Work is essential for life, development and personal fulfilment. Unfortunately, indispensable activities such as food production, extraction of raw materials, manufacturing of goods, energy production and services involve processes, operations and materials which can, to a greater or lesser extent, create hazards to the health of workers and those in nearby communities, as well as to the general environment.

However, the generation and release of harmful agents in the work environment can be prevented, through adequate hazard control interventions, which not only protect workers’ health but also limit the damage to the environment often associated with industrialization. If a harmful chemical is eliminated from a work process, it will neither affect the workers nor go beyond, to pollute the environment.

The profession that aims specifically at the prevention and control of hazards arising from work processes is occupational hygiene. The goals of occupational hygiene include the protection and promotion of workers’ health, the protection of the environment and contribution to a safe and sustainable development.

The need for occupational hygiene in the protection of workers’ health cannot be overemphasized. Even when feasible, the diagnosis and the cure of an occupational disease will not prevent further occurrences, if exposure to the aetiological agent does not cease. So long as the unhealthy work environment remains unchanged, its potential to impair health remains. Only the control of health hazards can break the vicious circle illustrated in figure 1.

Figure 1. Interactions between people and the environment

However, preventive action should start much earlier, not only before the manifestation of any health impairment but even before exposure actually occurs. The work environment should be under continuous surveillance so that hazardous agents and factors can be detected and removed, or controlled, before they cause any ill effects; this is the role of occupational hygiene.

Furthermore, occupational hygiene may also contribute to a safe and sustainable development, that is “to ensure that (development) meets the needs of the present without compromising the ability of the future generations to meet their own needs” (World Commission on Environment and Development 1987). Meeting the needs of the present world population without depleting or damaging the global resource base, and without causing adverse health and environmental consequences, requires knowledge and means to influence action (WHO 1992a); when related to work processes this is closely related to occupational hygiene practice.

Occupational health requires a multidisciplinary approach and involves fundamental disciplines, one of which is occupational hygiene, along with others which include occupational medicine and nursing, ergonomics and work psychology. A schematic representation of the scopes of action for occupational physicians and occupational hygienists is presented in figure 2.

Figure 2. Scopes of action for occupational physicians and occupational hygienists.

It is important that decision makers, managers and workers themselves, as well as all occupational health professionals, understand the essential role that occupational hygiene plays in the protection of workers’ health and of the environment, as well as the need for specialized professionals in this field. The close link between occupational and environmental health should also be kept in mind, since the prevention of pollution from industrial sources, through the adequate handling and disposal of hazardous effluents and waste, should be started at the workplace level. (See “Evaluation of the work environment”).

Concepts and Definitions

Occupational hygiene

Occupational hygiene is the science of the anticipation, recognition, evaluation and control of hazards arising in or from the workplace, and which could impair the health and well-being of workers, also taking into account the possible impact on the surrounding communities and the general environment.

Definitions of occupational hygiene may be presented in different ways; however, they all have essentially the same meaning and aim at the same fundamental goal of protecting and promoting the health and well-being of workers, as well as protecting the general environment, through preventive actions in the workplace.

Occupational hygiene is not yet universally recognized as a profession; however, in many countries, framework legislation is emerging that will lead to its establishment.

Occupational hygienist

 An occupational hygienist is a professional able to:

• anticipate the health hazards that may result from work processes, operations and equipment, and accordingly advise on their planning and design
• recognize and understand, in the work environment, the occurrence (real or potential) of chemical, physical and biological agents and other stresses, and their interactions with other factors, which may affect the health and well-being of workers
• understand the possible routes of agent entry into the human body, and the effects that such agents and other factors may have on health
• assess workers’ exposure to potentially harmful agents and factors and to evaluate the results
•  evaluate work processes and methods, from the point of view of the possible generation and release/propagation of potentially harmful agents and other factors, with a view to eliminating exposures, or reducing them to acceptable levels
• design, recommend for adoption, and evaluate the effectiveness of control strategies, alone or in collaboration with other professionals to ensure effective and economical control
• participate in overall risk analysis and management of an agent, process or workplace, and contribute to the establishment of priorities for risk management
• understand the legal framework for occupational hygiene practice in their own country
• educate, train, inform and advise persons at all levels, in all aspects of hazard communication
• work effectively in a multidisciplinary team involving other professionals
• recognize agents and factors that may have environmental impact, and understand the need to integrate occupational hygiene practice with environmental protection.

It should be kept in mind that a profession consists not only of a body of knowledge, but also of a Code of Ethics; national occupational hygiene associations, as well as the International Occupational Hygiene Association (IOHA), have their own Codes of Ethics (WHO 1992b).  

Occupational hygiene technician

An occupational hygiene technician is “a person competent to carry out measurements of the work environment” but not “to make the interpretations, judgements, and recommendations required from an occupational hygienist”. The necessary level of competence may be obtained in a comprehensive or limited field (WHO 1992b).

International Occupational Hygiene Association (IOHA)

IOHA was formally established, during a meeting in Montreal, on June 2, 1987. At present IOHA has the participation of 19 national occupational hygiene associations, with over nineteen thousand members from seventeen countries.

The primary objective of IOHA is to promote and develop occupational hygiene throughout the world, at a high level of professional competence, through means that include the exchange of information among organizations and individuals, the further development of human resources and the promotion of a high standard of ethical practice. IOHA activities include scientific meetings and publication of a newsletter. Members of affiliated associations are automatically members of IOHA; it is also possible to join as an individual member, for those in countries where there is not yet a national association.

Certification

In addition to an accepted definition of occupational hygiene and of the role of the occupational hygienist, there is need for the establishment of certification schemes to ensure acceptable standards of occupational hygiene competence and practice. Certification refers to a formal scheme based on procedures for establishing and maintaining knowledge, skills and competence of professionals (Burdorf 1995).

IOHA has promoted a survey of existing national certification schemes (Burdorf 1995), together with recommendations for the promotion of international cooperation in assuring the quality of professional occupational hygienists, which include the following:

• “the harmonization of standards on the competence and practice of professional occupational hygienists”
• “the establishment of an international body of peers to review the quality of existing certification schemes”.

Other suggestions in this report include items such as: “reciprocity” and “cross-acceptance of national designations, ultimately aiming at an umbrella scheme with one internationally accepted designation”.

The Practice of Occupational Hygiene

The classical steps in occupational hygiene practice are:

• the recognition of the possible health hazards in the work environment
• the evaluation of hazards, which is the process of assessing exposure and reaching conclusions as to the level of risk to human health
• prevention and control of hazards, which is the process of developing and implementing strategies to eliminate, or reduce to acceptable levels, the occurrence of harmful agents and factors in the workplace, while also accounting for environmental protection.

The ideal approach to hazard prevention is “anticipated and integrated preventive action”, which should include:

• occupational health and environmental impact assessments, prior to the design and installation of any new workplace
• selection of the safest, least hazardous and least polluting technology (“cleaner production”)
• environmentally appropriate location
• proper design, with adequate layout and appropriate control technology, including for the safe handling and disposal of the resulting effluents and waste
• elaboration of guidelines and regulations for training on the correct operation of processes, including on safe work practices, maintenance and emergency procedures.

The importance of anticipating and preventing all types of environmental pollution cannot be overemphasized. There is, fortunately, an increasing tendency to consider new technologies from the point of view of the possible negative impacts and their prevention, from the design and installation of the process to the handling of the resulting effluents and waste, in the so-called cradle-to-grave approach. Environmental disasters, which have occurred in both developed and developing countries, could have been avoided by the application of appropriate control strategies and emergency procedures in the workplace.

Economic aspects should be viewed in broader terms than the usual initial cost consideration; more expensive options that offer good health and environmental protection may prove to be more economical in the long run. The protection of workers’ health and of the environment must start much earlier than it usually does. Technical information and advice on occupational and environmental hygiene should always be available to those designing new processes, machinery, equipment and workplaces. Unfortunately such information is often made available much too late, when the only solution is costly and difficult retrofitting, or worse, when consequences have already been disastrous.

Recognition of hazards

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:

• which agents may be present and under which circumstances
• the nature and possible extent of associated adverse effects on health and well-being.

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.

Occupational hygiene evaluations

Occupational hygiene evaluations are carried out to assess workers’ exposure, as well as to provide information for the design, or to test the efficiency, of control measures.

Evaluation of workers’ exposure to occupational hazards, such as airborne contaminants, physical and biological agents, is covered elsewhere in this chapter. Nevertheless, some general considerations are provided here for a better understanding of the field of occupational hygiene.

It is important to keep in mind that hazard evaluation is not an end in itself, but must be considered as part of a much broader procedure that starts with the realization that a certain agent, capable of causing health impairment, may be present in the work environment, and concludes with the control of this agent so that it will be prevented from causing harm. Hazard evaluation paves the way to, but does not replace, hazard prevention.

Exposure assessment

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:

• initial studies to assess workers’ exposure
• follow-up monitoring/surveillance
• exposure assessment for epidemiological studies.

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:

• evaluating the adequacy, testing the efficiency or disclosing possible failures in the control systems
• detecting whether alterations in the processes, such as operating temperature, or in the raw materials, have altered the exposure situation.

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.

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:

• source identification and characterization
• spotting of critical points in closed systems or enclosures (e.g., leaks)
• determination of propagation paths in the work environment
• comparison of different control interventions
• verification that respirable dust has settled together with the coarse visible dust, when using water sprays
• checking that contaminated air is not coming from an adjacent area.

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 a 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.

Hazard prevention and control

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 recognized 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:

• containing them
• removing them immediately beyond the source
• interfering with their propagation
• reducing their concentration or intensity.

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 happens 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.

The Links among Occupational Hygiene, Risk Assessment and Risk Management

Risk assessment

Risk assessment is a methodology that aims at characterizing 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 characterize specific risk situations. It involves hazard identification, the establishment of exposure-effect relationships, and exposure assessment, leading to risk characterization.

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.

Figure 3 is presented as an illustration of different elements of risk assessment.

Figure 3. Elements of risk assessment.

Risk management in the work environment

It is not always feasible to eliminate all agents that pose occupational health risks because some are inherent to work processes that are indispensable or desirable; however, risks can and must be managed.

Risk assessment provides a basis for risk management. However, while risk assessment is a scientific procedure, risk management is more pragmatic, involving decisions and actions that aim at preventing, or reducing to acceptable levels, the occurrence of agents which may pose hazards to the health of workers, surrounding communities and the environment, also accounting for the socio-economic and public health context.

Risk management takes place at different levels; decisions and actions taken at the national level pave the way for the practice of risk management at the workplace level.

Risk management at the workplace level requires information and knowledge on:

• health hazards and their magnitude, identified and rated according to risk assessment findings
• legal requirements and standards
• technological feasibility, in terms of the available and applicable control technology
• economic aspects, such as the costs to design, implement, operate and maintain control systems, and cost-benefit analysis (control costs versus financial benefits incurred by controlling occupational and environment hazards)
• human resources (available and required)
• socio-economic and public health context

to serve as a basis for decisions which include:

• establishment of a target for control
• selection of adequate control strategies and technologies
• establishment of priorities for action in view of the risk situation, as well as of the existing socio-economic and public health context (particularly important in developing countries)

and which should lead to actions such as:

• identification/search of financial and human resources (if not yet available)
• design of specific control measures, which should be appropriate for the protection of workers’ health and of the environment, as well as safeguarding as much as possible the natural resource base
• implementation of control measures, including provisions for adequate operation, maintenance and emergency procedures
• establishment of a hazard prevention and control programme with adequate management and including routine surveillance.

Traditionally, the profession responsible for most of these decisions and actions in the workplace is occupational hygiene.

One key decision in risk management, that of acceptable risk (what effect can be accepted, in what percentage of the working population, if any at all?), is usually, but not always, taken at the national policy-making level and followed by the adoption of occupational exposure limits and the promulgation of occupational health regulations and standards. This leads to the establishment of targets for control, usually at the workplace level by the occupational hygienist, who should have knowledge of the legal requirements. However, it may happen that decisions on acceptable risk have to be taken by the occupational hygienist at the workplace level—for example, in situations when standards are not available or do not cover all potential exposures.

All these decisions and actions must be integrated into a realistic plan, which requires multidisciplinary and multisectorial coordination and collaboration. Although risk management involves pragmatic approaches, its efficiency should be scientifically evaluated. Unfortunately risk management actions are, in most cases, a compromise between what should be done to avoid any risk and the best which can be done in practice, in view of financial and other limitations.

Risk management concerning the work environment and the general environment should be well coordinated; not only are there overlapping areas, but, in most situations, the success of one is interlinked with the success of the other.

Occupational Hygiene Programmes and Services

Political will and decision making at the national level will, directly or indirectly, influence the establishment of occupational hygiene programmes or services, either at the governmental or private level. It is beyond the scope of this article to provide detailed models for all types of occupational hygiene programmes and services; however, there are general principles that are applicable to many situations and may contribute to their efficient implementation and operation.

A comprehensive occupational hygiene service should have the capability to carry out adequate preliminary surveys, sampling, measurements and analysis for hazard evaluation and for control purposes, and to recommend control measures, if not to design them.

Key elements of a comprehensive occupational hygiene programme or service are human and financial resources, facilities, equipment and information systems, well organized and coordinated through careful planning, under efficient management, and also involving quality assurance and continuous programme evaluation. Successful occupational hygiene programmes require a policy basis and commitment from top management. The procurement of financial resources is beyond the scope of this article.

Human resources

Adequate human resources constitute the main asset of any programme and should be ensured as a priority. All staff should have clear job descriptions and responsibilities. If needed, provisions for training and education should be made. The basic requirements for occupational hygiene programmes include:

• occupational hygienists—in addition to general knowledge on the recognition, evaluation and control of occupational hazards, occupational hygienists may be specialized in specific areas, such as analytical chemistry or industrial ventilation; the ideal situation is to have a team of well-trained professionals in the comprehensive practice of occupational hygiene and in all required areas of expertise
• laboratory personnel, chemists (depending on the extent of analytical work)
• technicians and assistants, for field surveys and for laboratories, as well as for instrument maintenance and repairs
• information specialists and administrative support.

One important aspect is professional competence, which must not only be achieved but also maintained. Continuous education, in or outside the programme or service, should cover, for example, legislation updates, new advances and techniques, and gaps in knowledge. Participation in conferences, symposia and workshops also contribute to the maintenance of competence.

Health and safety for staff

Health and safety should be ensured for all staff in field surveys, laboratories and offices. Occupational hygienists may be exposed to serious hazards and should wear the required personal protective equipment. Depending on the type of work, immunization may be required. If rural work is involved, depending on the region, provisions such as antidote for snake bites should be made. Laboratory safety is a specialized field discussed elsewhere in this Encyclopaedia.

Occupational hazards in offices should not be overlooked—for example, work with visual display units and sources of indoor pollution such as laser printers, photocopying machines and air-conditioning systems. Ergonomic and psychosocial factors should also be considered.

Facilities

These include offices and meeting room(s), laboratories and equipment, information systems and library. Facilities should be well designed, accounting for future needs, as later moves and adaptations are usually more costly and time consuming.

Occupational hygiene laboratories and equipment

Occupational hygiene laboratories should have in principle the capability to carry out qualitative and quantitative assessment of exposure to airborne contaminants (chemicals and dusts), physical agents (noise, heat stress, radiation, illumination) and biological agents. In the case of most biological agents, qualitative assessments are enough to recommend controls, thus eliminating the need for the usually difficult quantitative evaluations.

Although some direct-reading instruments for airborne contaminants may have limitations for exposure assessment purposes, these are extremely useful for the recognition of hazards and identification of their sources, the determination of peaks in concentration, the gathering of data for control measures, and for checking on controls such as ventilation systems. In connection with the latter, instruments to check air velocity and static pressure are also needed.

One of the possible structures would comprise the following units:

• field equipment (sampling, direct-reading)
• analytical laboratory
• particles laboratory
• physical agents (noise, thermal environment, illumination and radiation)
• workshop for maintenance and repairs of instrumentation.

Whenever selecting occupational hygiene equipment, in addition to performance characteristics, practical aspects have to be considered in view of the expected conditions of use—for example, available infrastructure, climate, location. These aspects include portability, required source of energy, calibration and maintenance requirements, and availability of the required expendable supplies.

Equipment should be purchased only if and when:

• there is a real need
• skills for the adequate operation, maintenance and repairs are available
• the complete procedure has been developed, since it is of no use, for example, to purchase sampling pumps without a laboratory to analyse the samples (or an agreement with an outside laboratory).

Calibration of all types of occupational hygiene measuring and sampling as well as analytical equipment should be an integral part of any procedure, and the required equipment should be available.

Maintenance and repairs are essential to prevent equipment from staying idle for long periods of time, and should be ensured by manufacturers, either by direct assistance or by providing training of staff.

If a completely new programme is being developed, only basic equipment should be initially purchased, more items being added as the needs are established and operational capabilities ensured. However, even before equipment and laboratories are available and operational, much can be achieved by inspecting workplaces to qualitatively assess health hazards, and by recommending control measures for recognized hazards. Lack of capability to carry out quantitative exposure assessments should never justify inaction concerning obviously hazardous exposures. This is particularly true for situations where workplace hazards are uncontrolled and heavy exposures are common.

Information

This includes library (books, periodicals and other publications), databases (e.g. on CD-ROM) and communications.

Whenever possible, personal computers and CD-ROM readers should be provided, as well as connections to the INTERNET. There are ever-increasing possibilities for on-line networked public information servers (World Wide Web and GOPHER sites), which provide access to a wealth of information sources relevant to workers’ health, therefore fully justifying investment in computers and communications. Such systems should include e-mail, which opens new horizons for communications and discussions, either individually or as groups, thus facilitating and promoting exchange of information throughout the world.

Planning

Back

Air pollution management aims at the elimination, or reduction to acceptable levels, of airborne gaseous pollutants, suspended particulate matter and physical and, to a certain extent, biological agents whose presence in the atmosphere can cause adverse effects on human health (e.g., irritation, increase of incidence or prevalence of respiratory diseases, morbidity, cancer, excess mortality) or welfare (e.g., sensory effects, reduction of visibility), deleterious effects on animal or plant life, damage to materials of economic value to society and damage to the environment (e.g., climatic modifications). The serious hazards associated with radioactive pollutants, as well as the special procedures required for their control and disposal, also deserve careful attention.

The importance of efficient management of outdoor and indoor air pollution cannot be overemphasized. Unless there is adequate control, the multiplication of pollution sources in the modern world may lead to irreparable damage to the environment and mankind.

The objective of this article is to give a general overview of the possible approaches to the management of ambient air pollution from motor vehicle and industrial sources. However, it is to be emphasized from the very beginning that indoor air pollution (in particular, in developing countries) might play an even larger role than outdoor air pollution due to the observation that indoor air pollutant concentrations are often substantially higher than outdoor concentrations.

Beyond considerations of emissions from fixed or mobile sources, air pollution management involves consideration of additional factors (such as topography and meteorology, and community and government participation, among many others) all of which must be integrated into a comprehensive programme. For example, meteorological conditions can greatly affect the ground-level concentrations resulting from the same pollutant emission. Air pollution sources may be scattered over a community or a region and their effects may be felt by, or their control may involve, more than one administration. Furthermore, air pollution does not respect any boundaries, and emissions from one region may induce effects in another region by long-distance transport.

Air pollution management, therefore, requires a multidisciplinary approach as well as a joint effort by private and governmental entities.

Sources of Air Pollution

The sources of man-made air pollution (or emission sources) are of basically two types:

• stationary, which can be subdivided into area sources such as agricultural production, mining and quarrying, industrial, point and area sources such as manufacturing of chemicals, nonmetallic mineral products, basic metal industries, power generation and community sources (e.g., heating of homes and buildings, municipal waste and sewage sludge incinerators, fireplaces, cooking facilities, laundry services and cleaning plants)
• mobile, comprising any form of combustion-engine vehicles (e.g., light-duty gasoline powered cars, light- and heavy-duty diesel powered vehicles, motorcycles, aircraft, including line sources with emissions of gases and particulate matter from vehicle traffic).

In addition, there are also natural sources of pollution (e.g., eroded areas, volcanoes, certain plants which release great amounts of pollen, sources of bacteria, spores and viruses). Natural sources are not discussed in this article.

Types of Air Pollutants

Air pollutants are usually classified into suspended particulate matter (dusts, fumes, mists, smokes), gaseous pollutants (gases and vapours) and odours. Some examples of usual pollutants are presented below:

Suspended particulate matter (SPM, PM-10) includes diesel exhaust, coal fly-ash, mineral dusts (e.g., coal, asbestos, limestone, cement), metal dusts and fumes (e.g., zinc, copper, iron, lead) and acid mists (e.g., sulphuric acid), fluorides, paint pigments, pesticide mists, carbon black and oil smoke. Suspended particulate pollutants, besides their effects of provoking respiratory diseases, cancers, corrosion, destruction of plant life and so on, can also constitute a nuisance (e.g., accumulation of dirt), interfere with sunlight (e.g., formation of smog and haze due to light scattering) and act as catalytic surfaces for reaction of adsorbed chemicals.

Gaseous pollutants include sulphur compounds (e.g., sulphur dioxide (SO₂) and sulphur trioxide (SO₃)), carbon monoxide, nitrogen compounds (e.g., nitric oxide (NO), nitrogen dioxide (NO₂), ammonia), organic compounds (e.g., hydrocarbons (HC), volatile organic compounds (VOC), polycyclic aromatic hydrocarbons (PAH), aldehydes), halogen compounds and halogen derivatives (e.g., HF and HCl), hydrogen sulphide, carbon disulphide and mercaptans (odours).

Secondary pollutants may be formed by thermal, chemical or photochemical reactions. For example, by thermal action sulphur dioxide can oxidize to sulphur trioxide which, dissolved in water, gives rise to the formation of sulphuric acid mist (catalysed by manganese and iron oxides). Photochemical reactions between nitrogen oxides and reactive hydrocarbons can produce ozone (O₃), formaldehyde and peroxyacetyl nitrate (PAN); reactions between HCl and formaldehyde can form bis-chloromethyl ether.

While some odours are known to be caused by specific chemical agents such as hydrogen sulphide (H₂S), carbon disulphide (CS₂) and mercaptans (R-SH or R1-S-R2) others are difficult to define chemically.

Examples of the main pollutants associated with some industrial air pollution sources are presented in table 1 (Economopoulos 1993).

Table 1. Common atmospheric pollutants and their sources

Source: Economopoulos 1993

Clean Air Implementation Plans

Air quality management aims at the preservation of environmental quality by prescribing the tolerated degree of pollution, leaving it to the local authorities and polluters to devise and implement actions to ensure that this degree of pollution will not be exceeded. An example of legislation within this approach is the adoption of ambient air quality standards based, very often, on air quality guidelines (WHO 1987) for different pollutants; these are accepted maximum levels of pollutants (or indicators) in the target area (e.g., at ground level at a specified point in a community) and can be either primary or secondary standards. Primary standards (WHO 1980) are the maximum levels consistent with an adequate safety margin and with the preservation of public health, and must be complied with within a specific time limit; secondary standards are those judged to be necessary for protection against known or anticipated adverse effects other than health hazards (mainly on vegetation) and must be complied “within a reasonable time”. Air quality standards are short-, medium- or long-term values valid for 24 hours per day, 7 days per week, and for monthly, seasonal or annual exposure of all living subjects (including sensitive subgroups such as children, the elderly and the sick) as well as non-living objects; this is in contrast to maximum permissible levels for occupational exposure, which are for a partial weekly exposure (e.g., 8 hours per day, 5 days per week) of adult and supposedly healthy workers.

Typical measures in air quality management are control measures at the source, for example, enforcement of the use of catalytic converters in vehicles or of emission standards in incinerators, land-use planning and shut-down of factories or reduction of traffic during unfavourable weather conditions. The best air quality management stresses that the air pollutant emissions should be kept to a minimum; this is basically defined through emission standards for single sources of air pollution and could be achieved for industrial sources, for example, through closed systems and high-efficiency collectors. An emission standard is a limit on the amount or concentration of a pollutant emitted from a source. This type of legislation requires a decision, for each industry, on the best means of controlling its emissions (i.e., fixing emission standards).

The basic aim of air pollution management is to derive a clean air implementation plan (or air pollution abatement plan) (Schwela and Köth-Jahr 1994) which consists of the following elements:

• description of area with respect to topography, meteorology and socioeconomy
• emissions inventory
• comparison with emission standards
• air pollutant concentrations inventory
• simulated air pollutant concentrations
• comparison with air quality standards
• inventory of effects on public health and the environment
• causal analysis
• control measures
• cost of control measures
• cost of public health and environmental effects
• cost-benefit analysis (costs of control vs. costs of efforts)
• transportation and land-use planning
• enforcement plan; resource commitment
• projections for the future on population, traffic, industries and fuel consumption
• strategies for follow-up.

Some of these issues will be described below.

Emissions Inventory; Comparison with Emission Standards

The emissions inventory is a most complete listing of sources in a given area and of their individual emissions, estimated as accurately as possible from all emitting point, line and area (diffuse) sources. When these emissions are compared with emission standards set for a particular source, first hints on possible control measures are given if emission standards are not complied with. The emissions inventory also serves to assess a priority list of important sources according to the amount of pollutants emitted, and indicates the relative influence of different sources—for example, traffic as compared to industrial or residential sources. The emissions inventory also allows an estimate of air pollutant concentrations for those pollutants for which ambient concentration measurements are difficult or too expensive to perform.

Air Pollutant Concentrations Inventory; Comparison with Air Quality Standards

The air pollutant concentrations inventory summarizes the results of the monitoring of ambient air pollutants in terms of annual means, percentiles and trends of these quantities. Compounds measured for such an inventory include the following:

• sulphur dioxide
• nitrogen oxides
• suspended particulate matter
• carbon monoxide
• ozone
• heavy metals (Pb, Cd, Ni, Cu, Fe, As, Be)
• polycyclic aromatic hydrocarbons: benzo(a)pyrene, benzo(e)pyrene, benzo(a)anthracene, dibenzo(a,h)anthracene, benzoghi)perylene, coronen
• volatile organic compounds: n-hexane, benzene, 3-methyl-hexane, n-heptane, toluene, octane, ethyl-benzene xylene (o-,m-,p-), n-nonane, isopropylbenzene, propylbenezene, n-2-/3-/4-ethyltoluene, 1,2,4-/1,3,5-trimethylbenzene, trichloromethane, 1,1,1 trichloroethane, tetrachloromethane, tri-/tetrachloroethene.

Comparison of air pollutant concentrations with air quality standards or guidelines, if they exist, indicates problem areas for which a causal analysis has to be performed in order to find out which sources are responsible for the non-compliance. Dispersion modelling has to be used in performing this causal analysis (see “Air pollution: Modelling of air pollutant dispersion”). Devices and procedures used in today’s ambient air pollution monitoring are described in “Air quality monitoring”.

Simulated Air Pollutant Concentrations; Comparison with Air Quality Standards

Starting from the emissions inventory, with its thousands of compounds which cannot all be monitored in the ambient air for economy reasons, use of dispersion modelling can help to estimate the concentrations of more “exotic” compounds. Using appropriate meteorology parameters in a suitable dispersion model, annual averages and percentiles can be estimated and compared to air quality standards or guidelines, if they exist.

Inventory of Effects on Public Health and the Environment; Causal Analysis

Another important source of information is the effects inventory (Ministerium für Umwelt 1993), which consists of results of epidemiological studies in the given area and of effects of air pollution observed in biological and material receptors such as, for example, plants, animals and construction metals and building stones. Observed effects attributed to air pollution have to be causally analysed with respect to the component responsible for a particular effect—for example, increased prevalence of chronic bronchitis in a polluted area. If the compound or compounds have been fixed in a causal analysis (compound-causal analysis), a second analysis has to be performed to find out the responsible sources (source-causal analysis).

Control Measures; Cost of Control Measures

Control measures for industrial facilities include adequate, well-designed, well-installed, efficiently operated and maintained air cleaning devices, also called separators or collectors. A separator or collector can be defined as an “apparatus for separating any one or more of the following from a gaseous medium in which they are suspended or mixed: solid particles (filter and dust separators), liquid particles (filter and droplet separator) and gases (gas purifier)”. The basic types of air pollution control equipment (discussed further in “Air pollution control”) are the following:

• for particulate matter: inertial separators (e.g., cyclones); fabric filters (baghouses); electrostatic precipitators; wet collectors (scrubbers)

• for gaseous pollutants: wet collectors (scrubbers); adsorption units (e.g., adsorption beds); afterburners, which can be direct-fired (thermal incineration) or catalytic (catalytic combustion).

Wet collectors (scrubbers) can be used to collect, at the same time, gaseous pollutants and particulate matter. Also, certain types of combustion devices can burn combustible gases and vapours as well as certain combustible aerosols. Depending on the type of effluent, one or a combination of more than one collector can be used.

The control of odours that are chemically identifiable relies on the control of the chemical agent(s) from which they emanate (e.g., by absorption, by incineration). However, when an odour is not defined chemically or the producing agent is found at extremely low levels, other techniques may be used, such as masking (by a stronger, more agreeable and harmless agent) or counteraction (by an additive which counteracts or partially neutralizes the offensive odour).

It should be kept in mind that adequate operation and maintenance are indispensable to ensure the expected efficiency from a collector. This should be ensured at the planning stage, both from the know-how and financial points of view. Energy requirements must not be overlooked. Whenever selecting an air cleaning device, not only the initial cost but also operational and maintenance costs should be considered. Whenever dealing with high-toxicity pollutants, high efficiency should be ensured, as well as special procedures for maintenance and disposal of waste materials.

The fundamental control measures in industrial facilities are the following:

Substitution of materials. Examples: substitution of less toxic solvents for highly toxic ones used in certain industrial processes; use of fuels with lower sulphur content (e.g., washed coal), therefore giving rise to less sulphur compounds and so on.

Modification or change of the industrial process or equipment. Examples: in the steel industry, a change from raw ore to pelleted sintered ore (to reduce the dust released during ore handling); use of closed systems instead of open ones; change of fuel heating systems to steam, hot water or electrical systems; use of catalysers at the exhaust air outlets (combustion processes) and so on.

Modifications in processes, as well as in plant layout, may also facilitate and/or improve the conditions for dispersion and collection of pollutants. For example, a different plant layout may facilitate the installation of a local exhaust system; the performance of a process at a lower rate may allow the use of a certain collector (with volume limitations but otherwise adequate). Process modifications that concentrate different effluent sources are closely related to the volume of effluent handled, and the efficiency of some air-cleaning equipment increases with the concentration of pollutants in the effluent. Both the substitution of materials and the modification of processes may have technical and/or economic limitations, and these should be considered.

Adequate housekeeping and storage. Examples: strict sanitation in food and animal product processing; avoidance of open storage of chemicals (e.g., sulphur piles) or dusty materials (e.g., sand), or, failing this, spraying of the piles of loose particulate with water (if possible) or application of surface coatings (e.g., wetting agents, plastic) to piles of materials likely to give off pollutants.

Adequate disposal of wastes. Examples: avoidance of simply piling up chemical wastes (such as scraps from polymerization reactors), as well as of dumping pollutant materials (solid or liquid) in water streams. The latter practice not only causes water pollution but can also create a secondary source of air pollution, as in the case of liquid wastes from sulphite process pulp mills, which release offensive odorous gaseous pollutants.

Maintenance. Example: well maintained and well-tuned internal combustion engines produce less carbon monoxide and hydrocarbons.

Work practices. Example: taking into account meteorological conditions, particularly winds, when spraying pesticides.

By analogy with adequate practices at the workplace, good practices at the community level can contribute to air pollution control - for example, changes in the use of motor vehicles (more collective transportation, small cars and so on) and control of heating facilities (better insulation of buildings in order to require less heating, better fuels and so on).

Control measures in vehicle emissions are adequate and efficient mandatory inspection and maintenance programmes which are enforced for the existing car fleet, programmes of enforcement of the use of catalytic converters in new cars, aggressive substitution of solar/battery-powered cars for fuel-powered ones, regulation of road traffic, and transportation and land use planning concepts.

Motor vehicle emissions are controlled by controlling emissions per vehicle mile travelled (VMT) and by controlling VMT itself (Walsh 1992). Emissions per VMT can be reduced by controlling vehicle performance - hardware, maintenance - for both new and in-use cars. Fuel composition of leaded gasoline may be controlled by reducing lead or sulphur content, which also has a beneficial effect on decreasing HC emissions from vehicles. Lowering the levels of sulphur in diesel fuel as a means to lower diesel particulate emission has the additional beneficial effect of increasing the potential for catalytic control of diesel particulate and organic HC emissions.

Another important management tool for reducing vehicle evaporative and refuelling emissions is the control of gasoline volatility. Control of fuel volatility can greatly lower vehicle evaporative HC emissions. Use of oxygenated additives in gasoline lowers HC and CO exhaust as long as fuel volatility is not increased.

Reduction of VMT is an additional means of controlling vehicle emissions by control strategies such as

• use of more efficient transportation modes

• increasing the average number of passengers per car

• spreading congested peak traffic loads

• reducing travel demand.

While such approaches promote fuel conservation, they are not yet accepted by the general population, and governments have not seriously tried to implement them.

All these technological and political solutions to the motor vehicle problem except substitution of electrical cars are increasingly offset by growth in the vehicle population. The vehicle problem can be solved only if the growth problem is addressed in an appropriate way.

Cost of Public Health and Environmental Effects; Cost-Benefit Analysis

The estimation of the costs of public health and environmental effects is the most difficult part of a clean air implementation plan, as it is very difficult to estimate the value of lifetime reduction of disabling illnesses, hospital admission rates and hours of work lost. However, this estimation and a comparison with the cost of control measures is absolutely necessary in order to balance the costs of control measures versus the costs of no such measure undertaken, in terms of public health and environmental effects.

Transportation and Land-Use Planning

The pollution problem is intimately connected to land-use and transportation, including issues such as community planning, road design, traffic control and mass transportation; to concerns of demography, topography and economy; and to social concerns (Venzia 1977). In general, the rapidly growing urban aggregations have severe pollution problems due to poor land-use and transportation practices. Transportation planning for air pollution control includes transportation controls, transportation policies, mass transit and highway congestion costs. Transportation controls have an important impact on the general public in terms of equity, repressiveness and social and economic disruption - in particular, direct transportation controls such as motor vehicle constraints, gasoline limitations and motor vehicle emission reductions. Emission reductions due to direct controls can be reliably estimated and verified. Indirect transportation controls such as reduction of vehicle miles travelled by improvement of mass transit systems, traffic flow improvement regulations, regulations on parking lots, road and gasoline taxes, car-use permissions and incentives for voluntary approaches are mostly based on past trial-and-error experience, and include many uncertainties when trying to develop a viable transportation plan.

National action plans incurring indirect transportation controls can affect transportation and land-use planning with regard to highways, parking lots and shopping centres. Long-term planning for the transportation system and the area influenced by it will prevent significant deterioration of air quality and provide for compliance with air quality standards. Mass transit is consistently considered as a potential solution for urban air pollution problems. Selection of a mass transit system to serve an area and different modal splits between highway use and bus or rail service will ultimately alter land-use patterns. There is an optimum split that will minimize air pollution; however, this may not be acceptable when non-environmental factors are considered.

The automobile has been called the greatest generator of economic externalities ever known. Some of these, such as jobs and mobility, are positive, but the negative ones, such as air pollution, accidents resulting in death and injury, property damage, noise, loss of time, and aggravation, lead to the conclusion that transportation is not a decreasing cost industry in urbanized areas. Highway congestion costs are another externality; lost time and congestion costs, however, are difficult to determine. A true evaluation of competing transportation modes, such as mass transportation, cannot be obtained if travel costs for work trips do not include congestion costs.

Land-use planning for air pollution control includes zoning codes and performance standards, land-use controls, housing and land development, and land-use planning policies. Land-use zoning was the initial attempt to accomplish protection of the people, their property and their economic opportunity. However, the ubiquitous nature of air pollutants required more than physical separation of industries and residential areas to protect the individual. For this reason, performance standards based initially on aesthetics or qualitative decisions were introduced into some zoning codes in an attempt to quantify criteria for identifying potential problems.

The limitations of the assimilative capacity of the environment must be identified for long-term land-use planning. Then, land-use controls can be developed that will prorate the capacity equitably among desired local activities. Land-use controls include permit systems for review of new stationary sources, zoning regulation between industrial and residential areas, restriction by easement or purchase of land, receptor location control, emission-density zoning and emission allocation regulations.

Housing policies aimed at making home ownership available to many who could otherwise not afford it (such as tax incentives and mortgage policies) stimulate urban sprawl and indirectly discourage higher-density residential development. These policies have now proven to be environmentally disastrous, as no consideration was given to the simultaneous development of efficient transportation systems to serve the needs of the multitude of new communities being developed. The lesson learnt from this development is that programmes impacting on the environment should be coordinated, and comprehensive planning undertaken at the level where the problem occurs and on a scale large enough to include the entire system.

Land-use planning must be examined at national, provincial or state, regional and local levels to adequately ensure long-term protection of the environment. Governmental programmes usually start with power plant siting, mineral extraction sites, coastal zoning and desert, mountain or other recreational development. As the multiplicity of local governments in a given region cannot adequately deal with regional environmental problems, regional governments or agencies should coordinate land development and density patterns by supervising the spatial arrangement and location of new construction and use, and transportation facilities. Land-use and transportation planning must be interrelated with enforcement of regulations to maintain the desired air quality. Ideally, air pollution control should be planned for by the same regional agency that does land-use planning because of the overlapping externalities associated with both issues.

Enforcement Plan, Resource Commitment

The clean air implementation plan should always contain an enforcement plan which indicates how the control measures can be enforced. This implies also a resource commitment which, according to a polluter pays principle, will state what the polluter has to implement and how the government will help the polluter in fulfilling the commitment.

Projections for the Future

In the sense of a precautionary plan, the clean air implementation plan should also include estimates of the trends in population, traffic, industries and fuel consumption in order to assess responses to future problems. This will avoid future stresses by enforcing measures well in advance of imagined problems.

Strategies for Follow-up

A strategy for follow-up of air quality management consists of plans and policies on how to implement future clean air implementation plans.

Role of Environmental Impact Assessment

Environmental impact assessment (EIA) is the process of providing a detailed statement by the responsible agency on the environmental impact of a proposed action significantly affecting the quality of the human environment (Lee 1993). EIA is an instrument of prevention aiming at consideration of the human environment at an early stage of the development of a programme or project.

EIA is particularly important for countries which develop projects in the framework of economic reorientation and restructuring. EIA has become legislation in many developed countries and is now increasingly applied in developing countries and economies in transition.

EIA is integrative in the sense of comprehensive environmental planning and management considering the interactions between different environmental media. On the other hand, EIA integrates the estimation of environmental consequences into the planning process and thereby becomes an instrument of sustainable development. EIA also combines technical and participative properties as it collects, analyses and applies scientific and technical data with consideration of quality control and quality assurance, and stresses the importance of consultations prior to licensing procedures between environmental agencies and the public which could be affected by particular projects. A clean air implementation plan can be considered as a part of the EIA procedure with reference to the air.

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