Improperly stored linseed-oil rags spontaneously combusted in the spring heat and caused a dramatic apartment fire in Vancouver's West End over the weekend, fire investigators have concluded.

Flames and thick, black smoke could be seen billowing from a balcony at the Pacific Surf building along English Bay's waterfront late Sunday afternoon.

Vancouver Fire Rescue Chief Darrell Reid said in a tweet that crews extinguished the fire on the 15th floor of the building, at Pacific Street and Jervis Street. No firefighters or residents were injured.

On Tuesday, fire officials said linseed-oil rags that had been used to stain furniture were to blame for the fire.

Happened to witness this fire develop in the West End today (link: <a href="https://t.co/WFltMWG9uL">https://t.co/WFltMWG9uL</a>) <a href="https://t.co/WFltMWG9uL">https://t.co/WFltMWG9uL</a> <a href="https://twitter.com/charliesmithvcr?ref_src=twsrc%5Etfw">@charliesmithvcr</a><br> <a href="https://twitter.com/hashtag/Vancouver?src=hash&ref_src=twsrc%5Etfw">#Vancouver</a> <a href="https://twitter.com/hashtag/WestEndYVR?src=hash&ref_src=twsrc%5Etfw">#WestEndYVR</a> <a href="https://twitter.com/hashtag/fire?src=hash&ref_src=twsrc%5Etfw">#fire</a> <a href="https://twitter.com/hashtag/firefighters?src=hash&ref_src=twsrc%5Etfw">#firefighters</a> <a href="https://twitter.com/hashtag/PacificStreet?src=hash&ref_src=twsrc%5Etfw">#PacificStreet</a> <a href="https://t.co/YjI1yBaWGp">pic.twitter.com/YjI1yBaWGp</a> —@Cinecraig

Linseed oil, or flaxseed oil, dries through the same chemical process that generates fire: oxidation. As the oil comes into contact with oxygen, it generates heat. A pile of rags acts as an insulator and heat builds up in the cloth until the heap eventually ignites.

"The rags were laid on top of some cardboard on top of some wood decking," a fire official told reporters on Tuesday. "What exacerbated this was it was an extremely hot day and it was facing the sun."

Fire crews said the cardboard was leaning on a glass window, which shattered as heat from the fire grew. Flames leapt into the suite but didn't spread far, according to officials, due to the quick response from fire crews and the fact that the building is made of concrete.

Fire in apartment building just off pacific. <a href="https://twitter.com/hashtag/vancouver?src=hash&ref_src=twsrc%5Etfw">#vancouver</a>. <a href="https://twitter.com/hashtag/emergency?src=hash&ref_src=twsrc%5Etfw">#emergency</a> <a href="https://t.co/aoAQqxgmI8">pic.twitter.com/aoAQqxgmI8</a> —@Rhonda_Sherwood

Fire crews recommend laying linseed oil rags flat on a non-flammable surface, like a concrete driveway, on their own and away from the house as they dry. Rags and other applicators like paint brushes should be stored in a non-combustible container with a tight lid — also on a non-flammable surface.

Vancouver Fire Rescue says it has responded to 39 calls for fires started by spontaneous combustion since 2016.

"It happens more often that you think," one official said.

The fire department estimates around 10 people on the floor affected by smoke damage have been displaced for about a month as a result of the fire.