The Danbury Fire Dept. responded to a reported structure fire on Friday March 30 at 5 pm. When the first units arived there was heavy fire venting out a fourth floor window on side A and D.We thought we had the fire out when all of the sudden the roof was getting weak and started to colpase on to the fourth floor. We had 4 firefighters in the building when the roof started to go we had to use the air horns to evucate the building we did it for 5 minutes and still no one was getting out.We tried calling them on the radio and still no luck .I was on the saftey team ready to go in and do a rescue but the finally emerged out of the building.We went to extiror attack on the building wich was fully involved the whole top floor.We pumped 7 millon gallons of water into the building We had 4 deck guns to on the roof of the ajoing building and 2 on the ground on side c. After about 3 hours later the portion of the wall came crumbling down and injuring one firefighter. It took 9 engines 3 ladders 2 squads and about 100 firefighters to extinguish the blaze we were on scene from 5 pm friday to 8 am sunday moring.The fourth floor was gone.