Sunday August 14, 2005
Mask this smell
IT’S logical that any barrier can offer some sort of protection. The question is, to what degree?
While makeshift masks (for example, handkerchiefs) are inexpensive and may be used by a large segment of the population, their effectiveness must be questioned.
There are many different masks available. These are designed for different functions. However, the most basic requirement for these masks to work is that they must provide an airtight seal around the face. Otherwise, what’s the point?
Studies have evaluated dust masks, which are generally not approved by health and safety authorities, for their filtration efficiency. These masks are designed for coarse dusts and not for the fine particles present in biomass smoke. Handkerchiefs and tissues were also tested.
Although the smallest particle size used in testing was 1.5 µm, they found no difference between wet and dry handkerchiefs and in general found the penetration of 1.5 µm particles to be quite high (60-90%) for all dust masks tested. Penetration for handkerchiefs and tissues was 70-97%. In all cases, higher airflow was associated with increased filtration (Wake and Brown 1988).
Surgical masks are not very useful in preventing the inhalation of fine particle emission from vegetation fires. These masks generally cannot filter out particles less than 10 µm in size.
However, in the absence of better alternatives, it is likely that the benefits (even partial) of wearing masks will outweigh the (physiological and economic) costs.
Respirators, on the other hand, are special masks designed for the protection of workers exposed to occupational health hazards. Typically these respirators can filter out 95% or more of fine particles produced during vegetation fire episodes.
However, while respirators may be useful, they are uncomfortable and increase the effort of breathing.
Respirators may have a role for those with chronic cardio-respiratory illness, but they should be used on the recommendation of attending doctors.
During intense haze, the public should avoid outdoor activity, rather than put on a mask and stay outdoors for prolonged periods.
However, for those who cannot avoid going outdoors, the use of respirators would provide some relief.
In the case of those with cardiopulmonary illness who need to use masks on the recommendation of their doctors, they should choose the right respirators, i.e., those designed for particles removal.
In the US, the Occupational Safety and Health Administration (OSHA) and the National Institute for Occupational Safety and Health (NIOSH) have defined standards that regulate the use and certification of respirators (NIOSH, 1995; OSHA, 1998b). Under these regulations (42 CFR Part 84) NIOSH, for example, will certify three classes of filters (N, R, and P), with three levels of efficiency (95, 99, and 99.97%) in each class.
The efficiency indicates the degree to which the filter removes small (0.3 µm) particles. N series (not resistant to oil) respirators protect against particles that are free of oil or other severely degrading aerosols. These respirators have no time limitations, except for particle clogging, and are suitable for vegetation fire smoke.
In Europe, the European Committee for Standardisation (CEN) also has standards for respiratory protection and classification (CEN, 1999). For particles, there are 3 types of filter efficiency levels: P1 (80%), P2 (94%) and P3 (99.97%). P1 respirators would be suitable for protecting the population from vegetation fire smoke.
The selection of a NIOSH- or CEN-approved respirator would depend on the availability within the specific region or country. There are also other agencies that approve respirators in different countries and their selection will depend on the local current standards.
Extracted from: World Health Organisation, Guidelines on vegetation fire emergencies for public health protection; www.who.int/docstore/peh/Vegetation_fires/Health_Guidelinesfinal_3.pdf
Related stories:
The haze and you
People at risk
Mitigation measures
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