The Value and Application of Threshold Limit Values

Birkner, Lawrence
(McIntyre Birkner & Associates, Inc., Thousand Oaks, CA)

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The Industrial Revolution produced, among other things, an abundance of occupational injuries and disease. In 1831 Thackrah, a British physician, observed that fork grinders who used dry grindstones died before age 32, but knife grinders who used wet stones survived to between 40 and 50 years of age. Today, occupational hygienists are faced with ever more subtle issues with more complex outcomes, from the ergonomic design of work tasks impacting health and productivity to the control of highly toxic gases in heavily populated work environments. Occupational health guidelines, based on the best available science, are essential for the safe design and operation of the work environment. The American Conference of Governmental Industrial Hygienists Threshold Limit Values (TLVs) establish a foundation for protecting workers from chemical, physical and biologic hazards. TLVs, first adopted in 1946, refer to airborne concentrations of substances or intensities of physical agents to which it is believed that nearly all workers may be repeatedly exposed, day after day, without adverse health effects. TLVs are not bright lines between safe and unsafe, nor are they a cover to provide employers with a sense of security that all is well. TLVs must be used by experienced professionals who understand their scientific basis and their limitations. To help assure that they are used safely, consideration must be given to factors such as multiple exposures and unique operating conditions of the workplace, as well as the demographics of the workforce. The Boot Camp presentation will review the history of the TLVs, the basis for their construction, their application, and potential pitfalls in their use. A case study built around the application of a TLV will be presented.

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