Description
This comprehensive set of university notes provides an in-depth analysis of chemical hazards in occupational settings, authored by Allan R. Mbewe. The material is designed for tertiary-level students pursuing degrees, diplomas, or certificates in occupational health, environmental health, public health, industrial hygiene, or related professional programmes. It offers a detailed classification of hazardous chemical substances based on their physical forms, including solids, liquids, gases, vapours, aerosols, fumes, smoke, mists, and smog. The notes extensively cover the adverse toxicological effects of chemical exposures, such as irritation, asphyxiation, anaesthesia, systemic injury, allergic hypersensitivity, and idiosyncratic reactions. It further explains the critical distinctions between acute and chronic effects, delving into long-term outcomes like cancer, mutations, birth defects, and reproductive impairment. The resource also details the various interactions that influence toxicity, such as additive, synergistic, and antagonistic effects, and concludes with general preventive and control measures. This is an essential reference for students, lecturers, and health professionals seeking authoritative material on chemical risk assessment and management, directly supporting academic study and exam preparation for Zambian tertiary institutions. Download these detailed notes to build a robust understanding of occupational chemical hazards and their control.
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Chemical hazards Allan R. Mbewe Classification of Hazardous chemical substances 1. Solid • Grinding, abrasion or disintegration of a large piece of material may produce dust. • A dust is defined as a group of airborne solid particles ranging from 0.1 to 100 micrometers in diameter (1 micron = 0.001mm or µm). 2. Liquids • Liquids, like solids, can cause physical damage as well as poisoning. • Fluidity gives liquids mobility and leads to problems containment as they are readily converted to aerosols and vapours. • Liquids can dissolve and react with other substances – which may have profound effects and harm to living organisms Classification of Hazardous chemical substances Cont’d. 3. Gases • Gases can cause either physical or chemical damage e.g. an inert gas could kill simply by displacing air. • Chemicals in gas phase are most hazardous from point of acute toxicity since the lungs have evolved to facilitate uptake of oxygen and readily absorb most gases. • Absolved gases enter the general blood circulation directly, unlike substances absolved from the intestine, which are often transformed by the liver. Classification of Hazardous chemical substances Cont. 4. Vapour • Vapours are the gaseous form of substances which are normally in solid or liquid form at the existing temperature and pressure. • Vapours are in equilibrium with the solids or liquids from which they originate. • The equilibrium changes with changes in temperature and pressure. • Vaporization increases with increase in temperature or with decrease in pressure. • Substances with high vapour pressure and liquids with low boiling points vaporise readily Classification of Hazardous chemical substances Cont’d. 5. Aerosols An aerosol is a suspension in a gas of liquid droplets or solid particles, ranging from 0.001 to 100 µm effective aerodynamic diameter. Mass concentration may range from 10 -9 to 10 gm per cubic meter gas. Amongst aerosols, a distinction should be made between dusts, fumes, smoke, mist and fog (smog). Classification of Hazardous chemical substances Cont’d. 6. Fumes These are solid particles formed by condensation from gaseous or vapour phase. Fumes usually result from chemical reactions such as oxidation or from sublimations or distillation process followed by condensation e.g. oxides of iron and copper. Fumes may flocculate and coalesce. Fume particles are usually less than 1µm in diameter and can be breathed into the alveoli but are usually breathed out again and so may be less of a hazard than larger particles in the 0.5 to 10 µm range. Classification of Hazardous chemical substances Cont. 7. Smoke Smoke results from combustion of fossil or biofuels, asphaltic materials and wood. Smoke consists of soot, liquid droplets and, in the case of wood and coal, ash. Smoke contains polycyclic aromatic hydrocarbons which are identified as carcinogens and is associated with increased risk of lung cancer and should be kept to a minimum Classification of Hazardous chemical substances Cont. 8. Mist, fogs and smog • Mist and fogs consist of suspended droplets formed by condensation of gas or vapour or by dispersal of liquid by splashing or foaming or by deliberate atomization e.g. oil mist from cutting and grinding operations and pesticide mists from spraying operations. Mists and fogs may carry harmful micro-organisms in suspension. Smog is a term coined in 1905 to describe the mixture of smoke and fog that plagued industrial England. The air pollutants (sulphur oxides and particulates) combine with atmospheric moisture to form the greyish haze called smog, especially in winter. Points to note in physical forms of chemicals • Chemical substances can change from one physical form to another depending upon the environmental conditions, especially temperature and pressure • Sunlight can cause photochemical processes to occur and large changes in the chemistry of exposed systems such as, ultraviolet radiation and X- rays • Most work environmental samples will contain chemicals in a variety of states and these will determine the exposure conditions for people or other organisms at risk. It is important that environmental conditions are known before any hazard characterization or risk assessment is made. Points to note in physical forms of chemicals cont’d Electromagnetic and electrostatic fields may affect the distribution of particulates and consequently both exposures and related chemical processes • Radon is …
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