More than 50 workers at Agrium’s Vanscoy potash mine near Saskatoon, Canada, were safely evacuated over the weekend after a fire erupted underground, forcing them to stay overnight in emergency shelters. The incident took place on a swing shift Friday night.

The site’s general manager, Mike Dirham, told local radio the blaze started at about 9:45 p.m. (CST) on an LHD; the operator failed to extinguish the flames before the 54 men sought refuge in a shelter.

An emergency response team descended into the mine and extinguished the fire. At that point, the mine was ventilated to clear the smoke, but several more hours passed before the air was deemed safe enough for crews to escort everyone to the surface at 1:30 p.m.

Dirham said the cause of the fire remains under investigation by the company with the help of provincial mine safety inspectors. Underground operations, meanwhile, will remain suspended until it is declared safe again; in all, the operation employs 650 miners.

In 2013, 318 miners raced to underground refuge stations after flames broke out at Mosaic’s K2 potash mine near Esterhazy, Saskatchewan. Workers waited there for three hours as crews fought the fire and then a few hours more while the smoke cleared.

The year before, a fire at PotashCorp’s Rocanville mine in eastern Saskatchewan similarly forced 20 miners to seek shelter in a refuge. No one was injured in either incident.