Laboratory evaluation of a disposable half-face mask for protection against ozone.

The ability of disposable half-face masks containing activated carbon to protect against inhaled ozone (O2) (nominal experimental exposure concentration, 0.5 ppm) was tested using a specially designed mechanical device simulating the breathing of a moderately exercising human, and then tested further by 18 volunteers exposed to O2 in a controlled-environment chamber for 2 h with intermittent mild exercise. As a control experiment, masks containing no activated carbon were tested similarly. On the mechanical device, carbon-impregnated masks removed 96 to 98% of ambient O3, whereas masks with no carbon removed 32 to 37%. Volunteers experienced typical respiratory irritation and temporary loss of forced expiratory function during O3 exposures when they wore the masks without carbon. These untoward effects were substantially reduced when masks containing carbon were worn. Volunteers tolerated the half-masks reasonably well, although some complained of discomfort. Disposable masks may be of significant benefit in protecting sensitive people from O2 exposures that they cannot readily avoid by other means.