The truck was driving into the city from the off-ramp on the highway when it caught fire around 10 p.m. local time Wednesday.
Fire Chief Denis Pilon said something ruptured in the truck, spraying fuel over the truck's engine, and as it drove under a bridge, it exploded.
He says the driver couldn't get out of his door, so he jumped out the passenger window to safety.
Mounties were driving by and called the fire in, and Pilon said when he arrived about 10 minutes later, the cab of the truck was fully on fire.
Since there was no risk to people, and there were explosives in the back, Pilon decided to let the fire burn out.
"So we spent about an hour and a half watching the fireworks go off and cooling it, and cooling the bridge."
Pilon said he has seen trucks on fire with hazardous things in them before, but not like this.