2. Limit values
Limit values are limits with which we want to compare a calculated or measured exposure. Limit values for external exposure are usually established for certain effects that occur when exposures occur above this limit value, during a certain period, according to the route (inhalation, oral, dermal) for which the limit value was derived. There are different types of limit values: health limit values for which no effects occur, limit values for which no harmful effects occur, legal limit values, action values, typical limit values, ...Within the legislative framework, one will be mainly handling values by which one will show no adverse effects on human health and "the" limit value of a substance is usually based on the first adverse effect that occurs at the lowest exposure (the so-called critical effect). If we take the example of hydrogen sulfide: the first (non-harmful) effect that occurs is irritation of the nose(<1ppm), higher exposures lead to irritation of the eyes (harmful effect around 10 ppm), higher concentrations paralyze the olfactory (around 100 ppm), and the most harmful effect, of course, is death (> 800 ppm). The Belgian legally binding limit value for hydrogen sulfide in the ambient air is currently set at 5 ppm (7 mg / m³) for inhalatory exposure over 8h.People who are exposed to this concentration during 8 h, 5 days per week, will probably have no eye-irritation. In addition to the limit values for external exposure, there are also internal exposure limit values, so-called biological limit values, which are usually set at a certain concentration in a human sample (urine, blood, plasma, hair, teeth, ...) after a certain external exposure. At this moment, the only legally binding biological limit value in Belgium is the biological limit value for lead in blood (70 µg Pb/100 ml blood).
- NBN EN 689:1995 Workplace atmospheres - Guidance for the assessment of exposure by inhalation to chemical agents for comparison with limit values and measurement strategy
- Nederlandse Leidraad (Dutch) to deduce a limit value yourself in case no value exists
- NVvA-BOHS Testing Compliance with Occupational Exposure Limits for Airborne Substances suggestion for an alternative assessment strategy for NBN EN 689:1995
- ECETOCTR101 Guidance for setting occupational exposure limits: Emphasis on data-poor substances (2006)
- Bekman 2011 (Dutch) How to determine the private limit value for hazardous substances?
- http://ec.europa.eu/ has a theme page on the scientific committee on occupational exposure limits (SCOEL)
- http://osha.europa.eu/ has a theme page on occupational exposure limits
- http://www.arboportaal.nl/ (Dutch) has a theme page on limit values (Dutch)
- http://www.hse.gov.uk/coshh/ has a theme page on workplace exposure limits
- http://www.rivm.nl/ has a theme page limit values (Dutch)
- http://www.employment.belgium.be/ has a specific page on chemical agents (Dutch) as well as on the public consultation procedure (Dutch) concerning the limit values for occupational exposure