Fire heavily damaged one section of a wood-frame duplex house in the 1400 block of N. Main St., Hampstead, in a two-alarm blaze that broke out about 10:45 p.m. Thursday.

The fire started in the vacant part of the building, and the occupants of the other side escaped without injury, according to Hampstead Fire Chief Herb Raver.

Mr. Raver said the fire started in the unoccupied house around the chimney. Its cause is under investigation.

About 70 firefighters from Hampstead, Manchester, Westminster, and Arcadia and Boring of Baltimore County worked for about an hour to bring the fire under control.

They spent an additional two hours checking for possible extension of the fire within the walls and into the occupied portion of the building.

Traffic on Route 30 was detoured around the fire site by police from Hampstead.

The second alarm was sounded for additional personnel to relieve the firefighters dispatched on the first alarm.