FACE MASK HALF DESCREIPTION

The disposable facepiece or the half-mask respirator fits over the nose but does not cover the whole face. A full face mask respirator does cover the whole face; the wartime ‘gas mask’ is of this type. A powered respirator has a fan to assist the flow of air through the filter.

Each type of respirator is available in three performance classifications. Thus, half-mask and full face mask respirators may be of the PI, P2, or P3 specification.

The filters available for respirators are of three types: (1) filters for particular gases and vapors only, (2) filters for dusts and other particulate materials, and (3) combination filters for particular gases and vapors and for dusts and other particulates.

As already stated, the air-purifying respirator differs fundamentally from the air-supplied RPE in that it is not itself a source of air and is therefore of little use unless breathable air can be drawn through it from the surrounding atmosphere. It will not sustain breathing in an asphyxiating atmosphere.

The concentration of oxygen in normal air is approximately 21%. A person breathing air with an oxygen concentration of less than about 16% may manage to do light work for a few minutes, but is likely to exhibit symptoms ranging from labored breathing to unconsciousness or death.

Respirators are produced for military, fire fighting, and industrial uses. In the former case, they are commonly referred to as ‘gas masks.’ A respirator intended for one type of application should not be used for another.

The purifying element may work in several ways. Usually it adsorbs the gas. Alternatively, it may act as a catalyst: carbon monoxide is oxidized catalytically to carbon dioxide.

The element is designed to protect against a particular chemical or group of chemicals and should not be used for other substances. There are a number of toxic gases for which a respirator is quite unsuitable. Respirators should not generally be used against gases which have a high odor threshold or no odor at all, since odor is the only warning of failure of the respirator.

Some toxic gases are irritant to the face and for these full face protection should be used.

It is essential that respirators be kept in good condition and not held too long in stock; otherwise, the air-purifying element and/or the facepiece may deteriorate. The purifying element should be replaced after use or after the elapse of a certain time according to a specified policy.

It will be apparent that, although respirators are the most convenient form of RPE and have many legitimate applications, they also have some serious drawbacks and the circumstances in which they are used should be carefully considered.