All living organisms come into contact with a wide array of agents that hold the potential to elicit adverse effects or “stress”. Those agents that can elicit stress come from both the universe of chemicals and non-chemicals. These “stressors” can act alone or in concert. Rarely is any organism exposed to but a single stressor at any time, but rather, simultaneously to a combination of multiple or a multitude of stressors (aggregate and cumulative exposure).
Stress is difficult to define because researchers approach it in different ways. Some use the term stress to refer to circumstances that threaten well-being or to refer to the response people have to threatening circumstances. Others think of stress as the process of evaluating and coping with threatening circumstances. Yet others use the term to refer to the experience of being threatened by taxing circumstances.
A Stressor is defined as “a stimulus that causes stress”.
Recognition of stressors is a fundamental step in the practice of occupational hygiene, indispensable for the adequate planning of hazard evaluation and control strategies, as well as for the establishment of priorities for action. For the adequate design of control measures, it is also necessary to physically characterize contaminant sources (stressors) and contaminant propagation paths (exposure paths).
For purposes of this discussion, the model by Berenice I. Ferrari Goelzer from the International Labour Office centralises stressors between a specific workplace and the management of occupational health risks.
The three stressors distinguished in this model are:
The numerous other stressors such as emotional, financial, psychological, cultural, etc. are not included in the scope of this discussion as these are addressed at various other centres within a working environment. It is however important to be aware of such factors where it may have a direct impact on safety and occupational health. Pilots of passenger planes may be expected to react differently to emotional stressors than a Preacher!
To anticipate something is to expect it.
“Anticipating something” also often implies that you are preparing to take some action because of your expectations — like when you anticipate your chess opponent’s next move and plan a counterattack. The word anticipate can also mean “to come beforehand” — as in a certain musical trend anticipating another.
With reference to occupational health stressors, “anticipate” focuses on the probability of specific stressors occurring, at what level of intensity, by what means or paths it could impact on the person, and how severe the resultant stress would be.
In the work environment a baseline hazard identification and risk assessment (HIRA) is conducted covering all the tasks and activities expected from employees. A baseline HIRA includes normal as well as abnormal (emergency or maintenance or other activities that are only performed at specific intervals and that does not form part of employees’ daily responsibilities) activities to ensure that all hazards associated with company operations are identified and assessed for its risk potential. By identifying potential risks management can then plan to control and manage these risks appropriately to eliminate or mitigate occupational health stressors.
Industry experience also provides organisations with information on occupational hygiene stressors that are common to the industry.
Recognition of hazards is a fundamental step in the practice of occupational hygiene, indispensable for the adequate planning of hazard evaluation and control strategies, as well as for the establishment of priorities for action. For the adequate design of control measures, it is also necessary to physically characterize contaminant sources and contaminant propagation paths.
The recognition of hazards leads to the determination of:
The identification of hazardous agents, their sources and the conditions of exposure requires extensive knowledge and careful study of work processes and operations, raw materials and chemicals used or generated, final products and eventual by-products, as well as of possibilities for the accidental formation of chemicals, decomposition of materials, combustion of fuels or the presence of impurities. The recognition of the nature and potential magnitude of the biological effects that such agents may cause if overexposure occurs requires knowledge on and access to toxicological information. International sources of information in this respect include International Programme on Chemical Safety (IPCS), International Agency for Research on Cancer (IARC) and International Register of Potentially Toxic Chemicals, United Nations Environment Programme (UNEP-IRPTC).
Agents which pose health hazards in the work environment include airborne contaminants; non-airborne chemicals; physical agents, such as heat and noise; biological agents; ergonomic factors, such as inadequate lifting procedures and working postures; and psychosocial stresses.
Risk assessment is a methodology that aims at characterising the types of health effects expected as a result of a certain exposure to a given agent, as well as providing estimates on the probability of occurrence of these health effects, at different levels of exposure. It is also used to characterise specific risk situations. It involves hazard identification, the establishment of exposure-effect relationships, and exposure assessment, leading to risk characterisation.
The first step refers to the identification of an agent—for example, a chemical—as causing a harmful health effect (e.g., cancer or systemic poisoning). The second step establishes how much exposure causes how much of a given effect in how many of the exposed persons. This knowledge is essential for the interpretation of exposure assessment data.
Exposure assessment is part of risk assessment, both when obtaining data to characterize a risk situation and when obtaining data for the establishment of exposure-effect relationships from epidemiological studies. In the latter case, the exposure that led to a certain occupational or environmentally caused effect has to be accurately characterized to ensure the validity of the correlation.
Although risk assessment is fundamental to many decisions which are taken in the practice of occupational hygiene, it has limited effect in protecting workers’ health, unless translated into actual preventive action in the workplace.
Risk assessment is a dynamic process, as new knowledge often discloses harmful effects of substances until then considered relatively harmless; therefore the occupational hygienist must have, at all times, access to up-to-date toxicological information. Another implication is that exposures should always be controlled to the lowest feasible level.
Exposure assessment aims at determining how much of an agent workers have been exposed to, how often and for how long. Guidelines in this respect have been established both at the national and international level—for example, EN 689, prepared by the Comité Européen de Normalisation (European Committee for Standardization) (CEN 1994).
In the evaluation of exposure to airborne contaminants, the most usual procedure is the assessment of inhalation exposure, which requires the determination of the air concentration of the agent to which workers are exposed (or, in the case of airborne particles, the air concentration of the relevant fraction, e.g., the “respirable fraction”) and the duration of the exposure. However, if routes other than inhalation contribute appreciably to the uptake of a chemical, an erroneous judgement may be made by looking only at the inhalation exposure. In such cases, total exposure has to be assessed, and a very useful tool for this is biological monitoring.
The practice of occupational hygiene is concerned with three kinds of situations:
A primary reason for determining whether there is overexposure to a hazardous agent in the work environment, is to decide whether interventions are required. This often, but not necessarily, means establishing whether there is compliance with an adopted standard, which is usually expressed in terms of an occupational exposure limit. The determination of the “worst exposure” situation may be enough to fulfil this purpose. Indeed, if exposures are expected to be either very high or very low in relation to accepted limit values, the accuracy and precision of quantitative evaluations can be lower than when the exposures are expected to be closer to the limit values. In fact, when hazards are obvious, it may be wiser to invest resources initially on controls and to carry out more precise environmental evaluations after controls have been implemented.
Follow-up evaluations are often necessary, particularly if the need existed to install or improve control measures or if changes in the processes or materials utilized were foreseen. In these cases, quantitative evaluations have an important surveillance role in:
Whenever an occupational hygiene survey is carried out in connection with an epidemiological study in order to obtain quantitative data on relationships between exposure and health effects, the exposure must be characterized with a high level of accuracy and precision. In this case, all exposure levels must be adequately characterized, since it would not be enough, for example, to characterize only the worst case exposure situation. It would be ideal, although difficult in practice, to always keep precise and accurate exposure assessment records since there may be a future need to have historical exposure data.
In order to ensure that evaluation data is representative of workers’ exposure, and that resources are not wasted, an adequate sampling strategy, accounting for all possible sources of variability, must be designed and followed. Sampling strategies, as well as measurement techniques, are covered in “Evaluation of the work environment”.
Interpretation of results
The degree of uncertainty in the estimation of an exposure parameter, for example, the true average concentration of an airborne contaminant, is determined through statistical treatment of the results from measurements (e.g., sampling and analysis). The level of confidence on the results will depend on the coefficient of variation of the “measuring system” and on the number of measurements. Once there is an acceptable confidence, the next step is to consider the health implications of the exposure: what does it mean for the health of the exposed workers: now? in the near future? in their working life? will there be an impact on future generations?
The evaluation process is only completed when results from measurements are interpreted in view of data (sometimes referred to as “risk assessment data”) derived from experimental toxicology, epidemiological and clinical studies and, in certain cases, clinical trials. It should be clarified that the term risk assessment has been used in connection with two types of assessments—the assessment of the nature and extent of risk resulting from exposure to chemicals or other agents, in general, and the assessment of risk for a particular worker or group of workers, in a specific workplace situation.
In the practice of occupational hygiene, exposure assessment results are often compared with adopted occupational exposure limits which are intended to provide guidance for hazard evaluation and for setting target levels for control. Exposure in excess of these limits requires immediate remedial action by the improvement of existing control measures or implementation of new ones. In fact, preventive interventions should be made at the “action level”, which varies with the country (e.g., one-half or one-fifth of the occupational exposure limit). A low action level is the best assurance of avoiding future problems.
Comparison of exposure assessment results with occupational exposure limits is a simplification, since, among other limitations, many factors which influence the uptake of chemicals (e.g., individual susceptibilities, physical activity and body build) are not accounted for by this procedure. Furthermore, in most workplaces there is simultaneous exposure to many agents; hence a very important issue is that of combined exposures and agent interactions, because the health consequences of exposure to a certain agent alone may differ considerably from the consequences of exposure to this same agent in combination with others, particularly if there is synergism or potentiation of effects.
The primary goal of occupational hygiene is the implementation of appropriate hazard prevention and control measures in the work environment. Standards and regulations, if not enforced, are meaningless for the protection of workers’ health, and enforcement usually requires both monitoring and control strategies. The absence of legally established standards should not be an obstacle to the implementation of the necessary measures to prevent harmful exposures or control them to the lowest level feasible. When serious hazards are obvious, control should be recommended, even before quantitative evaluations are carried out. It may sometimes be necessary to change the classical concept of “recognition-evaluation-control” to “recognition-control-evaluation”, or even to “recognition-control”, if capabilities for evaluation of hazards do not exist. Some examples of hazards in obvious need of action without the necessity of prior environmental sampling are electroplating carried out in an unventilated, small room, or using a jackhammer or sand-blasting equipment with no environmental controls or protective equipment. For such recognised health hazards, the immediate need is control, not quantitative evaluation.
Preventive action should in some way interrupt the chain by which the hazardous agent – a chemical, dust, a source of energy – is transmitted from the source to the worker. There are three major groups of control measures: engineering controls, work practices and personal measures.
The most efficient hazard prevention approach is the application of engineering control measures which prevent occupational exposures by managing the work environment, thus decreasing the need for initiatives on the part of workers or potentially exposed persons. Engineering measures usually require some process modifications or mechanical structures, and involve technical measures that eliminate or reduce the use, generation or release of hazardous agents at their source, or, when source elimination is not possible, engineering measures should be designed to prevent or reduce the spread of hazardous agents into the work environment by:
Control interventions which involve some modification of the source are the best approach because the harmful agent can be eliminated or reduced in concentration or intensity. Source reduction measures include substitution of materials, substitution/modification of processes or equipment and better maintenance of equipment.
When source modifications are not feasible or are not sufficient to attain the desired level of control, then the release and dissemination of hazardous agents in the work environment should be prevented by interrupting their transmission path through measures such as isolation (e.g., closed systems, enclosures), local exhaust ventilation, barriers and shields, isolation of workers.
Other measures aiming at reducing exposures in the work environment include adequate workplace design, dilution or displacement ventilation, good housekeeping and adequate storage. Labelling and warning signs can assist workers in safe work practices. Monitoring and alarm systems may be required in a control programme. Monitors for carbon monoxide around furnaces, for hydrogen sulphide in sewage work, and for oxygen deficiency in closed spaces are some examples.
Work practices are an important part of control—for example, jobs in which a worker’s work posture can affect exposure, such as whether a worker bends over his or her work. The position of the worker may affect the conditions of exposure (e.g., breathing zone in relation to contaminant source, possibility of skin absorption).
Lastly, occupational exposure can be avoided or reduced by placing a protective barrier on the worker, at the critical entry point for the harmful agent in question (mouth, nose, skin, ear) – that is, the use of personal protective devices. It should be pointed out that all other possibilities of control should be explored before considering the use of personal protective equipment, as this is the least satisfactory means for routine control of exposures, particularly to airborne contaminants.
Other personal preventive measures include education and training, personal hygiene and limitation of exposure time.
Continuous evaluations, through environmental monitoring and health surveillance, should be part of any hazard prevention and control strategy.
Appropriate control technology for the work environment must also encompass measures for the prevention of environmental pollution (air, water, soil), including adequate management of hazardous waste.
Although most of the control principles hereby mentioned apply to airborne contaminants, many are also applicable to other types of hazards. For example, a process can be modified to produce less air contaminants or to produce less noise or less heat. An isolating barrier can isolate workers from a source of noise, heat or radiation.
Far too often prevention dwells on the most widely known measures, such as local exhaust ventilation and personal protective equipment, without proper consideration of other valuable control options, such as alternative cleaner technologies, substitution of materials, modification of processes, and good work practices. It often seems that work processes are regarded as unchangeable when, in reality, changes can be made which effectively prevent or at least reduce the associated hazards.
Hazard prevention and control in the work environment requires knowledge and ingenuity. Effective control does not necessarily require very costly and complicated measures. In many cases, hazard control can be achieved through appropriate technology, which can be as simple as a piece of impervious material between the naked shoulder of a dock worker and a bag of toxic material that can be absorbed through the skin. It can also consist of simple improvements such as placing a movable barrier between an ultraviolet source and a worker, or training workers in safe work practices.
Aspects to be considered when selecting appropriate control strategies and technology include the type of hazardous agent (nature, physical state, health effects, routes of entry into the body), type of source(s), magnitude and conditions of exposure, characteristics of the workplace and relative location of workstations.
The required skills and resources for the correct design, implementation, operation, evaluation and maintenance of control systems must be ensured. Systems such as local exhaust ventilation must be evaluated after installation and routinely checked thereafter. Only regular monitoring and maintenance can ensure continued efficiency, since even well-designed systems may lose their initial performance if neglected.
Control measures should be integrated into hazard prevention and control programmes, with clear objectives and efficient management, involving multidisciplinary teams made up of occupational hygienists and other occupational health and safety staff, production engineers, management and workers. Programmes must also include aspects such as hazard communication, education and training covering safe work practices and emergency procedures.
Health promotion aspects should also be included, since the workplace is an ideal setting for promoting healthy life-styles in general and for alerting as to the dangers of hazardous non-occupational exposures caused, for example, by shooting without adequate protection, or smoking.
Measurements for control
Measurements with the purpose of investigating the presence of agents and the patterns of exposure parameters in the work environment can be extremely useful for the planning and design of control measures and work practices. The objectives of such measurements include:
Direct-reading instruments are extremely useful for control purposes, particularly those which can be used for continuous sampling and reflect what is happening in real time, thus disclosing exposure situations which might not otherwise be detected and which need to be controlled. Examples of such instruments include: photo-ionization detectors, infrared analysers, aerosol meters and detector tubes. When sampling to obtain a picture of the behaviour of contaminants, from the source throughout the work environment, accuracy and precision are not as critical as they would be for exposure assessment.
Recent developments in this type of measurement for control purposes include visualization techniques, one of which is the Picture Mix Exposure—PIMEX (Rosen 1993). This method combines a video image of the worker with scale showing airborne contaminant concentrations, which are continuously measured, at the breathing zone, with a real-time monitoring instrument, thus making it possible to visualize how the concentration varies while the task is performed. This provides an excellent tool for comparing the relative efficacy of different control measures, such as ventilation and work practices, thus contributing to better design.
Measurements are also needed to assess the efficiency of control measures. In this case, source sampling or area sampling are convenient, alone or in addition to personal sampling, for the assessment of workers’ exposure. In order to assure validity, the locations for “before” and “after” sampling (or measurements) and the techniques used should be the same, or equivalent, in sensitivity, accuracy and precision.