The Ottawa police arson unit is investigating a Tuesday morning fire at St. Francis of Assisi School that caused an estimated $1 million in damage.

Several people called 911 just after 2 a.m. reporting an explosion and flames coming from the school at 795 Watters Rd., off Charlemagne Boulevard in Orléans.

Cellphone video taken by a neighbour shows flames on the roof, followed by an explosion.

According to Ottawa police arson investigator Martin Cardinal, construction supplies were being stored on the roof as part of a resurfacing job.

"It appears as though at least one propane tank exploded as a result of the fire," said Cardinal.

Burnt foam litters neighbourhood

Burnt foam litters Como Crescent in Orleans, near St-Francis of Assisi School (Giacomo Panico/CBC) It took firefighters more than an hour to bring the flames under control and to stop fire from spreading through the school's duct work. No injuries have been reported.

Cardinal said the explosion and the heat from the flames were enough to scatter burnt pieces of foam up to half a kilometre away.

Many nearby residents spent part of their Tuesday morning picking up the charred debris.

Mike McGeein, whose home backs onto Watters Road, had bigger plans for July 4. It's normally a day off for him because he works for an American company.

Como Crescent resident Rick Loughlin collects burnt pieces of foam from his front lawn Tuesday morning. (Giacomo Panico/CBC) "Woke up this morning, there was debris all over our house, back and front roof, debris all over the yard in the back, including in the pool," said McGeein.

Charred debris was also strewn along Como Crescent, where Rick Loughlin collected pieces of foam from his yard and the roof of his car.

"[Police] just told us to wear gloves in case there's any chemicals in the plastic, [and to] get it out so the animals and the kids can't eat it," said Loughlin.

Ottawa Fire Services confirmed residents can add the debris to their regular curbside waste collection rather than treat it as hazardous waste.

According to Ottawa Fire Services, roofing supplies were being stored on the school's roof for resurfacing work. (Giacomo Panico/CBC) As of Tuesday afternoon, there were no reports of any damage caused by the debris.

Fireworks a possible factor

Several neighbours told CBC that fireworks have been regularly launched from Watters Park, next to the school.

While he stressed that the investigation into the cause of the fire is still in its infancy, Cardinal said investigators have not rules out the possibility that fireworks may have landed on the roof and started the fire.

"It's certainly something we'll look at," said Cardinal.

Charlemagne Boulevard was closed from Watters Road to Princess Louise Drive, but has since reopened.