1. Electrical Safety in the Laboratory Joshua D. Horvath Andrew J. Gellman Carnegie Mellon University Department of Chemical Engineering February 18, 2003

2. Accidents Electrical shock from laser power supply Electrical shock from electrophoresis power supply

3. 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

4. AC vs. DC Electricity Direct current (DC) Alternating current (AC)

5. Electrical Components Capacitors Resistors Integrated circuits

6. Measuring Voltage + 5V - Connect Probe Connect Probe

7. Safety Devices High Voltage Probe Connects to normal multimeter. Reduces voltage by factor of 1000. Should only be used with training or assistance. Dangerous if used improperly. You could be KILLED.

8. Measuring Current (DC) + 5V - Connect Probe Connect Probe

9. Safety Devices Clamp-on Ammeter Measures AC current through a single conductor. Does not work for DC current. If both wires (positive and negative) pass through the clamp, no current reading is possible.

10. Lab Equipment Power requirements (input) EquipmentVoltsAmpsWatts PC1206.0720 Monitor1201.5180 Turbopump1204.0480 Cryopump24012.02,880 Heating tape (big)1206.92830 FT-IR1205.0600 Heat gun12014.01680

11. Lethal Electricity Chart below assumes 1 second hand to foot exposure to 120 volt, 60 cycle AC power supply. CurrentReaction 1 mAPerception 5 mASlight shock felt; not painful but disturbing 6-30 mAPainful shock; "let-go" range 50-150 mAExtreme pain, respiratory arrest, severe muscular contraction 1,000-4,300 mAVentricular fibrillation 10,000+ mACardiac arrest, severe burns and probable death Laboratory wall outlets provide 20,000 mA !!

12. Safety Devices Fuses Protect electrical wiring from carrying too much current. Protect malfunctioning equipment from drawing too much current. Conductor melts if too much current flows through fuse. Can only be used once. Always use the correct fuse. New fuseBlown fuse

13. Safety Devices Circuit Breakers Protect electrical wiring from carrying too much current. Mechanical switch is driven by an electromagnet. Can only be reset many times.

14. Safety Devices Circuit Breakers (in action)

15. Safety Devices Circuit Breakers How much equipment can one 20A circuit breaker handle? Not enough to bake an entire vacuum chamber. DeviceCurrent Heat tape (1 inch by 8 feet)6.92 A Heat 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 Total23.5 A

16. Safety Devices Circuit Breakers One circuit breaker may cover many electrical receptacles in a lab. Receptacles in some labs are labeled with a number that corresponds to a circuit breaker.

17. Preventing Accidents Avoid contact with energized circuits. Disconnect the power source before servicing or repairing electrical equipment. Work with only one hand, keeping the other hand behind you or in a pocket. If water or a chemical is spilled onto equipment, shut off power at the main switch or circuit breaker and unplug the equipment. If an individual comes in contact with a live electrical conductor, do not touch the equipment, cord or person. Disconnect the power source from the circuit breaker or pull out the plug using a leather belt.

18. 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 is probably overloaded. Amperage0-55-77-1212-1616-20 Cord length (feet)Wire gauges 25 50 75 100 150 200 18 16 14 12 18 16 14 12 10 16 14 12 10 14 12 10 12 10 Sizes smaller than wire gauge 10 are not normally available as flexible wire.

19. Preventing Accidents Electrical Fires Unplug equipment first. Use dry chemical fire extinguisher. If fire is large, unplug equipment and call fire dept. Never use water!!

20. Conclusions Be careful with electricity. Ask someone for help if you are unsure.