Occupational exposure

Occupational exposure is a measure of the intensity and/or extent to which the human body experiences a particular hazard. For a given hazard, the greater the exposure the greater the risk of an adverse effect on health. This is because of the exposure-response relationship. Exposure is determined by various factors including the time-exposed (duration), and factors such as the concentration of a substance inhaled, the intensity of a radiation field, etc. What matters most is the actual ‘personal’ exposure of the worker and this in turn determines the uptake of the potentially harmful agent.

For example in the image (above), a radiographer may be exposed to X-ray radiation or to chemicals resulting from film processing, such as glutaraldehyde, sulphur dioxide or acetic acid. A common example of the measurement of personal exposure relates to X-ray dosimetry in hospitals. The image shows a blue coloured personal dosimeter pinned just above the left hand pocket of the radiographer.

Occupational exposure limits (OEL)

What do OELs mean?

First it should be said that there is no cast-iron defintion of an OEL since there are scientific and legal interpretations and the latter especially vary from country to country with the use of all sorts of terms and acronyms such as Occupational Exposure Standards (OES), Threshold Limit Values (TLV), etc.

Secondly it is almost easier to say what OELs are not: they are not levels above that harm will definitely arise and they are certainly NOT levels which are definitely safe i.e. below which harm will not arise.

A rough rule of thumb is that they are levels below which most of the working population could be exposed on a regular basis with a low risk to health (but one which might still be there and which could result in severe effects).

Derivation of exposure standards/limits: basic steps

An important part of the strategy of controlling risks to health is the derivation of exposure limits. There is a sequence of steps in this process:

1. Determine the nature of the relevant health effects:
   • What exactly are they?
     (It is more important to have lower exposure limits to reduce the frequency of severe health effects, e.g. cancers, than it is for minor, e.g. irritant health effects.)
   • Are they acute or chronic?
2. Identify the ‘Critical’ Health Effect - this is usually the one effect that can occur at the lowest exposure out the various effects in question.
   (Benzene can cause dizziness, nause and even loss of consciousness at high concentrations, but exposure limits are not set just with the intention of protecting against these consequences but at much lower levels to protect against the risk of leukaemia.)
3. Determine the Exposure-Response relationships. Remember that one may need to consider carefully the population from which the data were derived, the measurement methods, how the time-weighting was carried out, etc.
4. Derive the information necessary for a health-based exposure standard, but bear in mind that the eventual standard adopted depends on:
   • Consideration of the acceptability of risk, and the extent of uncertainty in the scientific data
   • Monitor the implementation of the exposure standard
   • Improve the standard by a process of review and revision (after an appropriate interval).