1. 9/6/20151

2. 2 INTRODUCTION Three Important Commodities – Air, Water and Electricity Electricity – Clean and Efficient form of Energy Respect Electricity it respects you Direct Working – Engineers, Technicians and Professionals Indirect Working – Every Individual

3. 9/6/20153 Electricity? Form of Energy – i.e. power to do or move things Generated in power plants Brought to users ( termed loads) through transmission lines – distribution lines When a device is plugged in circuit is completed Electricity travels through conductors – Al / Cu Human body – a good conductor – mostly water Electricity propagates at SPEED of Light 300 m/us

4. 9/6/20154 Electricity ? (Contd…) Insulators – Confine Electricity – Glass – Plastic – Ceramic – Rubber If Insulation - damaged or broken – Electricity – leaks causes shock If an outlet – overloaded – Insulation overheats and melts => Fire or Shock

5. 9/6/20155 How Does Electricity Hurt? Attempts to flow to ground Takes short cuts Good conductors give easy path Water & metals are good conductors Human body containing mostly water is a great conductor If human body in the path – seriously hurt or killed Desirable to keep appliances away from electric circuits

6. 9/6/20156 Electricity Hazards Shock – when human body in the path Direct effect – Injury or death ~ 30 mA causes death Indirect effects – result in falls or movement leading to injury or death Basic ways Shock arises: 1.When in contact with both wires 2.When in contact with a wire and ground 3.When in contact with a metal part in contact with a wire in a circuit and ground

7. 9/6/20157 Electricity Hazards (Contd…) Burns : 1.When in contact with electrical circuit 2.Improperly used or maintained equipment 3.Typically on the hands ( arms) Arc Blast: 1.Arise from high current arcs through air 2.Initiated by contact between energized parts 3.Accidentally by persons working on energized parts 4.Equipment failure due to fatigue or abuse 5.Temperatures reach 35,000 0 F

8. 9/6/20158 Arc Blast Hazards Thermal Radiation : 1. degree of injury depends on Skin Color, area of contact and type of clothing 2.Minimized by Proper Clothing, maintaining working distances and over-current protection Pressure Wave Generation: 1.High Energy Arcing Faults lead to High Pressure 2.Typically 2’ away from 25 kA pressure experienced 480 pounds 3.Leads to serious ear damage – memory loss – due to mild concussions

9. 9/6/20159 Arc Blast Hazards (Contd…) Projectiles : 1.Pressure waves propel large objects over considerable distances 2.Enough to melt copper and aluminum components 3.Burns more intense than injury from projectiles Explosions: 1. occur due to ignition of explosive mixtures in the atmosphere ( or environment) 2.Flammable vapors generated by source and process 3.Ignition due to overheated conductors or equipment or normal arcing at switch contacts M.Sudhakaran

10. 9/6/201510 Electrical Fires Electricity is most common cause of Fire – both at home and in office Main cause is use of defective electrical equipment and misuse of electrical apparatus High resistance connections being primary source of ignition High resistance connections occur either due to improper splicing of wires or improper connection of receptacles/ switches specially when employing aluminum conductors

11. 9/6/201511 Effect of Shock on Human Body Factors responsible : 1. Current 2. Voltage 3. Resistance 4. Path Through the body 5. duration of Shock and 6.Muscular Structure Less Musculature lower threshold current

12. 9/6/201512 Electric Current (1 second contact) Physiological Effect 1 mAThreshold of feeling, tingling sensation. 5 mAAccepted as maximum harmless current 10-20 mA Beginning of sustained muscular contraction ("Can't let go" current.) 100-300 mA Ventricular fibrillation, fatal if continued. Respiratory function continues. 6 A Sustained ventricular contraction followed by normal heart rhythm. (Defibrillation). Temporary respiratory paralysis and possibly burns.

13. 9/6/201513 Electric Current (1 second contact) Voltage required to produce the current with assumed body resistance: 1 mA 100 V1 V 5 mA 500 V5 V 10-20 mA 1000 V10 V 100-300 mA 10000 V100 V 6 A 600000 V6000 V 100,000 ohms1,000 ohms

14. 9/6/201514 Shock Parameters Current & voltage 1.Though at High Voltages – massive destruction at the point of contact 2.Current causes detrimental effect of Electric shock, 3.Though I = v/r holds good, contact resistance varies depending on local conditions 4.All domestic appliances can give fatal currents

15. 9/6/201515 Effect of Currents Currents > 10 mA cause painful shock 100 – 200 mA can be lethal As ac current increases tingling sensation finally leading to contraction of the muscles Accompanied by heat sensation Develops pain and voluntary control is lost Around 15 mA victim can not let go termed “Let – go threshold” M.Sudhakaran

16. 9/6/201516 Effect of Currents Contd… Around 100 mA – ventricular fibrillation occurs i.e. very rapid uncoordinated contractions of the ventricles of the heart with loss of synchronization between heart beat and pulse beat Finally leads to death (Ventricular fibrillation (VF) is a severely abnormal heart rhythm (arrhythmia) that can be life-threatening).arrhythmia

17. 9/6/201517 Resistance Varies with 1.Moisture Content 2.Pressure at the Contact Point 3.Area of Contact Epidermis presents very high resistance under dry conditions, becomes lower when wet, or due to cuts or break in skin Shock severity higher 1.With increase in contact pressure 2.With increase in contact area Resistance decreases with voltage Due to Broken skin at higher voltages

18. 9/6/201518 Current Paths Path Affects the degree of injury Small current from one extremity, through heart, to the other extremity causes severe injury or electrocution When current flows through a portion of limb without passing through trunk may cause only burning of limbs Often path involves arms to legs through heart and lungs leading to fatal shock

19. 9/6/201519 Shock Duration Net effect depends on duration Short duration may give painful experience @100 mA even few s of shock can be fatal Remember light duty portable drill draws about 3 A ( i.e. 30 times fatal current) High Currents for even appreciable duration lead to inevitable death

20. 9/6/201520 Summary of Effects Current > “let go” threshold lead to collapse or unconscious or death Duration greater than 5s lead to asphyxiation and heart failure are the causes Current through chest, neck, head or respiratory centres lead to respiratory failure by disruption of nerve impulses associated with respiration. Very dangerous as effect continues after cessation of current flow

21. 9/6/201521 Summary of Effects contd.. Most dangerous effect – even fairly small current flows through heart region Causes ventricular fibrillation resulting in death with in minutes Asynchronous movement causing heart beat to stop If large currents flow through heart – heart activity stops immediately Secondary effect could be tissue damage and damage to internal organs when current flows through major portions of the body

22. 9/6/201522 Causes of Electrical accidents Inadequate wiring Exposed parts Contact with overhead power lines Defective or Inadequate insulation Improper grounding of equipment Overloaded circuits Damaged Power tools or equipment Static Electrification Inadequate Protection to Lightning

23. 9/6/201523 Causes of Electrical accidents contd.. Aggravated by 1.Inadequate training 2.Unsafe work environment - wet work surfaces - inclement weather - toxic chemicals - excessive noise - flammables

24. 9/6/201524 Accident Prevention Most Electrical Accidents are preventable Desirable prevention technique is to eliminate or reduce Hazard at source De-energize and lock out equipment prior to repair or inspection

25. 9/6/201525 Accident Prevention Measures Other Measures Include: 1.Provide Proper Insulation 2.Guarding or Cordon off 3.Elevation of live wires at least 8’ above floor or ground 4.Provide protection devices like GFCI 5.Ground both system and equipment 6.Provide proper safety labels or signs FORE WARNED is FORE ARMED!

26. 9/6/201526 Accident Prevention Measures Contd.. At Work Place : 1.Provide Proper Training 2.Use tools in good condition 3.Use proper wire and connectors 4.Avoid contact with overhead power lines 5.Maintenance carried out by qualified electricians aware of lock out procedures 6.Provide written Instructions on Lockout and tagging procedures 7.Avoid wet or damp conditions 8.Never work alone

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29. 9/6/201529 Harmonized Symbol

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33. 9/6/201533 Accident Prevention Measures Contd.. 1.Install Safety Switch 2.Never use faulty or wet appliances 3.Never stack power points 4.Take care around water 5.Never throw water on electrical fire 6.Keep appliances away from water.

34. 9/6/201534 Thank you