The money isn't even relevent unless you get out alive. I wouldn't weld in a shed any more than I would in a bedroom. Bottom line if it goes up in smoke you've got to get out of either.
I'm sure there are lots of precautions to take to make things a little safer I'm just not too comfortable about the idea of welding in a wooden box. A lot goes on around us that we are oblivious to when the lid is snapped down
Ive caught my trousers alight before and as you say didn't even notice till the lid was lifted and that's the only time it felt hot when I noticed lolyes, actually that is the reason i stopped welding in there...i was quite comfortable with my ability to put any fires out but not comfortable with the fact that i didnt notice the fire had started until i had finished welding and lifted the lid...if i had been doing a long run the entire shed would have been on fire before i noticed...i actually made that very point in my comment about it being a bad idea to weld in a bedroom...
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Ive caught my trousers alight before and as you say didn't even notice till the lid was lifted and that's the only time it felt hot when I noticed lol