Not long after the SAA Combi fire I had a SAA Capt. under supervision with our airline as a new entrant, and this, his first trip with his new airline, was a 747-200 freighter.
Shortly after take off we had a main deck cargo fire warning.
Due to the trainee Capt's status we also carried a regular F/O, so we were 4 on the flight deck and I was able to send the F/O to the back of the upper deck to initially look through the viewing window, and he came back to report that all appeared well, no sign of anything amiss on the main deck as far as he was able to see - at that stage.
The tech.log had evidence of a previous false warning, but was I going to show a recent SAA Captain that his new airline ignored fire warnings ? On top of which I had my own hide to consider !
I returned, and just before commencing the approach decided that as all still seemed OK, we would dump fuel to max landing weight instead of boring straight in overweight.
As we eventually taxied in the fire warning light extinguised, so when the engineers came aboard - like - wots' the problem !!
Turned out that the aeroplane had not long before carried a cargo of Durians, an obnoxious fruit with a very heavy, sickly, sh**ty type smell ! and the heavy vapour was still lingering in the fire detection censors - maybe ?
I was not officially censured but quietly criticised by some in management. Too bad, we were all still alive with a - more or less - servicable aeroplane.