Lesson 1

The first lesson deals with electrical safety…….this involves more than just getting shocked……but that’s what gets your immediate attention. In general, electricians have good safety records because the penalty of not following procedure or general safety rules is immediate. ….you get shocked. This can range from a mild buzz to the extreme of death. Electricity is extremely unforgiving….it’s not to be feared, but respected.

In most cases, an electrician's primary safety concern is with electrical shock. This can range from a "Buzz" that just makes you mad to severe burns to neurological problems to death. The severity of injury depends on voltage, the amount of current / amperage, the type of power (DC vs. AC), the body's resistance to the current, the current's path through the body, and how long the body remains in contact with the current. The interplay of these factors can produce effects ranging from barely noticeable tingling (Buzz) to instant death; every part of the body is vulnerable. Although the severity of injury is determined primarily by the voltage, low voltage can be just as dangerous as high voltage under the right circumstances. People have been killed by shocks of just 42 volts.

One instructive example of the nature of voltage is the fact that a bird can sit on a high voltage wire without harm, since both of its feet are at the same voltage. You can also see that the bird is not "grounded" -- you will not be shocked by touching a high voltage if there is no path for the current to reach the Earth or a different voltage point. Typically if you touch a 120 volt circuit with one hand, you can escape serious shock if you have insulating shoes which prevent a low-resistance path to ground. This fact has led to the common "hand-in-the-pocket" practice for engineers and electrical workers. If you keep one hand in your pocket when touching a circuit which might provide a shock, you are less likely to have the kind of path to ground which will result in a serious shock.

Strange as it may seem, most fatal electrical shocks happen to people who should know better. Here are some "electro-medical" facts that should make you think twice before taking chances…….

It's not the voltage but the current that kills. People have been killed by 100 volts AC in the home and with as little as 42 volts DC. The real measure of a shock's intensity lies in the amount of current (in milliamps) forced through the body. Any electrical device used on a house wiring circuit can, under certain conditions, transmit a fatal amount of current.

Currents between 100 and 200 milliamp (0.1 amp and 0.2 amp) are fatal. Anything in the neighborhood of 10 milliamp (0.01 amp) is capable of producing painful to severe shock.

As the current rises, the shock becomes more severe. Below 20 milliamp, breathing becomes labored; it ceases completely even at values below 75 milliamp. As the current approaches 100 milliamp ventricular fibrillation occurs. This is an uncoordinated twitching of the walls of the heart.

Electrical shock occurs when a person comes in contact with two conductors of a circuit or when the body becomes part of the electrical circuit. In either case, a severe shock can cause the heart and lungs to stop functioning. Also, severe burns may occur where current enters and exits the body.

How electric shocks affect the skin is determined by the skin's resistance, which in turn is dependent upon the wetness, thickness, and cleanliness of the skin. Thin or wet skin is much less resistant than thick or dry skin. When skin resistance is low, the current may cause little or no skin damage but severely burn internal organs and tissues…..or high skin resistance can produce severe skin burns but prevent the current from entering the body.

The nervous system (the brain, spinal cord, and nerves) is particularly vulnerable to injury. In fact, neurological problems are the most common kind of nonlethal injury suffered by electric shock victims. Some neurological damage is minor and clears up on its own or with medical treatment, but some is severe and permanent. Neurological problems may be apparent immediately after the accident, or gradually develop over a period of up to three years.

Damage to the respiratory and cardiovascular systems is the most severe at the moment of injury. Electric shocks can paralyze the respiratory system or disrupt heart action, causing instant death. Also at risk are the smaller veins and arteries, which dissipate heat less easily than the larger blood vessels and can develop blood clots. Damage to the smaller vessels is probably one reason why amputation is often required following high-voltage injuries.

Many other sorts of injuries are possible after an electric shock, including cataracts, kidney failure, and substantial destruction of muscle tissue. An electric arc may set clothing or nearby flammable substances on fire. Strong shocks are often accompanied by violent muscle spasms that can break and dislocate bones. These spasms can also freeze the victim in place and prevent him or her from breaking away from the source of the current.

Don't forget to take the quiz!

Discussion One: Introduction

Tell us:

Why you took the course;
what you hope to learn;
where you live (city and state are fine),
and anything else you feel comfortable sharing that is appropriate for the class to hear.