Magazine article Occupational Hazards

Redefining Particulate Exposures

Magazine article Occupational Hazards

Redefining Particulate Exposures

Article excerpt

New exposure definitions, new sampling methods and equipment and previously collected data vs. new data: Are you ready for the new size-selective particulate exposure guidelines?

Workers in many different types of industries are exposed to airborne particulate matter, including dusts, fumes, mists and smoke.

The hazard potential of these compounds is determined not only by their chemical composition and mass concentration, but also by the size of the individual particles. To better assess the possible health effects of airborne particulate matter, exposure guidelines have typically been issued for different sizes of particles.

Over the last several years, new size-selective exposure guidelines have been adopted by various agencies around the world, including the International Standards Organization (ISO), the Comite Europeen de Normalisation (CEN), the American Conference of Governmental Industrial Hygienists (ACGIH) and the American Society for Testing and Materials (ASTM).

The 1998 threshold limit values (TLV[R]) booklet issued by ACGIH specifies inhalable and respirable TLVs for many compounds in accordance with a new set of definitions (See Table 1). Companies that adopt TLVs as their in-plant standards should use sampling devices that meet the new definitions.

Comparing exposure levels obtained using the traditional definitions and sampling methods with those obtained using the new approach is a very complex, controversial issue at this time. Health and safety professionals in the United States face a particular problem in that OSHA has not yet adopted the new definitions. Professionals face the choice of adopting the latest developments in science and technology or following the methods that would be used in case of an OSHA inspection.

If companies follow ACGIH TLVs, health and safety personnel may need to address several key issues. These issues include the use of different sampling equipment, the adoption of new exposure guidelines for some chemicals, and the comparison of new data with data collected using traditional definitions and air sampling methods.

New Sampling Equipment

Traditional size-selective exposure guidelines and air sampling methods for particulates in the workplace have been expressed as:

* Total Dust - Materials, both respirable and nonrespirable, that can be trapped onto a 37 mm filter cassette.

* Respirable Dust - Materials which can penetrate the alveolar section of the lung.

The new guidelines adopted by ISO, CEN, ACGIH and ASTM define particulate exposures in terms of:

* Inhalable Particulate Mass- Materials that are hazardous when deposited anywhere in the respiratory tract.

* Thoracic Particulate Mass - Materials that are hazardous when deposited anywhere within the lung airways and the gas-exchange region.

* Respirable Particulate Mass - Materials that are hazardous when deposited anywhere in the gas-exchange region.

Particle-size selective sampling devices including cyclones are defined in terms of their collection efficiency (i.e., the percentage of a certain size particle a collection device can effectively trap at a specific flow rate). The collection efficiency is frequently described in terms of the 50 percent (or median) cut-point. The 50 percent cut-point is the particle size that the sampling device collects with 50 percent efficiency. Particles smaller than the 50 percent cut-point will be collected with an efficiency greater than 50 percent; larger particles will be collected with an efficiency less than 50 percent.

INHALABLE particulate samplers. Sampling devices designed to collect inhalable particulates have a 50 percent cut-point of 100 microns ([Mu]). As such, they can effectively collect large particles that may deposit in the nose and mouth, as well as the small particles that would typically deposit in the lung airways and gas exchange region. …

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