Actually, I think the real story was that he simply collapsed and died of a heart attack.
If you've watched the famous documentary from those two French film students who were embedded with the FDNY engine company in lower Manhattan all summer and just happened to be there with them on a call when the whole thing unfolded, you can see some brief clips of him and then a segment where the firefighters in the WTC haul him out with them after the first tower came down. He had no obvious signs of trauma and was inside the lobby of the other building the whole time.
I have that DVD, as well as a recording in S-VHS from when it was originally shown. No idea what the truth is. But if miserare is correct about the firemen’s humor, that would put the two stories into conflict. When I get a chance, I’ll try to do a comparison of the original playing of that video on TV versus the DVD to see if the story changed.
After all the rumors, that was what I heard to be the final explaination also.