In addition to safety responsibilities, supervisors – together with management and safety personnel – must make sure that the work area is free from conditions that could be detrimental to health. Supervisors can then request assistance from industrial hygienists, who work with medical, safety, and engineering personnel to eliminate or safeguard against such hazards.  Industrial hygiene is defined by the American Industrial Hygiene Association (AIHA) as "that science and are 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, citizens of the community".

1.1 Introduction

Most occupational diseases, however, develop relatively slowly. Exposure to an injurious contaminant may go on for many years before a pathological change occurs. These long – term exposures may eventually lead to a chronic disease that is usually irreversible. An example is the class of occupational diseases known as pneumoconiosis (diseases of the lungs), which are produced by the long–term inhalation of reparable particles of dust such as silica. Short–term or acute exposures usually refer to high exposures to a toxic substance over a short period of time, resulting in an acute effect that is an illness form which the individual usually recovers without a permanent effect. It is the prevention, evaluation, and control of these types of occurrences that is the role of the industrial hygienist. 

Occupational Safety and Health Act (OSHA) has in effect united safety and industrial hygiene. Although the two specialties will continue to be separate and distinct, the frequently general implementation problems with which both contented often may be solved with the same solutions. In the final analysis, it probably makes little difference to workers, for example, if they were to be fatally overcome by a sudden intense exposure to a chlorinated hydrocarbon or fatally sickened with cirrhosis of the liver after prolonged exposure to small, but still dangerous, amounts of the compound. The control approaches may be essentially the same in both instances, although the first case probably, would be in the safety specialist's area of responsibility, while the second would be in the industrial hygienist's. The frequent overlapping of interests leads to the advisability of each specialty having a good understanding of the other's methods and information.

Industrial hygiene is the professional specialty concerned with preserving the health of employees while at work. It is of major concern because many industrial processes and operations either produce or use compounds that may be harmful to the health of workers. The manager of a safety program will refer to a professional industrial hygienist in cases where the occupational health exposures have such significance and frequency that specialized assistance is necessary. In order to be familiar with industrial health hazard exposures, it is necessary for the safety program manager to have acknowledged of the more common toxic compounds found in industry and the principles for their control.

1.2 Industrial Toxicology  

In order to be able to effectively deal with potential toxic chemical hazards in the workplace, the industrial hygienist must have an adequate understanding and knowledge of general toxicology. The word toxicology is derived from the Greek word for the poison that arrows were dipped in. Toxicology is the science that deals with the poisonous toxic properties of substances. A toxic effect can be defined as any noxious effect on the body. Reversible or irreversible, any chemically induced tumor, benign of malignant, any mutagenic or teratogenic effect, or death as a result of contact with a substance via the respiratory tract, skin, eye, mouth, or any other route.

Toxic effects are undesirable disturbances of physiological function caused by poisons. Toxicity is a property of matter. It is a physiological property that defines the capacity of a chemical to do harm or produce injury to a living organism by other than mechanical means.

1.3 Acute and Chronic Poisoning  

Industrial poisoning accurse in two principal types: acute and chronic. The first results from a single exposure to a heavy concentration of a toxic substance. The second is the result of repeated exposures to smaller concentrations. For repeated prolonged periods may cause serious physiological damage, this would be a chronic poisoning. However, exposure to a concentration of between 64,000 to 80,000 parts per million for as short a period as 30 – 60 minutes has caused immediate of later fatality.

The chances of recovery from acute poisoning, if the dose is not lethal, are greater than for chronic poisoning. The later effects are much more significant, for they are not so readily apparent and their slowly developing, insidious results are apt to be more damaging.

1.4 Industrial Heath Hazards  

The list of known industrial poisons is long, and their effects and means of control are generally understood. However, the problem of safeguarding personnel is complicated by the introduction annually of many new compounds whose toxicity is somewhat uncertain. Also, compounds of chemical materials often will sell their products under trade names that do not indicate the chemical constituents of the compounds. Request for information on the compounding formulas of proprietary industrial chemicals often produces a negative response from the supplier, who will wish, understandably, to protect the secrecy of the formulation. It is generally possible to secure from him or her sufficient knowledge of the toxic and other properties of the compound without asking for divulgence of its formula.

Industrial hygienists define their work as “the recognition, evaluation, and control of environmental conditions that may have adverse effects on health, that may be uncomfortable or irritating, or that may have some undesired effect upon the ability of individuals to perform their normal work”. It is possible to group these environmental conditions or stresses into four general categories: chemical, physical, and ergonomic.

1.5 Chemical Stresses

Chemical compounds in the form of dusts, fumes, smoke, aerosols, mists, gases, vapors, and liquids may cause health problems by:

-         Inhalation (breathing):  Contaminants inhaled into the lungs can be classified as gases, vapors, and particulate matter.

-         Absorption (through direct with the skin): Many compounds that exist either in liquid or gaseous form, or both, can be absorbed through intact skin. Ex: arsenic, mercury, nitrobenzene, aniline…

-         Ingestion (eating and drinking): Toxic compounds capable of being absorbed from the gastrointestinal tract into the blood – for example, lead oxide – can create serious exposure problems if people working with these substances are allowed to eat or smoke in their work areas.

1.5.1 Liquid Chemicals: Solvents

Solvents are usually further categorized as aqueous or organic. Aqueous solvents are those that readily dissolve in water. Many acids, alkalis, or detergents, when mixed with water, form aqueous solvent systems.

The term solvent, however, is commonly used to mean organic solvents. Many of these chemicals do not mix easily with water but do dissolve other organic materials, such as greases, oils, and fats.

Organic solvents generally have some effect on the central nervous system. They may cause nervous system depression, in which the victim experiences short-term (acute) dizziness, feelings of intoxication and nausea, and a decrease in muscular coordination. Higher levels of exposure may cause loss of consciousness, coma, long-term damage to the liver or other organs, or affect the worker's reproductive ability, and, in some cases, death.

Substantial exposures, fortunately, can be controlled – spry-painting booths can be ventilated and degreasing tanks can be exhausted.

The point to remember is not how much solvent is used at the job site, but the actual degree of exposure by inhalation or by skin absorption.

1.5.2 Selection and Handling of Solvents

Getting the job done without hazard to employees or property is dependent upon the proper selection, application, handling, and control of solvents and an understanding of their properties. A good working knowledge of the nomenclature and effects of exposure to solvents is helpful in making a proper assessment of damage or harm. Here Table 1.1 of potentially hazardous operations and air contaminants:

Table 1.1: Potentially hazardous operations and air contaminants