Post on 05-Apr-2018
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Electrical Safety in the
LaboratoryJoshua D. Horvath
Andrew J. Gellman
Carnegie Mellon University
Department of Chemical Engineering
February 18, 2003
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Accidents
Electrical shock from laserpower supply
Electrical shock fromelectrophoresis powersupply
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Relationship between power,current, voltage and resistance:
P = power (watts)
I = current (amperes)
V = voltage (volts)
R = resistance (ohms)
Example:Heating tape uses 5 amps at 120 volts.
Power dissipated by this device is 600 watts.
Introduction
VIP
RIV
RIP 2
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AC vs. DC Electricity
Direct current (DC)
0 300 600 900
-1
0
1
2
Pote
ntial(volts)
Time
Alternating current (AC)
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Electrical Components
Capacitors
Resistors
Integrated circuits
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Measuring Voltage
+ 5V -
ConnectProbe
ConnectProbe
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Safety Devices
High Voltage Probe Connects to normal multimeter.
Reduces voltage by factor of 1000.
Should only be used with trainingor assistance.
Dangerous if used improperly.You could be KILLED.
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Measuring Current (DC)
+ 5V -
ConnectProbe
ConnectProbe
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Safety Devices
Clamp-on Ammeter Measures AC current through a
single conductor.
Does not work for DC current.
If both wires (positive andnegative) pass through the clamp,no current reading is possible.
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Lab Equipment
Power requirements (input)
Equipment Volts Amps WattsPC 120 6.0 720
Monitor 120 1.5 180
Turbopump 120 4.0 480
Cryopump 240 12.0 2,880
Heating tape (big) 120 6.92 830
FT-IR 120 5.0 600
Heat gun 120 14.0 1680
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Lethal Electricity
Chart below assumes 1 second hand to footexposure to 120 volt, 60 cycle AC power supply.
Current Reaction
1 mA Perception5 mA Slight shock felt; not
painful but disturbing
6-30 mA Painful shock; "let-go"range
50-150 mA Extreme pain, respiratoryarrest, severe muscularcontraction
1,000-4,300 mA Ventricular fibrillation
10,000+ mA Cardiac arrest, severeburns and probable death
Laboratory wall outlets provide 20,000 mA !!
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Safety Devices
Fuses Protect electrical wiring from
carrying too much current.
Protect malfunctioning equipment
from drawing too much current.
Conductor melts if too muchcurrent flows through fuse.
Can only be used once.
Always use the correct fuse.
New fuse Blown fuse
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Safety Devices
Circuit Breakers Protect electrical wiring from
carrying too much current.
Mechanical switch is driven by anelectromagnet.
Can only be reset many times.
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Safety Devices
Circuit Breakers (in action)
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Safety Devices
Circuit Breakers How much equipment can one 20A
circuit breaker handle?
Not enough to bake an entirevacuum chamber.
Device Current
Heat tape (1 inch by 8 feet) 6.92 AHeat tape (1 inch by 8 feet) 6.92 A
Heat tape (1/2 inch by 5 feet) 2.58 A
Heat tape (1/2 inch by 10 feet) 4.33 A
Infrared lamp (inside chamber) 2.75 A
Total 23.5 A
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Safety Devices
Circuit Breakers One circuit breaker may cover
many electrical receptacles in alab.
Receptacles in some labs arelabeled with a number thatcorresponds to a circuit breaker.
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Preventing Accidents
Avoid contact with energized circuits.
Disconnect the power source beforeservicing or repairing electricalequipment.
Work with only one hand, keeping theother hand behind you or in a pocket.
If water or a chemical is spilled ontoequipment, shut off power at the main
switch or circuit breaker and unplug theequipment.
If an individual comes in contact with alive electrical conductor, do not touch
the equipment, cord or person.
Disconnect the power source from thecircuit breaker or pull out the plug usinga leather belt .
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Preventing Accidents
Extension Cords Do not plug one extension cord
into another extension cord.
Do not exceed safety ratings.
If cord is warm to touch, it isprobably overloaded.
Amperage 0-5 5-7 7-12 12-16 16-20
Cord length
(feet) Wire gauges
25
50
75100
150
200
18
18
1614
12
12
18
16
1412
12
10
16
14
1210
14
12
10
12
10
Sizes smaller than wire gauge 10 are not normally available as flexible wire.
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Preventing Accidents
Electrical Fires
Unplug equipment first.
Use dry chemical fireextinguisher.
If fire is large, unplugequipment and call firedept.
Never use water!!
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Conclusions
Be careful with electricity.
Ask someone for help ifyou are unsure.