A fire Monday night at the Berry Plastics plant in northern Lawrence was accidental and caused by a molding machine that ignited, and the fire spread to a heating and cooling unit on the roof, said Eve Tolefree, a Lawrence Douglas County Fire Medical spokeswoman.

Manager Steve Cooper said Tuesday morning that officials at the plant, 2300 Packer Road, were investigating what caused the older injection molding machine to catch fire and were assessing damage. He said the plant returned to normal operation Tuesday after cleaning up overnight. Production work on the plastic cups on the damaged machine was transferred to another machine.

The fire was reported about 7:30 p.m. Tuesday. No one was injured, and employees followed proper evacuation procedures, Cooper said. Tolefree said later Tuesday the fire caused an estimated $75,000 in damage.