Definition - What does Gas Mask mean?
A gas mask is also known as an air purifying respirator. It consists of a mask with chemical cartridge or canister for air purification. It is intended for air purification purposes and does not have an independent supply of oxygen. The gas mask is secured with straps around the head and a sealed fit is important to proper functioning.
Safeopedia explains Gas Mask
Gas masks can be used for a wide variety of applications, but the selection of the appropriate filter is essential. There are no universal cartridges that protect the wearer from all airborne pollutants. Thus, different types of cartridges are used for spray-painting, pesticide application, etc.. Cartridges must be changed on a regular basis. The expiration date of the cartridge acts as guideline, but cartridges may be required to be changed more frequently depending on exposure to pollutants and frequency of use.