Element 7: Chemical and biological agents

7.1 Hazardous substances

Chemical agents occur as dusts, fibres, fumes, gases, mists, vapours and liquids. Biological agents include fungi, bacteria and viruses.

Acute effects appear quickly after a short exposure (for example a chemical burn or a headache). Chronic effects develop slowly after repeated or long exposure (for example silicosis or cancer).

Health hazard classes used in the classification of chemicals: acute toxicity; skin corrosion or irritation; serious eye damage or irritation; respiratory or skin sensitisation; germ cell mutagenicity; carcinogenicity; reproductive toxicity; specific target organ toxicity (single and repeated exposure); and aspiration hazard.

Key terms

• Acute effect: A health effect that appears soon after exposure.
• Chronic effect: A health effect that develops over time.

Study tip: Know the difference between acute and chronic, with an example of each.

Practice questions for 7.1

7.2 Assessment of health risks

Substances enter the body by inhalation, ingestion, absorption through the skin and injection (for example needlestick). The body has defences such as the filtering and coughing in the airway, skin as a barrier, and the liver and kidneys that process and remove toxins; these can be overcome by high or repeated exposure.

An assessment considers the substance and its hazards, the form it is in, the routes of entry, how much exposure there is and for how long, who is exposed and the effectiveness of existing controls.

Sources of information are product labels and safety data sheets (SDS). The supplier must provide an SDS, which gives details such as identification, hazards, composition, first aid, firefighting, handling and storage, exposure controls, and disposal.

The information has limits: it may be general, may not cover mixtures or the way the substance is actually used, and may not be up to date.

Monitoring of hazardous substances (for example air sampling) shows exposure levels, but it only gives a snapshot of a particular time and place.

Key terms

• SDS: Safety data sheet: a supplier's document that gives hazard and safety information on a substance.

Study tip: Remember the four routes of entry.

Practice questions for 7.2

7.3 Introduction to occupational exposure limits

An occupational exposure limit is the airborne concentration of a substance to which workers may be exposed without being expected to suffer harm. Its purpose is to set a benchmark for judging whether controls are adequate.

Long-term limits relate to an average over a working day (usually 8 hours, a time-weighted average). Short-term limits relate to shorter periods (often 15 minutes) to control peaks. Time-weighted averages are used because the effect of many substances depends on the total dose over time.

Limits have limitations: they do not apply to all substances; they do not cover skin absorption unless indicated; they assume healthy adults; individuals vary; and they do not allow for combined exposure to several substances. Measurements are compared with recognised standards.

Key terms

• TWA: Time-weighted average: exposure averaged over a reference period.

Study tip: A reading below the limit does not mean the exposure is safe, only that it meets a standard.

Practice questions for 7.3

7.4 Control measures

The first aim is to prevent exposure. If that is not reasonably practicable, control it adequately. Common measures:

• Eliminate or substitute with a less hazardous substance
• Change the process
• Enclose the process
• Local exhaust ventilation
• General ventilation
• Reduce the number of people exposed and the time
• Good housekeeping and cleaning
• Hygiene facilities and procedures
• Storage and labelling
• Training and information
• PPE and respiratory protective equipment (RPE) as a last resort
• Health surveillance

Substances that can cause cancer, asthma, or genetic damage that can be passed from one generation to the next need extra controls, for example preventing exposure rather than only controlling it, tighter access, enclosed systems and health surveillance.

Study tip: PPE and RPE always come last.

Practice questions for 7.4

7.5 Specific agents

Asbestos (excluding removal and disposal): found in older buildings in insulation, boards, roof sheets and pipe lagging. Fibres inhaled cause asbestosis, lung cancer and mesothelioma, often many years later. Controls: find out whether it is present, do not disturb it, manage it in place, and use licensed specialists for work that disturbs it.

Blood-borne viruses (such as hepatitis B, hepatitis C and HIV): spread by blood and some body fluids, for example through sharps injuries. Found in healthcare, waste handling, first aid and emergency work. Controls: avoid sharps, safe disposal, vaccination where available, gloves, and clear procedures after exposure.

Carbon monoxide: a colourless, odourless gas from incomplete combustion, found where fuel burning appliances or engines are poorly ventilated. It reduces the blood's ability to carry oxygen. Controls: maintenance, ventilation, detectors and alarms.

Cement: wet cement is alkaline and can cause burns and dermatitis; dust irritates the eyes and lungs. Controls: avoid skin contact, gloves and boots, washing facilities, and prompt washing.

Legionella: bacteria that can grow in water systems (cooling towers, hot and cold water systems) at temperatures roughly between 20 and 45 degrees C. People who breathe in contaminated droplets may get Legionnaires' disease. Controls: assess the system, keep hot water hot and cold water cold, avoid stagnant water, clean and treat, and keep records.

Leptospira: bacteria spread in the urine of rats and other animals, causing leptospirosis (Weil's disease). Found where there are rats or contaminated water, for example sewers, farms and canals. Controls: rodent control, covering cuts, gloves and boots, washing, and informing workers.

Silica: dust from sand, stone, concrete and bricks. Fine (respirable) dust causes silicosis and increases the risk of lung cancer. Controls: wet cutting, extraction, enclosure and RPE.

Wood dust: from sawing and sanding. It can cause dermatitis, asthma and, with hardwood dust, nasal cancer. Controls: extraction, good housekeeping (vacuum, not brushing) and RPE.

Study tip: For each agent, learn a health effect, a typical place and a control.

Practice questions for 7.5