Air-purifying respirators are generally classified into three different types:
This type of respirator offers protection against certain types of airborne particles such as dust, mists and fumes but does not protect users against vapors, gases and oxygen deficiency. This type of respirator comes equipped with permanent or replaceable filters that removes contaminants from the air.It generally becomes more effective as particles accumulate on the filter and plug spaces between the fibers. However, filters should be replaced when user finds it difficult to breathe through them.
There are nine classes of particulate filters as defined in the regulation 42 CFR 84 (also popularly known as "part 84") which was developed by NIOSH. These nine classes are based on three levels of filter efficiency and three categories of resistance to filter efficiency degradation.
- N-Series(Not resistant to oil): May be used in any atmosphere where there is no oil particulate.
- N-100 = 99.97% efficiency
- N-99 = 99% efficiency
- N-95 = 95% efficiency
- R-Series (Resistant to oil): May be used in any atmosphere where there is no oil particulate, or up to one shift where there is oil particulate present. "One shift" means eight hours of continuous or intermittent use.
- R-100 = 99.97% efficiency
- R-99 = 99% efficiency
- R-95 = 95% efficiency
- P-Series (Oil-Proof): May be used in any atmosphere, including those with oil particulates, for more than one shift. If the filter is used in atmospheres with oil particulates, contact the manufacturer to find out the service life of the filter.
- P-100 = 99.97% efficiency
- P-99 = 99% efficiency
- P-95 = 95% efficiency
Advantages: inexpensive, lightweight, disposable and relatively comfortable to use
Limitation: do not protect against chemicals, gases, or vapors
This type of respirators are normally used when there are only hazardous gases and vapors in the air. Chemical filters (called cartridges or canisters) contain special filter media or sorbent materials to remove dangerous gases or vapors from the air. This type of filter do not protect against airborne particles although some are equipped with pre-filters to filter out airborne particles before the air enters the chemical filters. Chemical respirators are effective only if used with the correct cartridge or canisters for a particular biological or chemical substance. Selecting the proper filter can be a complicated process. There are cartridges available that protect against more than one hazard, but there is no “all-in-one” cartridge that protects against all substances. It is important to know what hazards you will face in order to be certain you are choosing the right cartridges or canisters.
It can also provide protection as long as the filter's absorbing capacity is not depleted. The service life of the filter depends upon many factors and may be shortened by improper handling and storage after use.
This type of respirators are normally used in atmospheres that contain hazards of both particulates and gases. It contains both particulate filters and gas/vapor filters.
Limitation:May be heavier.