Updated at 11:30 a.m. with additional details.

Updated at 4:30 p.m. with additional details.

A fire killed one woman in a Mountlake Terrace mobile home early Monday morning.

Fire crews were dispatched at 3:28 a.m. to a fence fire in the 5500 block of 242nd St. S.W. When crews arrived, they discovered a mobile home on fire on the other side of the fence.

More trucks were dispatched, and the fire was contained to a bedroom. Damage to the mobile home is estimated at $75,000. The fire did not spread to neighboring mobile homes, according to South Snohomish Fire spokeswoman Leslie Hynes.

“Firefighters located one person inside the mobile home and treated the patient at the scene. The patient died at the scene,” Hynes said. “A cat also died in the fire.”

The victim was described as a woman in her 50s.

Fire investigators believe the woman lived alone in the mobile home. Their work was interrupted after they uncovered what appeared to be an explosive device while sifting through fire debris, Hynes said. A bomb technician was called and determined the device was a hand grenade that had been disarmed and modified for use as a cigarette lighter.

Fire investigators resumed work Monday afternoon, but do not expect to have information on the cause of the fire until later in the week. The fire does not appear to be suspicious at this time. South Snohomish Fire investigators are working with Mountlake Terrace Police to determine the cause of the fire, which is standard for a fire death in the city, Hynes said.

–Photos by Doug Petrowski