EN 12941/A2 This European Standard specifies minimum requirements for powered filtering devices incorporating a helmet or a hood with gas, particle or combined filter(s). It does not cover devices designed for use in the oxygen deficency environments (oxygen less than 17% by volume). It does not cover respiratory protective devices designed for escape purposes as well.

EN 12942/A2 This European Standard specifies minimum requirements for power assisted respiratory protective devices which incorporate a full face mask, half mask or a quarter mask together with gas, particle or combined filter(s). It does not cover devices designed for uses in the oxygen deficiency environments (oxygen less than 17% by volume). Also, it does not cover respiratory protective devices designed for escape purposes. It must protect the user even if the PAPR is off.

EN 14594:2005 This European Standard specifies minimum requirements for continuous flow compressed air line breathing apparatus and a hood or a mask.

Workplace Exposure Limits (WELs) – WELs are occupational exposure limits (concentrations) of a specific airborne substance averaged over a reference period, to which workers may be exposed without experiencing significant adverse health effects. There are two reference periods for which the WELs may be set:
TWA – 8 hour (long term)
TWAs are set to help preventing health effects which require prolonged or accumulated exposure.
STEL – 15 minute (short term)
The short term limits (STELs) are set to help prevents health effects which may be seen after short exposure (e.g. eye irritation which could occur after a few minutes).

Nominal protection factor – Theoretical level of protection of Respiratory Protective Equipment calculated using performance data measured in the laboratory. It indicates the mathematically calculated maximum protection performance. Calculated by dividing 100 by the total value of maximum inward leakage as specified in the relevant standard.