The Regina Fire Department released its final report on the $77-million blast Wednesday.
Fire marshal Randy Ryba says a pipe froze and ruptured following some maintenance on a polymerization unit, which is used to make gasoline.
Once the air temperature warmed, Ryba says product was released through the line, which resulted in the explosion and subsequent fire.
No one was injured, but Ryba says that's only because many workers had already gone home to be with their families.
The report says the explosion was preventable and not an equipment malfunction.
"It was more of a maintenance issue as far as making sure the water was completely extracted out of the main feed line, which didn't happen," Ryba said.
"Certainly the fluctuating weather played a huge factor, if it wasn't for the extreme temperature swings, the incident wouldn't have happened at all."
The refinery normally produces 130,000 barrels, but reduced that level to 60,000 after the explosion.
It was the fourth fire in about two years at the refinery.
In February 2013, a fire in a coker unit sent flames shooting nearly 20 metres in the air, but was quickly brought under control.
In October 2011, corrosion in a pipe triggered a fireball that sent several workers to hospital and forced 1,400 workers from the facility. No one was injured.
In May 2012, a much smaller fire occurred when an overheated crude oil pump ignited. There were no injuries.
(CKRM, The Canadian Press)