An occupational hygienist will often be called upon to make judgements about levels of exposure to chemical nuisance (chemical products, dust, etc.) without carrying out direct measurements. This happens if he does not have at his disposal the necessary measuring methods or financial resources, or does not have enough time. For example, during general risk analyses in order to draw up a catalogue of risks, the exposure level is often estimated in the absence of objective data.
This situation is particularly common for occupational health professionals in developing countries. They often have very limited means for measuring exposure to chemicals and dust. Nevertheless, choices have to be made and these can have serious human and financial consequences.
These decisions are actually based on the occupational hygienist’s experience, his knowledge of the scientific literature and his observations as a professional (smells, observation of dust, deposits on surfaces, etc.). It must be acknowledged, however, that without objective data it is not easy to assess the air concentration of a pollutant. It is not a matter of estimating the weight of a parcel or the length of a pole; the air concentration is a much less instinctive dimension which is not part of our everyday world. Nevertheless, the occupational hygienist does take decisions under these conditions.
Even when an exposure measurement is taken, we know that this information is particular to a precise moment of exposure (usually one specific day). Given that this varies widely and unpredictably over time, a great deal of uncertainty must be attached to this result.
Another possibility is to take advantage of measurements carried out in other situations, either from the literature or by using exposure databases. This is what the occupational hygienist is doing informally when he bases his judgement on his professional experience. In this context, IST puts at the disposal of professionals a database containing measurements carried out in workplaces (exposure databank).
IST is currently interested in developing skills and tools to alleviate these problems. The aim is to develop tools that will enable the occupational hygienist to take decisions in a less vague context. Given the current state of our knowledge, these tools cannot claim to be absolute and perfect. However, they should allow exposure assessment to be reduced to the estimation of other, more readily accessible, variables; combining these variables and using model-based calculations should lead to the exposure concentration.
Three mathematical tools are currently being developed at IST in this field:
A physical model, enabling exposure to be estimated on the basis of a workplace representation in the form of two symmetrical compartments (near to the source NF – near-field ; far from the source FF – far-field).
A modified physical model, enabling exposure to be estimated on the basis of the above model but integrating the observation that the pollutants at the workplace are not distributed symmetrically.
A global Bayesian model enabling several sources of information to be integrated, namely: measurements, data from the physical model and historical data via a statistical model.
These tools are supplied without guarantee upon request. They must be regarded as experimental tools that contribute to a process of long-term improvement in exposure assessment. They are a first step towards more objective and robust exposure assessment by the occupational hygienist. The intention is also to encourage discussion in this field and promote an exchange of experiences between professionals.