easily operated battery-powered fan with particle or combination filters; the SR 500 is a battery-powered fan, which, along with a filter and approved hood, is part of the Sundström powered air respiratory protective device; the 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 harsh conditions, in heat, or for long-term work; the human interface can consist of a hood, face shield, half mask, or full-face mask; the fan is equipped with a filter and filtered air is supplied through a hose to the human interface