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      Predictive value of the user seal check in determining half-face respirator fit


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          Guidelines issued by the Centers for Disease Control and Prevention and the World Health Organization state that healthcare workers should wear N95 masks or higher-level protection during all contact with suspected cases of severe acute respiratory syndrome. Before use, the manufacturer recommends performing a user seal check to ensure that the mask is fitted correctly. This study aimed to test the ability of the user seal check to detect poorly fitting masks. This study is a retrospective review of a mask-fitting programme carried out in the intensive care unit of the Prince of Wales Hospital in Hong Kong. In this programme, all staff were tested with two types of N95 mask and one type of N100 mask. The results of the documented user seal check were then compared with the formal fit-test results from a PortaCount. Using a PortaCount reading of 100 as the criterion for a correctly fitted mask, the user seal check wrongly indicated that the mask fitted on 18–31% of occasions, and wrongly indicated that it did not fit on 21–40% of occasions. These data indicate that the user seal check should not be used as a surrogate fit test. Its usefulness as a pre-use test must also be questioned.

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          Laboratory performance evaluation of N95 filtering facepiece respirators, 1996.

          In 1995, CDC's National Institute for Occupational Safety and Health (NIOSH) introduced a new classification scheme for particulate air-purifying respirators. Most health-care workers use type N95 half-mask filtering facepiece respirators (i.e., N95 respirators) to prevent occupational transmission of tuberculosis. As a result, NIOSH received inquiries about how well N95 respirators fit, whether they need to be fit tested, and whether they can be quantitatively fit tested. In response to these inquiries, NIOSH evaluated the performance of 21 N95 respirator models on a 25-person panel. This report summarizes the results of this evaluation, which indicate that fit testing is needed to ensure at least the expected level of protection (i.e., the concentration of airborne contaminants inside the respirator is < or =10% of ambient levels).
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            A modified protocol for quantitative fit testing using the PortaCount.

            A modified quantitative fit testing method has been developed for testing half masks using the TSI PortaCount respirator fit tester. This approach focuses on shortening the time for each exercise during fit testing; however, the shortened protocol is applied only to the very good-fitting masks. For marginal-fitting masks, the testing is carried out according to the full Occupational Safety and Health Administration (OSHA) respiratory protection standard (29CFR1910.134).(1) The shortened protocol (currently not approved by OSHA) still uses all the exercises required by the OSHA standard but for a shorter time (30 seconds [s] for each exercise instead of the usual 60 s). How good the fit has to be to qualify for a shortened exercise is determined by the statistical analysis of a large data set containing pass and fail fit-test data. The statistical analysis involves calculating the sensitivity and specificity of the pass and failed fit tests on half masks. From this analysis, a multiplication factor (K) to the OSHA pass/fail criterion was developed. For a respirator to undergo the shortened protocol, the fit factor obtained during any exercise must be K times the OSHA pass/fail criterion of 100 for half masks. Hence, this approach is more conservative than fit testing protocols that involve shortened exercises regardless of the fit. Nevertheless, this approach still saves time without compromising the accuracy of the fit test expressed in terms of sensitivity and specificity. For the existing data, 85 percent of the fit tests would have been performed according to the faster test protocol while only 15 percent of the tests would have been tested according to the full-length OSHA test protocol.
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              Determination of known exhalation valve damage using a negative pressure user seal check method on full facepiece respirators.

              A negative pressure user seal check (NPUSC) method was evaluated for its ability to adequately detect known exhalation valve leakage into a respirator. Three valves with different types of damage were included. Twenty-six test subjects, wearing full facepiece respirators, were asked to perform a NPUSC. Their responses as to whether they passed or failed the user seal check were compared to fit testing results from two quantitative fit test methods: ambient aerosol and controlled negative pressure. In addition, equipment developed at the University of Cincinnati was used to measure in-mask pressures that are generated during the performance of NPUSCs. This technique was employed to assess the ability of respirator wearers to properly conduct user seal checks. The data were analyzed to determine if the user seal check procedure is an effective method for detecting known exhalation valve damage. All test subjects reported passing the user seal check with the undamaged valve. With the warped valve installed, 95 percent of test subjects reported passing the user seal check. With the slit valve installed, 73 percent of test subjects reported passing. With the dirty valve installed, 65 percent reported passing. All fit factors, measured with the damaged valves, were below the Occupational Safety and Health Administration-recognized pass/fail criteria except one fit test with the respirator equipped with the slit valve. Results from the in-mask pressure measurements confirmed whether or not the subject properly conducted a user seal check, but did not detect respirator leakage. In conclusion, the performance of a NPUSC rarely helped to identify damaged exhalation valves. These results support the need for respirator inspection prior to donning with periodic fit testing and the performance of user seal checks as necessary components of an adequate respiratory protection program.

                Author and article information

                J Hosp Infect
                J. Hosp. Infect
                The Journal of Hospital Infection
                The Hospital Infection Society. Published by Elsevier Ltd.
                1 December 2004
                February 2005
                1 December 2004
                : 59
                : 2
                : 152-155
                [a ]Department of Anaesthesia and Intensive Care, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China
                [b ]Department of Medicine and Therapeutics, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, Hong Kong, China
                Author notes
                [* ]Corresponding author. Tel.: +852 2632 2735; fax: +852 2637 2422. jamesderrick@ 123456pobox.com
                Copyright © 2004 The Hospital Infection Society. Published by Elsevier Ltd. All rights reserved.

                Since January 2020 Elsevier has created a COVID-19 resource centre with free information in English and Mandarin on the novel coronavirus COVID-19. The COVID-19 resource centre is hosted on Elsevier Connect, the company's public news and information website. Elsevier hereby grants permission to make all its COVID-19-related research that is available on the COVID-19 resource centre - including this research content - immediately available in PubMed Central and other publicly funded repositories, such as the WHO COVID database with rights for unrestricted research re-use and analyses in any form or by any means with acknowledgement of the original source. These permissions are granted for free by Elsevier for as long as the COVID-19 resource centre remains active.

                : 14 October 2003
                : 19 September 2004

                Infectious disease & Microbiology
                respiratory protective devices,severe acute respiratory syndrome,safety,occupational,disease transmission,patient-to-professional,aerosols,infection control


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