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Occupational Exposure, and its Limits.


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. 

An estimate of exposure may be obtained in various ways ranging from a detailed history taking plus a workplace visit to the use of sophisticated background or personal monitoring devices.

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 accompanying image 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 accompanying image shows a blue coloured personal dosimeter pinned just above the right hand pocket of the radiographer. 

radiographer
 

Occupational Exposure Limits (OELs).

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), Maximum Exposure Limits (MELs) Threshold Limit Values (TLV), etc etc 

Secondly it is almost easier to say what OELs are not: they are not levels above which 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 a likelihood which albeit small might still be there and which could in some instances rarely result in severe effects). 

You may wish to consult a more detailed account on Occupational Exposure Limits 

Derivation of Exposure Standards/Limits - The 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: 
  • Determine the Nature of the relevant Health Effects: 
      What exactly are they? (It is more important to have lower exposure limts 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? 
       

  • 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.)
  • 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 
  • 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)