Measuring hazardous substances

To me, the main aim of occupational hygiene is controlling exposure to hazardous agents, including hazardous substances, to do that its important to understand the degree of risk. That’s the only way we can ensure we’re directing our effort, energy and money at the real problems. With hazardous substances, measurement of their airborne concentration is often needed to help us to understand the risks, and so is a very important part of the science and practice of occupational hygiene.

This week we’re running the BOHS Module M102 “Measurement of Hazardous Substances”. in Chester, While reviewing the materials in preparation for the course, it occurred to me that the methods we use to measure hazardous substances haven’t really changed since I started work just over thirty years ago.  We still  capture particulates on a filter held in a “sampling head” which determines the particle size distribution captures, used in conjunction with a small sampling pump. Adsorption tubes are still the main approach used to assess exposure to organic vapours.

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There have been some developments. The IOM sampler is now the preferred sampling head for inhalable particulates, rather than the old “7 hole head”, but this was a redesign and development of an exiting technique, rather than an entirely new approach. The use of size selective foams in conjunction with the IOM sampler has made it easier to sample for the respirable fraction, although there are some doubts as to whether this method is valid for all types of dust.

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Equipment manufacturers have made some improvements to sampling pumps. They are generally lighter, more reliable with a more stable flow changes rather than radical new developments.  In some cases manufacturers have added extra “bells and whistles” to their pumps, but these “enhancements”, which tend to increase the cost of the devices, are rarely necessary.

The standard methods work, so there hasn’t been any need for major changes.  The old saying, “if it isn’t broke, don’t fix it” comes to mind. They are relatively easy to use, usually reliable and, an important consideration, they are relatively inexpensive. These are important factors, as, due to the large range of variability in occupational exposures, it’s desirable to collect as many samples as practicable to achieve a reasonably accurate assessment of exposure and the associated risk.

Having said that, sometimes something new comes along which requires us to re-evaluate how we do things. A recent example of this is the challenges presented by the measurement and assessment of nanoparticles. Although sub micron particles are not new – there are natural sources (e.g. forest fires, wood stoves, volcanoes) and are present in  traffic exhaust fume, welding fume, plastic fume and materials such as carbon black – the development and manufacture of “engineered” nanoparticles has increased dramatically in recent years. Research suggests that the toxicity of these particles is related to their surface area rather than their mass concentration, so the traditional methods we use for measuring dust exposures, which evaluate the latter, are unlikely to be appropriate. Although some methods are available for measuring nanoparticles, further work is needed to develop a cost effective method that can be used in the workplace.

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