BOSTON -- A fire at the Old Plymouth County Hospital in Hanson was intentionally set, State Fire Marshal Stephen D. Coan and Hanson Fire Chief Jerome A. Thompson said.

The fire at 224 High St. was discovered by police officers making routine patrols Thursday morning, and officials said it had been set sometime in the past 18 hours, but had self-extinguished.

"Fortunately, no one was injured fighting this fire. Vacant building fires are extremely dangerous to firefighters because they get a head start before anyone notices it and because of the dangers posed by the interior of the structure. More firefighter injuries occur fighting fires in vacant buildings than anywhere else," Coan said.

"There have been past fires in this building and two adults and two juveniles were arrested for setting a 2005 fire," Thompson said.

Anyone with information was asked to call Arson Hotline at 1-800-682-9229.