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January 2020
Ver.1.5
Basic
Electrical SafetyFaculty of Science & Health
Safe-Lab ModuleAlan Hughes
January 2020 Ver.1.5 2
Why this Module!Encouraging Electrical Safety
In an Educational & Active Research Environment
Specifically Avoid Injury, Death – You & Others Avoid Equipment Damage & Loss of Research Awareness of your moral & legal responsibility
to yourself, colleagues & to all others
By increasing your awareness of potential dangers & how to avoid
creating them awareness of your skills & your limitations awareness of sources of advice & information
January 2020 Ver.1.5 3
Overview of today!
….. Increased Safety by awareness of ….
Your Permissions your Limitations
Information sources
Education Overview of Electrical Basics
Electrical Equipment
Specific laboratory examples
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January 2020 Ver.1.5 4
January 2020 Ver.1.5 5
Information sources Your Supervisor, Manager, Head of Department
Department Safety Statements
Department Safety Committees & Safety Officer
DCU safety - WEB
Edinburgh University H&S - WEB
University London H&S – WEB
These PP slides Faculty Safety web site
‘Safety in Schools’ Department of education document
January 2020 Ver.1.5 6
Electricity & Safety
[ I ] Basic Electrical Theory [ Ladybird version, no maths ]
Voltage & Current
Electricity in the body & effects on the body
Electricity & associated hazards
[ II ] Electrical Equipment Electrocution
General Electrical Guidelines & Precautions
Safety features: fuses, ELCBs, cables, connections, equipment design
[ III ] Specific Hazards & Personal Safety A few Do’s , Don’ts & Watch-out-for’s
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[ I ]
ElectricityBasic Electrical Theory
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Basic Electrical Theory
Voltage [a driving force] causes Current [e - ] to flow AC / DC - - Negligible difference wrt Safety
Single Phase / Three Phase. - if 3 phase get a professional
SI units
Volts , Amps / milli-Amps and for power Watts, energy kWHrs
Circuit necessary for current to flow
a start point - a route - an end point
Cannot keep pouring water into a bottle
Electricity is the flow of electrons around a circuit
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Voltage, Current and Resistance
Voltage increases => Current increases
Resistance decreases => Current increases
Voltage = Current / Resistance - Ohms Law
Water analogy
Water flow : electrical current flow
Water pressure : voltage
Conductor : pipe
Pump : battery
High resistance : Narrow, long pipe
Low resistance : Wide short pipe
Switch : Slam shut, on/off valve
January 2020 Ver.1.5 11
Voltages AC == DC
Low Voltage 0 => 50V Batteries: AA, AAA, PP3
Car, trucks, busses 12 / 24 / 48
Phone or laptop charger, Christmas tree LEDs, Garden lights
High Voltage [high tension, HT ] 100 => 500V IE/EU Mains
Electrophoresis, DART power lines, Capacitors SM-PSUs
Very High Voltage [ EHT ] 1kV + ESB pylons, oldTV tubes, photocopiers, X-Ray machines, Mass
Spectrometers
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The complete circuit
A complete Circuit or loop is
necessary for current to flow
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A complete circuit
- Complete Circuit or loop
is necessary for current to flow
- Current takes the path of least resistance
.
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Summary - basic Electrical Theory
Voltage causes
a Current to flow
Big voltage => Big current
Water analogy
A Complete Circuit
is necessary for
current to flow Bird on H.T. wires
Insulation to prevent a circuit
Power Voltage X Current
January 2020 Ver.1.5 15
Electricity
&
Human Body
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‘Normal’ Electricity in the body
Muscles Muscles control all body movements
They are activated using small electrical currents
Including & very importantly, those that keep us
alive: our Breathing and our Heart beat
The brain controls voluntary muscles using
small current pulses along nerves
Some local autonomous circuits for involuntary
muscles e.g. Heart
Electrical synapse
October 2016 Ver. 1.4 17
Biological
mechanical and
electrically conductive link
between two
neighbouring neurons
January 2020 Ver.1.5 18
‘External’ Electricity in the body
External Current through the body overrides
all biological control :
Loss of muscle control, respiratory, paralysis
including ‘Inability to let go’
Spasms & Involuntary movement
Fibrillation of the Heart [no co-ordinated heart beat]
Burns - external & internal
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Just a little current can kill
It is the
Currentdriven through
the body
by Voltagethat creates
danger
• Keep voltages low
• Do not make your
body part of a circuit
Just a Little Current Can Kill • 1 mA A slight tingle is felt.
• 5 mA light shock is felt, not painful but disturbing.
Average individual can let go
• 6-25 mA painful shock, muscular control is lost
involuntary reactions can lead to injuries.
• 9 – 30 mA Called the freezing current or “let-go” range.
many humans cannot get their muscles to work, and
they can’t open their hand to let go of a live conductor.
• 50-150 mA There will be extreme pain, respiratory arrest,
severe muscular contractions.
Individual cannot let go, death is possible.
• 1000-4300 mA There is ventricular fibrillation. Muscular contraction
and nerve damage occur. Death is most likely.
• 10,000+ mA Cardiac arrest, severe burns and probable death.
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Electricity
&
Associated Hazards
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Electricity - associated hazards Life support muscles
Diaphragm and breathing Heart Fibrillation Random, uncoordinated heart contractions
Defibrillators High voltages (3000 V at 20 A) fraction of a second
Burns - death of tissue Internal [organs] External [skin] Usually at Entry & Exit areas
Indirect - Injury Falls from ladder Thrown back. Fall to ground, onto sharp edge Drop objects, injure an innocent bystander Thermal burns – Very hot equipment surface, explosion
Indirect - Wires & cables Indirectly probably the most common “electrical” injury
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Electricity - associated Hazards
Wires & cablesTrailing leads
Trips, falls & injury
Equipment damage
Re-route, tidy up, cover over
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Exit & entry Burns
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END
[ I ] Electrical Theory Section
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Electrical Appliances
Safety guiding principles
keep currents and voltages to a minimum
inside apparatus and away from our bodies
when a fault is detected, Trip out
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Electrical Appliances
Minimise voltages [ and thus minimise current ]
Inherently safe - Low voltage / low current
Keep Voltages away from our bodies Enclosures
Insulation
Connections safe & secure
Trip out when fault detected Safety features – Fuses, ELCBs, Switches
January 2020 Ver.1.5 30
Electrical cables & plugs
Mains cable Brown Live - power
Blue Neutral
Green/yellow Earth
January 2020 Ver.1.5 31
Electrical plugs, cables & fuses
Mains cable
Brown Live power
Blue Neutral
Green/yellow Earth
L
N
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Electrical fuses & ELCBs
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Live, Neutral, Earth & FusesL
N
L
N
E
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Live, Neutral, Earth & Fuses
L
N
January 2020 Ver.1.5 35
ELCB Electric Leakage Circuit Breaker
RCD Residual Current Device
RCCB Residual Current Circuit Breaker
MCB Magnetic Circuit Breakers
RCBO Residual Current Breaker
with Over-current protection
current difference of > 30 mA
for a duration of ~ 30 ms
L
N
E
L
N
January 2020 Ver.1.5 36
Fuse Vs ELCB
A Fuse breaks the circuit When too much current attempts to flow through an appliance Usually the excess current is in Amps [Very dangerous] and it
happens in less than a second Must be replaced
An ELCB breaks the circuit
When there is a difference between the current flowing in the Liveand in the Neutral wires
Usually operates when the difference is ~ 30mA [borderline safe]
Operates very fast, in a small fraction of a second
Is resettable
January 2020 Ver.1.5 37
Electrical extension boards
Emergency Stop Switch
• Avoid where possible
• Do not daisy-chain
• Check total current
• Know where they are
• Check occasionally
January 2020 Ver.1.5 38
Electricity summary The Live and Neutral wires carry current to equipment
The Earth wire is there to protect you. The Earth wire can act like a back-up Neutral wire,
Many appliances have metal cases e.g. kettles, toasters, dishwashers, washing machines etc.
The Fuse is very thin piece of wire. The wire has a quite low melting point. As current flows through the wire it heats up.
If too large a current flows it melts, thus breaking the circuit
Use appropriate fuse size/rating
ELCBs, RCDs Important Safety Devices Leakage-to-earth sensors with trip out
January 2020 Ver.1.5 39
Electricity Safety Summary
High Voltage causes High current Keep voltages low
Electricity require a circuit Ensure your body does nor complete the circuit
Electric current takes the easiest path Ensure that all equipment has an earth connection
When a fault occurs All equipment should have fuses and ELCBs
Wires & cables
Probably the single most common electrical hazard
January 2020 Ver.1.5 40
END
[ II ]
Theory Section
Electrical Appliances
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Equipment & Laboratory Guidelines
Use low & safe voltages: Mains voltages are dangerous 230 VAC
Select equipment appropriate for environment & use
Avoid electricity where its use could be dangerous.
Use equipment as per manufacturer’s instruction & design
Ensure adequate maintenance, damaged case, frayed leads
Insulate and enclose live parts
Ground casings to earth
Prevent conducting parts from becoming live. Earth, double
insulation, separate supply from earth, limit electric power
Rubbing, Induction & Capacitance effects can build up static
electricity
Avoid use of daisy-chained power extension boards
Toxic - Beryllium heat sinks, Incomplete burning can produce
carbon monoxide & other toxicfumes
January 2020 Ver.1.5 44
Good General Electrical Safety
Safety in Schools Department of education document
1.3 Electrical Services & equipment Pages 10 & 11
3.1 General Electrical safety precautions Pages 20 & 21
Good Housekeeping Well organised & laid out laboratories slips, trips & falls
Adequate Class control
Water Water & electricity do not go well together
Water makes you a better conductor allowing MORE current to flow
Mains Avoid direct working with mains. Use low voltages
Check all leads for: Fraying, Proper clamping, Proper earthing.
Repairing Do not repair, competency required
Trust nobody, remove fuse, use phase tester
One hand behind back, tip cautiously with back of hand
Note: Switch Mode PSU, laptop chargers, CF lamps [high voltages persists on capacitors long after switch off]
Environmental issues
Don’t waste power -Turn off 15c per kWh
Use Low power versions of equipment Flat screen Vs old CRT tube TV
Lighting: LED, fluorescent, CFL, Filament
Reduce and recycle, waste considerations!
Avoid hazardous materials Mercury fluorescent tubes & CFLs
Cadmium & lead from re-chargeable batteries
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Electrical Hazards & Personal Safety
Used where! Office & home 95%
Laboratory 5% Trailing wires, faulty wires
Mains Avoid direct working with mains. Use low voltages
Check all leads for: Fraying, Proper clamping, Proper earthing.
Repairing Do not repair, competency required
Trust nobody, remove fuse, use phase tester
One hand behind back, tip cautiously with back of hand
Note: Switch Mode PSU, laptop chargers, CF lamps [high voltages persists on capacitors long after switch off]
January 2020 Ver.1.5 48
Some examples of electrical hazards
Electronics experiments Use acceptable low voltage Mains operated LT power supplies
Wrong connection – IC / electrical component over heats, shatters
Van De Graaff generator High voltage Low current !
Teltron tubes High voltage Vacuum implosion
Magnetic experiments High currents Heart pace makers
Hot plates Burns
Electrophoresis High voltages
Trailing Power and Signal wires - Protect & Tidy them up
January 2020 Ver.1.5 49
Sometimes forgotten hazards
Medical / Sports equipment Very strict regulations on equipment operation, design, repair Never modify or tamper with such equipment ECG measurements. even a few micro amps direct across the heart can
have massive consequences [basis of a heart pacemaker ]
Pace makers Susceptible to strong magnetic fields [NMR! ], Possibly RF & Micro waves interference
Chemical Solvents Flammable environments require specialised electrical equipment
E.g. Spark-free fridge for storage of samples dissolved in solvents
Cold rooms / water cooling Equipment moved from cold room can get condensation on its internal
electrical circuits. Avoid this movement, Use L.T. and give lots of time to acclimatise
January 2020 Ver.1.5 50
Yet more examples
RF & µW Capacitive coupling, no need to touch,
Both can burn severely internally and externally depending on how
focused. Think of them like an open air μ-wave oven
EHT Static, OK [Very low current, moderate power] nearby Solvents!
Will jump considerable distances,
Beware of capacitors
Power Heating effect in body => internal burns / damage
Contact burns, deep burns & necrosis
Trailing Power and Signal wires - Protect & Tidy them up
January 2020 Ver.1.5 51
Specific Hazards & Personal Safety
Other Laboratory Situations ?
Other Office Situations ?
Other Home Situations ?
January 2020 Ver.1.5 53
Electrocution
Prevention & Training : Where are red mushroom switches ?
Response: Immediately cut power, red buttons / switch / plug
If in any doubt - Do not touch victim.
One hand behind back, stand on insulation, tip with back
of hand
Use insulating rod / stick to move wires from victim.
Call for assistance
Talk & reassure victim
If unconscious then use first aid, CPR
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SUMMARY
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Summary Awareness
Of the need for electrical safety
Of your personal limitations & permissions
Potential Sources of electrical dangers
Aware of your responsibility to take care of
Yourself and Others
Note Safety Sources for future use
If unsure never be afraid to ask or to say ‘NO’
January 2020 Ver.1.5 58
Where to get more information
Your Supervisor, Manager, Head of Department
Department Safety Statements
Department Safety Committees & Safety Officer
DCU safety - WEB
Edinburgh University H&S - WEB
University London H&S – WEB
http://sce.e-smartonline.net/elec_safety-smart/index.html
January 2020 Ver.1.5 59
END
Thanks for your attention
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