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According to the best available estimates 100 million workers are injured and 200,000 die each year in occupational accidents and 68 million to 157 million new cases of occupational disease are attributed to hazardous exposures or workloads. Such high numbers of severe health outcomes contribute to one of the most important impacts on the health of the world's population. Occupational injuries and diseases play an even more important role in developing countries, where 70% of the working population of the world lives. By affecting the health of the working population, occupational injuries and diseases have profound effects on work productivity and on the economic and social well-being of workers, their families and dependents. According to recent estimates, the cost of work-related health loss and associated productivity loss may amount to several per cent of the total gross national product of the countries of the world. (Source: WHO)

The officially registered working population constitutes 60%-70% of the adult male and 30%-60% of the adult female population of the world. When work at home and informal work are taken into consideration the percentage is even higher. In unfavourable cases the levels and intensities of hazardous exposures may be 10 or even 1,000 times greater at work than elsewhere. Workers in the highest risk industries, such as mining, forestry, construction and agriculture, are often at an unreasonably high risk and one-fifth to one-third may suffer occupational injury or disease annually, leading in extreme cases to high prevalences of work disability and even to premature death. Less dramatic but well-defined occupational health problems also prevail in service and office occupations, where psychological stressors and ergonomic problems often increase the workload, cause job dissatisfaction and affect health and productivity. (Source: WHO)

On the other hand, a number of studies have provided convincing evidence of a positive association between health, well-being, well-organized work and a healthy work environment where safety and health are considered and where conditions conducive to one's professional and social development are provided. The occupational health standards of workers and workplaces vary substantially according to economic structure, level of industrialization, developmental status, climatic conditions, and traditions in occupational health and safety. Twenty per cent to fifty per cent of workers may be subject to hazardous exposures at work in industrialized countries and the rate may be even higher in the developing and newly industrialized countries. Mechanical factors and physical and chemical agents are the main problems in manufacturing industries, while pesticides, heavy physical work, organic dusts, biological factors and accidents are the occupational burdens of agricultural workers. A number of studies show that in the most unfavourable conditions 50%-100% of the workers in some hazardous industries may be exposed to levels of chemical, physical or biological factors that exceed the occupational exposure limits applied in the industrialized countries. (Source: WHO)

Occupational health hazards may mean (1) conditions that cause legally compensable illnesses, or it may mean (2) any conditions in the workplace that impair the health of employees enough to make them lose time from work or to cause significant discomfort. Both are undesirable. Both are preventable. Their correction is properly the responsibility of management. The basic principle applied is to "eliminate the danger at the source." This may involve:

• Elimination of a hazardous substance;
• Substitution of a less hazardous substance;
• Modification of the process;
• Control of the danger at the source (e.g., local exhaust ventilation);
• Control of the danger in the workplace (e.g., dilution ventilation);
• Use of personal protective equipment (e.g., respiratory protection);
• Administrative controls (e.g., work schedules).

Industrial hygiene is "that science and art devoted to the anticipation, recognition, evaluation and control of those environmental factors or stresses arising in or from the workplace, which may cause sickness, impaired health and well-being, or significant discomfort among workers or among citizens of the community." Industrial hygiene is primarily concerned with materials, chemicals, pressures and energies encountered by man in his occupations. According to the American Academy of Industrial Hygiene Code of Ethics for the professional, the practice of industrial hygiene, the primary responsibility of the industrial hygienist is as follows:

To employees:

• To protect the health of employees;
• To maintain an objective attitude toward the recognition, evaluation and control of health hazards regardless of external influences, realizing that the health and welfare of workers and others may depend upon the industrial hygienist's professional judgment;
• To counsel employees regarding the health hazards and necessary precautions to avoid adverse health effects.

To employers:

• To respect confidences, advise honestly and report findings and recommendations accurately;
• To act responsibly in the application of industrial hygiene principles toward the attainment of a healthful working environment;
• To hold responsibilities to the employer or client subservient to the ultimate responsibility to protect the health of employees.

Industrial hygiene chemistry is a branch of analytical chemistry devoted to the laboratory analysis of environmental samples collected in the workplace by industrial hygienists.

Epidemiology is concerned with disease patterns in natural populations or groups of people such as nations or communities. Occupational epidemiology is a branch of epidemiology primarily concerned with the study of disease occurrence in worker populations. Occupational epidemiology attempts to relate the occurrence of disease to worker exposures to hazardous substances.

Industrial toxicology is concerned with the evaluation of human health effects posed by chemicals used in the workplace. The primary objectives are (1) to determine the tolerable limits of human exposures to chemicals in the workplace, and (2) to determine the tolerable biological concentrations of industrial chemicals or their metabolites in human tissues (blood, urine, breath, fat, etc.).

Industrial safety is primarily concerned with mechanical hazards such as falling, tripping, being caught in or between things, fire and explosion. These hazards are evaluated and controlled by safety engineers, safety professionals or other safety specialists. Other hazards fall into the field of industrial hygiene.

The occupational health physician depends on the skills, techniques and knowledge of the industrial hygienist to provide insight into the health background of an employee's job. In many cases it is extremely difficult to differentiate between the symptoms of occupational and non-occupational disease. The industrial hygienist, by pointing out the work operations and their associated hazards, enables the physician to correlate the employee's condition and complaints with the known potential job health hazards. The physician uses the information provided by the industrial hygienist on the hazards present in the industrial environment to:
• Determine employee response to the work environment;
• Correlate employee complaints with potential hazards areas;
• Undertake special biochemical tests to determine if normal bodily functions have been impaired;
• Provide the employee medical guidance on general health problems in relation to the physical requirements of the job;
• Through physical examinations, select workers for job assignments where pre-existing conditions will not be aggravated nor will the worker's presence endanger the health and safety of others.