CTV news is reporting that a falling object that triggered a safety system at Agrium’s Vanscoy potash mine forced four employees to remain stuck in an elevator for several hours overnight.

The four were coming up the mine shaft in the elevator at about 10:30 p.m. Wednesday when an object fell down the shaft.

The falling object activated a safety device and caused the elevator to come to a stop. The employees were confined in the elevator for six hours until staff were sure the elevator could safely return to the surface.

None of the employees were injured.

Agrium is investigating the cause of the incident.