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 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.
•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 internal
hemorrhages 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 mA1 mA no sensationno sensation
11--3 mA3 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 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.

• 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 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 work
practices.

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 R
V = 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 witht 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.
A
B
C
D
Outlet or
Power
Strip
Plug
Short
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 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.
Switches
Hot Line In
Neutral Line In
GFCI
Receptacle
Current
Sensor
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 inGFCIs constantly monitor electricity flowing in
a circuit.a circuit.
• If the electricity flowing into the circuit differsIf the electricity flowing into the circuit differs
by even a slight amount from that returning, theby even a slight amount from that returning, the
GFCI will quickly shut off the current flowingGFCI will quickly shut off the current flowing
through that circuit.through that circuit.
• The advantage of using GFCIs is that they canThe advantage of using GFCIs is that they can
detect even small variations in the amount ofdetect even small variations in the amount of
leakage current, even amounts too small toleakage 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 protectGFCIs work quickly, so they can help protect
consumers from severe electric shocks andconsumers 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 mannerAll GFCIs work in the same manner
to protect people against groundto protect people against ground
faults.faults.
• However, unlike the receptacle GFCI,However, unlike the receptacle GFCI,
the circuit breaker type GFCI alsothe circuit breaker type GFCI also
provides overload protection for theprovides overload protection for the
electrical branch circuit.electrical branch circuit.

The GFCI should tripThe GFCI should trip

• Some things GFCI do not protect youSome things GFCI do not protect you
from.from.
• A GFCI does not protect a person whoA GFCI does not protect a person who
comes in contact with two hot wires orcomes 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 fromA GFCI does not protect a person from
feeling and reacting to shockfeeling 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 WorkSafety-Related Work
PracticesPractices
• Protection of Employees
• Passageways and Open Spaces
• Lockout and Tagging of Circuits

Safety-Related MaintenanceSafety-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 ElectricalAgainst 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 be
furnished 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!

11
Stay 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.
DonDon’’t lett let anyoneanyone touch it.touch it.

44
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 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 onAlways inspect extension cords and cords on
tools and appliances before plugging them in.tools and appliances before plugging them in.

55
Stay 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 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

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