Electrical Safety - Protecting Yourself Against Electrical Injuries. from NIOSH Electrical Safety Student Manual

Transcription

1 Electrical Safety - Protecting Yourself Against Electrical Injuries from NIOSH Electrical Safety Student Manual Oct 9 11:26 AM 1

2 Electricity is Dangerous There is a risk of an electrical injury - 1. Whenever you work with power tools. 2. Whenever you work with electrical circuits. Oct 9 11:28 AM 2

3 Electrical workers are exposed to greater danger because - 1. work may be fact-paced. 2. the job site may be cluttered with tools and materials. 3. the job site may be open to the weather. 4. many jobs require electric power tools. Oct 9 11:31 AM 3

4 4 main types of electrical injuries are - 1. electrical shock 2. electrocution 3. burns 4. falls Oct 9 11:34 AM 4

5 In order to understand how electrical injuries occur, you need to understand the following definitions - 1. Ground - a direct electrical connection to the earth, with an arbitrary voltage = Conductor - a substance that transmits a flow of electrons. 3. Voltage - The difference in electrical potential energy between 2 points in an electric field. 3. Current - the rate of flow of electrical charges. 4. Ampere - unit for measuring current. 5. Milliampere - 1/1000th of an ampere Oct 9 9:25 PM 5

6 Electric Shock In most household wiring, the black and red wires are + or volts. The white wires are at 0 volts because they are connected to ground. Electricity only flows if there is a difference in the electrical potential (voltage) between 2 wires or locations. Oct 9 11:39 AM 6

7 2 Ways you can Receive an Electrical Shock - 1. You touch any live wire (wire with voltage) to an electrical ground. Your body is a conductor (albeit not a great one). If you come in contact with both a live wire and ground, your body will conduct the flow of electricity to ground. Oct 9 11:57 AM 7

8 Oct 9 12:11 PM 8

9 2 Ways you can Receive an Electrical Shock - 2. You touch any live wire to another live wire at a different voltage. During an alternating current cycle one live wire may be at +120 volts while the other may be at -120 volts - a difference of 240V! Oct 9 12:06 PM 9

10 Dangers of Electrical Shock The severity of injury from electrical shock depends on the amount of electrical current and the length of time the current passes through the body. Less than 10 ma - May lose control of muscles of arm and hand. Above 10 ma - Muscles may 'freeze' so that person cannot release tool, wire or other object - results in longer exposure to shocking current. Oct 9 12:19 PM 10

11 At 30 ma -The muscles that control breathing can become frozen and 'respiratory paralysis' can occur. At 75 ma - Ventricular Fibrillation (very weak ineffective heartbeat) can occur. This condition will cause death within a few minutes unless a defibrillator is used. A defibrillator is an electrical device that restores normal heartbeat by applying a brief electrical shock. At 4 amps - Heart paralysis can occur (the heart does not pump at all). Oct 9 12:33 PM 11

12 Oct 9 12:42 PM 12

13 Conditions affecting severity of shock - 1. Voltage - Greater voltages produce greater currents, so there is a greater danger of electrical shock with high voltage. 2. Skin condition - Resistance hinders current. Dry skin may have a resistance of 100,000 ohms or more; wet skin - 1,000 ohms. Wet skin will allow more current to enter body and give a greater shock. 3. Path of current - Current through head can damage nervous system. Current through body (left to right side) can damage heart and lungs and cause electrocution. Oct 9 12:42 PM 13

14 Electrocution - death caused by the passage of electric current through the body. Oct 9 1:03 PM 14

15 Danger from Electrical Burns Burns caused by electricity may be of three types - 1. Electrical contact burns 2. Arc burns 3. Thermal contact burns Oct 9 1:15 PM 15

16 Electrical contact burns result when a person touches electrical wiring or equipment that is used or maintained improperly. Typically electrical contact burns occur at the points where the current enters and exits the body. Oct 9 1:23 PM 16

17 Burn severity is measured in degrees. Symptoms of 1st degree burn - redness, pain and swelling. Affects outer layer of skin. Symptoms of 2nd degree burn - Affects outer layer and underlying layer of skin. Symptoms include redness, pain and blisters. Symptoms of 3rd degree burn - skin white, black or charred, skin feels numb, affects deep tissue, may cause faintness and shock. Oct 9 9:32 PM 17

18 The knee on the left was energized and the knee on the right was grounded. Oct 9 1:28 PM 18

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21 What is Arcing? Arcing occurs when electrons jump between conductors. For arcing to take place there must be a high voltage difference between conductors. Arcing gives off thermal radiation(heat) and intense light, which can cause burns. Oct 9 1:35 PM 21

22 Dangers from Arcing 1. A high-voltage arc can cause a pressure wave blast. A person 2 ft away from a 25,000 amp arc can feel a force of 480 lbs. The pressure blast can cause ear damage and memory loss due to concussion. 2. A high voltage arc can melt copper and aluminum components. The blast can carry the droplets great distances, causing serious burns. Oct 9 1:41 PM 22

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24 Thermal Contact Burns Thermal contact burns are burns caused by heat energy, generally as a result of fire. If clothing ignites as a result of an arc blast it can cause thermal contact burns. Oct 9 1:46 PM 24

25 PPE - Personal Protective Equipment. Important PPE includes - 1. Non-conductive head protection if you are working in an area that presents a hazard to your head 2. Face shields and safety glasses whenever there is a possibility of electrical arcs or explosions. 3. Flame resistant natural fiber clothing covering arms and legs. 4. Electrically rated steel-toed boots. 5. Rubber insulating gloves to provide protection against shock. 6. Leather protector gloves to be worn over rubber insulating gloves. Oct 9 1:57 PM 25

26 NFPA mandates the use of PPE under different circumctances. Oct 9 2:31 PM 26

27 Arc Resistant Clothing should be worn when working on live electrical equipment, when testing to verify the absence of coltage, during load interruption, during visual inspection to ensure all disconnecting devices are open, and during all lockout/tagout procedures. PPE is the last line of defense against injury. Safe working practices is the first! Oct 9 2:24 PM 27

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