Five firefighters were taken to the hospital while battling a Friday night blaze inside a recycling plant on Lincoln Avenue in Holbrook, a fire official said.
Three suffered heat exhaustion, one had a leg injury, and another experienced chest pains.
"We were rotating through often. It was very hot and humid," said 1st Assistant Chief Richard Stack of the Holbrook Fire Department.
About 150 firefighters responded to the blaze, reported to authorities shortly before 10 p.m.
The fire began in an area of the building used to separate construction debris at the Town of Islip Multipurpose Recycling Facility at 1155 Lincoln Ave., Stack said.
The fire was knocked down in three hours, but crews stayed until 5 a.m. Saturday after discovering the fire extended farther than initially thought, Stack said.
The official cause is still under investigation, but Suffolk County police said hot weather and spontaneous combustion might have played a role. With Matthew Chayes