My department responded to the above fire. We were one of several mutual aid departments responding. The 2 ff who went through the floor were from our department. While they did not fall all the way through it was still a problem situation. The ff sounded the floor before proceeding into the room however once inside the floor started to give way. The most likely cause, though unconfirmed at this time, of this was another MA department cutting out the floor joists during overhaul operations in the room below just previous to entry to the room. Just goes to show you need to pay attention and communicate always.