SASKATOON -- Investigators believe they have confirmed the cause of a potash mine fire that forced 20 workers to hole up underground for the better part of a day.

No one was hurt when the blaze erupted at PotashCorp.'s mine near Rocanville last month, about 245 kilometres east of Regina.

But it was 18 hours before the workers could leave refuge stations and safely return to the surface.

Damage was minimal.

The Saskatoon-based company says a wooden cable spool overheated as it was dragged through the mine.

Spokesman Bill Cooper says the company is deciding whether to switch to steel spools or change how they're transported through the mines.