Investigators say a pipe rupture caused several explosions and a fire at the Co-op refinery in Regina that sent 13 workers to hospital last October.

The rupture, caused by corrosion within the reactor effluent line, released a mixture of fuel and hydrogen that ignited, triggering the explosions and fire.

The incident injured a total of 52 people, 13 of whom needed immediate medical attention.

Co-op says the fire damaged an area of about half an acre at the 640-acre complex.

The cost of damage and lost production from the incident is estimated at $100 million.