On April 24th at 2110 the Danbury Fire Dept recived 911 calls for a structure fire at the site of the Mallory Hat factory.Dispatched were E21,E22,E23,T2,C30,vol Squad6,E4,and E8,A1 and Medic1.Upon Arrival C30 reported that they have heavy fire in the debrie piles. C30 told E23and squad6 to strech a line onto the grounds of the fire. Myself and my Lt. streached a 2-1/2 inch line bwecause the building in the back was still standing and started to catch fire. All units were in operation with deck guns and hand lines.The fire was declared under controlled at 2330. The asst. chief called for 2 more engine companies.At 0030 E24,and E25 were called to the scene.At 0125 most of the units were returned to service. E21,E24, and squad6 remained on scene until 0335. Squad6 set up lights for the city payloader.At 1225 the next day all untis returned to serivce. It was determined that arson was the cause of the fire.