum at the school and either last week or a couple of weeks ago, they had made a barbecue out of a similar drum. It wasn't something they did on a regular basis," he said.

"In an auto shop like that, occasionally there's a bit of down time when there aren't cars to be repaired, so they'll take on other projects like that using the same tools and equipment.

"They had made this barbecue ... a week or so ago and used it at a school event and people thought it was a great idea and there was requests for a few more."

Hanlon added none of the board's other schools were building barbecues. Nonetheless, the board has emailed its schools to warn them not to undertake similar barbecue projects.

Ontario's Ministry of Education, meanwhile, was looking into whether other schools in the province use similar types of drums in shop classes.

Mother Teresa reopened Friday with psychologists, counsellors, staff and chaplains on hand to help students cope with Leighton's death.