Abstract: The invention utilizes a chemical/biological hood with a filter-blower system that is attached to the chemical/biological hood. The filter-blower system provides overpressure to the hood only. The hood is fitted to or attached to a chemical/biological mask. Overpressure created by the filter-blower around the mask is created and is independent of the wearer's respiration so that over-breathing of the positive pressure is not possible. Typically this system would be available as a hood capable of providing enhanced protection. However, the filter-blower and hood system could be integrated with the mask. Cinching or sealing the hood at the neck can improve overpressure performance.

Abstract: Assessing visibility through an optical material by capturing a digital image of a target through the material, determining its intensity, and using such intensity to determine a visual acuity index for the material. An apparatus for performing the method can assess visibility through an optical material exposed to environmental conditions. The apparatus includes an imaging system with a camera for acquiring digital images of the target through the optical material, a system for exposing the material to environmental conditions, and a system for processing intensities of the target in the acquired digital images. The processing system includes programming for relating the intensity of the target to the visual acuity index, whereby visibility through the optical material is determined.