Monthly Round Up of Important Ideas and Standards in
Industrial Hygiene and Safety
IN THIS ISSUE: Setting Occupational Exposure Standards
The development of a chemical exposure standard is a complex process. Factors such as the route of entry, the amount or dose entering the body, the toxicity of the chemical, speed of removal from the body, and biological variation such as age, gender, and sensitization must be considered. Determining the relative toxicity of the chemical is key. This is delineated from data from three sources:
- Experimental animal studies
- Human studies
- Industrial experience obtained through clinical and epidemiologic studies of workers.
When developing a new product, animal studies are the most common way of determining the toxic effect of a chemical. The objective is to determine the relationship between the amount of substance and its effect, known as dose-response. Developing the dose is central to determining “safe” and “hazardous” levels to which humans are exposed. The toxicologist designs an animal study to best model a chemicals effect. This may include testing on animals who best model humans or testing on tissue samples and cellular studies. Given a compound with no known toxicity data, a range of effect is needed. A dose is administered to the animal and increased. At the lower end, all animals survive. At the upper end all die. From the dose-response curve, the dose (LD50) or concentration (LC50) that will kill 50 percent of the animals can be calculated and used to determine the relative toxicity of the chemical.
|Toxicity Classes: Hodge and Sterner Scale|
|Routes of Administration|
|Oral LD50||Inhalation LC50||Dermal LD50|
|Toxicity Rating||Commonly Used Term||(single dose to rats) mg/kg||(exposure of rats for 4 hours) ppm||(single application to skin of rabbits) mg/kg||Probable Lethal Dose for Man|
|1||Extremely Toxic||1 or less||10 or less||5 or less||1 grain (a taste, a drop)|
|2||Highly Toxic||1-50||10-100||5-43||4 ml (1 tsp)|
|3||Moderately Toxic||50-500||100-1000||44-340||30 ml (1 fl. oz.)|
|4||Slightly Toxic||500-5000||1000-10,000||350-2810||600 ml (1 pint)|
|5||Practically Non-toxic||5000-15,000||10,000-100,000||2820-22,590||1 litre (or 1 quart)|
|6||Relatively Harmless||15,000 or more||100,000||22,600 or more||1 litre (or 1 quart)|
Source: Canadian Centre for Occupational Safety and Health. Available at https://www.ccohs.ca/oshanswers/chemicals/ld50.html.
Going from the animal data to an occupational standard may include a safety factor, a benchmark dose, an acceptable daily intake determination based on extrapolation from human clinical experience, and extrapolation using carcinogenicity models to determine a significantly low increased risk of cancer.
The American Conference of Governmental Industrial Hygienists is the only standard developing organization that is widely recognized by industrial hygienists. It develops voluntary exposure standards known as the threshold limit values (TLV) on many chemicals. Unlike the OSHA standards, the TLVs are not developed as a consensus between industry, labor, and science. They are based solely on health factors and do not give consideration to economic or technical feasibility. The standards are at a level of exposure that the typical worker can experience without adverse health effects.
For more information on this topic and to discuss your company’s safety and industrial hygiene needs call OccuSafe at (214) 662-6005 or visit us at www.occusafeinc.com
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