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Development of an objective method for assessing the fogging of complete eye protectors

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An objective method has been developed for testing the resistance to fogging of industrial eye protectors. A sample eye protector is attached to a model human head equipped to simulate perspiration. A television (TV) camera in one eye views a target of closely-spaced stripes. As condensation forms on the lens of the eye protector, the visibility of the stripes falls. The times for the visibility to fall to 75% and 50% are recorded and used to derive a 'fogging resistance'. A series of tests were conducted on the samples, to determine the times at which visibility fell to 75% and 50% of the starting value. Each sample was tested with the head at temperatures of 5 C, 10 C and 15 C above the temperature of the air. As expected, the greater the temperature difference the more rapidly fogging set in. The results showed that the behaviour of the protectors varies considerably according to their design. Uncoated lenses become fogged and stay fogged, while some coated lenses clear after an initial period of fogging. The more fog-resistant eye protectors stayed clear for more than 15 minutes, the maximum duration of the test. Less expensive eye protectors, ventilated by perforations in the frame, showed considerable variability between samples both because the holes were not of consistent size and because of the difficulty of forming a good seal to the face. By statistical analysis of the results, each type of protector was assigned a ' fogging resistance'(FR) which is the fogging time in seconds which will be exceeded by 95% of samples. Further tests have been conducted in which a human subject wears the eye protectors while walking on a treadmill. They show generally good agreement with the objective tests.

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