Capt. Jeff Bowen with Rescue 301 was among the first on the scene and was inside working to ensure the building was evacuated.
It was later reported that the building had no sprinkler system, and firefighters had trouble with standpipes.
He called a Mayday upon reaching the top floor and Firefighter Jay Bettencourt -- who was with him -- also sustained injuries in the blaze.
Bowen, 37, went into cardiac arrest after being exposed to the intense heat and smoke and efforts to revive him were unsuccessful.
The autopsy report lists smoke and fume inhalation as the cause of death and a black, soot-like material was found in his upper airways.
Officials have said that the July 28 fire inside a five-story medical office building on in the city's downtown is believed to have been intentionally set.
No one has been charged with setting the fire and the investigation remains ongoing.
