Gas masks and filters are used to protect the body from the harmful affects of chemical and biological agents. Many chemicals such as chlorine, hydrogen cyanide, phosgene, mustard agent and others were used during World War I. This caused a number of casualties among allied forces and created the need for a protective mask. You can find armed force surplus where you can find not only tents but a variety of gas masks.
Since then it has evolved and gas masks to protect against all types of chemical and biological materials known. gas masks use different techniques to protect users. But common components such as the face piece, hood, eyepieces and filters are present in almost all the masks.
The most basic masks using filtration techniques. Pollutants generally have larger particles of oxygen and by using either the mesh can be kept out. The only drawback is that the air supply is also limited in this process. Other processes using quality absorb certain chemicals such as activated charcoal to control harmful agents. The mask has been in limited use, because they are able to absorb only a few chemicals.
Now the mask using a chemical neutralization method. This mask contains a chemical filter that neutralizes harmful chemicals present in the air. Some also have a tube for drinking water, communication systems and winterization kits to prevent fogging during cold weather conditions.