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Ohm’s Law

To calculate the the current or voltage in a circuit we use Ohm’s law.

V=IR , Voltage= Current * Resistance

As long as you two of the inputs you can figure out the missing input.

R=V/I or I=V/R

If you increase the resistance there will be less current flowing in a circuit. Also as you increase the voltage in a circuit you will increase the current flowing in the circuit.

Electrical Shock

•When the human body contacts an electrical circuit, the body closes the loop to ground

•Electricity will pass through the human body to the ground

•Severity of the injuries are based on

•The amount of electricity that passes through the body

•The length of time the body is in contact with the circuit

•The path the electricity takes through the body

It is not the volts that kills you it is the amps. The chart below show the body’s response to different amounts of current.

The chart is in milliamps. 1 amp is equal to 1000 milliamps.

•Voltage is the force that moves electricity through circuit also known as electromotive force

•High Force = High Voltage

•Low Force = Low voltage

•> 600 volts is considered high voltage

•Freezing Affect •A “Freezing” effect results when the electric shock causes the muscles to contract.

• The longer the exposure, the greater the risk of death

Burns Caused by Electricity

The most common shock-related, nonfatal injury is a burn. Burns caused by electricity may be of three types: electrical burns, arc burns, and thermal contact burns.

Electrical burns can result when a person touches electrical wiring or equipment that is used or maintained improperly.

Electrical burns are one of the most serious injuries you can receive. Typically, such burns occur on the hands.

They need to be given immediate attention. Additionally, clothing may catch fire and a thermal burn may result from the heat of the fire.

Arc Blasts

Arc-blasts occur when powerful, high-amperage currents arc through the air. Arcing is the luminous electrical discharge that occurs when high voltages exist across a gap between conductors and current travels through the air. This situation is often caused by equipment failure due to abuse or fatigue. Temperatures as high as 35,000°F have been reached in arc-blasts. A common example of arcing is the flash you sometimes see when you turn a light switch on or off. This is not dangerous because of the low voltage.

There are three primary hazards associated with an arc-blast.

(1) Arcing gives off thermal radiation (heat) and intense light, which can cause burns. Several factors affect the degree of injury, including skin color, area of skin exposed, and type of clothing worn. Proper clothing, work distances, and overcurrent protection can reduce the risk of such a burn.

(2) A high-voltage arc can produce a considerable pressure wave blast. A person 2 feet away from a 25,000-amp arc feels a force of about 480 pounds on the front of the body. In addition, such an explosion can cause serious ear damage and memory loss due to concussion. Sometimes the pressure wave throws the victim away from the arc-blast. While this may reduce further exposure to the thermal energy, serious physical injury may result. The pressure wave can propel large objects over great distances. In some cases, the pressure wave has enough force to snap off the heads of steel bolts and knock over walls.

(3) A high-voltage arc can also cause many of the copper and aluminum components in electrical equipment to melt. These droplets of molten metal can be blasted great distances by the pressure wave. Although these droplets harden rapidly, they can still be hot enough to cause serious burns or cause ordinary clothing to catch fire, even if you are 10 feet or more away.

Thermal contact burns

Thermal contact burns are caused when the skin touches hot surfaces of overheated electric conductors, conduits, or other energized equipment. Thermal burns also can be caused when clothing catches on fire, as may occur when an electric arc is produced.

First Aid for Electrical Exposure

Shut off the electrical current if the victim is still in contact with the energized circuit. If this is not possible, use boards, poles, or sticks made of wood or any other nonconducting materials and safely push or pull the person away from the contact. It’s important to act quickly, but remember to protect yourself as well from electrocution or shock. While you do this, have someone else call for help. Do not touch the victim yourself if he or she is still in contact with an electrical circuit! You do not want to be a victim, too!

Once you know that electrical current is no longer flowing through the victim, call out to the victim to see if he or she is conscious (awake). If the victim is conscious, tell the victim not to move. It is possible for a shock victim to be seriously injured but not realize it. Get a first aid kit and put on a pair of protective gloves and quickly examine the victim for signs of major bleeding. If there is a lot of bleeding, place a gauze pad over the wound and apply pressure. If the wound is in an arm or leg and keeps bleeding a lot, gently elevate the injured area while keeping pressure on the wound. Keep the victim warm and talk to him or her until help arrives.

If the victim is unconscious, check for signs of breathing. While you do this, move the victim as little as possible. If the victim is not breathing, someone trained in CPR should begin artificial breathing, then check to see if the victim has a pulse. Quick action is essential! To be effective, CPR must be performed within 4 minutes of the shock.

Electrocution

Electrocution results from electrically-induced ventricular fibrillation, and is most likely when a low-resistance path directly delivers current to the heart.

Ventricular fibrillation (VF) results in sudden faintness and loss of consciousness, cessation of respiration, and death. During VF the heart muscle does not contract but “quivers”; therefore, there is no heartbeat (cardiac arrest) and no blood is pumped out of the heart. Death occurs within minutes if the abnormal heart rhythm is not corrected. Ventricular fibrillation requires electrical countershock within three minutes to change this life-threatening rhythm to normal heartbeats.

Cardiopulmonary resuscitation (CPR) must be instituted immediately to maintain a blood supply to the brain until a defibrillator is available, hopefully within a few minutes.