N95 Filtering Facepiece Respirator Deadspace Temperature and Humidity

The objective of this study was to determine the levels of heat and humidity that develop within the deadspace of N95 filtering facepiece respirators (N95 FFR). Seventeen subjects wore two models each of N95 FFR and N95 FFR with an exhalation valve (N95 FFR/EV) while exercising on a treadmill at a low-moderate work rate for 1 and 2 hr in a temperate ambient environment. FFR deadspace temperature and relative humidity were monitored by a wireless sensor housed within the FFR. Each PER was weighed pre- and post-testing to determine moisture retention. After 1 hr, FFR deadspace temperature and humidity were markedly elevated above ambient levels, and the FFR deadspace mean apparent heat index was 54 degrees C. N95 FFR/EV use resulted in significantly lower deadspace temperatures than N95 PER (p = 0.01), but FFR deadspace humidity levels were not significantly different (p = 0.32). Compared with the first hour of use, no significant increase in PER deadspace heat and humidity occurred over the second hour PER mean moisture retention was < 0.3 grams over 2 hr N95 FFR/EV offer a significant advantage in deadspace heat dissipation over N95 PER at a low-moderate work rate over 1 hr of continuous use but offered no additional benefit in humidity amelioration. Moisture retention in N95 PER and N95 FFR/EV is minimal after 2 hr of use. [Supplementary materials are available for this article. Go to the publisher's online edition of Journal of Occupational and Environmental Hygiene for the following five supplemental resource: a file containing N95 filtering facepiece respirator deadspace mean RH and temperature recordings for 17 subjects treadmill exercising at 5.6 Km/H over 1 hour.]