Exposure Modelling

This month we’ve been running revision courses for both the BOHS Certificate oral exam and the Diploma exam. I particularly enjoy being involved in the latter as it’s not often that I get the chance to sit down and talk advanced occupational hygiene with a group of experienced practitioners from different backgrounds for a whole week.

One of the topics we discussed during the Diploma course was the role of exposure modelling. This has been a “hot topic” for a while now, particularly with the advent of REACH where modelling is seen as a way of generating exposure data that is needed to assign “risk management measures” (i.e. exposure controls) for a large number of “exposure scenarios”. Consequently a lot of research effort has been put into developing exposure models, including the Advanced Reach Tool (ART).

A number of occupational hygienists I’ve talked to over the past couple of years have expressed the opinion that exposure modelling is the future of our profession. Others have taken the opposite view – that exposure modelling can never replace air sampling and other types of measurements to evaluate worker exposure to chemical agents.

Personally, I think its inevitable that exposure modelling techniques are going to be more widely used in the future, but its unlikely that they can completely replace traditional occupational hygiene methods such as air sampling. Modelling will become another tool that we can use, adding to those already well established in our “toolbox”. In fact we already use modelling approaches. Control banding techniques, such as “COSHH Essentials”, are essentially simple exposure models. And mathematical modelling is well established as an approach for heat stress assessment. The “rational” heat stress indices such as HSI and its modern equivalent, the Predicted Heat Strain Index, are mathematical models which attempt to predict how the body will respond to the main environmental, personal and work related factors that affect our response to the thermal environment.

During the Diploma course we had a good discussion on the use of modelling and drew up a list of strengths and weaknesses of this approach.

The main “pros” identified were that they:

• can be used predictively so potential exposures can be assessed without the need for workers to be exposed to the contaminant
• can be used to define controls before a process is introduced
• allow the user to tap into collective expertise
• provide consistent results
• are more amenable to statistical analysis than the results from most air sampling surveys (where only a limited number of results are obtained)
• can be more cost effective than air sampling surveys

The main “cons” identified were that :

• the quality of the data obtained is not as good as the results from a thorough air sampling survey
• they need to be based on a large database of high quality air sampling data
• it is difficult for them to be designed to incorporate all the factors that affect exposure in the workplace
• it is difficult to take account of human behaviour, which is a major determinant in worker exposure
• it is easy for them to be misused, so users need to be properly trained
• during air sampling surveys additional information is collected by observations and other techniques,

Of course this is not an exhaustive list, but I felt that the discussion pulled out the major issues.

Exposure modelling is an important current issue for occupational hygienists, and this post has only scratched the surface. I think that it’s something I’ll return to in the future

Photo credit: Stock.XCHNG