Arson investigators are trying to find out who set a Newburg agricultural building on fire early Thursday and then did it again Friday, causing about $1 million in damage, according to the State Fire Marshal's Office.

W. Faron Taylor, the deputy state fire marshal, said that nearly 50 volunteer firefighters were called to the first blaze about 2 a.m. Thursday. The structure was on the Plainfield Farm at 3100 Victoria Rd. in southern Charles County.

On fire was a 40-by-125-foot wooden pole building and several pieces of farm machinery, including a tractor and trailer and other vehicles, Taylor said.

The firefighters from Newburg, Cobb Island, Bel Alton, La Plata, Waldorf, Hughesville, Mechanicsville and King George County in Virginia battled the blaze for about 45 minutes before bringing it under control and saving an attached office area, Taylor said.

Dousing the blaze was difficult because of the vehicles inside and the makeup of the structure, Taylor said.

"It's one thing to extinguish a burning vehicle when it's out in the open," Taylor said, "but you have vehicles inside of a building, and the building itself is sheathed in metal. When those things start to collapse, it creates pockets of burning material that prevents hose streams from penetrating, so they have to tear apart much of that sheath steel before getting to the fire."

No firefighters were injured, and damage in the Thursday blaze was estimated at $750,000, Taylor said.

About 25 hours later, nearly the same crew of volunteer firefighters was called out again to battle a blaze at the Victoria Road site, Taylor said.

At 2:20 a.m. Friday, firefighters arrived to find that fire had destroyed the remaining 40-by-40-foot office portion of the building, Taylor said. Damage was estimated at $250,000.

Taylor said investigators have been able to tell that both fires were intentionally set, but he declined to say how they had come to that conclusion.

"One of the methods of being able to apprehend an arsonist is to know exactly how they did it," Taylor said. "And if we publicize that, then it increases our potential for suspects exponentially. Right now, only the person that did it and us know the method they used."

Taylor said authorities have not ruled out anything in their investigation, including whether the two blazes were set by the same person or people.