The SR 500 is a battery-powered fan that, together with a filter and an approved head top, is included in the Sundström fan-assisted respiratory protective device systems. The SR 500 can be used as an alternative to filter respirators in all situations in which these are recommended. This applies particularly to work that is hard, warm or of long duration. The human interface may consist of a hood, face shield, half mask or full face mask. The fan is equipped with a filter, and the filtered air is fed through a hose to the human interface. The pressure then generated prevents surrounding pollutants from penetrating into the mask.