International Review of Surveillance and Control of Workplace Exposures: NOHSAC Technical Report 5
3. Literature Review
There has been a substantial amount written about the need for surveillance of workplace exposures and the establishment of exposure databases. There has also been some limited discussion of the operation, value and shortcomings of routine surveillance systems, workforce and task-based systems, national versus industry systems, and retrospective versus prospective systems. However, a significant event in the development of thinking and the pulling together of ideas around the subject was the Third Ministerial Conference on Environment and Health, held in June 1999 in London, at which a need to strengthen the information systems on OHS was noted. The Conference supported the idea of a comprehensive approach in the development of national indicators for OHS to support the design and follow-up of the implementation of appropriate national policies. As a consequence, the Finnish Institute of Occupational Health (FIOH) published a working paper on country profiles and national surveillance indicators in OHS in 2001 and, in the process, clarified much of the debate and rationale for development of surveillance systems.
The FIOH working paper is used as a backdrop for the exploration of other published ideas in the following literature review, which is, in turn, used to provide a framework for the presentation and discussion of the results of the review of surveillance systems that were targeted within this project. This framework was chosen given the working paper was compiled to inform the development of a comprehensive approach to collection of national indicators for health and safety at work throughout Europe. Thus, its scope is of value to the development of national approaches in New Zealand and Australia.
Within the range of OHS-related professions, the lack of common definitions of terminology in everyday use has hindered understandings and the ability of the various disciplines to move forward with shared meanings. This problem is apparent within the literature pertaining to exposure surveillance, with terms such as “exposure”, “hazard”, “surveillance” and “incidence” being used interchangeably and inconsistently. Thus, there are misunderstandings of differences between activities that focus, on the one hand, on the surveillance of workplace exposures and, on the other hand, on surveillance of injury and disease indicators.
In their review of an international system on occupational exposure to carcinogens
(CAREX), Rantanen et al
found that the concept of exposure
differed between countries. The contexts within which terms in the surveillance field are
used are varied and ambiguous, and the definition is often dependent upon the situation
under review. For example, Burdor
In an attempt to draw together an agreed definition for the activities pertaining to surveillance, Rantanen et al use the term “occupational health surveillance” to embrace both “workers’ health surveillance” and “work environment surveillance” (p12) and thus are able to introduce the concept of indicators of change that are either “exposure indicators” or “effect indicators” (p17).
These terms are consistent with and further explained by Fine, who suggests that exposure surveillance “is the ongoing and systematic collection, analysis and interpretation of data related to either occupational exposures (hazard surveillance) or adverse health outcomes (injuries, disorders or disease)... this definition expands the traditional focus of exposure surveillance to include hazard surveillance, which is either information relating to the number of workers exposed to a specific hazard or an environmental measurement of exposure”. This may be illustrated as shown in Figure 1.
Making the distinction between “workers’ health surveillance” and “work environment surveillance” slightly less clear, Rantanen et al suggest that it is possible to construct “hybrids”, i.e. exposure-effect indicators which combine information on the outcomes and their determinants. They offer examples, including “incidence of work accidents due to falling” and “incidence of occupational diseases due to exposure to asbestos”. They caution, however, that construction of such indicators requires that a causal relationship is established between exposure and effect, and when this relationship is unknown, or one wants to survey all effects of a given exposure or a specific effect of all exposures, “pure” exposure indicators and effect indicators are the only option.
Given that the various uses of the term “exposure” suggest that it can be considered as a current, past and future occurrence, some further clarification can be derived from Viner’s generalised time sequence model.
The generalised time sequence model, as shown in Figure 2, was developed for use primarily with physical hazards but provides a useful framework for consideration of matters relating to occupational health surveillance. The model, which defines hazards as potentially damaging energies, provides an opportunity to detect, recognise and react to the development of damaging conditions so long as the evolution time, energy release time and transfer time is sufficiently long enough to avoid or reduce the damage of the loss of control of the potentially damaging energy or hazard. Put simply, the “event” in Viner’s model is the point in time at which control of a potentially damaging energy is lost. The period immediately preceding the event, within time zone 2, is generally short. The loss of control of the energy begins, and there is an opportunity to regain control in this short period. The time zone 1 period is generally long and is the period during which organisational and physical factors create the circumstances under which the event may later occur. The period immediately following the event, in time zone 2, is generally short and is the period during which activities to minimise damage may be undertaken. The time zone 3 period is generally long and is the period during which medical, rehabilitation and counselling activities are undertaken to minimise loss.
Thus, exposure surveillance or “work environment surveillance” systems are dealing with exposure to hazards in time zones 1 and 2 while injury and disease focused “workers’ health surveillance” systems are dealing with outcomes that fall into time zone 3.
Notwithstanding the above, uncertainties and anomalies arise. For example, the Canadian National Surveillance of Occupational Exposure to the Human Immunodeficiency Virus uses incidence of needlestick injury to measure potential exposure to blood-borne pathogens.
To this point, it is apparent that there is much ambiguity and inconsistency in terminology, particularly around the use of the terms “exposure” and “exposure surveillance”. Thus, the terminology used to identify exposure surveillance systems is that of “work environment surveillance”, which describes the ongoing and systematic collection, analysis and interpretation of data related to occupational exposures. This definition is based on an amalgamation of the definitions of Fine and Rantanen and is demonstrated diagrammatically in Figure 1.
This definition, together with the ideas encapsulated within Viner’s time sequence model, have become the framework for driving the review of the formal and informal literature and have aided the selection of the surveillance systems to evaluate in more depth.
The sections which follow draw together the ideas in the literature, focusing on the importance and significance of surveillance (particularly work environment surveillance) and the operation and use of surveillance systems.