The Optical Properties of Smoke-Protective Devices

Optical properties of 13 smoke-protective devices were determined. The devices tested comprised 8 goggles and 5 fullface oxygen masks (3 rigid one-piece masks and 2 flexible hoods). Those properties evaluated were: (i) light transmission, (ii) optical haze, (iii) prismatic deviation, (iv) refractive power, (v) optical distortion, and (vi) surface curvature. Data were compared with optical requirements formulated by USA Standard USAS Z 87.1 and Military Specification MIL-L-38169(USAF). All clear transparencies met or exceeded standards for light transmission, and all but one (an experimental hood) met the standards for optical haze. All but 2 of 11 devices exceeded standards for spherical refractive power. Three fullface masks and two goggles with steep surface curvatures did not meet the optical requirements for prismatic deviation. Only 4 of 11 devices evaluated by a photographic method attained the standard for optical distortion; however, when the criterion of visible distortion was employed, as outlined in the military specification, 9 of the 11 devices conformed to the standard. Optical anomalies may be caused by facepiece configuration and surface curvature found in some of the smoke-protective devices. (Author)