easily operated battery-powered fan with particle or combination filters; SR 500 is a battery-powered fan that, together with a filter and approved hood, is part of the Sundström powered air respiratory protection system; SR 500 can be used as an alternative to filtering respirators in all situations for which they are recommended; this is especially true for work in tough conditions, heat, or long-term work; 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 supplied through a hose to the human interface