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Fit Tester Frequently Asked Questions
What is the principle of operation for the OHD Fit Tester 3000?The OHD Fit Tester 3000 Operates on the principle of Controlled Negative Pressure (CNP). Negative pressure created inside air purifying respirators during inhalation is the driving force that causes air contaminants to leak into the respirators. Contaminant leakage paths result from such things as poor facepiece-to-face seals, dirty inhalation valves, or faulty cartridge gaskets. CNP fit test technology is designed to directly measure air leakage into respirators by creating and maintaining the same driving force that causes contaminant leakage. CNP technology measures respirator leakage by exhausting air from a temporarily sealed respirator facepiece to generate a constant negative pressure (challenge pressure) inside the facepiece. The respirator is temporarily sealed during a CNP fit test by 1) replacing filters or cartridges with sealed test adapters and 2) having the test subject hold his/her breath for approximately 10 seconds. The CNP challenge pressure is selected to replicate the mean inspiratory pressure (driving force) that causes leakage into the respirator under normal use conditions. The rate of air exhaust is controlled so that the challenge pressure is maintained in the respirator during the fit test. With the challenge pressure held constant, air flow exhausted from out of the respirator is exactly equal to air flow leak into the respirator. Therefore, measuring the exhaust air stream that is required to hold the challenge pressure constant in the temporarily sealed respirator yields a direct measure of leakage air flow into the respirator. CNP technology directly measures air leakage into a respirator at the speed of sound. This capability represents a significant improvement in mask leakage measurement relative to aerosol-based technologies. As soon as the CNP challenge agent (air molecules) enters a leak site, the leak is detected at sonic velocity by pressure wave propagation. In other words, the air molecule that leaks into the respirator does not have to physically migrate to the CNP pressure transducer to be detected as respirator leakage. Aerosol-based fit test systems can detect mask leakage only if their challenge agent (aerosol particles) passes through the leak site and then physically migrates to the system’s particle detector. Since most entering particles are carried by inspired air to the lungs instead of to the aerosol sampling probe, aerosol-based systems have well-documented in-mask sampling biases that tend to grossly under-estimate respirator leakage. The Controlled Negative Pressure technology of the OHD Fit Tester 3000 allows the mask to be challenged in ways that are impractical, if not impossible, for other systems. Because CNP uses pressure to replicate the negative pressure force of inhalation, the OHD Fit Tester 3000 can be set to increase the negative force in mask pressure to simulate the effect of increased amounts of air exchanged as breathing increases to rates of up to 100 liters of air per minute or greater and provide results in an 8-second measurement. Other systems might be able to test at this level only if the wearer were to breathe at that high rate continuously for SEVERAL minutes. Therefore, other systems can create GREAT stress on the respirator wearer! CNP puts the pressure on the mask- NOT on you! Does the OHD Fit Tester 3000 use alcohol or other liquid?The OHD Fit Tester 3000 does not use any alcohol or other liquids. How much does the OHD Fit Tester 3000 weigh?The weight of the OHD Fit Tester 3000 is exactly 15 pounds and three ounces. How long is OHD Fit Tester 3000 guaranteed?The warranty is 12 months parts and labor. Has OSHA evaluated the OHD Fit Tester 3000?The OHD Fit Tester 3000 has been fully evaluated and accepted by OSHA. What software is required?Software developed for the OHD Fit Tester 3000 has been field tested and approved. It allows computerized fit testing and scheduling, as well as test result storage and retrieval. The software is available from OHD. What hardware is required to run the OHD Fit Tester 3000 software? Windows 95,or Better OS How do I get a demonstration?Contact OHD to arrange a demonstration of OHD Fit Tester 3000 at your facility.
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