099: Working Live
Facilitator duties for this
session:
Ensure the Company Live work
policy is available for
distribution, ensure it is
understood by all.
Why this is important
Every time you work on energised circuits you risk an arc blast or electric shock.
Many State Regulators and companies have very strict policies on working live
and what safety precautions must be observed. Please ensure you fully
understand these policies.
If you take the necessary precautions, you can eliminate the risks.
Obtain various electrical PPE,
such as flame resistant
clothing, to discuss proper use
during the discussion session.
The potential harm
What this Safety Talk
covers:
Also, it takes very little electricity to electrocute you.
Temperatures and energy releases generated by short-term contact with a circuit
even as low as 240V can be many times greater than what it takes to totally
destroy your body tissues. (skin, muscle etc)!
How to reduce the risks of an
arc blast or electric shock.
The amount of current it takes to light a 75W lamp is past the threshold of what it
takes to cause fibrillation. When you think of fibrillation, think of your heart being
out of control. Worse still, electrocution burns take place from the inside out.
Discussion notes:
Minimising contact time is an important determinant in limiting the severity of
damage. The less time the better.
Company live work policy
NECA OHS Manual
Work Method Statements
Live work procedures
Other factors that determine the severity of damage include voltage, resistance,
frequency, and victim characteristics such as age, physical condition, and size,
plus some environmental factors.
Shock characteristics
At 50 Hz, a shock produces a tingling sensation that ranges from slight to violent.
A DC shock produces a warmth sensation that ranges from warm to burning hot.
When current through your body reaches a certain point, it paralyses your arm
muscles so you can’t let go. This is what people are talking about when they
refer to “let-go current.”
The let-go current threshold decreases as frequency increases. It takes less
current to pass the let-go threshold when you are working on a 400 Hz UPS than
when you are working on a 50Hz system. So the higher the frequency, the
quicker you reach the point where you cannot let go.
Shock current path
The path the current takes through your body can determine whether you survive
or not. That’s why where possible, you should take measurements with one hand
on the probe and one hand in a pocket, rather than with both hands on probes as
this can create a path across the heart.
That’s why we also try to eliminate pathways between feet and hands.
Review and Discussion
Why is it important to know the
principles of working live?
What are characteristics of AC
shock?
What are characteristics of
DC?
What is let-go current?
Regarding hands and feet,
what is the proper way to use
test instruments to take
measurements, and why?
What is your first line of
defence for preventing electric
shock?
How hot can an arc blast get?
Is the pressure wave from an
arc blast powerful? How so?
What are some clothing and
PPE issues, in regard to arc
flash and arc blast?
How can you prevent an arc
fault in the first place?
Your heart is on your left side. Thus, if you must choose a path that includes a
hand and a foot, choose the right hand and foot rather than the left hand and foot.
Preventing electric shock
Working on de-energised circuits is an obvious way to prevent shock, but this
depends on proper lockout / tagout, proper testing for voltage and using safety
earths.
However, non-compliance with policy and safe working practices that require
circuits are de-energised is rampant. The body count from this non-compliance is
high. Too many people take far too many risks. Remember it is your life you
may be gambling with.
Using the appropriate PPE and following the appropriate live work procedures
must be your first line of defence, not your last!
Electric arc blast characteristics
The risk of electric shock hazard is well recognised but the risk of creating an
electric arc blast are often overlooked. Yet the electric arc blast can be the cause
of the most horrific injuries.
The heat from an electric arc can reach temperatures four times as hot as the
surface of the sun. Also there is an instinctive reaction to draw breath if this
happens, causing these super heated gases to burn the wind pipe and airways,
so causing death through your inability to breathe.
Further the pressure wave generated by an arc fault can hurl you away from the
heat source, causing even further injuries. In worst case scenarios, the pressure
wave acts like a giant hammer. The pressure waves are sometimes strong
enough to level concrete walls.
Protection from flash
Always wear the required PPE, such as a flash suit, hood, and full face shield.
Always wear clothing resistant to flash flame wherever exposure to an electric arc
flash is possible. In the several seconds it takes to remove clothing or extinguish
flames, you can be subjected to deep and possibly fatal burns.
Reduce the likelihood of arc faults to begin with. For example, make test
connections one lead at a time to prevent creating an ionised path that completes
a circuit between an energised terminal and earth. Another way is to remove as
many loads from the equipment as possible before working on it.
Finally, whenever working near live electrical parts (especially switchboards and
busbars) remember a tool can slip, fall, or otherwise create an explosion, even
when you are not working live.
Notes:
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__________________________________________________________________________
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© 2005 National Electrical and Communications Association. All rights reserved
099: Working Live
Review and Assessment
Participant Name:_____________________________________________
Please circle the correct answer to the following questions.
Every time you work on energised circuits you are at risk of
an arc blast or electric shock.
True
False
Many State Regulators and companies have very strict policies
on working live and what safety precautions must be observed.
True
False
Temperatures and energy releases generated by short-term
contact with a circuit even as low as 240V can be many times
greater than what it takes to totally destroy your body tissues.
True
False
Electrocution burns take place from the inside out.
True
False
Factors that determine the severity of damage include voltage,
resistance, frequency, and victim characteristics such as age,
physical condition, and size, plus some environmental factors.
True
False
When current through your body reaches a certain point, it
paralyses your arm muscles so you can’t let go.
True
False
Using the appropriate PPE and following the appropriate live
True
work procedures must be your first line of defence, not your last.
False
The heat from an electric arc can reach temperatures forty
times as hot as the surface of the sun.
True
False
Never wear PPE, such as a flash suit, hood, and full face shield.
True
False
Make test connections one lead at a time to prevent creating
an ionised path that completes a circuit between an energised
terminal and earth.
True
False
Participants Signature:__________________________ Date:__________
© 2005 National Electrical and Communications Association. All rights reserved
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099: Working Live
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