By Dan Morse
Washington Post Staff Writer
Friday, August 1, 2008

Montgomery County fire officials said yesterday that a "spontaneous combustion," possibly of oily wood-finishing rags, was the most likely cause of a fire that destroyed a mansion under construction by John Marriott, the son of Marriott International Chief Executive Bill Marriott.

The 26,000-square-foot house in Potomac was about 35 percent complete and was empty at the time of the fire, which started about 10 p.m. Wednesday, officials said.

No one was hurt in the fire, which investigators said caused as much as $4.5 million in damage. When finished, the house would have been worth about $14 million, they said.

When firefighters arrived at the house, in the 10800 block of Pleasant Hill Drive in the Potomac Falls area, they saw what appeared to be a relatively small fire in the garage area. The house had been framed, with a roof, plywood floors and unfinished walls.

"The conditions were favorable for rapid fire spread," said Pete Piringer, a spokesman for the Montgomery Fire and Rescue Service.

Flames shot up about 100 feet, Piringer said, as about 90 firefighters battled the blaze. Large embers fell nearby, starting a fire on a neighbor's roof that was quickly doused, he said. Firefighters controlled the blaze within 40 minutes.

During their investigation yesterday, officials interviewed construction workers and used heavy equipment to dig through the rubble. They said they had ruled out arson and noted that because the house was in the early stages of construction, it had no electrical or gas systems.

Investigators determined that the fire began in the garage, where workers were finishing boards, Piringer said. Workers often use oily rags for such work, leading officials to believe that organic compounds in the rags smoldered and eventually burst into flames, he said.

Roger Conner, a spokesman for Marriott International, confirmed that the house was owned by John Marriott. Marriott is chief executive of JWM Family Enterprises and runs his family's investments.