In the workplace, workers encounter several types of hazards; such as chemical hazards (liquids, solids, dusts, vapours and gases), physical hazards (noise, vibration, unsafe machinery, inadequate lighting, radiation, extreme temperatures), biological hazards (bacteria, viruses, parasites or infectious waste) and psychological hazards (stress and strain). Since the body's own defence systems cannot always win the war against these hazards, it is important to learn what types of hazards exist in the workplace and what steps can be taken to prevent exposure to them. Knowledge of hazards helps workers work with their union and employer to eliminate them.