Experience Sharing – Electrical Safety
Architectural Services Department
p
3 October 2012
3/10/2012
1
Topics covered:
•
•
•
•
•
•
•
•
•
•
IIntroduction
t d ti
Electricity Principles
Electrical Hazards
Electrical Safety Devices
Legislative requirements
DEVB Policy on Electrical Safety
ArchSD Site Safety Requirements on Electrical Safety
Good Site Practice on Electrical Safety
Common Personal Protective Equipment
Lessons learnt
3/10/2012
2
Introduction:
On 3 October 2011, an experience sharing
session has been held with ArchSD contractors
and site supervisory staff to promote and
enhance awareness on electrical safety.
safety The
same powerpoint presentation materials used
in the experience sharing session is posted in
the ArchSD internet for reference.
3/10/2012
3
ELECTRICITY PRINCIPLES
3/10/2012
4
OHM’S LAW
V=IxR
V
R
I
3/10/2012
Based on the above formula,,
during an electric shock of the
human body, the current (I) is
inversely proportional to the
resistance (R), i.e. a reduction
in resistance in the human
body will lead to higher
electrical currents p
passingg
through the body, the more
serious will be the injury.
5
ELECTRICAL HAZARDS
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6
Electric Shock
The electric shock is caused
by a current passing through
the body. The lethality of an
electric shock is dependent
on:
¾ Current (the higher the
current, the more likely it is
lethal);
¾ Duration (the longer the
duration, the more likely it is
lethal);
¾ Voltage (the higher the
g , the more likelyy it is
voltage,
lethal);
¾ Pathway (if current flows
muscle it is
through the heart muscle,
more likely to be lethal)
3/10/2012
Diagram showing how electric shock occurs: The severity of electric shock
depends on the current flowing through the body (I) in Ampere, which is a function
of the electromotive force (E) in volts, and the contact resistance (R) in ohms.
F
Formula:
l I=E÷R
I E R
7
Electric Shock
¾Dry skin (resistance around 10,000Ω)
Current = 220V ÷ 10,000Ω = 0.022A
¾Wet skin (resistance around 500Ω)
Current = 220V ÷ 500 Ω = 0.44A
The effect of current passing through the human body is shown below:
Current (amperes)
Physiological effect
0.001A
Threshold of feelingg an electric shock,, p
pain
0.005A
Maximum current which would be harmless. Sustained
muscular contraction.
0 01 0 02A
0.01‐0.02A
V
Ventricular
i l fibrillation.
fib ill i
0.05A
Can be fatal.
0 1‐0 3A
0.1‐0.3A
Sustained ventricular contraction followed by normal heart
rhythm.
6A
These are the operation levels for a defibrillator. Temporary
respiratory
i t
paralysis
l i and
d possibly
ibl b
burns.
3/10/2012
8
Effect of Electric Shock
Heartbeat Failure
(M i cause off death):
(Main
d h)
¾ When current passes through the heart,
it will disrupt the rhythmic pumping
action
ti off th
the heart
h t and
d eventually
t ll
ceases heart beat.
¾ The heart does not resume without
external assistance.
assistance Unless quickly
treated, death is rapid.
B
Breathing
hi FFailure
il
¾ Current passing through the respiratory
centre in the brain may disturb the
nerve centre
t and
d stop
t respiration
i ti
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9
EFFECT OF ELECTRIC SHOCK
Suffocation:
¾
Current passing through the
upper limbs and across the chest
contracts and holds the muscles
as long as the current flows,
eventually causing death from
suffocation
Muscle Contraction:
¾
Continuous contraction of the
forearm muscles when current is
passing through, thus unable to
get free from the electric source
3/10/2012
10
ELECTRICAL HAZARD
z
Electric burns
During an electric shock,
shock the current
passing through the body may lead to
burns on the skin, muscles or internal
organs As electric shocks and burns are
organs.
closely related, preventative measures
should be considered together.
z
Fires and explosions
High
g temperatures
p
caused byy currents under abnormal
conditions, may result in accidental fires and explosions. The
common causes leading to high temperatures include:
¾Overloading of electricity
¾Insulator breakdowns or short circuits
¾Improper contact of electrical circuit
¾Improper maintenance of electrical appliances or wiring
¾Poor ventilation, etc.
3/10/2012
11
CAUSES OF ELECTRIC SHOCK
Direct Contact
A direct contact refers to a
person coming into contact with
a Live conductor
Indirect Contact
An indirect contact refers to a
person coming into contact with
a conductive part which is not
normally alive, but has become
alive accidentally (due to
insulation failure or some other
causes)
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12
ELECTRICAL SAFETY DEVICES
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13
Electrical Safety Devices
Electrical circuit are mainly protected by the
following safety devices:
z FFuse
¾ It must be installed on “live” wires;
¾ It is a copper wiring with a set current
f i value;
fusion
l
¾ If the current exceeds the set fusion
value, the fuse will blow and cut‐off the
electrical circuit
circuit.
z Circuit breakers (MCB)
¾ Tripping of circuit breakers are based
on the thermal and electromagnetic
principle.
¾ Under short circuit condition, the MCB
will trip instantaneously by
electromagnetic force.
¾ Under overload condition, the MCB will
t i with
trip
ith time
ti
delay
d l by
b thermal
th
l
principle.
z3/10/2012
14
Fuse for 13A plug
Miniature circuit breaker
Electrical Safety Devices
z EEarth
th LLeakage
k
Ci
Circuit
it B
Breaker
k (ELCB) or Residual
R id l currentt
device (RCD)
¾ It monitors the operation of the “neutral” or “live” wires in
the electrical circuit
circuit.
¾ During current leakage, the current flows to electrical
appliance via the “live” wire are not equal to the current
returns through the “neutral”
neutral wire;
¾ Such imbalance current flow detected by RCD or ELCB is
then cut‐off the electrical source;
¾ Rating of the tripping current shall not exceed 30mA.
During the leakage of
electricity the return current
(I out) is less than the
entering current (I in). The
residual
id l currents
t flows
fl
away
after passing through the
human body or the earth. So
the difference of magnetic
field produced and resulted
in an automatic p
power cutoff in tripping device.
3/10/2012
15
ELECTRICAL SAFETY DEVICES
z Earthing Connection
¾ Earthing provides a low resistance way of discharging electricity to
th ground
the
d in
i case off currentt leakage;
l k
¾ The current passes through the “earth” wire and is prevented from
enteringg the human bodyy and causingg injury.
j y
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16
ELECTRICAL SAFETY DEVICES
z Double Insulation
The basic requirement is that no single failure
can result in dangerous voltage becoming
exposed so that it might cause an electric
shock and that this is achieved without relying
on an earthed
th d metal
t l casing.
i This
Thi is
i usually
ll
achieved at least in part by having two layers
of insulating material surrounding live parts or
by using reinforced insulation.
Electrical appliances with double insulation
bear the “回”
回 mark.
z Extra‐low Voltage (ELV)
Electrical tools using extra‐low voltage not
exceeding 50 V a.c. may minimise injury in
case of electric shock.
¾ Voltage (V) ≤ 50V A.C.
3/10/2012
17
Electric drill engraved with a “double insulated”
symbol: “回”
回 by the manufacturer.
manufacturer
CABLE COLOUR CODE
Since 99% of colour blind
people
l are suffering
ff i from
f
red‐green colour
blindness and
combination of them (e.g.
yellow), new cable colour
identification was
enforced for the electrical
installation since 1 July
2009 to
t ffacilitate
ilit t cable(s)
bl ( )
identification for the
people
p
p who are colour
blindness or colour
deficient.
Diagram 1:
For single phase: Brown denotes phase (line) conductor, Blue denotes neutral conductor,
Green-and-Yellow denotes earth conductor.
For 3 phase: Brown denotes line 1 phase conductor, Black denotes line 2 phase conductor,
Grey denotes line 3 phase conductor; Blue denotes neutral conductor; Green-and-Yellow
denotes earth conductor.
Diagram 2:
A example
An
l off 13 Amp
A
power plug
l
connected to new colour code cables
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18
LEGISLATIVE REQUIREMENTS
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19
Legislative requirements:
FACTORIES AND INDUSTRIAL UNDERTAKINGS ORDINANCE
(CAP. 59), Enforced by Labour Department
– Factories
F t i and
d Industrial
I d t i l Undertakings
U d t ki
(El
(Electricity)
t i it )
Regulations,
– Construction Site (Safety) Regulations
Regulations, etc
etc.
ELECTRICITY ORDINANCE (CAP.
(CAP 406)
406),
Enforced by Electrical and Mechanical Services Department
– Electricity (Wiring) Regulations,
Regulations
– Electricity Supply Lines (Protection) Regulation, etc.
3/10/2012
20
Legislative requirements:
FACTORIES AND INDUSTRIAL UNDERTAKINGS
(ELECTRICITY) REGULATIONS
Cover page of the “Reference
Manual for Inspection Reports on
Construction Sites” published by
Labour Department
3/10/2012
21
Legislative requirements:
ELECTRICITY ORDINANCE (CAP.
(CAP 406)
Electricity (Wiring) Regulations 2009
Clause26K ‐ Temporary Supply Installation for Construction and
Demolition Sites or Repair and Testing Purposes
Extract phrase of EMSD’s Code of Practice on Electricity (Wiring) Regulations 2009: Clause 26K – Temporary Supply Installation for Construction and Demolition
Sites or Repair and Testing Purpose – The parts “operating voltage” and “lighting accessible to public”
3/10/2012
22
Legislative requirements:
ELECTRICITY ORDINANCE (CAP.
(CAP 406)
Electricity (Wiring) Regulations 2009
Clause26K ‐ Temporary Supply Installation for Construction and
Demolition Sites or Repair and Testing Purposes (cont’)
Extract phrase of EMSD’s Code of Practice on Electricity (Wiring) Regulations 2009: Clause 26K – Temporary Supply Installation for Construction and Demolition
Sites or Repair and Testing Purpose – The parts “selection and erection of installation” and “protection of circuits”
3/10/2012
23
Legislative requirements:
ELECTRICITY ORDINANCE (CAP.
(CAP 406)
Electricity (Wiring) Regulations 2009
Clause26K ‐ Temporary Supply Installation for Construction and
Demolition Sites or Repair and Testing Purposes (cont’)
Extract phrase of EMSD’s Code of Practice on Electricity
(Wiring) Regulations 2009: Clause 26K – Temporary
Supply Installation for Construction and Demolition Sites or
Repair and Testing Purpose – The parts “protection against
earth leakage” and “precaution against danger”
3/10/2012
24
Legislative requirements:
ELECTRICITY ORDINANCE (CAP.
(CAP 406)
Electricity Supply Lines (Protection) Regulation
Diagram 1, 2, 3 & 4:
Same as the descriptions
p
on the top of the respective
diagrams
3/10/2012
25
Legislative requirements:
ELECTRICITY ORDINANCE (CAP.
(CAP 406)
Electricity Supply Lines (Protection) Regulation (cont’)
Diagram 5, 6, 7 & 8:
Same as the descriptions
on the top of the
respective
ti diagrams
di
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26
DEVB POLICY REQUIREMENTS
ON ELECTRICAL SAFETY
3/10/2012
27
DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
A. Weekly Safety Walk
•
•
•
‡
3/10/2012
Checkingg that the temporary
p
y lighting
g
g and electricallyy powered
p
hand‐held tools and equipment are all rated at 110V CTE (centre
tapped to earth) in compliance with Particular Specification
clause no.
no 14(3)
Checking scaffolding
Checking site tidiness and cleanliness
The Contractor shall prepare and agree with the Architect's Representative
a comprehensive check‐list for use during safety walk and site inspections.
It shall contain a table listing out the deficiencies identified during the walk
/inspection with the proposed rectification measures, the names of the
persons responsible for taking any necessary rectification measures and the
corresponding completion dates.
28
DEVB policy requirements on Electrical Safety:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
A. Weekly Safety Walk (cont’)
‡
The Contractor shall take prompt action to rectify those deficiencies
identified during the walk and shall report the status of actions taken at the
forthcoming SSMC meeting.
B P.S.
B.
P S on Site Safety ‐ Clause 15 Electrical Safety
(1) Employ Registered Electrical Worker (REW) to handle the entire temporary
electrical systems (TES)
(2) Upon completion of TES, REW// REC to complete an individual Work Completion
Certificate (WR1). Each of such Certificates shall include a circuit diagram.
(3) TES, such as lighting fittings, distribution boards, socket outlets, plugs and cable
couplers in outdoor or damp environment shall be of IP 54 or above.
(4) The sheath of all electric portable cables shall be of heavy‐duty type. They shall be
hung overhead as far as possible. PVC cables shall be enclosed in metallic
conduits or trunkings and properly maintained.
3/10/2012
29
DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’)
(5) Develop checklists and agreed by Architect
Architect’ss Representative
for routine inspections. Monthly comprehensive checking
include checking the followings with the REW’s signature: ‐
–
–
–
–
–
TES,
temporary generators,
functional test of earth leakage circuit breakers,
breakers
integrity of cables and connections,
measurement of earthing resistance and those items listed in Checklists Nos.
3 and
d 4 off the
h COP where
h
appropriate
i
(6) Establish regular maintenance programme for permit‐to‐
work system and/or lock‐off system
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30
DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’)
(7) Maintain updated circuit diagrams (affixed inside the cover
of the temporary distribution boards), WR1 (complete with
supporting documents) and records of inspection and
checking of the TES by REW/REC in a dedicated file for
inspection by site supervisory staff upon request.
(8) Keep lock all temporary electrical distribution boards and
accessible only by authorized persons. Legible warning
notices (Danger‐
(Danger Electricity) in both Chinese and English,
English
names and telephone numbers of such authorized persons
shall be p
posted on the temporary
p
y distribution boards.
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31
DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’)
(10) For occupied buildings,
buildings except prior approval
approval, no
connection of fixed electric equipment directly to any existing
permanent distribution boards, only through temporary
distribution boards.
(11) For arc welding machines and electrode holders: ‐
‐ comply with BS 638 : Part 7, IEC 60974 – 1 (or BSEN60974 –
1) and BS EN 60974 – 11 or equivalent standards,
‐ fitted with no‐load voltage reducing device
‐ enclosed type with metal casing connected to earth, cable
terminals
l effectively
ff
l insulated
l d
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32
DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’)
(12) Hand
Hand‐held
held electrical tools and portable equipment (e.g.
(e g
submersible pumps)
‐ examined byy the REW ((visual inspection
p
for ggeneral condition,,
functional checking for continuity, polarity and insulation aspects,
‐ registered and recorded for each after examination,
‐ identification labels (i.e. registration no., type, name of the
owner and date of examination stamped with the Contractor's
company chop)
‐ re‐examine every 3‐month or after repairs
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DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
2) P.S. on Site Safety ‐ Clause 15 Electrical Safety (cont’)
(13) Portable and hand
hand‐held
held tools and temporary site lighting shall
be operated at a voltage of 110V or less supplied from a step‐
down transformer with its output winding centre‐tapped to
earth and comply with BS 3535 : Part 2 : 1990 or equivalent. All
cables shall be terminated within the transformer enclosure of
Cl I and
Class
d IP55 and
d the
th outgoing
t i circuit
i it shall
h ll be
b provided
id d with
ith
short circuit protection. In confined and damp environment, the
voltage of temporary lighting and hand‐held
hand held tools shall not
exceed 25V.
((14)) For heavyy equipment
q p
such as hoists,, tower cranes,, etc.,, use
voltage in excess of 110V equipped with an earth leakage circuit
3/10/2012
34
breaker.
DEVB policy requirements:
Chapter 3 – Contractual Provision of Construction Safety
( Construction Site Safety Manual) Rev. in Feb 2011
C. Safety Plan (14 elements)
• Site Safety Cycle, e.g. Pre
Pre‐work
work activity, HIA, etc.
• Safety Training, e.g. tool‐box talk on electrical safety
((talks on trainingg kits p
published byy HKCA,, etc.))
• Safety Inspection ‐ TES
• Process Control Programme – one of the high
high‐risk
risk
activities : Electrical Equipment and Installations
–
3/10/2012
include safety rules, regulations, safe working procedures, and
in particular method statements and permit‐to‐work systems
incorporating the findings of risk assessments conducted;
y
adopted
p
if workingg near or over water, or
co‐worker system
electrical work at or near exposed live conductors
35
DEVB policy requirements:
Construction Site Safety Handbook (CSSH)
D. Chapter 3 of CSSH
• 3.9
3 9 Electric Arc Welding
• 3.16 Electric Hand Tools
E. Chapter 7 of CSSH
y Protection
• 7.2 Eye
• 7.8 Safety Footwear
• 7.10
7 10 Hand Protection
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36
ARCHSD SITE SAFETY
REQUIREMENTS ON ELECTRICAL
SAFETY
3/10/2012
37
ArchSD Site Safety requirements on Electrical Safety
A. Follow DEVB policy
B. Guidance Notes on Supervising High Risk Activities
on Construction sites: ‐
– Item 16. Electrical works
– Item 19
19. Excavation.
Excavation Special care when near underground
utility services
– Item 20
20. Working near overhead electrical power line
– Item 28. others risk (relating to electrical safety)
high risk site activities for at least next two months
• forecast of high‐risk
and prepare risk assessment;
• discuss in SSEMC meeting;
• routine updating of risk assessment, wherever necessary. 38
3/10/2012
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012
1. Electrical installation
a Were all electrical installations carried out and tested on completion by Registered
a.
Electrical Worker (REW)?
b. Are there checklists developed by REW for carrying out periodic comprehensive
checking on the temporary electrical system (TES)?
c.
Are electrical circuit diagrams and WR1/WR1a of the TES updated and kept by the
Contractor?
d. Are circuit breakers or suitable fuses installed?
e. Are earth leakage circuit breakers installed?
f.
Is the poster of “First‐Aid for Electric Shocks” displayed?
g Have there been any regular repairs and maintenance?
g.
h. Is the tower crane connected to a lightning protection system?
i.
Are the metal hoardings connected to earth by equipotential bonding conductors?
j.
Is the contact information of REW displayed at power distribution boards?
S = Satisfactory; IR = Improvement is required; IIR = Immediate improvement is required; N/A = Not applicable
3/10/2012
39
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 ((cont’))
h. Are there sufficient working space provided for on‐site maintenance of the temporary
electrical power supply, e.g. switchboards, diesel generator set, step‐down transformers,
etc.?
2. Electrical appliances and equipment
a. Do the lighting fittings, distribution boards, sockets outlets, plugs and cable couplers meet
g
and contractual requirements?
q
the legislative
b. Are there any cables lying on the ground?
c.
Is there any damage to cable sheathe?
d Are
d.
A the
h earth
h wires
i correctly
l earthed?
h d?
e. Do emergency stop buttons properly function? (e.g. bench saw, steel bar cutting/bending
machine, etc.)
f.f
Are the
h temporary site
i lighting
li h i operated
d at 110V or less?
l ?
g. Are the electrical workers provided with proper Personal Protective Equipment (PPE) and
are the PPE correctly used when carrying out electrical work, e.g. wiring work, testing/
maintenance/ repairing works, etc.?
h. Is there any excessive plugging of sockets which may lead to overloading of the circuit?
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40
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
3. Portable electric tools
a Is the register of portable electric tools properly maintained?
a.
b. Are the portable electric tools affixed with labels identifying their registration number,
owner’s name and date of examination by competent electrician?
c.
Are the portable electrical tools connected to the earth or are they having double
insulation for protection?
portable electric tools use low voltage?
g ((e.g.
g 110V or less))
d. Do the p
e. Do the plugs meet the legislative requirements?
f.
Is there any damage to cable sheathe?
g. IIs the
th site
it environment
i
t for
f electrical
l t i l workk wett or having
h i the
th risk
i k off getting
tti electric
l ti
shock in the vicinity of the electrical equipment?
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41
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
4. Special process (electric arc welding)
a Is the working place close to where flammable substances are stored?
a.
b. Are the tools and work pieces correctly earthed?
c.
provided with suitable PPE and are the PPE correctlyy used?
Are the welders p
d. Is the ventilation in good condition?
e. Are there water puddles in the working place or is the environment wet?
f.
Are the welding machines fitted with no‐load voltage reducing device for protection
against electric shock at the output side?
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42
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
5. General
a Are waterproof cables and plugs used for outdoors and industrial purpose?
a.
b. Are the ladders made of non‐conductive materials?
c.
Is there permit‐to‐work system or co‐worker system put in place for works that cannot
be done safely by a person working alone? (For example,
example electrical work at or near
exposed live conductors, etc.)
d. Are doors to switch rooms or covers to fuse and miniature circuit breaker (MCB) boards
locked shut and the keys held by a responsible person?
e. Are there any signs of damage or overheating to the cables, plugs, sockets, etc.?
f.
Are emergency procedures planned for electric shock?
g. Are the warning signs displayed before carrying out maintenance work on power supply?
h. Are all places that are liable to fire hazards provided with fire‐fighting equipment, e.g. fire
extinguishers?
i.
Are tool‐box talks or trainings on electrical safety provided for new workers?
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43
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
6. Working under overhead cables or near underground cables
a Has a “Safe system of work” established to prevent any damage to the overhead electricity
a.
lines or underground electricity cables prior to commencement of work on site?
b. Was a competent person (e.g. registered in EMSD) employed to conduct underground
y
of work” to p
protect underground
g
electricityy cables detection and ensure a “Safe system
electricity cables prior to commencement of work on site?
7. Completion of installation, testing and commissioning for operation and
maintenance
a. Has the contractor completed the testing and commissioning works to the satisfaction of
the consultant or ArchSD on the proper function of the low voltage cubicle switchboard
installation? (by demonstrating a duly signed “testing and commissioning certificate on low
voltage
l
cubicle
bi l switchboard
i hb d installation”
i
ll i ” after
f a series
i off tests including
i l di insulation
i l i test,
dielectric test, polarity check for current transformer, secondary injection test, primary
injection test, ductor test, temperature‐rise limit test, functional test of all devices, voltage
test, phase sequence test, etc.)
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44
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
7. Completion of installation, testing and commissioning for operation and
maintenance (con’t)
b. Has the contractor completed the testing and commissioning works to the
satisfaction of the consultant or ArchSD on the proper function of the systems
after installation? (by demonstrating a duly signed “testing and commissioning
certificate on electrical installation
installation” after a series of tests or measurements on
continuity of circuits, continuity of protective conductors, polarity, insulation
resistance, earth electrode resistance, earth fault loop impedance, function of all
devices including overcurrent protective devices, additional checks for
installations in hazardous environment, etc. )
c.
Has the contractor verified through a series of tests and adjustments on the performance of
the permanent installed equipment/systems (e.g. charger and battery set, lightning
protection system, luminaries, power sockets, water pumps, electric motors, fans, heaters,
electromagnetic equipment,
equipment etc.)
etc ) meeting with the specified design intent?
d. Has the contractor captured, recorded and submitted the performance data (e.g. load
distribution, total operating currents, power factor, etc.) of the whole installation for future
operation and maintenance?
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45
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
7. Completion of installation, testing and commissioning for operation and
maintenance (con’t)
e. Has the contractor checked on the integrity and connections of earthing of exposed
conductive parts including the metallic conduits, trunkings and ducting for enclosure of
cable(s)?
f.
Has the contractor checked on the integrity and connections of earthing of exposed
conductive parts including the metallic enclosures of current distribution equipment, such
as switchgear and controlgear assemblies?
g Has the contractor checked on the integrity and connections of equipotential bonding and
g.
supplementary bonding connecting to the main earthing terminals for all extraneous
conductive parts (e.g. main water pipes, gas installation pipes, other service pipes and
ducting, exposed metallic ceiling grids/window/structural framework, etc.) by means of
circuit protective conductors?
3/10/2012
46
ArchSD Site Safety requirements on Electrical Safety
C. Electrical Safetyy Audit Checklist 2012 (cont’)
(
)
8. Documentary check for some electrical equipment/ systems which might have
been energized near project final stage)
a. Has the contractor demonstrated an example or a completed record of Permit‐to‐
work form for enhancement of safely isolation of circuit or proper earthing of
electrical equipment concerned?
b. Where the isolation of circuit is by means of circuit breaker or switch, the circuit
breaker or switch should be locked off where practicable and a warning notice for
repair affixed. The keys for locks used to lock off the circuit breaker or the switch
should be kept under the control of the REW. Has the contractor demonstrated a
record
d off this
thi lock‐off
l k ff system
t
b means off a log
by
l book
b k in
i which
hi h records
d are
properly kept?
c. Has the contractor demonstrated an example or a record of a completed risk
assessment form signed by the competent person (e.g.
(e g REW) detailed with the
associated specific safety precautions in line with Appendix 15 of the COP by
EMSD prior to carrying out live work where it is considered unavoidable as stated
in the conditions of the COP?
d. Has the
h contractor demonstrated an example
l or a record off a completed
l
T&C
records for those energized outgoing sub‐main and final circuits?
3/10/2012
47
ArchSD Site Safety requirements on Electrical Safety
Electrical
Installation work
REW
Power energization ?!
3/10/2012
T&C Inspection
Handover of the
Installation
Safety measures:
• Permit-to-work ?
• Isolation of circuit
with lock-off system
and warning signs ?
• Risk Assessment ?
• T&C Record ?
• Co-worker ?
…….
48
GOOD SITE PRACTICE ON
ELECTRICAL SAFETY
3/10/2012
49
Good Practice on Site Safety – Electrical Safety
110V Temporary Power Supply
3/10/2012
Schematic wiring diagram
50
Good Practice on Site Safety – Electrical Safety
110V Temporary Power Supply
with protective device
3/10/2012
110V Temporary Power Supply with
warning signs
51
Good Practice on Site Safety – Electrical Safety
Temporary Power Supply Board indicated
with name of Competent Person (REW)
3/10/2012
In‐house safety rules –
No unauthorized use of electricity
52
Good Practice on Site Safety – Electrical Safety
Checklist for Temporary Power Supply
signed by Competent Person (REW)
3/10/2012
Work Completion Certificate
(Form WR1 )
53
Good Practice on Site Safety – Electrical Safety
Electric Cables Properly Hung Overhead
3/10/2012
54
Good Practice on Site Safety – Electrical Safety
Temporary Power Supply for
Fixed Installation
3/10/2012
Generator Set
Sitted at Proper Position
55
Good Practice on Site Safety – Electrical Safety
Effective Lightning Protection System
3/10/2012
56
Good Practice on Site Safety – Electrical Safety
Metal ladder with rubber base
3/10/2012
Electrical Safety Promotion
57
Good Practice on Site Safety – Electrical Safety
Portable Hand Tools Properly
Registered and Recorded
1.
2.
3.
4.
3/10/2012
Identification label
marked with registration
number,
b
type of the tool,
name of the owner and
date of examination
58
Other Practices on Site Safety – Electrical Safety
References from BS Site Supervisory Staff on Site Safety and OHS
Wit posters on Electrical Safety for promotion in construction sites: (1) welding machine with no load protection device, (2) 110V transformer
3/10/2012
59
Important Points on Electrical Safety
– Avoid live work. If this cannot be avoided, special safety
provisions should be taken: ‐
• Prior risk assessment
• Proper PPE
• Screen to avoid danger from advertent contact with energized
conductors
• Warning signs and notices for repair, barriers and screens
• Short duration and p
precise of work
• Isolation point should be clearly identified
– Poor prevailing site conditions, such as wet weather, space
constraints, surrounded by earthed structures
– Clear instruction to workers on site
– Co‐worker system as far as practicable
3/10/2012
60
COMMON PERSONAL
PROTECTIVE EQUIPMENT ON
ELECTRICAL SAFETY
3/10/2012
61
Common Personal Protective Equipment
on Electrical Safety
•
•
•
•
•
Safety Helmet
Safety Footwear
Goggles
Face Shield
Leather Grooves
3/10/2012
62
Recommended Safety Measures
TES examined,
regular maintained
and certified by
REW
Planned Site
Supervision
by REW and
Safety
Supervisor
Hand-held
equipment/tool
equ
p e / oo at
a
110V by step-down
transformer with its
output winding
centre-tapped
pp to
earth
Effective earthing to
the TES and hand
tools/ equipment
Co worker
Co-worker
system
3/10/2012
Risk
Assessment
Engagement
of REW
RECOMMENDED
MEASURES FOR
ELECTRICAL
WORK
Proper
PPE
Tool-box talks to
the electricians,,
e.g. working at
height, working
platform, use of
the A-ladder, etc
Identify and
terminate all live
parts from sources
of electricity supply
before work by
REW
Permit-to-work
system, Lock the
switch
rooms/distribution
boards by a
designated key holder.
Display warning signs
to alert any stray
persons
63
Recommended Safety Measures
Welding
machine fitted
with a no-load
voltage
reducing device
Risk
Assessment
Avoid excessive
cables from welding
machine hung on or
twisted round the
steel workpiece to be
welded
RECOMMENDED
MEASURES FOR
ELECTRIC ARC
WELDING
Effective earthing to
the TES and hand
t l / equipment
tools/
i
t
Proper
PPE
3/10/2012
Engagement
of REW
Welding machine
complied with BS
EN 60974-1 and BS
EN 60974-11
Regular examined,
regular maintained
and certified by
REW with record
Tool-box talks to
the
h electricians,
l i i
e.g. working at
height, working
platform, use of
the
h A
A-ladder,
l dd etc
64
LESSONS LEARNT
3/10/2012
65
Lessons learnt – Electrical Safety
Case 1
•
The victim was assigned to carry out re‐wiring
work for office lighting on a public holiday.
•
While he worked at a corner of the office floor
being renovated he fallen down from a wooden
A‐ladder on a level about 1.5 m high above the
floor.
•
His forehead hit heavilyy on the floor and was
later certified dead after arrival at hospital.
•
Apparently, the cause of death was due to
falling from height.
height However,
However the autopsy
report indicated that the primary cause was
electrocution as burnt marks were observed on
the upper limbs of the victim.
victim
66
Lessons learnt – Electrical Safety
Case 1 ‐ Precautionary Measures
• Identifyy all p
possible sources of electricityy supply
pp y and
terminate all live parts prior to commencing work.
• Introduce permit‐to‐work
permit to work system and display warning signs
on switch rooms and distribution boards.
• Provide adequate safety tool‐box
tool box talks to electricians on
working at height.
• Provide suitable and safe working platform for working at
height.
• Avoid overtime work, unplanned work and working alone.
67
Lessons learnt – Electrical Safety
Case 2
•
•
•
•
While a worker attempted to operate an
electric
l t i grinder
i d for
f the
th metal
t l cladding,
l ddi he
h
was electrocuted.
He was certified dead after delivered to
h
hospital.
l
Site investigation revealed that the
earthing wire was not connected in the
plug and the neutral wire within the
grinder was touching its metal casing.
So when the victim touched the metal
casing of the grinder, a current flowed
through his body and caused
electrocution.
Diagram showing how the victim was electrocuted: (1) a multi-plugs
multi plugs was used on site
without earth connection, (2) the neutral wire inside the electric grinder touched the
grinder’s metal casing, (3) the neutral wire of the power cable was disconnected at its
plug.
68
Lessons learnt – Electrical Safety
Case 2 – Precautionary measures
• Hand‐held tools on site should be operated at 110V or less.
• Temporary electrical system and electric tools should be
properly maintained by REW and with records properly kept.
• A safety supervisor shall be assigned to conduct daily check
on temporary electrical systems and electric tools.
• Provide adequate tool‐box talks to site personnel or workers
on electrical safety.
• All electric tools should be protected by effective earthing and
residual current protective device.
69
Lessons learnt – Electrical Safety
Case 3:
An example of Work Safety Alert issued by the Labour
Department for contractors/employers where a list of 5
precautions are suggested to prevent electrical hazards
during electrical repairing work.
work
70
Lessons learnt – Electrical Safety
Case 3 ‐ Precautionary Measures
• Ensure all related live parts of the electrical system are
rendered dead before works
• Plan the work carefully with formulated safety measures and
procedures
• Lock out the isolated power sources with adequate notices
and signs before works
• Ensure workers received adequate
q
and p
proper
p trainingg and
have adequate knowledge and experience
• Exercise adequate management control and supervision to
ensure safety measures to be strictly followed
71
Lessons learnt – Electrical Safety
Case 4:
Another example of Work Safety Alert issued by the Labour Department for contractors/employers where a list of 3 precautions are suggested to prevent electrical hazards
d i electrical
during
l t i l repairing
i i work:
k
(1)
Identify electrically hazardous conditions n the sites;
(2)
Rectify electrically hazardous conditions n the sites;
(3)
Safeguard any person at work on the site against all electrically hazards conditions.
72
Lessons learnt – Electrical Safety
Case 4 ‐ Precautionary Measures
• Ensure all related live parts of the electrical system are
rendered dead before works
• Plan the work carefully with formulated safety measures and
procedures
• Lock out the isolated power sources with adequate notices
and signs before works
• Ensure workers received adequate
q
and p
proper
p trainingg and
have adequate knowledge and experience
• Exercise adequate management control and supervision to
ensure safety measures to be strictly followed
73
Lessons learnt – Electrical Safety
Case 5:
A newspaper cutting from a local newspaper (date 30.9.2012)
30 9 2012) describing the happening of a fatal industrial accident possibly due to electrocution
For Training Purpose
74
Lessons learnt – Electrical Safety
Case 5 ‐Precautionary Measures
• Ensure all related live parts of the electrical system are
rendered dead before works
• Plan the work carefully with formulated safety measures and
procedures
• Lock out the isolated power sources with adequate notices
and signs before works
• Ensure workers received adequate
q
and p
proper
p trainingg and
have adequate knowledge and experience
• Exercise adequate management control and supervision to
ensure safety measures to be strictly followed
75
END
3/10/2012
76