Masks are a good way to ensure you inhale the least pollutants, but certain things must be kept in mind to ensure they offer the most protection. The right mask must have the right filter type, right filter rating and right fit.
What you’re breathing
The smog over Delhi contains dust (dirt, cement, crushed brick/rock), pollen and sawdust, and noxious gases such as nitrous oxide, sulphur dioxide and carbon monoxide. Particulate pollutants can settle in the airways or make their way into the bloodstream, infusing it with carcinogens. Vapour pollutants can cause severe breathing problems by triggering inflammation of the air passage. Both types of pollutants must be taken into account while buying a filtration mask.
Masks can have an ‘N’, ‘R’ or ‘P’ type of filter. N type filters are designed to prevent the inhalation of particulate matter and aerosols that are non-oily in nature. The can remove “dust” particles related to coal, iron ore, flour, metal, wood, pollen and non-oil based liquids.
R type filters are effective for regular particles as well as for oil-based aerosols, but are rated for a life of only up to 8 hours. P type filters are the most versatile, offering protection from oily and non-oily aerosols, and have a life of up to 40 hours, or 30 days’ use.
The N type filter is sufficient for the current situation in Delhi.
Each of the three filter types has three efficiency ratings: 95, 99 and 100. For a given particle size (PM2.5 or PM10), a rating of 95 would mean that the filter is capable of trapping 95% of the pollutant particles. A filter with a rating of 100 offers the best protection — however, that does not mean that the filter rated 95 isn’t doing a good job.
They cannot be filtered out by a simple N, P or R type filter, and require an additional filter. Typically, this is a filter made of activated charcoal, which absorbs harmful organic vapours.
False comfort of ratings
Purchasing the best filter, with the highest efficiency rating does not mean that the air coming through is pure. What is never disclosed is that the efficiency ratings are derived when the level of particulate matter is within a few percentage points of the ‘safe’ limit. Delhi’s current pollution levels far exceed ‘safe’ limits and hence, a filtration mask may not be as effective as you would think. However, something is better than nothing, especially over short periods of exposure to outside air.
No matter how good the filter, its effectiveness will be negligible if it doesn’t form a proper seal around your nose and mouth. This is one of the biggest reasons why surgical masks are useless.
Choosing the right mask
Once you’ve found the right fit, it is essential to pick out the right filters. The R and P types may seem like the best option, but they’re a bit of an overkill, not to mention expensive. An N type filter with an efficiency rating of 99 is a good balance of efficiency and cost. In addition to the N type particulate filter, it is essential to have an organic vapour cartridge to block out noxious fumes.
3M makes respiratory masks that can be fitted with both an organic vapour cartridge and an N 99 filter; however, they tend to be bulky and can’t be used over extended periods of time due to the buildup of heat around the mouth. A good alternative is offered by the UK-based company Respro, whose masks do the same job, but are more compact than the 3Ms. While 3M’s filters are rated to last longer, Respro’s masks are made of neoprene, making them far more comfortable to wear.
Finally, the cost
A 3M face respirator mask with one set of organic vapour cartridges and a set of 10 P 95 filters costs roughly Rs 5,000 on Amazon US (yes, they do ship to India), excluding shipping and duty. Respro’s Techno mask (ideal for Delhi’s situation) will cost roughly Rs 3,000 (without any replacement filters); shipping is free worldwide.