We used to make these in junior high school, then we started making firecrackers and I screwed up big time. I was squeezing blanks to get the powder out of them and had a huge pile of powder built up. Normally, I would take the powder and move it to the can every few blanks, but nothing happened previously, so I didn't do it this time. I had about a pound of powder in a pile and squeezed a blank with the pliers and POOF! The powder dissapears and so does a good chunk of skin from the back of my right hand! It didn't hurt...for about 10 seconds, then it was amazingly painful. I had two places where it was down to raw meat, and most of the rest of the back of the hand was a bad 2nd degree. The only way I could stand it was to run cold water on it. I managed to hide it's severity from my mom and finally put some water and a couple of ice cubes in a plastic bag, than put another bag over that, filled with ice cubes, and went to bed. The next morning, it looked really bad, but didn't hurt, so my mother, who totally freaked out, decided to take me to the doctor on Monday, two days later.
The doctor comes in and yells at me, "WTF are you thinking about?" "Why didn't you go to the ER, you have two 3rd degree burn areas on your hand!" He tells me it would probably need skin grafts and I would be all scarred up. He gave me some horrible stinking yellow stuff to put on it, and chewed me out for making fireworks in the first place, and my mom for not taking me to the ER Friday night. He tells me to come back in two weeks, unless it gets infected, and then he will probably send me to the plastic surgeon to have skin grafts done.
Two weeks later I go back and he walks in, it's all healed up! The two worst places are bright pink, but all closed up and he calls in all the nurses to see it, he says he never saw anything like it before. All the nurses who saw it before are amazed how it's all healed up. For the nearly 20 years I went to him after that, he always looked at my hand and shook his head, My right hand looks just like my left. There are two very light scars on it, almost invisible unless I get a lot of sun and the scars don't tan.
Needless to say, I bought my fireworks after that..