Welcome to Safety Watch, a newsletter that provides an update on current loss-control regulatory and technical issues.

CONTENTS

How to assess employee health hazards in the workplace
(cover page)

Evaluating dust levels in the workplace

Employee accidents are a sign of faulty work processes

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Evaluating dust levels
in the workplace

People sometimes wonder why and how an industrial hygienist (IH) decides to evaluate employee exposure to dust in the workplace, and how to interpret the results from the laboratory.

An IH typically uses a relatively inexpensive method of evaluation known as gravimetric analysis. The IH will use the gravimetric process once he or she is certain that the particulate in question is of low toxicity, for example, containing less than 1 percent crystalline silica, and no asbestos. Airborne particulates are collected as total dust on a pre-weighed PVC filter cassette connected to a sampling pump. The results are obtained by re-weighing the filter after sampling. No specific chemical analysis is performed. Any other dust present in the environment is not identifiable and may result in over- or under-estimate exposures. In many cases, the substance is the only one being used and is clearly identifiable. Substances that fall into this category include aluminum oxide, calcium carbonate, aluminum metal, rouge, amorphous silica, glass beads and iron metal.

It should be noted that many of these substances can be chemically identified and analyzed using a different sampling media; however, this method is more time-consuming, and thus, more costly.

Some substances, such as carbon black, for which a specific industrial hygiene analytical method has not yet been developed, are also sampled as total dust on pre-weighed PVC filters.

More toxic substances, such as lead, are usually collected on a different type of filter and chemically identified and quantified. The size of airborne total particulate can be up to and exceeding 100 micrometers in diameter.

Crystalline silica in a total dust sample can be identified by an analytical method called x-ray diffraction. There is also a federal Occupational Safety and Health Administration (OSHA) Permissible Exposure Limit for crystalline silica (quartz) collected as total dust.

For dust that may contain crystalline silica, its respirable fraction usually is collected and analyzed by gravimetric analysis and x-ray diffraction because there is a well-established association between silicosis and respirable mass concentration. Industrial hygienists frequently sample respirable fraction of particulates for silica analysis to ascertain workers’ risk of crystalline silica exposure.

Respirable dusts are sampled on pre-weighed PVC filters in an MSA 10mm miniature cyclone at a pre-set air flow rate of 1.7 liters per minute. The size of respirable particles may be up to 10 micrometers in diameter.

Many minerals, including talc, calcium carbonate, coal, stone and gravel, may contain crystalline silica.

Respirable fraction of nuisance particulates also can be sampled since there is an OSHA Permissible Exposure Standard for it. The current Federal OSHA Permissible Exposure Limit for nuisance dust or particulate not otherwise regulated is 5 and 15 mg/M3 for respirable fraction and total dust, respectively.