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N95 filtering facepiece respirator deadspace temperature and humidity
Raymond J Roberge1, Jung-Hyun Kim, Stacey Benson
1National Institute for Occupational Safety and Health, National Personal Protective Technology Laboratory, Pittsburgh, Pennsylvania 15236, USA. dtn0@cdc.gov
Journal of Occupational and Environmental Hygiene
|March 15, 2012
Summary
N95 respirators create significant heat and humidity in deadspace during exercise. Respirators with exhalation valves reduce heat but not humidity, with minimal moisture retention over two hours.
Area of Science:
- Occupational Health and Safety
- Environmental Hygiene
- Respiratory Protection
Background:
- N95 filtering facepiece respirators (FFRs) are crucial for protecting against airborne contaminants.
- Understanding the thermal and humidity environment within FFRs during use is essential for user comfort and potentially for respirator efficacy.
- Previous research has not fully quantified the heat and humidity buildup in FFR deadspace during moderate exercise.
Purpose of the Study:
- To quantify the heat and humidity levels within the deadspace of N95 FFRs during low-moderate exercise.
- To compare the thermal and humidity performance of standard N95 FFRs versus N95 FFRs with exhalation valves (FFR/EV).
- To assess moisture retention of FFRs over a 2-hour period.
Main Methods:
- Seventeen subjects performed treadmill exercise at a low-moderate work rate for 1-2 hours.
- Wireless sensors monitored temperature and relative humidity within the FFR deadspace.
- FFRs were weighed before and after exercise to determine moisture retention.
Main Results:
- FFR deadspace temperature and humidity were significantly elevated above ambient levels after 1 hour, with a mean apparent heat index of 54°C.
- N95 FFR/EV demonstrated significantly lower deadspace temperatures compared to standard N95 FFR (p = 0.01).
- No significant difference in deadspace humidity was observed between N95 FFR and N95 FFR/EV (p = 0.32).
- Heat and humidity levels did not significantly increase from the first to the second hour of use.
- Mean moisture retention for both types of FFRs was less than 0.3 grams over 2 hours.
Conclusions:
- N95 FFRs generate a hot and humid microenvironment during moderate exercise.
- N95 FFR/EV provide a significant advantage in reducing deadspace heat compared to standard N95 FFR.
- Exhalation valves do not significantly improve humidity amelioration within the FFR deadspace.
- Moisture accumulation within N95 FFRs is minimal even after prolonged use.
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