A coworker of mine set a hotel on fire the other day welding a patch on a former oven hood. He was told by the people running the hotel that it was clean, and it was on the top side where he was welding. What he didn’t see was the 1/4" of old grease plastered on the back side...
Apparently while he was welding away, the whole thin gauge sheet of stainless suddenly sagged in the middle from the heat of the grease burning. THEN he picked up his helmet and noticed the smoke billowing around him. Lots of panic... a hole smashed in a roof to get to where the fire was, smoke on every floor of the hotel, lots of delays... All sorts of good stuff. That’s what the owners get for trying to rush everything along, they were supposed to open the renovated hotel this week.....
Guess that’s what fire watches are for eh?

Unfortunate that hotel management didn't know that grease catches fire when heated, but the professional welder on the job should have double checked the work of the hotel maintenance before even starting, its just safety precautions were over looked!!!