Elec Safety

7/31/2019 Elec Safety

1/20

Electrical Safety in the

LaboratoryJoshua D. Horvath

Andrew J. Gellman

Carnegie Mellon University

Department of Chemical Engineering

February 18, 2003


2/20

Accidents

Electrical shock from laserpower supply

Electrical shock fromelectrophoresis powersupply


3/20

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


4/20

AC vs. DC Electricity

Direct current (DC)

0 300 600 900

-1

0

1

2

Pote

ntial(volts)

Time

Alternating current (AC)


5/20

Electrical Components

Capacitors

Resistors

Integrated circuits


6/20

Measuring Voltage

+ 5V -

ConnectProbe

ConnectProbe


7/20

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.


8/20

Measuring Current (DC)

+ 5V -

ConnectProbe

ConnectProbe


9/20

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.


10/20

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


11/20

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 !!


12/20

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


13/20

Safety Devices

Circuit Breakers Protect electrical wiring from

carrying too much current.

Mechanical switch is driven by anelectromagnet.

Can only be reset many times.


14/20

Safety Devices

Circuit Breakers (in action)


15/20

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


16/20

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.


17/20

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 .


18/20


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.


19/20


Electrical Fires

Unplug equipment first.

Use dry chemical fireextinguisher.

If fire is large, unplugequipment and call firedept.

Never use water!!


20/20

Conclusions

Be careful with electricity.

Ask someone for help ifyou are unsure.

Elec Safety

Documents

Transcript of Elec Safety