They were surrounding (the original fire), attacking it, in...

They were surrounding (the original fire), attacking it, in every possible way, trying to get in there every possible way, ... Put the fire out as fast as they could so to avoid something like this. But, it must have been burning longer than they were aware of. There was probably more serious fire in the basement. It was visible as they began to get inside, and it just blew up without any warning.