What is a gas mask?
Gas masks are a protective device that is worn over the face to shield the eyes, nose, and mouth from harmful gases. Many people wear gas masks in factories. Gas masks can also be used to supply fresh air at high altitudes such as in a plane.
A gas mask is an air-purifying respiratory protective equipment (class 3 PPE) that covers the respiratory tracts (nose and mouth) as well as the eyes, allowing protection against certain toxic, irritating and/or corrosive substances. Like all air-purifying respirators, it can only be used in the presence of a sufficient oxygen level, over 19%.
The gas mask is a device used in situations where airborne pollutants and toxic gases are suspended in free air. The gas mask's purpose is to prevent the user from inhaling said pollutants. Gas masks are tight-fitting covers that cover a large portion of the head or the entire body.
It almost always covers the eyes and nose. It filters out harmful gases from the air. The reason that mouth, nose, and eyes need protection is that they all have very sensitive moist tissues.
Gases can be easily absorbed by moisture and turn into poisonous liquids. Because their eyes weren't covered, many people suffered blindness due to poison gasses in the First World War. Gas masks aren't just used for war as is often thought. When fighting a fire, firefighters wear gas masks.