Chemical and Biological Agents

7.1 Hazardous Substances

Physical forms of chemical agents

Chemicals appear in the workplace in several physical forms.

• Dusts are finely divided solid particles. Examples: wood dust and silica dust.
• Fibres are like dusts but elongated in shape. Examples: asbestos and fibreglass.
• Fumes are even smaller particles, usually formed when a solid metal is heated and vaporised and then condenses into tiny particles.
• Gases are substances that are normally airborne at room temperature.
• Vapours are the gaseous form of a substance that is normally a liquid or solid at room temperature, formed when a liquid evaporates.
• Mists are liquid droplets sprayed into the air.
• Liquids are the most common form in the workplace.
• Solids include metal, treated wood and plastic.

The physical form of a chemical makes a big difference to how easily it can enter the body.

Forms of biological agents

Biological agents are widely found in the natural environment, and so they turn up in many work sectors. They include:

• Fungi. Fungi are organisms that are neither plants nor animals. Most are multicellular, and some, such as yeasts, are single cells. A fungus gets its nutrition from plants, food and animals in damp, warm environments. Many fungal infections, such as athlete's foot and yeast infections, are not dangerous to a healthy person, but people with weakened immune systems, from diseases such as HIV or cancer, may develop more serious fungal infections.
• Bacteria. Bacteria are tiny single-celled organisms that take their nutrients from their surroundings. Some are good for the body: they keep the digestive system working and stop harmful bacteria moving in, and some are used to make medicines and vaccines. Bacteria can also cause trouble, as with cavities, urinary tract infections, ear infections and strep throat.
• Viruses. Viruses are even smaller than bacteria and are not even a full cell. They are genetic material (DNA or RNA) packaged inside a protein coat. They need a host cell to reproduce, but some remain infectious outside the body on surfaces or in material for a time. Survival varies by virus and conditions, so contaminated sharps and surfaces can still present a risk. Viruses spread easily and can make a person ill. They cause minor illnesses such as colds, common illnesses such as influenza, and very serious diseases such as smallpox and HIV/AIDS.

The difference between acute and chronic health effects

A toxic chemical can affect the body in two ways.

• Acute (short-term) effects appear immediately or soon after exposure. They may be minor, like nose or throat irritation, or serious, like eye damage or fainting from chemical vapours. What they share is that they happen right away.
• Chronic (long-term) effects persist or develop over time, often after repeated exposure or a long delay. They are not necessarily permanent or caused only by a large accumulated dose; effects depend on the agent and exposure.

Some chemicals cause both. Breathing solvent vapours might make you dizzy at once, which is an acute effect, but breathing the same vapours every day for many years might eventually damage the liver, which is a chronic effect.

Summary notes for Element 7 · Cheat sheet · Glossary. A study aid, not published or endorsed by NEBOSH.