I got the RV out to de-winterize it and get it ready to use this summer. Last fall I drained the hot water heater and then put the drain plug back in. The drain plug has a magnesium anodized rod attached to it. As I was unscrewing the drain plug, I could tell there was a lot of pressure built up in the tank, which is weird because it was just full of air.

When the last threads of the drain plug were unscrewed the plug and rod shot out of the tank, and a giant orange fireball followed. Fortunately I was wearing gloves, and they took the brunt of the explosion. Most of the skin on my right arm is shredded with shrapnel impacts though.

The tank itself is intact. After administering first aid, I blew out the tank with clean water, reinstalled the drain plug, and filled it up. It still works and is making hot water.

But what the heck happened??