Toronto Mayor David Miller has launched a review of the city's zoning policies in the wake of Sunday's massive propane plant blasts in a residential neighborhood.

"Is it wise to have a propane facility of this kind immediately adjacent to residential properties?" Miller asked rhetorically at a press conference on Monday.

"Obviously, in light of what happened, the answer is 'no.'"

The Sunrise Propane Industrial Gases facility, which was the epicentre of a series of explosions early Sunday morning, was completely destroyed by blasts that rocked neighborhoods kilometres away.

The explosions forced the temporary evacuation of hundreds from homes in a 1.6-kilometre-area.

By late Monday, most residents were allowed to return home, but fears of asbestos in the air and concerns about the structural integrity of some homes kept a few hundred residents away.

"The yard had a right to be there, a legal right," Miller said. "We're going to investigate whether that's appropriate from the city's perspective. We're also going to work with the provincial regulator who oversees these kinds of facilities to make sure the regulations are being followed and are adequate to protect Torontonians."

Public Safety Minister Stockwell Day said the ultimate decision of where to place these type of facilities rests in the hands of municipalities.

"At the federal level, there are rules that govern the transportation of dangerous and toxic compounds and that includes propane," he said. "When a city is looking at where they're going to locate a facility, all of those federal rules and regulations are applied. But it's up to the city to actually make the rules."

'Strict' safety rules

Miller said such facilities are not just bound by zoning laws, but must also get approval from the Technical Standards and Safety Authority (TSSA), a provincial agency.

Sunrise Propane applied to build the facility in 2005 and had to abide by stringent rules before it was allowed to open, said John Marshall, the TSSA's fuel safety program director.

Marshall said once builders prove their development plan abides to zoning bylaws, they need to show the TSSA their designs and provide them with information on their storage facilities and the distances between propane tanks, cylinders and property lines.

"We have very strict regulations in place and a very robust safety system," he said.

The TSSA is keeping a close eye on the investigation into the explosions, Marshall said.

Local residents say they're angry the propane yard was allowed to be built in their midst.

"If this is a 1.6 kilometre area of evacuation ... Why isn't (the propane yard) 1.6 kilometres away" one frustrated resident asked.

The location of the facility in a residential area also had specialists scratching their heads.

Norman Nibber, a chemical engineer, said he was surprised when he heard where the facility was located.

"I was very surprised to the see the pictures of the explosion," he said on Canada AM. "It's very typical of what you'd normally see in this type of the facility when things go awry.

Nibber, who is also the president of Independent Risk Control, said Toronto could have seen casualties similar to what Mexican residents experienced when a propane plant blew up just outside of Mexico City in the 1980s.

"Something like 500 people died in that explosion and (in Toronto) it could have been as bad as that," he said. "We're just fortunate that our fire department was able to get a lot of water on these tanks. When flame impinges on these pressurized tanks, they literally explode, sending shrapnel in all sorts of areas."

With files from The Canadian Press