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Predicting Inward Leakage for Negative Pressure Conditions in a Firefighter Respirator



Rodney A. Bryant


An analytical model of the flow across a resistive flow path such as an orifice or pipe was applied to predict the inward leakage in an SCBA facepiece during a steady negative facepiece pressure. Starting with a range of negative pressure conditions assembled from the literature, the model was used to estimate leakage rates with respect to the size of the leak. The results of the model were also used to make quantitative estimates of the protection level of the respirator. Experiments were designed to induce a continuous below-ambient pressure inside the facepiece of a pressure-demand SCBA attached to a head form. Negative facepiece pressure measured in the presence of a leak correlated with measured fit factor. The results show that the analytical model generated reasonable estimates of leakage rates during conditions of negative pressure inside the facepiece. Thus the analytical model performed well for constant flow conditions, demonstrating the potential to predict a compromise in respirator protection during negative facepiece pressure conditions.
Proceedings Title
12th International Conference on Fire Science and Engineering
Conference Dates
July 5-7, 2010
Conference Location


Respirator, Firefighter, SCBA, Leak, Inward Leakage


Bryant, R. (2010), Predicting Inward Leakage for Negative Pressure Conditions in a Firefighter Respirator, 12th International Conference on Fire Science and Engineering, Nottingham, -1, [online], (Accessed June 21, 2024)


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Created July 12, 2010, Updated February 19, 2017