By Guy Burdick
Filtering facepiece respirators (FFR) with exhalation valves, as well as a surgical mask or an unregulated face covering, can reduce a wearer’s aerosol emissions, according to a report released on December 9 by the National Institute for Occupational Safety and Health (NIOSH). With modifications, the respirators can offer the same level of source control as FFRs without exhalation valves.
Compared with other workers and the general public, healthcare workers have faced a greater risk and a longer duration of exposure during the COVID-19 pandemic. Healthcare workers have used FFRs extensively, when available, during the pandemic.
The Centers for Disease Control and Prevention (CDC) had questions about the effectiveness of FFRs with exhalation valves for source control, such as whether such respirators protect others from the wearers’ respiratory emissions.
NIOSH confirmed that approved FFRs like N95 respirators protect the wearer, filtering particle penetration to less than 5%. The report, “Filtering Facepiece Respirators with an Exhalation Valve: Measurements of Filtration Efficiency to Evaluate Their Potential for Source Control” (NIOSH Publication No. 2021-107), also confirmed that an FFR with an exhalation valve provided the same source control as commonly used measures like surgical masks, procedure masks, and cloth face coverings.
NIOSH researchers determined that modifications to FFRs with exhalation valves can further reduce particle emissions. Using an electrocardiogram (ECG) pad or surgical tape over the valve from the inside of the FFR can provide a source control similar to that of an FFR with no exhalation valve.
Exhalation valves are designed to increase the wearer’s comfort at high work rates and during longer periods of use. The exhalation valve closes during inhalation, only allowing inhaled breath to be pulled through the respirator’s filter media, and the valve opens in order to allow exhaled breath to be expelled from the respirator through the exhalation valve, as well as the filter media. Such models provide the wearer with a level of protection similar to that of an FFR without an exhalation valve.
Respiratory secretions expelled by wearers may exit along with air through the exhalation valve. NIOSH researchers set out to address concerns that FFRs with an exhalation valve could spread disease if unfiltered, virus-laden aerosols passed through the valve.
Current CDC guidance does not recommend using an FFR with an exhalation valve for source control. The CDC advises that if FFRs with exhalation valves are the only options available and source control is necessary, then the valves should be covered with a surgical mask, procedure mask, or cloth face covering that does not interfere with the respirator fit.
NIOSH’s National Personal Protective Technology Laboratory developed a study with three goals:
- Measure the filtration efficiency provided by FFRs with an exhalation valve both under conditions of inward airflow (inhalation) and outward airflow (exhalation).
- Evaluate how particle penetration in FFRs with an exhalation valve compares with particle penetration in surgical masks, procedure masks, cloth face coverings, and fabric from cotton t-shirts.
- Determine the filtration efficiency of three modifications to the exhalation valve in FFRs, with the goal of mitigating the emissions of unfiltered particles.
Modifications examined by researchers included covering the valve on the interior of the FFR with commonly available surgical tape, covering it with an ECG pad, and stretching a surgical mask over the outside of the FFR. Covering an FFR with a surgical mask was not the most effective modification. Covering the interior of the valve with either an ECG pad or surgical tape reduced particle emissions to 5%.
The researchers performed a total of 1,125 tests, examining 13 FFR models with exhalation valves. The study produced the first measurements of outward particle penetration through FFRs with an exhalation valve, which have important implications for guidance on source control and disease mitigation.