Electric Shock-Ahdab

Electric ShockElectric Shock

Professor Ahdab ElmorshedyProfessor Ahdab Elmorshedy

How Shock OccursHow 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

•The path of the current through the body

•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;

•Phase of the heart cycle when shock occurs

•General health of the person.

Shock & the Human BodyShock & 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.

•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.

• A difference of less than 100 mA exists between a current that is barely perceptible andone 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.

• For example, a current of 100 mA for 3 seconds is equivalent to a current of 900 mA applied for0.03 seconds in causing ventricular fibrillation.

•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!

•A severe shock can cause considerably more damage to the body than is visible.

•For example, a person may suffer internalhemorrhages and destruction of tissues, nerves, and muscles.

• 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.

How Electricity Hurts PeopleHow Electricity Hurts People

Current Impact on People

1 mA no sensation

1-3 mA sensation, no pain

3-15 mA pain, most people can get away

15-30 mA pain, half of people freeze

30-75 mA pain, breathing difficult, asphyxiation

75-200 mA possible ventricular fibrillation

200-300 mA certain ventricular fibrillation

300+ mA severe burns, heart stops

CurrentCurrent Impact on PeopleImpact on People

1 mA 1 mA no sensationno sensation

11--3 mA 3 mA sensation, no painsensation, no pain

33--15 mA15 mA pain, most people can get awaypain, most people can get away

1515--30 mA30 mA pain, half of people freezepain, half of people freeze

3030--75 mA75 mA pain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiation

7575--200 mA200 mA possible ventricular fibrillationpossible ventricular fibrillation

200200--300 mA300 mA certain ventricular fibrillationcertain ventricular fibrillation

300+ mA300+ mA severe burns, heart stopssevere burns, heart stops

Burns & Other InjuriesBurns & Other Injuries

The most common shock-related injury is a

burn. Burns suffered in electrical accidents

may be of three types: • Electrical• Arc• Thermal contact

• Electrical burns are the result of the electric current flowing through tissues or bone.

• Tissue damage is caused by the heatgenerated 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.

• Arc or flash burns are the result of high temp. near the body and are produced by an electric arc orexplosion.

• They should also be attended to promptly.• Thermal contact burns are those 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.

• All three types of burns may be produced simultaneously.

Preventing Electrical HazardsPreventing Electrical Hazards• Electrical accidents appear to be caused by a

combination of three possible factors: unsafe equipment and/or installation;

workplaces made unsafe by the environment; and unsafe work practices.

• There are various ways of protecting people from the hazards caused by electricity.

• These include: insulation; guarding; grounding; electrical protective devices; and safe workpractices.

Voltage is almost always a constant so electrical current levels are determined by the resistance to flow. When there is a potential for electrical shock we can protect ourselves by maximizing our resistance to current flow. This is done by wearing insulating shoes and gloves, and by not making direct contact with a source of ground potential such as plumbing or other sources of ground.

V = I RV = electrical potential (volts)

I = electrical current (amps)

R = resistance (ohms)

Ohm’s Law of Electricity

Our skin provides us with a natural barrier or resistance of approximately 1,000 to 100,000 ohms depending on several factors including skin thickness and surface moisture.

Lower levels of AC than DC will produce painful shocks in humans while lower levels of DC than AC can lead to fibrillation of the heart muscle. Women are more sensitive to the effects of both AC and DC than are men.

Effects of Electrical Shock on the Human Body

Direct Current Alternating Men Women Men Women

Perception Threshold 5.2 3.5 1.1 0.7 Painful Shock 0.5% 62 41 9.0 6.0 Painful Shock 99.5% 90 60 23 15 Ventricular Fibrillation 500 500 675 675

All Units are in milliamps

Extension cords are approved for temporary use only. If extended use is required, hard wiring such as a new outlet should be installed. Extension cords are easily frayed, a condition which may expose bare wires. If not properly placed, extension cords may also become a trip hazard.

Extension Cord Hazards

Power cords are doubly insulated and should be replaced if the outer layer of insulation becomes frayed exposing wires.

Common Power Cord Problems

Exposed Wires

Electrical Shock HazardsElectrical Shock Hazards

DonDon’’t use equipment with t use equipment with damaged insulationdamaged insulation

Shorts cause a great increase in the flow of current through the cord producing heat and perhaps initiating a fire.

Overloads occur when more current flows through a cord than it is rated to handle. Power strips can be overloaded if too many high current draw devices are plugged in at one time.

ABCD

Outlet or Power Strip

Plug

Sho

rt

Nor

mal

V = IR As resistance decreases, current increases.

Short circuit

Overloaded circuit

Another common way in which power cords can be overloaded is by plugging one power strip into another. All of the current drawn by any device plugged into any of the strips must flow through a single cord

Overloaded Circuit

Eyewashes should be located away from electrical devices and outlets. Outlets within six feet of a sink or other source of plumbing must be GFCI protected in order to minimize shock hazards. An unprotected outlet (non-GFCI) is illustrated above.

Outlet without GFCI

Water and Electricity

Transformers are potential sources of high voltage and may also contain polychlorinated biphenyls.

Typical Transformer

Working Safely with Electricity

Surge Suppressors and GFCIs

Lock Out/Tag Out

Safety Rules

First Aid

Fire Fighting

Several different outlet wiring color conventions exist, but don’t take anything for granted. It is always best to check rather than to assume that a wire is hot or neutral based upon the wire color. Typically the hot wire is black, the neutral or return wire is white, and the ground wire is green.

Outlet Wire Color Conventions

A GFCI or ground fault circuit interrupter shuts off the flow of current upon sensing a fault condition such as an electrical shock. Switches quickly open in the GFCI device in order to prevent the shock victim from receiving a lethal amount of electricity.

SwitchesHot Line In

Neutral Line In

GFCIReceptacle

CurrentSensor

Function of a Typical GFCI

Load

• A (GFCI) is an electrical device which protects personnel by detecting potentially hazardous ground faults and quickly disconnecting power from the circuit.

• Any current over 8 mA is considered potentially dangerous depending on the path the current takes, the amount of time exposed to the shock, and the physical condition of the person receiving the shock.

• A GFCI compares the amount of current in the ungrounded (hot) conductor with the amount of current in the neutral conductor.

• If the current in the neutral conductor becomes less than the current in the hot conductor, a ground fault condition exists.

• The amount of current that is missing is returned to the source by some path other than the intended path (fault current).

• A fault current as low as 4 mA to 6 mA activates the GFCI and interrupts the circuit.

• Once activated, the fault condition is cleared and the GFCI manually resets before power may be restored to the circuit

How does the GFCI workHow does the GFCI work • GFCIs constantly monitor electricity flowing in GFCIs constantly monitor electricity flowing in

a circuit. a circuit. • If the electricity flowing into the circuit differs If the electricity flowing into the circuit differs

by even a slight amount from that returning, the by even a slight amount from that returning, the GFCI will quickly shut off the current flowing GFCI will quickly shut off the current flowing through that circuit. through that circuit.

• The advantage of using GFCIs is that they can The advantage of using GFCIs is that they can detect even small variations in the amount of detect even small variations in the amount of leakage current, even amounts too small to leakage current, even amounts too small to activate a fuse or circuit breaker. activate a fuse or circuit breaker.

• GFCIs work quickly, so they can help protect GFCIs work quickly, so they can help protect consumers from severe electric shocks and consumers from severe electric shocks and electrocution.electrocution.

•

Do all GFCIs work in the same manner?Do all GFCIs work in the same manner?

• All GFCIs work in the same manner All GFCIs work in the same manner to protect people against ground to protect people against ground faults. faults.

• However, unlike the receptacle GFCI, However, unlike the receptacle GFCI, the circuit breaker type GFCI also the circuit breaker type GFCI also provides overload protection for the provides overload protection for the electrical branch circuit.electrical branch circuit.

The GFCI should tripThe GFCI should trip

• Some things GFCI do not protect you Some things GFCI do not protect you from.from.

• A GFCI does not protect a person who A GFCI does not protect a person who comes in contact with two hot wires or comes in contact with two hot wires or any hot wire and the neutral wire.any hot wire and the neutral wire.

• A GFCI does not protect a person from A GFCI does not protect a person from feeling and reacting to shock feeling and reacting to shock

Typical GFCI Outlet Receptacles containing a GFCI are noted by the test and reset buttons, and should be tested monthly to insure proper operation.

Any outlet within 6 feet of a sink or other source of plumbing should be equipped with a GFCI. Recalling Ohm’s law, V=IR, very low resistances such as an earth ground (plumbing etc.) allow for very high levels of current flow.

GFCI device may be located at a circuit breaker instead of an outlet. This arrangement allows several outlets to be protected with a single GFCI device.

GFCI Use

Ground-fault circuit-interrupterGround-fault circuit-interrupter

• The ground-fault circuit-interrupter (GFCI) receptacle protects against electrical shock caused by a faulty appliance, or a worn cord or plug

• It senses small changes in current flow and can shut off power in as little as 1/40 of a second.


• GFCls are now required in bathrooms, kitchens, garages, crawl spaces, unfinished basements, and outdoor receptacle locations

• Consult your local codes for any requirements regarding the installation of GFCI receptacles.


• The GFCI receptacle may be wired to protect only itself (single location)

• Or it can be wired to protect all receptacles, switches, and light fixtures from the GFCI "forward" to the end of the circuit (multiple locations).

The Cord-Connected Type of GFCI is an attachment plug incorporating the GFCI module. It protects the cord and any equipment attached to the cord.

The attachment plug has a non-standard appearance with test and reset buttons. Like the portable type, it incorporates a no-voltage release device that will disconnect power to the load if any supply conductor is open.

Portable Type GFCIs come in several styles, all designed for easy transport. Some are designed to plug into existing non-GFCI outlets, or connect with a cord and plug arrangement.

The portable type also incorporates a no-voltage release device that will disconnect power to the outlets if any supply conductor is open.

Units approved for outdoor use will be in enclosures suitable for the environment. If exposed to rain, they must be listed as waterproof.

Because GFCIs are so complex, they require testing on a regular basis. Test permanently wired devices monthly, and portable-type GFCIs before each use. All GFCIs have a built-in test circuit, with test and reset buttons, that triggers an artificial ground-fault to verify protection.

To insure the safety of repair personnel, electrical panels and equipment with electrical panels must be locked out and equipment tagged out of service before any repairs are performed. The lock must never be removed from an electrical panel until repairs have been completed, and only then by an individual with the appropriate authority. Repairs must only be performed by trained professionals.

Breaker locked in off position Lock out/Tag out

First Aid for Electrical Shock Victims

The most common symptom of electrical

shock is physical shock. Signs of physical

shock include:

1) Cold, clammy skin

2) Pale face

3) Chilled feeling or patient is physically shaking

4) Nausea or vomiting

5) Shallow breathing.

Approved Treatment for Physical Shock Patients

1) Keep patient lying down

2) Keep airway open

3) Elevate patients’ legs if no bones are broken

4) Keep patient warm if conditions are cool or damp

5) Give fluids if patient is able to swallow

6) Never give alcohol to patient

7) REASSURE the patient

Dry chemical extinguishers (also know as ABC extinguishers) are approved for fighting electrical fires. The label indicates the type of extinguisher that is present. Electrical fires should only be fought if the situation is well in hand. If you feel uncomfortable fighting a fire, pull the alarm and exit the building.

Small Nozzle

Test tag should be current

ABC indicated on label

Electrical Fires

Safety-Related Work Safety-Related Work PracticesPractices

• Protection of Employees

• Passageways and Open Spaces

• Lockout and Tagging of Circuits

Safety-Related Maintenance Safety-Related Maintenance PracticesPractices

• Maintenance of Equipment • Environmental Deterioration of Equipment

no conductors or equipment can be located: • In damp or wet locations. • Where exposed to gases, fumes, vapors, liquids• Where exposed to excessive temperatures.

ProtectionProtection Against Electrical Against Electrical InjuriesInjuries

• Using low (and safe) voltage • Insulating and/or enclosing live parts.• Preventing conducting parts not normally live from

becoming live:• by earthing and automatic disconnection of the supply .• By double insulation . • By separating the supply from earth • By limiting electrical energy .

• Selecting equipment suitable for the environment in which it is to be used.

• Using equipment as defined in the maker’s instructions.• Ensuring that electrical equipment is adequately

maintained.

Preventing Electrical HazardsPreventing Electrical Hazards

These include: • Insulation• Guarding• Grounding• Electrical protective devices• Safe work practices.

GroundingGrounding

• To offer enhanced protection, an additional ground, called the "equipment ground," must befurnished by providing another path from the tool or machine through which the current can flow to the ground.

• This additional ground safeguards the electric equipment operator in the event that a malfunction causes any metal on the tool to become accidentally energized.

• The resulting heavy surge of current will then activate the circuit protection devices and open the circuit.

Care of Cords & EquipmentCare of Cords & Equipment

• Power tools and extension cords must be inspected each time they are used.

• They must be taken out of service immediately upon discovery of worn or broken insulation.


• Electrical panel boxes must be secured and problems reported immediately.

• Junction boxes, outlets, receptacles, and switches must be closed and problems reported.


• Electrical within five (5) feet of any water source must have GFCI protection. Covers must be in place at all times.

• No flammable chemicals or liquids can be stored near electrical or in electrical service rooms.


• Electric panels must be kept clear of any obstructions at all times.

• Storage is not allowed in electrical vault or service panel rooms. Find another place for storage of materials, products, etc.


• If the power went out, and you needed to get to the electrical panel box breakers in this room, what could happen to you?

• Think about it carefully!

11Stay clear of bare exposed wiringwiring

Electrical Safety In ActionElectrical Safety In ActionElectrical Safety In Action

Keep covers inKeep covers inplace and cords place and cords

in good conditionin good condition

22Use GFCIs, They save Use GFCIs, They save lives!lives!

Electrical Safety In ActionElectrical Safety In Action

33Never Never ““retouchretouch”” any object or surface any object or surface from which you have received a surprise from which you have received a surprise tingle or shock. The next time could be tingle or shock. The next time could be fatal.fatal.


DonDon’’t let t let anyoneanyone touch it.touch it.

44Electrical Safety In ActionElectrical Safety In Action

Protect the insulation of cables and cords. Protect the insulation of cables and cords. Never step on, drive over, pinch or crush cables Never step on, drive over, pinch or crush cables or extension cords lying on the floor or ground. or extension cords lying on the floor or ground.

Always inspect extension cords and cords on Always inspect extension cords and cords on tools and appliances before plugging them in.tools and appliances before plugging them in.

55Stay away Stay away

fromfrom


Power LinesPower Lines

Overhead, Overhead, Underground, Underground,

or Downedor Downed

Stay clear of bare wires.Stay clear of bare wires.

Use GFCIs, they save lives!Use GFCIs, they save lives!

Never retouch anything that Never retouch anything that has given you a shock.has given you a shock.

Protect cord insulation.Protect cord insulation.

Stay clear of power lines.Stay clear of power lines.

In Summary...In Summary...

Electric Shock-Ahdab

Engineering

Transcript of Electric Shock-Ahdab