7.2 Assessment of Health Risks

Routes of entry into the body

A chemical may cause local harm on contact, such as an eye or skin burn, or enter the body and affect other organs. Consider four main exposure routes.

• Breathing (inhalation). Breathing in gases, mists or dusts in the air. Once inhaled, some substances attack the nose, throat or lungs, while others pass through the lungs into the body and harm other parts, such as the liver.
• Skin or eye contact. Chemicals on the skin or in the eyes can damage the skin or be absorbed through it into the bloodstream. Skin becomes contaminated:
  • by direct contact, for example touching the substance or dipping the hands in it
  • by splashing
  • by substances landing on the skin, such as airborne dust
  • by contact with contaminated surfaces, including contamination inside protective gloves
• Swallowing (ingestion). This happens when chemicals have spilled or settled onto food, drink, cigarettes, beards or hands. People can carry chemicals from their hands to their mouths by eating or smoking without washing first.
• Skin puncture. Risks from puncture, such as butchery or needle-stick injuries, are rare, but they can bring infections or very harmful substances, such as drugs.

The body's defence mechanisms

Foreign agents, chemical and biological, can enter the body, but the body has defences.

• The surface of the eye is bathed in tears, which contain an enzyme called lysozyme that attacks bacteria and helps protect the eyes from infection.
• Hairs and mucus in the nose trap inhaled particles, and the walls of the respiratory tract are lined with cells that secrete mucus to trap particles and pathogens.
• The cells lining the respiratory tract have cilia, hair-like projections that beat together to sweep mucus and trapped particles up to the pharynx, where they can be swallowed or coughed up.
• Coughing and sneezing are mechanical ways of expelling pathogens and harmful chemicals.
• The digestive tract also offers barriers. Acid in the stomach and enzymes in the intestine destroy pathogens, and cells in the gut secrete a mucus barrier.
• Smooth muscle around the gut pushes its contents along in waves, called peristalsis. Harmful contents can be expelled by diarrhoea, which both flushes the gut with fluid and speeds up peristalsis. Vomiting is a complex reflex that gives another way to expel harmful material.
• The skin protects the internal organs from the outside environment. Its outer layer, the epidermis, is made of hardened dead cells that resist daily wear and tear, is tough and is very hard for pathogens to penetrate. A protective layer of oils and proteins on the skin also helps to prevent injury or penetration by harmful substances.

If pathogens do breach these barriers, one of the first active responses of the innate immune system is inflammation. Its main purpose is to build a physical barrier against the spread of infection. It also removes the initial cause of cell injury, clears dead cells and tissue damaged by the original insult and by the inflammatory process, and starts tissue repair. Inflammation is often a response to infection, but it can have other causes, including burns, frostbite and exposure to toxins. Its signs and symptoms are redness, swelling, warmth, pain and often some loss of function.

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