Wednesday, June 26, 2013

Every Industrial Hygienist should be a Modeler

If you are a practicing Industrial Hygienist (IH) you are a Risk Assessor.   You compare measured or estimated exposures to exposure limits and this activity characterizes or assesses the risk.   You typically do not develop exposure limits but you do estimate, measure other otherwise gauge the level of actual exposure to the agent in question.   We do this mostly with inhalation exposure.  When we actually measure and we do it by measuring the concentration of the agent in the potential breathing zone of the worker and, as mentioned before, comparing it to an occupational exposure limit (OEL) with the same units of concentration and the same time frame.  Thus the stock-in-trade of the IH is exposure estimation to be used in the context of risk assessment .

It has been well shown that the vast majority of occupational exposures are NOT measured but they are estimated using EXPERT JUDGEMENT.   Clearly the industrial hygienists are running some algorithm (that is a MODEL) subconsciously  in their mind that either concludes that the risk is insignificant or in need or further evaluation.   Explaining “expert judgment” has always proven to be very difficult. Some are better at invoking this hidden process than others. Indeed, the more experience you have as an industrial hygienist, the more you test or validate your subconscious models versus reality and the more skilled you become.

My point is that as tool-using animals, we are much better off if, as industrial hygienists, we raise the models we use to the level of consciousness so that we might be able to enjoy the following advantages over the subliminal approach. The critical advantages of separate and explicit exposure models include their inherent ability to be
  • Examined by the modeler and others in a critical review of their work or use
  • Explained to folks with a stake in the prediction and outcome 
  • Applied retrospectively (estimating past exposures)
  • Shared and passed on as technology transfer (education of the next generation)
  • Tested (validated) and improved using the scientific method  
When you learn and use exposure models you identify yourself as a technologist, someone who uses science to answer questions.  You enhance your standing with your employer and your charges.  You distance yourself from the characterization as a "Pump Jockey".   From a professional development perspective, becoming a modeler is well worth the effort.

Learning and using models is not simple but it is not impossible either.  I have found it is best to progress with  baby steps.  Start with relatively simply models, which I have found to be remarkably useful, and then progress to more sophisticated and detailed tools which are even more valuable.   There are lots of free software tools out their and some good educational material.   Depending on the response I get to this blog I may dedicate the next one or two to being more specific about these opportunities and resources.


  1. Hi Mike: Thanks for sharing your thoughts with us. I believe that you would also recommend that risk assessors who are not industrial hygienists should also consider becoming familiar with these models. You suggested starting with relatively simple models and then to more sophisticated ones. For those of us interested in knowing more about these models, which models do we start with? Best regards.

  2. I'm not an industrial hygienist but I am interested in exposure modeling and am interested in getting familiar with some of the models available to IHs.

  3. Please continue with this thread. I am a CIH that believes that this is the best path to approaching Risk Assessment too.I am already learning the Models available on the AIHA website (IHMOD and IHSTAT)and a more difficult model COMTAM 3.1 from NIST and would like to hear input from other IH professionals

  4. Many thanks for the above comments - that is all the encouragement I need to hopefully provide some useful insight into developing skills in exposure modeling. I hope to have something out in a blog next week.

  5. Hi Mike,
    You hit the nail on the head when you said that all hygienists need to become explicit modelers, not subliminal ones.
    Just the process of thinking about each input parameter to even a simple model will lead to a much better understanding of the workplace and the limitations in that understanding. I remember reading somewhere that these two elements correspond to knowledge and self knowledge.