They are vet masks. They are generic and come on different sizes. The largest one can fit several small animals. The smallest ones are for cats and tiny dogs. I think the largest one they make are for horses and cattle. But they have special fittings for straps. This ones are rubber ring ended so they are easier to use to makeshift a tiny gas chamber.
If you’re making it from scratch (with vaccinated chicken’s eggs) and eating it right away, the risk of contamination is very low. It’s industrial mixes and old (or poorly handled) mix that are a problem.