A gas mask is an air purifying respiratory protective equipment which covers the respiratory tracts (nose and mouth) as well as the eyes. It allows protection against certain toxic, irritating and corrosive substances.
Like all air purifying respirators, it can only be used in the presence of a sufficient oxygen level. A gas masking is a device to protect you from inhaling dangerous substances, such as chemicals and infectious particles.
Gas masks are also known as “air-purifying respirators” because they filter or clean chemical gases and possibly particles out of the air as you breathe. This respirator includes a mask, and a filter/cartridge. Straps secure the facepiece to the head.
Gas masks are effective only if used with the correct cartridge or filter for a particular biological or chemical substance. Selecting the proper filter can be a complicated process.
Self-contained breathing apparatus (SCBA) is the respirator commonly used by firefighters. These use their own air tank to supply clean air, so you don’t need to worry about filters.
They also protect against higher concentrations of dangerous chemicals. However, they are very heavy, and require very special training to use and to maintain them.
Also, the air tanks typically last an hour or less depending upon their rating and how hard you are breathing.