Hazards of Electricity Electrical Hazards Include Electrical Hazards Include Electrical Shock Electrical Shock Electrical Explosions Electrical Explosions Electrical Burns Electrical Burns These can result in severe injury or death These can result in severe injury or death

Electrical Injuries There are four main types of electrical injuries: Direct: Direct:  Electrocution or death due to electrical shock  Electrical shock  Burns Indirect - Falls Indirect - Falls

Electrical Shock An electrical shock is received when electrical current passes through the body. You will get an electrical shock if a part of your body completes an electrical circuit by… Touching a live wire and an electrical ground, or Touching a live wire and an electrical ground, or Touching a live wire and another wire at a different voltage. Touching a live wire and another wire at a different voltage.

electricity requires a complete path (circuit) to continuously flow Without two contact points on the body for current to enter and exit, respectively, there is no hazard of shock. This is why birds can safely rest on high-voltage power lines without getting shocked: they make contact with the circuit at only one point.

Shock Severity Severity of the shock depends on: Severity of the shock depends on: Path of current through the body Path of current through the body Amount of current flowing through the body (amps) Amount of current flowing through the body (amps) Duration of the shocking current through the body, Duration of the shocking current through the body, LOW VOLTAGE DOES NOT MEAN LOW HAZARD LOW VOLTAGE DOES NOT MEAN LOW HAZARD

Dangers of Electrical Shock Currents above 10 mA* can paralyze or “freeze” muscles. Currents above 10 mA* can paralyze or “freeze” muscles. Currents more than 75 mA can cause a rapid, ineffective heartbeat -- death will occur in a few minutes unless a defibrillator is used Currents more than 75 mA can cause a rapid, ineffective heartbeat -- death will occur in a few minutes unless a defibrillator is used 75 mA is not much current – a small power drill uses 30 times as much 75 mA is not much current – a small power drill uses 30 times as much * mA = milliampere = 1/1,000 of an ampere Defibrillator in use

How Shock Occurs The severity of the shock received when a person becomes a part of an electric circuit is affected by three primary factors: The amount of current flowing through the body (measured in amperes) The amount of current flowing through the body (measured in amperes) The path of the current through the body The path of the current through the body The length of time the body is in the circuit. The length of time the body is in the circuit. Other factors that may affect the severity of shock are the: Frequency of the current; Frequency of the current; Phase of the heart cycle when shock occurs Phase of the heart cycle when shock occurs General health of the person. General health of the person.

Shock & the Human Body The effects of electric shock depend upon the type of circuit, its voltage, resistance, current, pathway through the body, and duration of the contact. The effects of electric shock depend upon the type of circuit, its voltage, resistance, current, pathway through the body, and duration of the contact. Effects can range from a barely perceptible tingle to immediate cardiac arrest. Effects can range from a barely perceptible tingle to immediate cardiac arrest. There are no absolute limits or even known values that show the exact injury from any given current. There are no absolute limits or even known values that show the exact injury from any given current.

Shock & the Human Body A difference of less than 100 milliamperes exists between a current that is barely perceptible and one that can kill. A difference of less than 100 milliamperes exists between a current that is barely perceptible and one that can kill. Muscular contraction caused by stimulation may not allow the victim to free himself or herself from the circuit, and the increased duration of exposure increases the dangers to the shock victim. Muscular contraction caused by stimulation may not allow the victim to free himself or herself from the circuit, and the increased duration of exposure increases the dangers to the shock victim. For example, a current of 100 milliamperes for 3 seconds is equivalent to a current of 900 milliamperes applied for.03 seconds in causing ventricular fibrillation. For example, a current of 100 milliamperes for 3 seconds is equivalent to a current of 900 milliamperes applied for.03 seconds in causing ventricular fibrillation.

Shock & the Human Body The so-called low voltages can be extremely dangerous because, all other factors being equal, the degree of injury is proportional to the length of time the body is in the circuit. The so-called low voltages can be extremely dangerous because, all other factors being equal, the degree of injury is proportional to the length of time the body is in the circuit. LOW VOLTAGE DOES NOT IMPLY LOW HAZARD! LOW VOLTAGE DOES NOT IMPLY LOW HAZARD!

Shock & the Human Body A severe shock can cause considerably more damage to the body than is visible. A severe shock can cause considerably more damage to the body than is visible. For example, a person may suffer internal hemorrhages and destruction of tissues, nerves, and muscles. For example, a person may suffer internal hemorrhages and destruction of tissues, nerves, and muscles. In addition, shock is often only the beginning in a chain of events. In addition, shock is often only the beginning in a chain of events. The final injury may well be from a fall, cuts, burns, or broken bones. The final injury may well be from a fall, cuts, burns, or broken bones.

Shock & the Human Body Current / Reaction: 1 Milliampere / Perception level. Just a faint tingle. 1 Milliampere / Perception level. Just a faint tingle. 5 Milliamperes / Slight shock felt; not painful but disturbing. 5 Milliamperes / Slight shock felt; not painful but disturbing. Average individual can let go. However, strong involuntary reactions to shocks in this range can lead to injuries. Average individual can let go. However, strong involuntary reactions to shocks in this range can lead to injuries Milliamperes (women) / Painful shock, muscular control is lost Milliamperes (women) / Painful shock, muscular control is lost Milliamperes (men) / This is called the freezing current or "let-go" range Milliamperes (men) / This is called the freezing current or "let-go" range Milliamperes / Extreme pain, respiratory arrest, severe muscular contractions.* Individual cannot let go. Death is possible Milliamperes / Extreme pain, respiratory arrest, severe muscular contractions.* Individual cannot let go. Death is possible. 1,000-4,300 Milliamperes Ventricular fibrillation. (The rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely. 1,000-4,300 Milliamperes Ventricular fibrillation. (The rhythmic pumping action of the heart ceases.) Muscular contraction and nerve damage occur. Death is most likely. 10,000-Milliamperes Cardiac arrest, severe burns and probable death. 10,000-Milliamperes Cardiac arrest, severe burns and probable death.

BODILY EFFECT DIRECT CURRENT (DC) 60 Hz AC 10 kHz AC Slight sensation Men =1.0 mA 0.4 mA 7 mA felt at hand(s) Women = 0.6 mA 0.3 mA 5 mA Threshold of Men = 5.2 mA 1.1 mA 12 mA perception Women = 3.5 mA 0.7 mA 8 mA Painful, but Men = 62 mA 9 mA 55 mA voluntary muscle Women = 41 mA 6 mA 37 mA control maintained Painful, unable Men = 76 mA 16 mA 75 mA to let go of wires Women = 51 mA 10.5 mA 50 mA Severe pain, Men = 90 mA 23 mA 94 mA difficulty Women = 60 mA 15 mA 63 mA breathing Possible heart Men = 500 mA 100 mA fibrillation Women = 500 mA 100 mA after 3 seconds Shock & the Human Body

Current that flow through a body depends on the resistance of the human body. Current that flow through a body depends on the resistance of the human body. The skin consist of two layers. The outer one, composed of dead, scaly cells, has a high resistance when dry, it has an electrical resistance of to ohm depending of its thickness. The skin consist of two layers. The outer one, composed of dead, scaly cells, has a high resistance when dry, it has an electrical resistance of to ohm depending of its thickness. Internal body resistant is comparatively low, averaging 300 ohms (with a maximum of 500 ohms) for current flow from head to foot.This lower resistance results from the body fluids present, which make it moist and conductive. Internal body resistant is comparatively low, averaging 300 ohms (with a maximum of 500 ohms) for current flow from head to foot.This lower resistance results from the body fluids present, which make it moist and conductive. Average body resistance may be 500 ohm or less.This is due to a fact that current then pass to the inner skin layer, wich has less resistance Average body resistance may be 500 ohm or less.This is due to a fact that current then pass to the inner skin layer, wich has less resistance

(another reference) Average Body Resistance : 1000 Ω distribution :(another reference) Average Body Resistance : 1000 Ω distribution : 80 Ω 15 Ω 125 Ω 460 Ω 840 Ω 125 Ω 460 Ω 840 Ω

Rubber-soled shoes do indeed provide some electrical insulation to help protect someone from conducting shock current through their feet. However, most common shoe designs are not intended to be electrically "safe," their soles being too thin and not of the right substance. Also, any moisture, dirt, or conductive salts from body sweat on the surface of or permeated through the soles of shoes will compromise what little insulating value the shoe had to begin with. There are shoes specifically made for dangerous electrical work, as well as thick rubber mats made to stand on while working on live circuits, but these special pieces of gear must be in absolutely clean, dry condition in order to be effective. Suffice it to say, normal footwear is not enough to guarantee protection against electric shock from a power system. Research conducted on contact resistance between parts of the human body and points of contact (such as the ground) shows a wide range of figures (see end of chapter for information on the source of this data): Hand or foot contact, insulated with rubber: 20 MΩ typical. Hand or foot contact, insulated with rubber: 20 MΩ typical. Foot contact through leather shoe sole (dry): 100 kΩ to 500 kΩ Foot contact through leather shoe sole (dry): 100 kΩ to 500 kΩ Foot contact through leather shoe sole (wet): 5 kΩ to 20 kΩ Foot contact through leather shoe sole (wet): 5 kΩ to 20 kΩ As you can see, not only is rubber a far better insulating material than leather, but the presence of water in a porous substance such as leather greatly reduces electrical resistance.

Burns Most common shock-related injury Most common shock-related injury Occurs when you touch electrical wiring or equipment that is improperly used or maintained Occurs when you touch electrical wiring or equipment that is improperly used or maintained Typically occurs on hands Typically occurs on hands Very serious injury that needs immediate attention Very serious injury that needs immediate attention

Burns & Other Injuries The most common shock-related injury is a burn. Burns suffered in electrical accidents may be of three types: Electrical Electrical Arc Arc Thermal contact Thermal contact

Burns & Other Injuries Electrical burns are the result of the electric current flowing through tissues or bone. Electrical burns are the result of the electric current flowing through tissues or bone. Tissue damage is caused by the heat generated by the current flow through the body. Tissue damage is caused by the heat generated by the current flow through the body. Electrical burns are one of the most serious injuries you can receive and should be given immediate attention. Electrical burns are one of the most serious injuries you can receive and should be given immediate attention.

Burns & Other Injuries Arc or flash burns, on the other hand, are the result of high temperatures near the body and are produced by an electric arc or explosion. Arc or flash burns, on the other hand, are the result of high temperatures near the body and are produced by an electric arc or explosion. They should also be attended to promptly. They should also be attended to promptly.

Burns & Other Injuries Finally, thermal contact burns are those normally experienced when the skin comes in contact with hot surfaces of overheated electric conductors, conduits, or other energized equipment. Finally, thermal contact burns are those normally experienced when the skin comes in contact with hot surfaces of overheated electric conductors, conduits, or other energized equipment. Additionally, clothing may be ignited in an electrical accident and a thermal burn will result. Additionally, clothing may be ignited in an electrical accident and a thermal burn will result. All three types of burns may be produced simultaneously. All three types of burns may be produced simultaneously.

Burns & Other Injuries In addition to shock and burn hazards, electricity poses other dangers. In addition to shock and burn hazards, electricity poses other dangers. For example, when a short circuit occurs, hazards are created from the resulting arcs. For example, when a short circuit occurs, hazards are created from the resulting arcs. If high current is involved, these arcs can cause injury or start a fire. If high current is involved, these arcs can cause injury or start a fire. Extremely high-energy arcs can damage equipment, causing fragmented metal to fly in all directions. Extremely high-energy arcs can damage equipment, causing fragmented metal to fly in all directions. Even low-energy arcs can cause violent explosions in atmospheres that contain flammable gases, vapors, or combustible dusts. Even low-energy arcs can cause violent explosions in atmospheres that contain flammable gases, vapors, or combustible dusts.

Falls Electric shock can also cause indirect injuries Electric shock can also cause indirect injuries Workers in elevated locations who experience a shock may fall, resulting in serious injury or death Workers in elevated locations who experience a shock may fall, resulting in serious injury or death