What a bummer. I bet your father feels bad about it, since I got the impression that he was just trying to help.
I always get nervous seeing people welding or with a torch working around the rear of the car by the gas tank. Another area of concern is by the battery. I read in an issue of Practical Classic magazine were someone was putting a few tack welds on a body panel in the engine compartment, when some hydrogen gas had vented from the battery. You bet...BOOM! Luckily the guy was fully clothed and wearing a full face welding helmet, providing protection from the splash of electrolyte.
I'll admit to taking shortcuts myself, but please take precautions.