Apologies for the non technical description, but Hydrazine is a a highly toxic and dangerous unstable liquid. One of its many uses is in rocket fuel technology and on the above mentioned aircraft is utilized as an Alternate Power unit to provide electrical power.
From my distant memory, there was a flight safety poster on the subject detailing the staccato sound that the device would make when started and the dangers of being downwind from the fumes. Nasty bit of kit but we were never aware of its uses on the rest of the "F" fleet of American aircraft.
One of the photos shows a couple of military personnel looking into the smoking hole! Personally, I wouldn`t go anywhere near it until cleared! Gas masks offer no protection!