The Half mask VALUAIR medium is designed to work when external concentration allows it . The type of protection depends on the cartridges connected, gases , particules or combined. The threshold is depending on a theoretical calculation , based on the facial leakage and the efficiency of the adapted canister . The APF is evaluated from 12 to 50 . It allow the use of the Half mask from an external concentration between 12 time to 50 time the Occupational Exposure Limit . The half mask VALUAIR medium can be used only with certified T SERIES cartridges ( following the standard EN 141 , EN 143 ) The oxygene concentration has to be superior to 17 %.