Clearing the Fog on the Use of N95 Mask

Abstract

N95 respirator mask has become a household name due to the COVID-19 pandemic. In spite of the guidelines recommending its use only by healthcare workers in close contact with COVID-19-infected patients, during aerosol-generating procedures and environmental cleaning, it has been used extensively in the community during the pandemic.1 As per regulatory standardization, the N95 mask should be able to filter 95% of particulate matter from the environment if properly designed and donned. Due to the extensive demand, N95 masks started becoming available in all shapes and sizes, sometimes without proper standardization and many times donned inappropriately even by healthcare workers who are not used to wearing these masks earlier.2 In order to prevent the transmission of droplet and airborne infection like COVID-19, it is important that COVID-19 appropriate behavior like proper donning of a suitable mask is practiced universally.3 Regulatory bodies like Occupational Safety and Health Administration (USA) requires a fit test before certifying N95 masks for public use . The fit test for N95 masks could be qualitative or quantitative. Qualitative fit test is based on the principle of whether the subject wearing the mask is able to smell or taste the test substances (gas, vapor, or aerosol), if it leaks inside the mask. The chemical substances that are used are Saccharin vapor (sweet taste) and denatonium spray (bitter taste). The use of Irritant smoke has been discontinued for this test. The test is conducted after verifying the taste of the challenge agent by the subject wearing an unfiltered mask. There is much subjectivity in this test as it is dependent on reporting by the wearer. Moreover, this test is not currently recommended for tight-fitting mask like N95, due to its low sensitivity to detect leaks.4 Quantitative methods are more reliable and are based on the principle of measuring the concentration of the test substance (challenge agent) inside and outside the mask or determining the flow rate of air under the mask. The former is the most commonly used fit test. The challenge agent could be a natural atmospheric molecule like sodium chloride (particle size increased by a method of vapor condensation) or an artificially created chemical. The ratio of the concentration of the agent measured by the detection device (e.g., PortaCount, AccuFIT) that is capable of counting the test particle above 0.015 microns, by a laser beam technology, outside the mask as compared to inside is called as fit factor (FF). FF for a standardized N95 respirator is recommended to be more than 500 to compensate for the difference between static (test) and dynamic (workplace) conditions.5 In order to ensure the proper fitness of the N95 mask, it is advisable that the wearer should tightly press the mask flush against the face and at the bridge of the nose to seal any gaps. Moreover, a user seal check is recommended by the manufacturer for all wearers of the mask. This seal check is done by sharp inhalation and exhalation while wearing the mask and observing for an air leak around the nose and edges of the mask.6 This maneuver does