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8/4/2019 Outcome1 S5 Electric Shock
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Unit 1Working Effectively and Safely in an
Electrotechnical Environment
Outcome 1Identify the legal responsibilities of both employer
and employee and the importance of Health andSafety in the working environment
2
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Review of Health & Safety legislation
To briefly run through what we have learnt so far;
3
HASWA was introduced to provide a framework within which allother Health & Safety legislation would operate.
All employers have the legal responsibility, to ensure that thework place is safe for employees. Employees are responsible forthe safety of themselves and others.
Personal protective clothing is concerned with the whole body. Itis essential and should always be worn when appropriate.
For a fire to occur there needs to be three things, heat, fueland oxygen. There are 4 classes of fire and each needs adifferent type of extinguisher. All extinguishers are coloured
red. There are five types of warning signs which have colours instead
of words to distinguish their importance, and are now commonacross Europe.
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Outcomes from this session
At the end of this session you should beable to
4
State the basic action to be taken in the event
of an electric shock.State the need for isolation before any work iscarried out on an electrical installation orsystem.
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Electric Shock
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There is no point at which electricity is safe andtherefore should always be treated with respect
A definition of an electric shock is an unpleasant sensationproduced by the nerves response to a passage of electric
current through a part of the body.
To receive an electric shock you must become part of thecircuit.
The severity of a shock depends on many things, age, sex,state of health, moisture content of the surroundings. The
shock usually causes irregular beating of the heart and burnsto the body.
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Table Showing Levels at Which Electric Current Can Be
Perceived and the Possible Damage Caused
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Current inmA
Effect
0.5-2 Threshold of perception
2-10 Painful sensation, increasing with current
10-25 Cramp and inability to let go. Increase in bloodpressure. Breathing difficulties caused by muscularcontractions of the lungs
25-80 Severe muscular contractions sometimes with bonefractures. Increased blood pressure. Loss ofconsciousness from heart and breathing failure
80+ Burns at point of contact. Death from heart failure
From this you can see just how dangerous electricity can be
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Threshold of Perception
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Current is between 0.5mA to 2mA.
This is not very much at all.
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Let go Level
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Current ranges up to approximately 10mA. This level ofcurrent is likely to hurt. The pain increases with level ofcurrent.
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Hold on Level
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The point at which you are likely to find it difficult to let
go of the object ranges from 10mA to 25mA
Your blood pressure will rise and you may experience difficultybreathing.
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Throwing Level
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At current in excess of 25mA you are at risk from being thrownby the electric shock that you are receiving.
Bones maybe broken, blood pressure rises and there maybe loss ofconsciousness
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What to Do in the Case of an
Electric Shock ?
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Do not touch the person.
Shout for help.
Switch off the supply if possible.
If switching off the supply is not possible. Use some insulating
material such as a scarf, piece of wood, newspaper etc to pull theperson away from the contact.
If the heart has stopped breathing send for help before startingresuscitation or heart massage.
Treat burns.
Check for other injuries, treat if possible.
Do not try to give any treatment that you have not been trained to give.You could cause more harm than good.
Get help from experts as soon as possible
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Causes of Electric Shock
There are two ways of receiving an electric shock
BS7671:2008 17th Edition, covers this by giving us two terms that breakthese down, they are;
Basic Protectionand Fault Protection
(these were formerly know as Direct contact & Indirect contact
In the previous 16th edition of the BS7671)
I mention this as you may hear these terms or have been usedTo using them
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Basic Protection
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Is coming in contact with something that you would normally expectto be live
This could be youif you do not check
for hidden live cables
The person makes up the circuit from the source, through the person toearth.
No circuit - No shock
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Fault Protection
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Fault Protection is coming into contact with parts of anelectrical system that only become live under fault conditions
Main bondingconductors
Gas WaterEarth terminal in
Consumer unit
Cold Hot
This type of source is rarely 230V; that is not to say thatit is any less dangerous
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Isolation
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You will have realised that with this amount of danger it
is essential that a good means of isolation is used .
It is equally important that in the process of finding out
whether a circuit is live or not, no mistakes are made.
Safe procedures need to be observed not only when
working with equipment but also when testing.
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Test Equipment
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For testing a potentially live source two pieces of equipmentare required
Approved voltage tester (not a neon screwdriver) Voltage proving unit
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Approved Voltage TesterShould have the following;
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Adequate insulation Have finger barriers to stop hands slipping
Insulated tips so that more than 4mm (preferably 2mm) ofbare metal is showing
Fused leads Flexible and robust enough for use
Sheathed to prevent mechanical damage
Long enough for the purpose
No parts accessible to fingers even if the lead becomesloose
Coloured leads where necessary
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Diagram of an Approved Voltage
Tester
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Metal end tip not to protrudemore than 2mm when in use
Rubber insulatedflexible cable
Finger barrier
Spring loadedinsulated sleeves
Voltageindicator 50 400200100
56075 150 240
VOLTAGE INDICATOR
DC RANGE
AC RANGE
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Proving Unit
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A tester is no good if we are not sure of its
effectiveness, to guarantee effectiveness we need to use a
proving unit.
A proving unit is a d.c. voltage source that checks its own
status and is then a known reference voltage against which
the voltage tester can test itself.
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Safe Isolation Procedure
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You will need to have a lot more knowledge and training before you
start testing, there are a series of processes that you need to gothrough to complete the testing procedure. These have beensimplified into a block diagram
This may seem a long and
complicated process but to cut
corners might mean yours or
someone else's death.
Plan the jobUnplug anyequipment
Securely isolate it
Prove the testinstrument
Prove that theequipment is dead
Post caution andwarning notices
Attach temporaryearth leads if
necessary
Consider the need foradditional precautions
Re-prove thetest instrument
Ensure youunderstand the jobbefore you start it