It is natural that with the increase in biological or chemical threats, gas masks become a necessity. Before making the decision to buy and use a gas mask it is important to understand the technology behind the different types of available equipment. It is also important to understand that a gas mask alone will not give adequate protection from biological or chemical contamination.
Even the use of a protective suit will only give some protection from airborne contaminants. The only way to be fully protected is to use a suit that entirely covers the user and seals air tight, which means the use of SCBA gear is required.
Unfortunately, this type of gear is very expensive and is not practical for civilian use. You should not expect to be able to stay in an affected area for any period of time without this type of gear.
The least effective type of gas mask is known as a half-mask air-purifying respirator. These cover the nose and mouth allowing the user to breathe through the filtration system of the mask. A more effective type of mask is known as a full-face air-purifying respirator. These gas masks provide protection to the eyes, as well as the nose and mouth.