EN 143 Particulate Filters

European standard EN143:2000 covers particle filters and these are classified according to their filtering efficiency. Particle filters trap and hold particles (dust, mist, fume, smoke, micro-organisms) from the air flowing through them. Large particles are easier to trap than small ones. These filters can be used against both solid particles and liquid particles (mists, fine sprays and aerosols).

There are three classes of filter:

• P1. Low efficency. Filters at least 80% of airborne particles. These filters have a WEL* of 4 when attached to either a half or full face respirator.
• P2. Medium efficency. Filters at least 94% of airborne particles. These filters have a WEL* of 10 when attached to either a half or full face respirator.
• P3. High effiency. Filters at least 99.95% of airborne particles. These filters have a WEL* of 20 when attached to half face respirator and 40 when used with a full face respirator. 

*Workplace exposure limit.

WELs are British occupational exposure limits and are set in order to help protect the health of workers. WELs are concentrations of hazardous substances in the air, averaged over a specified period of time, referred to as a time-weighted average (TWA).

Two time periods are used:

• long-term (8 hours). Some adverse health effects require prolonged or accumulated exposure. The 8 hour TWA is to set to control these effects by restricting the total intake by inhalation over one or more shifts.
• short-term (15 minutes). Some adverse health effects may be seen after short exposures. 15 minute STEL may be applied to control these effects. For a substance assigned a 15 minute STEL WEL, this level of exposure should never be exceeded.

 In addition the filters will be marked as either 'R' (resuable) or 'NR' (not reusable).