The protection factor illustrates how effective the device is at reducing the levels of pollutants that enter the airways, i.e. the mask.
Assigned Protection Factor (APF): Based on measurements taken outside and inside the respiratory protection device, conducted in, amongst other places, real work environments and on working personnel. The APF is significantly lower than the theoretical protection factor.
Nominal Protection Factor (NPF): Based on laboratory measurements made in connection with approval of the respiratory protection device’s EN standard. Concept based on theoretical leakage percentage (e.g.: FFP3 mask with a max. leakage of 2% gives a protection factor of 100/2 = 50).
Hygiene Limit Value (HLV): Value set by the authorities (administrative norm) stating the maximum permissible average concentration throughout a workday as well as the maximum limit value. Administrative norms are published by the Norwegian Labour Inspection Authority.
Calculating recommended protection factor (RPF): Pollutant concentration/HLV (e.g. concentration 1,000 mg/m3 and a hygiene limit value of 100 mg/m3 gives a recommended protection factor of 10, i.e. a respiratory protection device with protection factor 10).