ELIZABETH, N.J. (AP) _ Six men trying to light a broken-down boiler were set afire when the boiler exploded, sending them running and rolling down a parking lot ramp in flames.

Mechanic Jorge Lau heard a loud bang Friday afternoon and ran toward the parking ramp with a fire extinguisher.

``There was a fellow on fire on the ramp,'' he said. ``There were five others falling on the ground already, like in a puddle of water. They were trying to put themselves out.''

Lau used the extinguisher to smother the fire on the first man.

``The one on the ramp asked me to take his coat off,'' Lau said. ``When I took his coat off, the skin came off, too.''

The men, three supervisors from the city Department of Public Works and three oil company subcontractors, were trying to ignite the boiler to heat the building, which has office space and a garage for sanitation trucks, deputy Fire Chief James Higgins said.

The men were taken to a hospital burn unit where four were in critical condition and two were stable, spokeswoman Robin Lally said.

The cause of the explosion was under investigation.