Abstract: Respirator apparatus 10, comprises a monocoque helmet 11, with a visor 14, which is pivotal between an inoperative raised position and an operative lowered position. The helmet 11 is formed of outer shells 17, 18 joined together along the rim and at strategic locations within the domed area of the helmet but are selectively spaced apart in various regions to provide an air chamber 19, at the rear of the helmet 11 and an air chamber 20 at the forwar part of the helmet. These chambers 19, 20 are interconnected by three ducts 21, 22, 23. The chamber 19, opens through the outer shell and is fitted with an air filter 25, to receive incoming air. The chamber 20 opens through the inner shell 17 and is fitted with a fan 26 to propel air through the ducts 21, 22, 23 into a breathing zone formed behind the visor 14. The rear portion of the helmet is provided with a chamber 29 which is isolated from the ducts 21, 22, 23 and which accommodates batteries for energizing the fan 26.