9/6/20151. 2 INTRODUCTION Three Important Commodities – Air, Water and Electricity Electricity – Clean and Efficient form of Energy Respect Electricity.

04/19/23 1

04/19/23 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

04/19/23 3

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

04/19/23 4

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

04/19/23 5

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

04/19/23 6

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

04/19/23 7

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 35,0000 F

04/19/23 8

Arc Blast Hazards

• Thermal Radiation :1. degree of injury depends on Skin Color, area of

contact and type of clothing2. Minimized by Proper Clothing, maintaining working

distances and over-current protection• Pressure Wave Generation:1. High Energy Arcing Faults lead to High Pressure2. Typically 2’ away from 25 kA pressure experienced

480 pounds3. Leads to serious ear damage – memory loss – due to

mild concussions

04/19/23 9

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

04/19/23 10

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

04/19/23 11

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

04/19/23 12

Electric Current

(1 second

contact)

Physiological Effect

1 mA Threshold of feeling, tingling sensation.

5 mA Accepted 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.

04/19/23 13

Electric Current (1 second contact)

Voltage required to produce the current with assumed body resistance:

1 mA 100 V 1 V

5 mA 500 V 5 V

10-20 mA 1000 V 10 V

100-300 mA 10000 V 100 V

6 A 600000 V 6000 V

100,000 ohms 1,000 ohms

04/19/23 14

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

04/19/23 15

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

04/19/23 16

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).

04/19/23 17

Resistance

• Varies with1. Moisture Content2. Pressure at the Contact Point3. 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 pressure2. With increase in contact area • Resistance decreases with voltage• Due to Broken skin at higher voltages

04/19/23 18

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

04/19/23 19

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

04/19/23 20

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

04/19/23 21

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

04/19/23 22

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

04/19/23 23

Causes of Electrical accidents contd..

• Aggravated by1. Inadequate training2. Unsafe work environment - wet work surfaces - inclement weather - toxic chemicals - excessive noise - flammables

04/19/23 24

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

04/19/23 25

Accident Prevention Measures

• Other Measures Include:1. Provide Proper Insulation2. Guarding or Cordon off3. Elevation of live wires at least 8’ above floor or

ground4. Provide protection devices like GFCI5. Ground both system and equipment 6. Provide proper safety labels or signs

FORE WARNED is FORE ARMED!

04/19/23 26

Accident Prevention Measures Contd..

• At Work Place :1. Provide Proper Training2. Use tools in good condition3. Use proper wire and connectors4. Avoid contact with overhead power lines5. Maintenance carried out by qualified electricians aware

of lock out procedures6. Provide written Instructions on Lockout and tagging

procedures7. Avoid wet or damp conditions8. Never work alone

04/19/23 27

04/19/23 28

04/19/23 29

Harmonized Symbol

04/19/23 30

04/19/23 31

04/19/23 32

04/19/23 33

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.

04/19/23 34

Thank you