Ottawa firefighters have cleared the scene after dousing hot spots for nearly 24 hours at a fibreglass warehouse in the city's south end.

The fire started in stacked fibreglass bales at the CertainTeed fibreglass plant on Belgreen Drive, near Hawthorne Road and Stevanage Drive, just before 8 p.m. Tuesday night.

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Fire started Tuesday night in a pile of stacked fibreglass at CertainTeed warehouse in the city's south end. (Twitter)

"There was a lot of smoke when we arrived, we did a 360-[degree] tour of the building and we could see open flames through two of the doors," said district fire chief Don Smith, who supervised firefighting efforts overnight.

Crews were stationed around the building and forklift operators wearing breathing equipment helped firefighters remove burning bales of fibreglass.

"We wanted to try and be sure that we could let our crews go in safely because of the type of material we had in there," said Smith. "We had big tall bales of insulation, so safety always comes first."

All employees at the warehouse have undergone safety training, said CertainTeed engineering manager, Frederic Gimeno.

"We know the place, we just try to help the firefighters be as most efficient as possible," said Gimeno.

Previous fires at same building

Fifteen employees managed to escape unharmed.

The CertainTeed fibreglass plant was partially shut down over safety concerns in 2011 following four separate fires in the span of 14 months.

"This was totally different, this was in a warehouse area," said Smith.

"I believe the fires that we've had in the past have been in the manufacturing plant. I mean, it's related, but it's totally unrelated."

Ottawa firefighters cleared the scene at 8 p.m. Wednesday night.

The cause of the fire remains under investigation.