I almost blew up/burned down my folks' house. I was about...oh, I donno, I guess I was maybe 12 or so, just on the edge of being old enough to be left alone in the house, mom and dad went out for the night. I was puttering around down in the basement and I tripped (again) over the floor drain grate. This was about a 7" diameter by ¼" thick cast iron grate that had rusted such that it no longer fit into its recess, and I was forever tripping over it. I decided cleaning and painting it would be a good project for the evening.
I grabbed the grate and a bottle of muriatic acid and headed up to the garage. All I needed, I figured, was something about the right size to put the drain grate in and soak it in the acid. After some looking around, I found something exactly the right size: A 9" aluminum pie pan.
I put the grate in the pan on the garage floor. I think I was wise enough to don rubber gloves, and I think I also put on eye goggles. I carefully poured in the acid until it was about 1¼" deep. Almost immediately, the acid began fizzing and brown gunk began floating off the grate. This was an encouraging sign, I thought.
And then things went very, very wrong. The fizzing turned to violent boiling, jetting two feet above the surface of the pan. Clouds of hot steam and nauseating gases were released. Eep! Realizing I needed to get the garage ventilated in a hurry, I punched the button for the electric garage door opener, which was directly above the erupting mess.
About halfway through the door's motorised upward travel, it occurred to me that the primary main gas being released directly below the garage door opener in great quantity was Hydrogen. I debated punching the (unshielded) button again to stop the door motor, risking a spark at the switch, or continue to risk sparks from the (unshielded) motor. While I was trying to figure out which was the least-worst option, the door reached the top and stopped.
I used a push broom to sweep the now-fizzling remains out of the garage and onto the driveway to be hosed away. They consisted of a very clean drain grate, a pile of stinking, steaming grey sludge, and a 9" aluminum pie ring with ragged, eaten lower edges. Oh, and a streaky area on the concrete garage floor so clean it was bright white. Later, my mother would accuse me of having spilled white paint in the garage. I truthfully denied it.
And that's the story.