Three firefighters working on the Tarkio fire along Interstate 90 west of Missoula were forced to see refuge in their fire shelters when the fire blew up Wednesday night, fire managers revealed.

At a morning news briefing Thursday, fire officials said all three firefighters were unharmed and have contacted their families to inform them of the evening's event.

Fire shelters are tent-like devices built of reflective materials designed to protect firefighters from burns in emergency situations. The fire shelters deployed during Wednesday night's blowup worked as intended, and saved the firefighters from harm.

Firefighting agencies consider deployment of fire shelters a serious event, and have initiatied an investigation to determine the sequence of events that resulted in the need to deploy the shelters, officials said Thursday.

Such investigations are routine, they said, and are intended to determine if the need for shelter deployment could have been prevented.