WELs (Workplace Exposure Limits) are occupational exposure limits (OELs) which are set to help protect the health of workers, but, they are not levels above which harm will definitely arise and they are NOT levels below which harm will not arise. WEL's/OEL's do not address safety issues such as flammable concentrations. They are the measurement of concentrations of hazardous substances in the air, averaged over a specified time referred to as a time-weighted average (TWA).
There are two time periods used a long term, over an 8 hour reference period, and a short term, over a 15 minute period. The short term (STELs) are set to help prevent effects, such as eye irritation, which could occur after a few minutes.
Unfortunately each country sets their own limits, so, if you are exporting substances you must be aware what the limits are in the destination country. For more information about different countries OEL's try this EU site.
In the UK the HSA publishes "EH40/2005 Workplace exposure limits", in Germany there is a publication "Technische Regeln für Gefahrstoffe" and in France "Valeurs limites d'exposition professionnelle aux agents chimiques en France". If a substance does not appear in your countries publication it does not mean that it is safe, it is for the employer to determine their own working practices using information from other sources, such as industrial associations and a search on the web for the substance.
Table data extracted from EH40/2005 Workplace exposure limits.
Depending on the nature of the substance and the pattern of exposure the effects of substances hazardous to health vary considerably, some effects require long term or accumulated exposure. The long-term exposure limit is intended to control such effects by restricting the total intake by inhalation over one or more workshifts, depending on the length of the shift. Other effects may be observed after a brief exposure, the short-term exposure limit may be applied to control these effects.
for concentrations of airborne particles (fume, dust etc) are usually shown in mg.m-3. In the case of dusts the limits refer to the 'inhalable' fraction unless indicated as 'respirable'.
Volatile substances are usually shown as both parts per million by volume (ppm) and milligrams per cubic metre (mg.m-3), for these substances the limit is set as ppm then a conversion to mg.m-3 is calculated. This conversion depends on the air temperature and pressure of the ambient air, which will very over time, the conversion calculations are based on a standard set of typical conditions.
For more information see the links above or a handbook written by the London Hazards Centre Trust which is aimed at union safety representatives and community organisers who need health and safety information.
There are two time periods used a long term, over an 8 hour reference period, and a short term, over a 15 minute period. The short term (STELs) are set to help prevent effects, such as eye irritation, which could occur after a few minutes.
Unfortunately each country sets their own limits, so, if you are exporting substances you must be aware what the limits are in the destination country. For more information about different countries OEL's try this EU site.
In the UK the HSA publishes "EH40/2005 Workplace exposure limits", in Germany there is a publication "Technische Regeln für Gefahrstoffe" and in France "Valeurs limites d'exposition professionnelle aux agents chimiques en France". If a substance does not appear in your countries publication it does not mean that it is safe, it is for the employer to determine their own working practices using information from other sources, such as industrial associations and a search on the web for the substance.
| Substance | CAS number | Workplace exposure limit | |||
|---|---|---|---|---|---|
| Long-term exposure limit (8-hour TWA reference period) | Short-term exposure limit (15-minute reference period) | ||||
| ppm | mg.m-3 | ppm | mg.m-3 | ||
| Nitric Acid | 7697-37-2 | 2 | 5.2 | 4 | 10 |
| Phosphine | 7803-51-2 | - | - | 0.3 | 0.42 |
| Plaster of Paris | 26499-65-0 | ||||
| inhalable dust | - | 10 | - | - | |
| respirable dust | - | 4 | - | - | |
Table data extracted from EH40/2005 Workplace exposure limits.
Depending on the nature of the substance and the pattern of exposure the effects of substances hazardous to health vary considerably, some effects require long term or accumulated exposure. The long-term exposure limit is intended to control such effects by restricting the total intake by inhalation over one or more workshifts, depending on the length of the shift. Other effects may be observed after a brief exposure, the short-term exposure limit may be applied to control these effects.
The units of measurement used are:-
For more information see the links above or a handbook written by the London Hazards Centre Trust which is aimed at union safety representatives and community organisers who need health and safety information.
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ReplyDeleteFirst I would like to give thanks to author of this post for share these important instructions on WEL /OEL limits. By read this post I am surprising to know that every country has their own WEL for one hazardous substance. Whatever now every chemical industry are using the MSDS for each hazardous substances which are available some authorizations like International Chemical Safety Data Solution or icsds.com.
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