Electrical Safety Understanding and Protecting Yourself from Electrical Shock Humbly Presented By Prof. Bitar

Factors Involved in Electrical Shock The Amount of Current (amps) The Current Path The Duration Q. So what about the Voltage?

What Does the Amount of Current Depend On? The amount of current that flows depends on the voltage applied as well as the body resistance. (ie. Ohm’s Law: I = V / R )

Dangerous Current Levels ( Based on a Body Weight of 150 Lbs. ) Effect / Feeling Current (mA) DC AC(60Hz) Incident Severity Slight Sensation 10.4 None Perception Threshold None Shock Not Painful 91.8 None Shock Painful 629 Spasm Indirect Injury Painful, Muscle Clamps (Can’t Let Go) 7616 Possibly Fatal Severe Pain Respiratory Arrest (Can’t Breathe) Frequently Fatal Heart Fibrillation (after 3 seconds) Probably Fatal Source: Environment, Safety, and Health Manual, Volume II, Part 16.1, U.S. Dept. of Energy at University of California Lawrence Livermore National Laboratory, Contract W-7405-ENG-48, Feb 1996.

Body Resistance (Ohms) Contact Points Dry (  Wet (  Wire Touched by Finger 40,000 – 1,000,0004,000 – 15,000 Hand Holding Wire 15,000 – 50,0003,000 – 5,000 Finger Thumb Grasp 10,000 – 30,0002,000 – 5,000 Hand Holding Pliers 5,000 – 10,0001,000 – 3,000 Palm Touch 3,000 – 8,0001,000 – 2,000 Hand Around Pipe 1,000 – 3, – 1,500 Two Hands Around Pipe 500 – 1, Source: Environment, Safety, and Health Manual, Volume II, Part 16.1, U.S. Dept. of Energy at University of California Lawrence Livermore National Laboratory, Contract W-7405-ENG-48, Feb 1996.

Scenario #1 An electrician with sweaty hands picks up a live 120VAC 60Hz circuit (finger- thumb grasp)… Q1:How much current will flow? Q2: Is this amount of current fatal?

Scenario #2 A lab power supply is set to +/- 30V DC with wires all over the bench. A coke is accidentally spilled, and a student wipes up the mess with paper towels… Q1:How much current will flow? Q2: Is this amount of current fatal?

Where is the Danger? How many volts are involved in a typical electrostatic shock? Isn’t this dangerous? If I grab the terminals of a 12V car battery, will I be electrocuted? What is the danger? Which is more dangerous, DC or AC?

Safe Working Habits One Hand... Never Alone… Safety Glasses… Shut Power Off… Unplug Equipment… Remove Obstacles… Be Neat… Discharge Capacitors…

Four Phases of Electrical Safety Based on Electrical Safety Training at Massachusetts Electric Co. Unconsciously Unsafe Consciously Unsafe Consciously Safe Unconsciously Safe

What About Protecting Components and Equipment? 1.Do Not Exceed… Voltage Ratings (Volts) Current Ratings (Amps) Power Ratings (Watts) 2.Use a Reasonable Safety Margin Commercial Industrial Medical Military / Aerospace

A Remarkable Story… 20,000 Volts 60Hz AC Estimated Current (50-100mA) Grabbing with Both Hands A Critical Path Longer than 3 Seconds “It is good to learn from one’s mistakes… but it is better to learn from the mistakes of others.” “There, but for the grace of God go I !” George Whitefield ( )