Rounding conventions of occupational exposure limits and health based exposure limits

When presenting the final value for either an occupational exposure limit (OEL) or a health based exposure limit (HBEL) it is important to not to overstate the precision associated with the recommended values. As is common practice in the industrial hygiene, occupational toxicology, and risk management professions, the presentation of the final value does not follow traditional mathematical rounding rules used by quality departments, but risk assessment rounding practices. The final values are typically presented with only 1 significant digit. The reason for this rounding convention is simply a matter of practically and an understanding of the imprecissness of the underlying values (large variability in human body weight, breathing volume, the imprecise nature of the selection of adjustment factors, etc.).

Examination of the United States Occupational Safety and Health Administration's (OSHA) Permissible Exposure Limits (PEL) Z-1 Table, the American Conference of Governmental Industrial Hygienist (ACGIH) threshold limit values (TLVs), and the UK's Health and Safety Executive's EH40/2005 Workplace Exposure Limits will further reveal this standard practice.

The imprecise nature of OELs and HBELs is also supported in the PIC/s HBEL inspection guidance where it states the following:

An analogy

The best way to relate to OEL and HBELs is to think about highway speed limits. If a highway had a speed limit of 83.3 km/h that would be much more difficult to comply with and communicate that 80 km/h. In addition, based on the underlying factors, the difference in overall risk would be trivial.

For additional information, see:

Setting Health-Based Exposure Limits to Support Pharmaceutical Development and Manufacturing (2016) Contract Pharma Magazine