Electricity

11.1 Hazards and Risks

Electric shock and its effects on the body

An electric shock happens when an electric current passes through the body. It can burn tissue inside and outside the body and cause organ damage. The symptoms depend on how severe the shock is. Possible symptoms include:

• loss of consciousness
• muscle spasms
• numbness or tingling
• breathing problems
• headache
• problems with vision or hearing
• burns
• seizures
• an irregular heartbeat

What affects the severity of an electric shock

These are the main factors that decide how severe a shock is once a person becomes part of an electrical circuit.

• The voltage. The higher the voltage, the greater the hazard.
• The frequency of alternating current. Frequency affects the severity of the effect. The 50 to 60 Hz of ordinary mains supplies is particularly dangerous to the heart and muscles.
• How long the contact lasts. The longer the current flows through the body, the greater the risk of severe injury. The shock can also lengthen the exposure if the victim cannot let go of the conductor because they have lost voluntary muscle control.
• Moisture. The resistance of the body differs from person to person, and for the same person it depends on the condition of the body: wet, damp or dry.
• The path the current takes through the body. If the path does not run through the chest and heart, survival is more likely. If it does run through the chest or heart, the shock is very dangerous.
• The type of current, AC or DC. Both can cause fatal injury, burns and involuntary movement. Mains-frequency AC can prevent release through muscle contraction. Do not assume DC throws a person clear or that either type is safe because of a supposed typical reaction.
• The amount of current flowing through the body. The more current, the more severe the effect.
• The physical condition of the person, including age and medical fitness.
• Contact pressure. The firmer the body part presses on the live part, the lower the contact resistance and the more dangerous the shock.
• The area of contact. The greater the area of the body in contact, the greater the effect.

Electrical burns

An electrical burn can happen by direct contact, or indirectly through an arc, flash or flame. When an electric current passes through the human body, it heats the tissue along the length of the current path. This can cause deep burns that often need major surgery and are permanently disabling. Burns are more common at higher voltages, but they can occur from domestic supplies if the current flows for more than a few fractions of a second.

Some burns are easy to recognise because they look like burns from contact with heat. Others seem harmless but are not: tiny charred craters indicate much more serious internal burns.

Electrical burns often affect internal organs. They are caused by the heat generated by the body's resistance to the current passing through it, so internal damage may be much more serious than the external injuries suggest.

Internal burns often have serious consequences: scarring, amputation, loss of function, loss of sensation and even death. If a lot of tissue is destroyed, for example, the large amount of waste it generates can cause serious kidney or blood circulation disorders.

Shock is not the only hazard. Electricity can jump across an air gap, especially at high voltages. Where arcing occurs, perhaps from an accidental short circuit, the heat can be intense, and even if it lasts only a very short time it can cause deep-seated, slow-healing burns.

Overloaded, faulty, wrongly maintained or short-circuited electrical equipment can get very hot, and some equipment gets hot in normal operation. Even low-voltage batteries, such as those in motor vehicles, can get hot and may explode if shorted out.

People can receive thermal burns if they get too near hot surfaces or are near an electrical explosion. Other injuries can result if the person pulls away quickly from a hot surface while working at height, or then accidentally touches nearby machinery.

A single low-voltage torch battery can make a spark powerful enough to cause a fire or explosion in an explosive atmosphere, such as in a paint spray booth, near fuel tanks, in sumps, or in many places where aerosols, vapours, mists, gases or dusts are present.

Summary notes for Element 11 · Cheat sheet · Glossary. A study aid, not published or endorsed by NEBOSH.