A gas mask is a breathing device that protects the wearer against harmful gases or particulates in the air. It consists of a tight-fitting facepiece with filters, an exhalation valve and transparent eyepieces, held to the head by straps. The filter elements clean the air but do not add oxygen to it, unless connected by a hose to an oxygen tank as in some military-style gas masks. A mechanical voice amplifier may be integrated to amplify the wearer’s voice for communication with others in close proximity.
Although it is possible to design filtering devices that would neutralize most toxic substances, the construction of military-style gas masks is geared towards counteracting those chemical weapons thought most likely to be used in wartime. As a result, it is impossible to provide complete protection against all chemical warfare agents; some will still be deadly when inhaled.
The need for a practical solution was abruptly heightened in 1915, when German troops first dispersed chlorine gas across the battlefield at Ypres in World War I, killing 1,100 Allied soldiers and causing untold numbers of injuries. The gas was delivered by artillery shells that were color-coded according to the type of poisoning agent inside. Green shells contained respiratory toxins such as chlorine, phosgene and diphosgene. Red shells contained tear gases such as phosphene and chloropicrin, and gold (or yellow) ones carried mustard gas.
Early gas masks had simple sorbent compounds that limited the effects of chloride gases, but newer models used more elaborate chemical absorbents and other technologies such as electrostatic charge to deactivate the chemicals. The Large Box Respirator, introduced in February 1916, had a tin can containing the absorbent materials connected by a hose. It was followed by a smaller model, the Small Box Respirator that was issued from August 1916 and was worn as an attachment to the helmet in the form of a pouch.
Modern gas masks can be worn in a wide variety of jobs. They are often used in mining, fire fighting, disaster cleanup, and by police and first responders in the event of a biological or chemical attack. A number of different types are available, with the choice largely based on the risk level and required performance standards.
Many people who wear a gas mask find it difficult to breathe through the device, especially children and those with lung diseases such as asthma or emphysema, elderly individuals and some with claustrophobia. It is important that anyone who wears a gas mask undergo adequate training and fit testing to ensure they are using the device properly. It is also advisable that those who wear the masks regularly are given regular breaks from wearing them, so that their faces can acclimate to the different pressures created by the mask and the lack of direct oxygenation. It is also a good idea to have an escape plan for those who cannot use their masks when needed, such as if the breathing apparatus becomes dislodged or obstructed by debris or other environmental factors.