Page 33 - Occupational Health & Safety, November 2018

lungs, thus creating either an immediate threat to the worker’s cardiovascular con- dition by passing from the lungs directly into the bloodstream, as in the case of ul- trafine metal particles (as demonstrated by NIOSH) or a long-term high probability of developing a devastating and debilitating illness, such as mesothelioma (asbestos- related cancer) or silicosis.
The three categories of dust are respi- rable, thoracic, and inhalable. Each type of dust exists in the air we breathe; the only difference between them is the diameter of the dust particle. Respirable dust par- ticles are under 10 microns, thoracic dust particles are under 25 microns, and inhal- able dust particles are under 100 microns in diameter.
The sampling method varies, depending upon the type of dust to be evaluated. One such method is the use of a “Cyclone”—a precisely designed and crafted chamber that uses the effect of centrifugal force to allow larger nonrespirable particles to be cast out, leaving only respirable particles behind.
Those respirable particles, 10 microns or smaller, are then captured on a filter that is housed in a “cassette” or cylindrical holder so that the material collected can be weighed and analyzed for its chemical makeup. A variety of methods are used for determining the chemical and material properties of the dust sample, including examination under an electron microscope for “speciating” or classifying different types of asbestos fibers, which have differ- ent carcinogenic properties.
Real-time Dust Measurement Versus Sampling
A real-time dust monitor typically uses an optical “forward light scattering” tech- nique to determine the relative concentra- tion of total dust passing through its sen- sor beam. The real advantage of a real-time monitor over a sampling pump for esti- mating personal exposures is that it gives a highly resolved picture of how the dust concentrations intensify or decrease with activities performed by the worker. For example, opening a barrel of granulated raw material and mixing it with another could produce very high levels of dust ex- posure for a short period of time. A sample pump, on the other hand, would be run- ning continuously throughout the shift to be able to measure the TWA value of ex- posure. If that TWA were above the allow-
able PEL for the material in use, it could be because the levels were so high during the mixing operation that the resulting TWA indicates a respirator should be worn throughout the work shift. In this example, however, a case could be made by using a real-time dust monitor in addition to the sample pump that the respirator need be worn only during the mixing operation. This may well ensure better worker com- pliance when knowing they are required to wear PPE only during truly hazardous work tasks, if other controls cannot be put in place to reduce the exposure.
Monitoring and sampling for dusts, gases, vapors, and mists should be a part of any personal exposure assessment initiative and is not only accepted practice, it repre- sents best practice when done correctly. Air sampling using a personal sampling pump can give highly accurate results but does not give time-resolved analysis of when and how the exposures occur, and this is true for all the airborne material classifica- tions we have described here.
It is sometimes difficult to know in ad- vance the more optimal monitoring meth-
od—and often the combination of the two approaches gives a better overall result. If in doubt, always consult an industrial hy- gienist, and don’t forget to use the equip- ment manufacturer as a knowledge base and active resource for choosing the right sampling and monitoring methods.
One thing is certain: Disregarding OSHA compliance requirements for limiting ex- posures for all regulated respirable hazards would be foolish and very hazardous to the well-being and health of your business, as well as that of your workers.
Steve Ochs is Casella’s Area Business Man- ager supporting Casella’s health safety and environmental boundary monitoring solu- tions. He assists in the reduction of work- place and environmental health exposures through the supply of effective monitoring solutions for noise and dust. Prior to joining Casella, he was responsible for account man- agement of analytical and scientific equip- ment in the rental industry for many years. He is particularly interested in data trace- ability through smart monitoring to support assessment programs.
www.ohsonline.com
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