Basically, electrical hazards can be categorized into three types. The first and most commonly recognized hazard is electrical shock. The second type of hazard is electrical burns and the third is the effects of blasts which include pressure impact, flying particles from vaporized conductors and first breath
considerations.
Electric shock occurs when the body becomes part of an electrical circuit. Shocks can happen in three ways.
• A person may come in contact with both conductors in a circuit.
• A person may provide a path between an ungrounded conductor and the ground.
• A person may provide a path between the ground and a conducting material that is in contact with an ungrounded conductor.
The terms high voltage and low voltage are relative terms. In transmission-line terminology, "low voltage" is much higher than the 600 volts. At home, you would not think of 600 volts as being low voltage.
Even when applied to 120-volt circuits, the term low voltage is deceiving. To some people low voltage means low hazard. Actually, low voltage does not necessarily mean low hazard, because potential difference is only one factor making up the dangerous effects of electricity. For purposes of this Lesson,you can think of "low voltage" as being a potential difference of 24-600 volts.
The extent of injury accompanying electric shock depends on three factors.
• The amount of current conducted through the body.
• The path of the current through the body.
• The length of time a person is subjected to the current.
The amount of the current depends on the potential difference and the resistance. The effects of low current on the human body range from a temporary mild tingling sensation to death. An electric shock can injure you in either or both of the following.
• A severe shock can stop the heart or the breathing muscles, or both.
• The heating effects of the current can cause severe burns, especially at points where the electricity enters and leaves the body.
Other effects include severe bleeding, breathing difficulty, and ventricular fibrillation. In addition, you may strike something, or have some other accident as a result of your response to the shock. The effects of electric current are listed in below.
The extent of injury accompanying electric shock depends on three factors.
• The amount of current conducted through the body.
• The path of the current through the body.
• The length of time a person is subjected to the current.
The amount of the current depends on the potential difference and the resistance. The effects of low current on the human body range from a temporary mild tingling sensation to death. An electric shock can injure you in either or both of the following.
• A severe shock can stop the heart or the breathing muscles, or both.
• The heating effects of the current can cause severe burns, especially at points where the electricity enters and leaves the body.
Other effects include severe bleeding, breathing difficulty, and ventricular fibrillation. In addition, you may strike something, or have some other accident as a result of your response to the shock.
Current is the killing factor in electrical shock. Voltage is important only in that it determines how much current will flow through a given body resistance. The current necessary to operate a 10 watt light bulb is eight to ten times more current than the amount that would kill a person. A pressure of 120 volts is enough to cause a current to flow which is many times greater than that necessary to kill.
The following values are given for human resistance to electrical current in Figure 1:
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| Figure 1: Resistance Values |
With 120 volts and a skin resistance plus internal resistance totaling 1200 Ohms, we would have 1/10 ampere electric current, that is 100 milli amperes. If skin contact in the circuit is maintained while the current flows through the skin, the skin resistance gradually decreases. During this time, proper first aid
can mean the difference between life and death. Sufficient circulation can sometimes be maintained by heart compression, which should always be supported with mouth-to-mouth resuscitation. This combination of treatments is commonly known as CPR.
