What is an OEL?
An Occupational Exposure Limit (OEL) is the maximum permissible concentration of a given gas, vapour, fibre or dust in the air in the workplace. It is intended to be the level at or below which, based on current knowledge, a given substance can be present in the air in the workplace without harming the health of employees and their offspring. This should be the case even if exposure to the substance at that level occurs repeatedly, or extends over a long period of time, up to and including an entire working life.
Why are OELs important?
To ensure the health and safety of the working population, clear-cut, quantified norms governing working conditions are required. They make it clear to employers what they need to provide and to employees what they can expect. They also provide an unambiguous basis for enforcement of these norms by the labour inspectorate. The existence of such norms is particularly important when hazardous substances or irritants are involved. OELs specify the permissible degree of exposure to such substances. The greater the risk created by exposure, the stricter the OEL must be.
What are OELs used for?
OELs are used by the authorities and by industry to check exposure levels and to assess working conditions. They are also used to monitor the effectiveness of measures (e.g., occupational hygiene measures) taken to minimise exposure levels. Furthermore, OELs are used as a guideline to the minimum level of protection that needs to be provided when designing new installations or monitoring emission sources.
Types of OEL
There are two types of OEL in the Netherlands (see Procedure for setting OELs):
- Public (i.e. statutory) OELs, set by the government
- Private OELS, set by companies.
Both types of OEL are health-based OELs, which means that exposure to these concentrations of substances in the workplace may not harm health.
OELs are not absolute limits, but rather time-weighted averages measured over an 8-hour period (expressed in the Netherlands as TGG-8u). During this period, exposure may at times exceed the OEL, providing that such higher levels of exposure are balanced by lower levels, so that the average level for the 8-hour period does not exceed the OEL.
OELs may also be defined with a ceiling value (expressed as -C). This is an absolute OEL that may not be exceeded at any time. For practical reasons, this ceiling value is occasionally converted into a time-weighted average over a 15- or 30-minute period. In addition, in some cases, to prevent high exposure levels over a short period of time (peak exposures), an OEL may be defined as a 15-minute time-weighted average (expressed as TGG-15min).
Carcinogens
As far as possible, OELs are also established for carcinogens. For carcinogens for which a safe threshold exists, the OEL is set at the level of that safe threshold.
- In the case of carcinogens for which no safe threshold can be determined (i.e., genotoxic carcinogens – substances that cause an immediate change in DNA that may lead to cancer), it is impossible, given current scientific knowledge, to indicate a safe OEL that would prevent cancer. The only way to eliminate any risk would be to impose a complete ban. However, as long as such substances are indispensable (or at least as long as society requires the use of such substances, e.g., cytostatics), the risk of exposure, and thus the risk of cancer, cannot be avoided. In setting OELs for these substances, use is made of the system of risk levels defined by the former Dutch Working Environment Council (now succeeded by the SER Working Environment Committee) in its advisory report on the setting of norms for genotoxic carcinogens (1992). In that report, the Council recommended using a ‘prohibitive risk level’ (prohibiting an additional risk of cancer higher than 10-4 per substance per year) and a ‘target risk level’ (10-6 per substance per year).
- In the case of non-genotoxic carcinogens, in principle a safe OEL can be defined. These OELs have the same status as OELs for ‘normal’ health-damaging substances.
Caveats and qualifications regarding OELs
A number of caveats and qualifications regarding OELs should be noted. They specifically relate to:
a. The health basis of OELs
b. The level of protection provided by OELs
c. The practical implementation of OELs.
a. The health basis of OELs
Most OELs are defined on the basis of health considerations. Some, however, are not. There are various reasons for this, including the following:
- There may be insufficient toxicological information about the substance to draw sound conclusions about its effects on human health.
- People’s sensitivity to the harmful effects of a substance may vary too much to establish a realistic and generally applicable limit on health grounds.
- No OELs for carcinogens for which there is no safe threshold can be based on health grounds.
b. The level of protection provided by OELs
OELs may provide insufficient protection under certain special circumstances:
- OELs are designed to provide protection in everyday work situations and processes. They have no application in the case of calamities or abnormal incidents.
- OELs are geared to a standard workload for healthy employees. They may not provide protection in the event of heavy labour, or to employees who are already in poor health. In these cases, the company’s own OEL will need to take the workload and employees’ health issues into account.
- Some employees may experience some discomfort or damage to their health even when exposed to levels below the OEL, due to large variations in people’s sensitivity to substances (see The health basis of OELs).
- OELs do not take into account the possibility that people may be exposed to the substance or substances in question outside the work environment (e.g., during leisure activities, odd jobs or voluntary work).
- OELs are defined with a working day of 8 hours and a 40-hour week in mind. Employees who work longer hours may be exposed longer, which may increase the risk to their health.
- In principle, OELs only apply to exposure to the pure substance. They do not necessarily apply to a mixture containing the substance. Although, in some cases, the harmful effect of a mixture may be the sum total of the effect of its component substances, in other cases exposure to a combination of substances may have an effect that is either more or less harmful than the effect of exposure to the substances separately. When there is simultaneous exposure to several substances, experts (e.g., from the Occupational Health & Safety Services) need to take this into account.
c. The practical implementation of OELs
In some cases, adequate methods of measurement for determining the concentration of a given substance in the air in the workplace may not be available.