Inspired by some plans from 1942, I made my own gas mask from a snorkel, a tin can, and some charcoal I made from coconut husks. It works great!. I varnished my boat and didn’t get a headache! I’m not wearing it now, I can smell the fumes from outside, and I AM getting a headache. This gas mask is very similar to the successful British Small Box Respirator used in WW1. Inside the familiar cloth hood with goggles it had a nose clip, a mouthpiece and a hose to a can full of charcoal and soda lime. My canister only uses carbon as the absorbing agent since I’m not concerned about “acid gases”. If you need to filter out military poisons or chemicals similar to them, add the soda lime and other ingredients.
Improvised gas mask