Insurance might not have worried him after running in that shed for many years with no problems. Of course, even if you insure it, without a regular electrical inspection, they would not pay out anyway.
I expect it would be high insurance having petrol inside. Many repair garages around here will not do welding due to the high insurance cost so my boy gets their work. Doing the sill of a Fiat Panda Today. 19 years old and just 1 hole so far.
He has no insurance as its a rented garage.