The Alberta Energy Regulator is investigating an explosion at a shut-in wellsite near Nampa, south of Peace River.

The July 27 explosion was strong enough to blow the tops off the two huge storage tanks on the site, said Marcel Maure, fire chief of the Municipal District of Smoky River.

The Municipal District of Smoky River Fire and Rescue took this video at the scene of the July fire at a Baytex Energy oil tank near Nampa, Alta. 1:05 The fire was quickly extinguished by the 16-member volunteer fire department, but the explosion frightened nearby residents.

"When I got onto the highway, you could see big black smoke coming from that area," Maure said. "And as you got closer, you could see flames popping out the top of the barrels."

Maure said the impact of the blast was felt by residents three kilometres away.

'It felt like someone had kicked the door to his house open'

It was especially troubling to the closest resident, who lives only 500 metres from the explosion, Maure said.

"He said it felt like someone had kicked the door to his house open and shot a shotgun in the house."

The wellsite is leased by Baytex Energy, an oil and gas company based in Calgary.

Fire chief Marcel Maure said he wants to know what caused the explosion at a shut-in wellsite. (MD Smoky River) The site was shut-in, meaning it was not producing and the well had been "valved off," said Andrew Loosley, director of stakeholder and community relations for Baytex Energy.

The company uses a process of bitumen extraction known as cold heavy oil production with sand, or CHOPS, where oil is pumped from the ground and stored in heated tanks.

The company was the subject of a public inquiry by the Alberta Energy Regulator in 2014.

The inquiry was launched after several families in the Peace River area were forced to move because of what they claimed were mysterious health complaints they believe were related to emissions from the bitumen extraction process.

The inquiry confirmed there were problems with emissions that could contribute to health problems. The AER ordered the company to install equipment to capture odour-causing emissions.

Baytex said it has taken steps since the inquiry to keep area residents more informed of the company's activities.

"We have an information network when incidents occur," said Loosley. "Whenever there's an incident ... we let them (residents) know."

Baytex Energy posted a notice of the explosion on its website and sent emails to people registered with the company's "good neighbour" email chain.

Though the cause is still under investigation, Maure said he was told by the company that pressure built up inside the tanks, which caused the explosion.

"It's something I talked to them (Baytex) about, and ensured I'd like a report on their findings so that we can prepare if it happens again."

Maure said he's concerned that the explosion happened on a wellsite that was supposed to be shut-in.

"We'll dig in deeper and ensure they do routine maintenance and make sure whatever system they're using to release the off gas is working 100 per cent."

McLennan RCMP say they're not investigating since there are no signs the cause of the explosion was "suspicious."