Duct radial fan for direct installation in rectangular duct systems, explosion-proof in accordance with ATEX. Housing made of galvanized sheet steel with standardized duct flange profiles on both sides, space-saving design, easy to service thanks to swing-out motor-impeller unit. Forward-curved drum impeller made of galvanized steel, good efficiency, low noise, aerodynamically optimized spiral housing, inflow via nozzle. Impeller-motor unit dynamically balanced. Drive: three-phase external rotor motor, explosion-proof in accordance with ATEX, closed design, maintenance-free, sealed, low-noise ball bearings with long-term lubrication, built-in PTC thermistor. If the PTC thermistor is connected to the MSA triggering device, speed control is permitted (however, the minimum voltage must not fall below 100 V).