It was an afternoon we would always remember. Mark sat in the middle of the shop, his legs straddling a customer's damaged gas tank. He positioned his special dent-puller—a handy tool that spot-welds small, steel stakes onto the tank, which he then pulls with a slide-hammer. He eyeballed its position, pulled the trigger, and … BAM! … the tank exploded, the cap hitting the shop's roof, 20 feet above us. Nick and I, previously standing 10 paces away, ran over to check Mark for damage, our ears ringing like clock-tower bells. No blood. No pain. Silent, we shared quick glances, and then, as if on cue, erupted in uproarious laughter! Apparently, that which doesn't kill you only makes you laugh harder. That day we all learned the importance of purging a gas tank of vapors before welding on it.