A small fire at Whitehorse's new F. H. Collins Secondary School in July could have been prevented if basic safety rules had been followed, CBC News has learned.

The fire started in the early hours of July 22, in a bag of oily rags. According to an email from Clark Builders, the main contractor building the new school, workers had been varnishing the gymnasium floor and left some used rags in a garbage bag.

Oily rags produce heat through oxidation, and will spontaneously burst into flames if they get hot enough. A fire inspection at F.H. Collins determined that's what happened.

"Luckily, the sprinklers had been installed and the sprinklers actually extinguished the fire. So that was lucky for us," said Wayne Smyth, who investigated the fire.

Smyth said he believes the risk of spontaneous combustion is common knowledge among contractors. 

New F.H. Collins Secondary School

Damage from the fire was minimal, investigators said. The new school will open on schedule in January, according to the Yukon government. (Claudiane Samson/Radio-Canada)

"The National Fire Code actually stipulates that rags and materials that are used in floor finishing have to be disposed of outside of the building, and they should be disposed of at the end of every work day," Smyth said.

All oils a potential hazard

Yukon College carpentry instructor Don Gillies agrees and said there are safety steps everyone should follow including people working with varnish-soaked rags at home.

"At the very least, do not bunch them up and leave them lying on the floor inside your house. Don't put them into containers with other combustibles," Gillies said.

He recommends laying rags outside to dry, then disposing of them in a sealed can with water.

"I would recommend treating all oils as a potential hazard," Gillies said.

The city of Whitehorse won't accept oily rags at the landfill, as they are considered hazardous waste. The city collects hazardous waste twice a year, in May and September. 

The F. H. Collins fire caused some water damage from the sprinklers, but Yukon government officials say construction is still on schedule. The new school is slated to open in January.

CBC contacted the contractor, Clark Builders, but has not received a response.