01/18/2013 10:52 EST | Updated 03/20/2013 05:12 EDT

About 70 homes evacuated, school shut after hazardous spill in B.C.

WILLIAMS LAKE, B.C. - Dozens of homes in British Columbia's Cariboo region were evacuated Friday and an elementary school was closed as hazmat crews worked to clean up ammonium nitrate which spilled from the wreckage of a tractor-trailer crash.

RCMP Insp. Warren Brown said crews were expected to be on the scene for most of the day after the truck left the road and rolled Thursday evening, leaving the driver with serious injuries.

The crash ruptured the truck and caused ammonium nitrate — a material that's used as a fertilizer and in explosives — to leak out.

Officials determined the blast radius if the ammonium nitrate ignited would be about 400 metres, prompting an evacuation order covering that distance, said Brown.

Brown said the order affected about 70 homes, which the regional district said would likely be under an evacuation order until at least 6 p.m. Wildwood Elementary School was also closed for the day.

"You don't have an ideal situation because of the way it's laying right now, it's very precarious," he said in an interview. "They wouldn't be able to unload it by a conventional means."

"There's some ingenuity here. My understanding is they take a hose, attach it to the tank, run it downslope to where the new tanker will be and somehow that's sucked out or pumped out."

Brown said it appeared the ammonium nitrate was intended to be used for blasting at a nearby mine.

Al Richmond, the chair of the Cariboo Regional District, said the homes weren't evacuated overnight because there wasn't a serious risk until the clean-up began.

"It's in a gel form, so they felt it was stable enough last night," Richmond said in an interview.

"But because they're actively pumping this material into another tanker today, which means they're going to handle it, it could become unstable. It's just a remote possibility, but we don't want to take any chances,"

An emergency centre was set up at a local Salvation Army building to assist people displaced by the evacuation order, the regional district said in a news release.

Aside from the explosive risk, short-term exposure to ammonium nitrate can also cause nausea, vomiting, headaches or dizziness.

The driver was airlifted to a Vancouver-area hospital with serious injuries. Police said it was too early to speculate about what caused the crash.