1. General Electrical Safety
Whether you have been with the District for fifteen years or fifteen minutes, or you are ready for retirement it is good to think about safety. After all, your own safety is in your hands or in the hands of your co-worker, and let me tell you, electrical safety is no joke. It is a very serious subject and I am sure you are aware that electricity can be deadly.
The OSHA e-tool electrical safety presentation was used to create this presentation
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2. Training Objectives Describe how electricity works
Describe how shocks occur
Describe how electrical current affects the body
Describe the most common ways individuals are injured using electricity
Provide solutions to avoid being injured while using electricity
Today, I am going to discuss with you certain unpleasant aspects of electricity, and how it can affect you. I am also going to discuss what you can do to protect yourself and others from its dangers.
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3. How Electricity Works Example: A Garden Hose Flow of Water
To Low Pressure
Water Moves from High Pressure
To understand how electricity can affect our bodies we must first understand how electricity does its work.
As the diagram shows above, electricity (like water) uses its current flow to perform its work and as it does so its voltage drops from high to low.
The same thing occurs in an Electrical Wire
Flow of Current
Current Moves from High Voltage
Slide 3 (of 24)
To Low Voltage

4. Electrical Shocks
Electricity travels in closed circuits, normally through a conductor
Shock results when the body becomes part of the electrical circuit
Current enters the body at one point and leaves at another
Note: Ground circuits provide a path for stray current to pass directly to the ground, and greatly reduce the amount of current passing through the body of a person in contact with a tool or machine that has an electrical short. Properly installed, the grounding conductor provides protection from electric shock.
In fact, electricity travels in a closed circuit normally through an insulated conductor as it does its work.
You will receive an electric shock only if you touch an open conductor, or other bare electrical component, and your body completes the electrical circuit by conducting the electricity to ground.
As shown above, current will enter your body at one point and then leave from another point. When this happens you will receive a shock.
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5. How Electrical Current Affects the Body
Cardiac arrest, severe burns and probable death. 10
Ventricular fibrillation.
Extreme pain, respiratory arrest, severe
muscular contractions.
This is called the freezing current or "let-go" range.
(Men)‏
Painful shock, muscular control is lost.
(Women)‏
Slight shock felt; not painful but disturbing.
Average individual can let go.
0.005
Perception level. Just a faint tingle.
0.001
Human Reaction
Current (Amps)‏
In fact if the current level is very low, say one milliamp, only a faint tingle will be felt. At five times this amount, a slight shock will be felt and most people will let go.
Above this level, it is much harder to let go, and extreme pain, respiratory arrest, and severe muscular contractions will occur. Cardiac arrest and death are likely to occur with a current of 10 amps or greater.
It is likely that you will be seriously injured in three different ways if you sustain an electrical shock.
Note: some smaller microwave ovens use 10.0 Amps (10,000 milliamps) and common florescent lights use 1 Amp (1,000 milliamps).
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6. Burns The most common shock-related injury is a burn. Burns
suffered in electrical incidents may be one or more of the
following three types:
Electrical Burns cause tissue damage, and are the result of heat generated by the flow of electric current through the body. Electrical burns are one of the most serious injuries you can receive and need to receive immediate medical attention.
High temperatures near the body produced by an electric arc or explosion cause Arc or Flash Burns (also need prompt medical attention).
Thermal Contact Burns occur when skin comes in contact with overheated electric equipment, or when clothing is ignited in an electrical incident.
Firstly:
The most common shock-related injury you will receive if you sustain a high amperage electrical shock is a nasty burn.
If you receive a burn you must receive immediate medical attention.
You, or your coworker must call dispatch (or 911 if need be) and ask for immediate medical assistance.
Note: the graphic pictures were not included. They can be viewed online at:
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7. Internal Injuries
Our bodies use small electrical currents to transmit signals through the nervous system and contract muscles,
Extra electrical current flowing through the body can cause serious damage.
Medical problems can include internal bleeding, tissue destruction, and nerve or muscle damage.
Internal injuries may not be immediately apparent to the victim or observers; however, left untreated, they can result in death.
Secondly:
Our bodies use tiny electrical to control our muscles. Any extra electrical current flowing through our bodies can cause serious medical problems. These internal injuries may not be visible and if untreated, may result in death.
Again, you must seek medical attention if you suffer an electric shock.
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8. Involuntary Muscle Contraction
Muscles violently contract when stimulated by excessive amounts of electricity.
These involuntary contractions can damage muscles, tendons, and ligaments, and may even cause broken bones.
If the victim is holding an electrocuting object, hand muscles may contract, making it impossible to drop the object.
Note: injury or death may result from a fall due to muscle contractions.
Thirdly and lastly:
Your muscles will violently contract when stimulated by electricity. In fact, if you are left holding a live conductor or piece of electrical apparatus your muscles may contract making it impossible for you to drop the object resulting in serious injury or death.
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9. Water and Conduction
Conductors- Substances with relatively little resistance to the flow of electrical current (e.g., metals).
Water- influences the conductive properties of some materials
Dry wood is a poor conductor
Wood saturated with water becomes a ready conductor
Use extreme caution when working with electricity where there is water in the environment or on the skin.
There are several other additional factors that can alter the effect of an electric shock on you.
First factor, water and electricity do not mix.
Water is a good conductor of electricity just as copper or aluminum conductors are.
This is also true of wood when it becomes saturated with water or your own skin when it becomes wet.
Remember, anything that becomes wet will become a conductor of electricity. Isolate energized electrical sources BEFORE working in wet conditions.
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10. Human Skin & Resistance
Dry Conditions Human Skin is Resistant
Current = Volts/Ohms = 120/100,000 = 1mA (0.001A)‏
Barely perceptible level of current
Wet Conditions Skin’s Resistance drops dramatically
Current = Volts/Ohms = 120/1,000 = 120mA (0.12A)‏
-Sufficient current to cause ventricular fibrillation
A low voltage electrocution becomes much more hazardous in a wet condition
Second factor (as mentioned in the last slide), wet skin will conduct electricity, whereas dry human skin is far more resistant to electricity.
Third factor, a low voltage electrocution becomes far more hazardous in wet conditions.
Last factor, high voltage electricity will quickly breakdown the resistance of the human skin when wet, resulting in a massive flow of current that will likely result in death.
As you have heard, wet conditions can become deadly unless YOU TAKE PROPER PRECAUTIONS. What can you do to protect yourself?
High voltage electrical energy greatly reduces the body's resistance by quickly breaking down human skin. Once the skin is punctured, the lowered resistance results in massive current flow.
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11. Low Voltage = Hazardous
Muscular contraction caused by stimulation does not allow a victim to free himself from a circuit.
The degree of injury increases with the length of time the body is in the circuit.
Thus even relatively low voltages can be extremely dangerous.
LOW VOLTAGE
DOES NOT IMPLY
LOW HAZARD!
An exposure of 100mA for 3 seconds can cause the same amount
of damage as an exposure of 900mA for .03 seconds.
To repeat what the last slide pointed out, low voltages can be hazardous.
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12. Ground-Faults (The Most Common Form of Electrical Shock)‏
A ground-fault occurs when current flowing to the load (drill, saw, etc.) does not return by the prescribed route.
In a simple 120 volt circuit, current travels through the black (ungrounded) wire to the load and returns to the source through the white (grounded) wire. If some or all of the current does not travel back through the white wire then it has gone somewhere else, usually to ground.
A person’s body can act as the path to ground when a fault occurs.
Now that we have talked about injuries that you can sustain from electric shock let’s talk about injuries that you can sustain from ground-faults.
By definition, a ground-fault occurs when the current flowing through the load does not return back by the proper path. In fact, your body can act as a conductor and provide a path to ground thus giving you an electrical shock.
In some of the remaining slides, you will see problems with electrical equipment.
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13. Use GFCI’s for protection against ground-faults
Ground-Fault Incidents
A double insulated drill (no ground pin) was used in a wet location. Water entered the drill housing and current flowed through the water and user, and then back to its source.
An individual with moist hands was electrocuted while winding up a damaged extension cord when their skin contacted exposed wiring in the extension cord.
(This fatality occurred in Utah)‏
What’s wrong with the picture on this slide?
How can we protect ourselves from shock?
This is a serious issue in a lot of industries (especially in construction).
Can we repair this cord? What should we do with it?
Cut the ends off and throw it away. Get a new one. A lot of people get hurt every year from this type of injury.
In the next few slides we will discuss different ways of protecting ourselves from the hazard of electric shocks.
Use GFCI’s for protection against ground-faults
Slide 13 (of 24)

14. Ground-Fault Protection
The ground-fault circuit interrupter (GFCI) works by comparing the amount of current going to and returning from equipment along the circuit conductors. When the amount going differs from the amount returning by approximately 5 milliamperes, the GFCI interrupts the current within as little as 1/40 of a second.
Who recognizes this device. Who can tell me where you might a Ground Fault Circuit Interrupter in your home?
Why is it installed there?
(Wet location – conductivity of water)‏
How does it work?
(Measures difference in current between hot and neutral – anything over 5mA will trip GFCI)‏
How do you test it?
Note: A GFCI will not protect you from line contact hazards (i.e. a person holding two "hot" wires, a hot and a neutral wire in each hand, or contacting an overhead power line). However, it protects against the most common form of electrical shock hazard, the ground-fault. It also protects against fires, overheating, and destruction of wire insulation.
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15. Ground-Fault Protection
Use ground-fault circuit interrupters (GFCIs) on all 120-volt, single-phase, 15- and 20-ampere receptacles that will be used to supply temporary power (i.e. hand tools and other portable equipment).
-Portable GFCIs, like this one, are available for situations where GFCI protection is not otherwise provided-
Who here uses this type of equipment for the job?
What is its purpose?
(Temporary power only)‏
Remember, plug this directly into the power source and NOT another extension cord.
Important - Plug this end directly into the electrical source, not another flexible cord.
Follow manufacturers' recommended testing procedure to insure GFCIs are working correctly.
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16. Grounding - How Do I Avoid Hazards
Ground all power supply systems, electrical circuits, and electrical equipment
Do not remove ground pins/prongs from cord- and plug-connected equipment or extension cords
Use double-insulated tools
Ground all exposed metal parts of equipment
In the next few slides we are going to discuss how YOU can avoid these electrical hazards. But first…
What is wrong with THESE pictures?
(Top picture - Ground prong missing/removed)‏
(Bottom picture - Dangling electrical bar. 3 to 2 prong adaptors = ground connection missing)‏
How do you avoid grounding hazards – anyone?
You must ground ALL power supplies and electrical equipment
You must NOT remove ground pins
Always use double insulated tools
Make sure that all metal parts on the equipment that YOU or your co-worker are using are grounded
You must examine equipment for damage EVERYTIME BEFORE USE
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17. Avoid Contact With Power Lines
Locate power lines in your work area before you begin working.
Prior to digging, call “Before You Dig” at (?) to have USA identify and mark any buried lines.
Keep yourself and all objects at least 10- feet away from all energized power lines.
Have power lines de-energized and grounded prior to beginning your work.
Use non-conductive ladders (fiberglass) and other tools.
If YOU are on a project and are working close to energized power lines take the precautionary measures outlined above:
YOU must locate all power lines prior to YOUR starting work.
Ensure that the planner, YOUR supervisor, or someone else in authority has called “Before you dig” to have the underground utilities identified for YOU – this is for YOUR protection. (I believe that the 800 number given above is correct.)‏
Keep YOURSELF and YOUR EQUIMENT at least 10 FEET AWAY from all energized power lines.
YOU must ensure that power lines have been de- energized and grounded before YOU start work.
Lastly, YOU must always use non-conductive tools and ladders in your work.
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18. Using Equipment in a Manner Not Prescribed By The Manufacturer
If electrical equipment is used in ways for which it is not designed, you can no longer depend on safety features built in by the manufacturer. This may damage property and cause employee injuries or worse.
What’s wrong with this picture?
Only use equipment in the way that it designed for use by the manufacturer. YOUR own personal safety depends on it!
What happens when you make contact with a bare conductor or ungrounded metal part and experience an electric shock?
(Tingling sensation, harder to let go of conductor, extreme pain, respiratory arrest, severe muscular contractions, cardiac arrest and even death)
What is the major effect of a contact with a high current?
(Burns, internal injuries, involuntary muscle contractions)‏
Add water to the equation?
(Potentially death)‏
Note: Junction boxes such as this one must be mounted properly.
Shock, fire, loss of life and property?
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19. Common Examples of Equipment Used in A Manner Not Prescribed
Using multi-receptacle boxes designed to be mounted by fitting them with a power cord and placing them on the floor.
Fabricating extension cords with ROMEX® wire.
Using equipment outdoors that is labeled for use only in dry, indoor locations.
Using circuit breakers or fuses with the wrong rating for over-current protection, e.g. using a 30-amp breaker in a system with 15- or 20- amp receptacles (protection is lost because it will not trip when the system's load has been exceeded).
Using modified cords or tools, e.g., removing face plates, insulation, etc.
Using cords or tools with worn insulation or exposed wires.
This slide shows inappropriate uses of electrical equipment.
YOU MUST NEVER, NEVER…
Use multi-receptacle boxes designed for mounting on the floor
Make extension cords from Romex wire
Use equipment designed for indoor use outdoors
Use circuit breakers or fuses with the wrong rating
Modify cords, tools or equipment
Use cords with bare or exposed wires
YOU MUST never use equipment in a manner that is not prescribed by the manufacturer
REMEMBER - ONLY USE EQUIPMENT IN A MANNER PRESCRIBED BY THE MANUFACTURER
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20. Flexible Cords Not Used Properly
The following cords are improperly wired directly to the electrical circuit, are not protected by a GFCI, and are two-wire cords that are not grounded and not rated for hard- or extra-hard service.
Temporary (flexible wiring) must not be used in place of permanent wiring. Multioutlet surge protection such as this can be used to supply power to equipment that needs surge protection, but not used to provide more outlets due to the lack of permanent wiring.
Please do NOT use cords as shown here.
No GFCI
Ungrounded two wire cords
Cords not suited for hard service
NEVER use temporary wiring as a substitute for permanent wiring
Extension type cords that are not 3-wire type, not designed for hard-usage, or that have been modified, increase your risk of contacting electrical current, and must not be used at CCSD.
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21. Flexible Cord Safe Practices
Only use factory-assembled cord sets.
Use only extension cords that have a ground wire (3- wire type).
Use only extension cords that are marked with a designation code S, ST, SO, and STO for hard service, and SJ, SJO, SJT, and SJTO for junior hard service.
Use only cords, connection devices, and fittings that are equipped with strain relief.
Remove cords from receptacles by pulling on the plugs, not the cords.
Remove from service flexible cords that have been modified or damaged.
I cannot stress this enough. It is YOUR duty to ensure that the cords you use are suitable for service.
It is YOUR responsibility to FOLLOW THESE BEST PRACTICES as outlined on the slide AT ALL TIMES
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22. Remember Visually inspect all electrical equipment before use.
Remove any equipment with frayed cords, missing ground prongs, cracked tool casings, etc. from service.
Apply a warning tag to any defective tool and do not use it until it has been properly repaired.
YOU MUST REMEMBER TO:
Visually inspect all electrical equipment before use
Take out of service any damaged equipment
Tag the defective equipment
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23. OHSA's e-tool can be viewed online at:
OSHA e-Tool
OHSA's e-tool can be viewed online at:
ctrical_incidents/mainpage.html
What should you do before you start working near energized lines?
What happens when you make contact with a bare conductor or ungrounded metal part and experience an electric shock? Anyone?
(Tingling sensation, harder to let go of conductor, extreme pain, respiratory arrest, severe muscular contractions, cardiac arrest and even death)
What is the major effect of a contact with a high current?
(Burns, internal injuries, involuntary muscle contractions)‏
Add water to the equation?
(Potentially death)‏
How can you protect yourself?
Inspect equipment and tools and remove immediately if defective
Use only properly grounded equipment protected by GFCI
Use equipment only for its intended service
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24. End of General Electrical Safety
Document your Training
If you have any further questions
or want to
receive additional training on
Electrical Safety please contact
CCSD Risk Management Department at
(702)
Any questions?
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