The pre-dawn fire that routed 50 occupants of Tooele's Ironwood Apartments smoldered in a sofa for hours before bursting into flames, investigators say.

"They were very lucky all of them got out unharmed," Fire Chief Marvin Lee said after finding the Wednesday fire's cause. "There was a party earlier in the night" in the apartment containing the sofa, which started smoldering after the party broke up about three hours before the 4 a.m. alarm, he said.Civic and religious groups and county agencies aiding the affected tenants continued to tally up personal losses Thursday. Many of the 13 families fleeing the flaming building on Tooele's east side lost everything they owned.

"I can guess their personal losses could easily total $20,000," Lee said after fire crews doused the flames. The fire did an estimated $100,000 or more damage to the building.