system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do gas masks work?

Like how do you get clean air in the gas mask when there's contamination around? Is it some sort of filter?
gpt
There are 2 types. One type is a air purifying, the other is air supplying.

An air purifying would use filters of different types to "clean" the air you breath. For instance, a P100 air filter would clean out dust and debris, as well as some organic material.

Air supplying is obviously, as it sounds, providing you with fresh air from a hose, usually attached to a bottle, with compressed air.