This sort of thing happened quite often in the early 1980s; few people could afford video recorders so things like this are only just getting on YT ( a lot of this stuff appears to be tapes ITV engineers have hoarded for 30 years or more which was highly against the rules (copyright) so they wait until they are retired and won’t lose work because of uploading it – unfortunately young engineers got in a lot of trouble when things like this happened as the bosses blamed them for it even if it was caused by outside suppliers sending them defective equipment….
It may have been the teleciné scanner for the feature film that caused the fire alert; these things had strong light shining onto the film from a cathode ray tube with about 25 000 V on the anode and high current heater supplies – plenty to catch fire in these devices!
https://www.youtube.com/watch?v=G0IXLEiQtfY
