The truth about whether masks and respirators protect us from Delhi’s air pollution

With face masks and respirators more visibly available than firecrackers in many upscale neighbourhood markets this winter, choosing the right one from a glut of options is becoming increasingly difficult.

Do all respirators and masks protect against pollution? Which type would work best for me? Are expensive respirators substantially better than disposable, surgical masks?

They do offer some protection, but a lot more depends on how they fit your face.

Pollution masks and respirators filter liquid and airborne particulate matter, both big and small (PM10 and PM2.5), but do not protect against chemicals, gases, and vapours. If worn properly, respirators protect against vehicle emissions, reducing the risk of respiratory and heart disease, while also protecting people from infection by blocking droplets and germs (viruses and bacteria).

The N-95 filtering respirators also protect against viruses and other infecting agents but only if they are discarded after single use. People with chronic respiratory, heart disease, infections and other health conditions that make breathing difficult may have trouble breathing through respirators, and must ask their doctor for the best available option.

Partly protective, at best

Most commercially-available face masks, including internationally certified ones, do not provide adequate protection against particulate matter and black carbon mostly because of poor facial fit, found a study on the effectiveness of a range of commercially-available face masks in China. The study, published in the BMJ journal, Occupational and Environmental Medicine in April 2018, recommended more attention be given to mask design and providing correct, evidence-based guidance to consumers.

For the China study, the filteration efficacy of nine masks claiming protection against fine particulates(PM2.5) and black carbon were tested by drawing airborne diesel exhaust through the filtering medium. The penetration ranged from 0.26% to 29%, depending on the flow rate and mask material.

Four masks that were tested on volunteers doing sedentary tasks and active tasks had higher average total inward leakage, ranging from 3% to 68% in the sedentary tests and from 7% to 66% in the active tests. Only one mask type tested had an average total inward leakage of less than 10% under both test conditions.

Fit matters most

Masks and respirator have to be adjusted to fit snugly and over the nose and mouth to stop polluted air leaking in. The effectiveness of masks, including those made using highly-efficient particle filtering material, is usually much lower than certified because of poor facial fit and movement.

Masks with head straps fit better than those with elasticated ear loops. Studies have shown that even for high-quality masks, a good fit is essential for protection as people breathe deeper and harder under a mask, which leads to more polluted air being drawn in through leaks that through the filtering material, which restricts air flow.

The ‘N95’ and ‘N99’ descriptors mean that in test conditions, the respirator blocks at least 95% to 99% of very small (0.3 micron) particles, respectively. If properly fitted, the filtration capabilities of N95 respirators are better than simple face or surgical masks, but exposure to pollution is not eliminated outside test conditions.

Unless they come with disposable filters, facemasks and respirators should be used only once. Reusing masks can aggravate risk of infections because masks trap humidity and heat (generated by inhaling and exhaling), which coupled with germs in the atmosphere, can lead to viral, bacterial and fungal contamination and infection. Damaged or soiled respirators must be discarded immediately.

Most respirators, including N95 and N99, are not designed for children or people with facial hair, so the fit is never snug enough to provide full protection.

First Published: Nov 04, 2018 16:59 IST

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