1-electric shock-ahdab

7/29/2019 1-Electric Shock-Ahdab

1/17Electrical Safety / Lock-out Tag-out

Electric Shock

Professor Ahdab Elmorshedy

How Shock Occurs

The severity of the shock received when aperson becomes a part of an electric circuit isaffected bythree primary factors:

The amount of current flowing through thebody

The path of the current through the bodyThe length of time the body is in the circuit.

Other factors that may affect the severity

Ofshock are the:

Frequency of the current;

Phase of the heart cycle when shockoccursGeneral health of the person.



Shock & the Human Body

The effects of electric shock depend upon thetype of circuit, its voltage, resistance, current,pathway through the body, and duration of thecontact.

Effects can range from a barely perceptible tingleto immediate cardiac arrest.

There are no absolute limits or even knownvalues that show the exact injury from any given

current.

A difference of less than 100 mA exists between acurrent that is barely perceptible andone that can kill.

Muscular contraction caused by stimulation maynot allow the victim to free himself or herself fromthe circuit, and the increased duration of exposureincreases the dangers to the shock victim.

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

The so-called low voltages can be extremelydangerous 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 LOWHAZARD!



A severe shock can cause considerably moredamage 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 beginningin 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

CurrentCurrentCurrentCurrent Impact on PeopleImpact on PeopleImpact on PeopleImpact on People

1 mA1 mA1 mA1 mA no sensationno sensationno sensationno sensation

1111----3 mA3 mA3 mA3 mA sensation, no painsensation, no painsensation, no painsensation, no pain

3333----15 mA15 mA15 mA15 mA pain, most people can get awaypain, most people can get awaypain, most people can get awaypain, most people can get away

15151515----30 mA30 mA30 mA30 mA pain, half of people freezepain, half of people freezepain, half of people freezepain, half of people freeze

30303030----75 mA75 mA75 mA75 mA pain, breathi ng diff icul t, asphyxi at ionpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiation

75757575----200 mA200 mA200 mA200 mA possible ventricu lar f ibrill ationpossible ventricular f ibrillationpossible ventricular f ibrillationpossible ventricular f ibrillation

200200200200----300 mA300 mA300 mA300 mA certain ventricular fibril lationcertain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillation

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

CurrentCurrentCurrentCurrentCurrentCurrentCurrentCurrent Impact on PeopleImpact on PeopleImpact on PeopleImpact on PeopleImpact on PeopleImpact on PeopleImpact on PeopleImpact on People

1 mA1 mA1 mA1 mA1 mA1 mA1 mA1 mA no sensationno sensationno sensationno sensationno sensationno sensationno sensationno sensation

11111111--------3 mA3 mA3 mA3 mA3 mA3 mA3 mA3 mA sensation, no painsensation, no painsensation, no painsensation, no painsensation, no painsensation, no painsensation, no painsensation, no pain

33333333--------15 mA15 mA15 mA15 mA15 mA15 mA15 mA15 mA pain, most people can get awaypain, most people can get awaypain, most people can get awaypain, most people can get awaypain, most people can get awaypain, most people can get awaypain, most people can get awaypain, most people can get away

1515151515151515--------30 mA30 mA30 mA30 mA30 mA30 mA30 mA30 mA pain, half of people freezepain, half of people freezepain, half of people freezepain, half of people freezepain, half of people freezepain, half of people freezepain, half of people freezepain, half of people freeze

3030303030303030--------75 mA75 mA75 mA75 mA75 mA75 mA75 mA75 mA pain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiationpain, breathing difficult, asphyxiation

7575757575757575--------200 mA200 mA200 mA200 mA200 mA200 mA200 mA200 mA possible ventricular fibrillationpossible ventricular fi brillationpossible ventricular fibrillationpossible ventricular fi brillationpossible ventricular fi brillationpossible ventricular fibri llationpossible ventricular fi brillationpossible ventricular fibri llation

200200200200200200200200--------300 mA300 mA300 mA300 mA300 mA300 mA300 mA300 mA certain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillationcertain ventricular fibrillation

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

Burns & 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 electriccurrent flowing through tissues or bone.

Tissue damage is caused by the heatgenerated by the current flow through thebody.

Electrical burns are one of the most seriousinjuries you can receive and should be givenimmediate attention.

Arc or flash burns are the result of high

temp. near the body and are produced by an

electric arc or explosion.

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 Hazards

Electrical accidents appear to be caused by acombination 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 fromthe 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)

Ohms 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 f ibrillation 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 6.0Painful 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 becomea 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

DonDonDonDonDonDonDonDont use equipment witht use equipment witht use equipment witht use equipment witht use equipment witht use equipment witht use equipment witht use equipment with

damaged insulationdamaged insulationdamaged insulationdamaged insulationdamaged insulationdamaged insulationdamaged 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.

AB

CD

Outlet or

Power

Strip

Plug

Normal

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 voltageand 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 dont takeanything 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 electr ical 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 bydetecting potentially hazardous ground faults and quicklydisconnecting power from the circuit.

Any amount of current above the level that may deliver adangerous shock.

Any current over 8 mA is considered potentially dangerousdepending on the path the current takes, the amount of timeexposed to the shock, and the physical condition of the personreceiving the shock.

Therefore, GFCls are required in such places as dwellings,hotels, motels, construction sites, marinas, receptacles nearswimming pools and hot tubs, underwater lighting, fountains,and other areas in which a person may experience a groundfault.

A GFCI compares the amount of current in theungrounded (hot) conductor with the amount ofcurrent in the neutral conductor.

If the current in the neutral conductor becomesless than the current in the hot conductor, a groundfault condition exists.

The amount of current that is missing is returnedto the source by some path other than the intendedpath (fault current).

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

Once activated, the fault condition is cleared andthe GFCI manually resets before power may berestored to the circuit

Typical GFCI OutletReceptacles 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 Ohms law,

V=IR, very low resistances such

as an earth ground (plumbing

etc.) allow for very high levels

of current flow.

GFCI device maybe located at a

circuit breaker instead of an

outlet. This arrangement allows

several outlets to be protected

with a single GFCI device.

GFCI Use



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 ordamp

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

ABCindicated

on label

Electrical Fires

Safety-Related WorkPractices

Protection of Employees

Passageways and Open Spaces

Lockout and Tagging of Circuits

Safety-Related MaintenancePractices

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.



Protection Against ElectricalInjuries

Using low (and safe) voltage

Insulating and/or enclosing live parts.

Preventing conducting parts not normally live frombecoming 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 inwhich it is to be used.

Using equipment as defined in the makers instructions.

Ensuring that electrical equipment is adequatelymaintained.

Preventing Electrical Hazards

These include:

Insulation

Guarding

Grounding

Electrical protective devices

Safe work practices.

Grounding

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 theground.

This additional ground safeguards the electricequipment operator in the event that a malfunctioncauses any metal on the tool to become accidentallyenergized.

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



Care of Cords & Equipment

Power tools and extension cords must be inspectedeach time they are used.

They must be taken out of service immediatelyupon discovery of worn or broken insulation.


Electrical panel boxes must be secured andproblems reported immediately.

Junction boxes, outlets, receptacles, and switches

must be closed and problems reported.


Electrical within five (5) feet of any water sourcemust have GFCI protection. Covers must be inplace at all times.

No flammable chemicals or liquids can be storednear electrical or in electrical service rooms.




Electric panels must be kept clear of anyobstructions at all times.

Storage is not allowed in electrical vault or servicepanel rooms. Find another place for storage ofmaterials, products, etc.


If the power went out, and you needed to get tothe 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 in

place and cordsplace and cords

in good conditionin good condition



22Use GFCIs, They saveUse GFCIs, They save

lives!lives!

Electrical Safety In ActionElectrical Safety In Action

33

NeverNever retouchretouch any object or surfaceany object or surface

from which you have received a surprisefrom which you have received a surprise

tingle or shock. The next time could betingle or shock. The next time could be

fatal.fatal.


DonDont lett let anyoneanyone touch it.touch it.

44


Protect the insulation of cables and cords.Protect the insulation of cables and cords.Protect the insulation of cables and cords.Protect the insulation of cables and cords.Protect the insulation of cables and cords.Protect the insulation of cables and cords.Protect the insulation of cables and cords.Protect the insulation of cables and cords.

Never step on, drive over, pinch or crush cablesNever step on, drive over, pinch or crush cablesNever step on, drive over, pinch or crush cablesNever step on, drive over, pinch or crush cablesNever step on, drive over, pinch or crush cablesNever step on, drive over, pinch or crush cablesNever step on, drive over, pinch or crush cablesNever 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.or extension cords lying on the floor or ground.or extension cords lying on the floor or ground.or extension cords lying on the floor or ground.or extension cords lying on the floor or ground.or extension cords lying on the floor or ground.or extension cords lying on the floor or ground.

Always inspect extension cords and cords onAlways inspect extension cords and cords onAlways inspect extension cords and cords onAlways inspect extension cords and cords onAlways inspect extension cords and cords onAlways inspect extension cords and cords onAlways inspect extension cords and cords onAlways inspect extension cords and cords on

tools and appliances before plugging them in.tools and appliances before plugging them in.tools and appliances before plugging them in.tools and appliances before plugging them in.tools and appliances before plugging them in.tools and appliances before plugging them in.tools and appliances before plugging them in.tools and appliances before plugging them in.


17/17

5Stay awayStay 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 thatNever retouch anything thathas 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...

1-electric shock-ahdab

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