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

Abstract

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.

Evaluation of the user seal check on gross leakage detection of 3 different designs of N95 filtering facepiece respirators

“…The characteristics of objective measurement and an automatic process increase the significance of QNFT, which now serves as the gold standard in worldwide guidelines and research literature. [10][11][12][13][14][15][16][17] Although QNFT warrants reliability of N95 respirator usage, any significant change in facial morphology, body weight, or donning method may contribute to on-site leakage. 10,18,19 Therefore, even if a given respirator is considered fit by the recognized fit testing, a user seal check is still suggested in order to check the appropriateness of every donning.…”

Selecting models for a respiratory protection program: What can we learn from the scientific literature?

“…Studies by Derrick et al 29 and Lam et al 30,31 evaluated the ability of user seal checks to predict acceptable fit for HCWs or student nurses. To address that objective, they reported fit test passing rates for respirators commonly found in Hong Kong health care settings using the N95-Companion.…”

Evaluation of the Benefit of the User Seal Check on N95 Filtering Facepiece Respirator Fit

“…However, the research done to date does not support that option. Recent findings from Lam et al, (15) Danyluk et al, (16) and Derrick et al (14) suggest that a USC is of limited value in detecting FFR leakage. A similar observation was made by Delaney et al (35) in a study to determine whether the USC could identify damaged exhalation valves in full-facepiece elastomeric respirators.…”

“…(13)(14)(15)(16) Prior to 1998 (when positive and negative pressure USCs were still called +/− fit checks), Myers et al (14) compared the number of successful donnings in two groups of 32 each inexperienced respirators users (one group was trained to perform a +/− fit check and the second was not) for three models of FFRs and one model of elastomeric dual-cartridge half mask respirator. In general, the group that performed the +/− fit check on the FFRs achieved fewer unsuccessful donnings and more consistent donnings; however, the +/− fit check was shown to be less useful when there was already a good initial fit of the FFR.…”

“…Derrick et al (14) conducted a retrospective review of nurses working in an intensive care unit in China. Study results indicated that the USC performed by subjects wearing N95 and N99 FFR wrongly indicated a good fit on 18-31% of occasions and wrongly indicated a bad fit on 21-40% of occasions.…”