Occupational hygiene

STUDY UNIT EIGHT

LEARNING OBJECTIVES
After having worked through this study unit, students are expected to:

• Appreciate the concepts in occupational hygiene

• Show an understanding of the classification of hazards
•  

8.0      OCCUPATIONAL HEALTH AND HYGIENE
8.1      Occupational hygiene
Occupational hygiene is defined by the British Occupational Hygiene Society as: ‘the applied science concerned with the identification, measurement, appraisal of risk, and control to acceptable standards, of physical, chemical and biological factors arising in or from the workplace which may affect the health or well-being of those at work or in the community’. It is thus primarily concerned with the identification of health hazards and the assessment of risks with the crucial purpose of preventing or controlling those risks to tolerable levels. This relates both to the people within workplaces and those who might be affected in the surrounding local environment.

Occupational hygiene deals not only with obvious threats to health but also in a positive sense with the achievement of optimal ‘comfort conditions’ for workers, i.e. the reduction of discomfort factors which may cause irritation, loss of concentration, impaired work efficiency and general decreased quality of life. The American Industrial Hygiene Association in its corresponding definition begins: ‘Industrial hygiene is that science and art devoted to the recognition, evaluation and control . . .’ indicating that although much of occupational and industrial hygiene is underpinned by proven scientific theory, a considerable amount relies on ‘rule of thumb’; thus in the practical application of occupational hygiene, judgemental and other skills developed by the experienced practitioner are important.

8.2      Identification and Classification of Hazards
Before any occupational hygiene investigation is performed the purpose must be clearly defined. The purpose of an occupational hygiene investigation might be to identify possible hazards, to evaluate existing risks at the workplace, to prove compliance with regulatory requirements, to evaluate control measures or to assess exposure with regard to an epidemiological survey. This article is restricted to programmes aimed at identification and classification of hazards at the workplace. Many models or techniques have been developed to identify and evaluate hazards in the working environment. They differ in complexity, from simple checklists, preliminary industrial hygiene surveys, job-exposure matrices and hazard and operability studies to job exposure profiles and work surveillance programmes. No single technique is a clear choice for everyone, but all techniques have parts which are useful in any investigation. The usefulness of the models also depends on the purpose of the investigation, size of workplace, type of production and activity as well as complexity of operations.

Identification and classification of hazards can be divided into three basic elements: workplace characterization, exposure pattern and hazard evaluation.
Workplace characterization
A workplace might have from a few employees up to several thousands and have different activities (e.g., production plants, construction sites, office buildings, hospitals or farms). At a workplace different activities can be localized to special areas such as departments or sections. In an industrial process, different stages and operations can be identified as production is followed from raw materials to finished products.
Detailed information should be obtained about processes, operations or other activities of interest, to identify agents utilized, including raw materials, materials handled or added in the process, primary products, intermediates, final products, reaction products and by-products. Additives and catalysts in a process might also be of interest to identify. Raw material or added material which has been identified only by trade name must be evaluated by chemical composition. Information or safety data sheets should be available from manufacturer or supplier.
Some stages in a process might take place in a closed system without anyone exposed, except during maintenance work or process failure. These events should be recognized and precautions taken to prevent exposure to hazardous agents. Other processes take place in open systems, which are provided with or without local exhaust ventilation. A general description of the ventilation system should be provided, including local exhaust system.

When possible, hazards should be identified in the planning or design of new plants or processes, when changes can be made at an early stage and hazards might be anticipated and avoided. Conditions and procedures that may deviate from the intended design must be identified and evaluated in the process state. Recognition of hazards should also include emissions to the external environment and waste materials. Facility locations, operations, emission sources and agents should be grouped together in a systematic way to form recognizable units in the further analysis of potential exposure. In each unit, operations and agents should be grouped according to health effects of the agents and estimation of emitted amounts to the work environment.
Exposure patterns
The main exposure routes for chemical and biological agents are inhalation and dermal uptake or incidentally by ingestion. The exposure pattern depends on frequency of contact with the hazards, intensity of exposure and time of exposure. Working tasks have to be systematically examined. It is important not only to study work manuals but to look at what actually happens at the workplace. Workers might be directly exposed as a result of actually performing tasks, or be indirectly exposed because they are located in the same general area or location as the source of exposure. It might be necessary to start by focusing on working tasks with high potential to cause harm even if the exposure is of short duration. Non-routine and intermittent operations (e.g., maintenance, cleaning and changes in production cycles) have to be considered. Working tasks and situations might also vary throughout the year.

Within the same job title exposure or uptake might differ because some workers wear protective equipment and others do not. In large plants, recognition of hazards or a qualitative hazards evaluation very seldom can be performed for every single worker. Therefore workers with similar working tasks have to be classified in the same exposure group. Differences in working tasks, work techniques and work time will result in considerably different exposure and have to be considered. Persons working outdoors and those working without local exhaust ventilation have been shown to have a larger day-to-day variability than groups working indoors with local exhaust ventilation. Work processes, agents applied for that process/job or different tasks within a job title might be used, instead of the job title, to characterize groups with similar exposure. Within the groups, workers potentially exposed must be identified and classified according to hazardous agents, routes of exposure, health effects of the agents, frequency of contact with the hazards, intensity and time of exposure. Different exposure groups should be ranked according to hazardous agents and estimated exposure in order to determine workers at greatest risk.
Qualitative hazard evaluation
Possible health effects of chemical, biological and physical agents present at the workplace should be based on an evaluation of available epidemiological, toxicological, clinical and environmental research. Up-to-date information about health hazards for products or agents used at the workplace should be obtained from health and safety journals, databases on toxicity and health effects, and relevant scientific and technical literature.

Material Safety Data Sheets (MSDSs) should if necessary be updated. Data Sheets document percentages of hazardous ingredients together with the Chemical Abstracts Service chemical identifier, the CAS-number, and threshold limit value (TLV), if any. They also contain information about health hazards, protective equipment, preventive actions, manufacturer or supplier, and so on. Sometimes the ingredients reported are rather rudimentary and have to be supplemented with more detailed information.

Monitored data and records of measurements should be studied. Agents with TLVs provide general guidance in deciding whether the situation is acceptable or not, although there must be allowance for possible interactions when workers are exposed to several chemicals. Within and between different exposure groups, workers should be ranked according to health effects of agents present and estimated exposure (e.g., from slight health effects and low exposure to severe health effects and estimated high exposure). Those with the highest ranks deserve highest priority. Before any prevention activities start it might be necessary to perform an exposure monitoring programme. All results should be documented and easily attainable.

In occupational hygiene investigations the hazards to the outdoor environment (e.g., pollution and greenhouse effects as well as effects on the ozone layer) might also be considered.

Chemical, Biological and Physical Agents
Hazards might be of chemical, biological or physical origin. In this section a brief description of the various hazards will be given together with examples of environments or activities where they will be found.
Chemical agents
Chemicals can be grouped into gases, vapours, liquids and aerosols (dusts, fumes, mists).
Gases
Gases are substances that can be changed to liquid or solid state only by the combined effects of increased pressure and decreased temperature. Handling gases always implies risk of exposure unless they are processed in closed systems. Gases in containers or distribution pipes might accidentally leak. In processes with high temperatures (e.g., welding operations and exhaust from engines) gases will be formed.
Vapours
Vapours are the gaseous form of substances that normally are in the liquid or solid state at room temperature and normal pressure. When a liquid evaporates it changes to a gas and mixes with the surrounding air. A vapour can be regarded as a gas, where the maximal concentration of a vapour depends on the temperature and the saturation pressure of the substance. Any process involving combustion will generate vapours or gases. Degreasing operations might be performed by vapour phase degreasing or soak cleaning with solvents. Work activities like charging and mixing liquids, painting, spraying, cleaning and dry cleaning might generate harmful vapours.
Liquids
Liquids may consist of a pure substance or a solution of two or more substances (e.g., solvents, acids, alkalis). A liquid stored in an open container will partially evaporate into the gas phase. The concentration in the vapour phase at equilibrium depends on the vapour pressure of the substance, its concentration in the liquid phase, and the temperature. Operations or activities with liquids might give rise to splashes or other skin contact, besides harmful vapours.
Dusts
Dusts consist of inorganic and organic particles, which can be classified as inhalable, thoracic or respirable, depending on particle size. Most organic dusts have a biological origin. Inorganic dusts will be generated in mechanical processes like grinding, sawing, cutting, crushing, screening or sieving. Dusts may be dispersed when dusty material is handled or whirled up by air movements from traffic. Handling dry materials or powder by weighing, filling, charging, transporting and packing will generate dust, as will activities like insulation and cleaning work.
Fumes
Fumes are solid particles vaporized at high temperature and condensed to small particles. The vaporization is often accompanied by a chemical reaction such as oxidation. The single particles that make up a fume are extremely fine, usually less than 0.1 mm, and often aggregate in larger units. Examples are fumes from welding, plasma cutting and similar operations.
Mists
Mists are suspended liquid droplets generated by condensation from the gaseous state to the liquid state or by breaking up a liquid into a dispersed state by splashing, foaming or atomizing. Examples are oil mists from cutting and grinding operations, acid mists from electroplating, acid or alkali mists from pickling operations or paint spray mists from spraying operations.

SELF-EVALUATION QUESTIONS:

Q1.      Describe the three basic elements in the Identification and classification of hazards