Electrical Safety Lecture Note

El ectricalSaf ety INSY 6010 Fall 2003

Introduction ~ 1000 accidental electrocutions/year  1 in 4 are industry or farm related  Electricity is invisible  Degree of complacency 

Introduction ~ 1000 accidental electrocutions/year  1 in 4 are industry or farm related  Electricity is invisible  Degree of complacency 

El ectricCurrent nt 

Flow of electrons

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Voltage

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Resistance

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Amperes

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Ohm’s Law--> I = E/R 

 TyypesofEl  T ectricalHazards  

Contact with bare conductors  –  Live overhead lines

7,200 Volts

 TypesofEl ectricalHazards  

Contact with bare conductors  –  Electrical systems open for repair 

12,000 Volts

 TypesofEl ectricalHazards  

Poor or failed (decayed) insulation

 TypesofEl ectricalHazards  

Equipment failure

161,000 Volt Substation

 TypesofEl ectricalHazards  

Equipment failure

 TypesofEl ectricalHazards  

Static electricity

El ectricalHazard:StaticEl ectricity 

Motion of two or more objects

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Dissimilar materials

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Transfer of electrons

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Charges the surface only

StaticEl ectricityHazards  

Potential of 15,000 volts

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Sparks

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Ignition source for fires

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Concern for handling sensitive electronic components (ESD)

StaticChargeSituations  

Transfer of liquid fuels

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High-velocity flow of liquid

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Flow of dust or small objects in a pipe

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Conveyor belts made of certain materials

 Nylon or wool carpet in the area of certain materials

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ControlofEl ectricalHazards  

Insulation of Electrical Equipment

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Insulation of Personnel

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Grounding

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Encapsulation

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Enclosure (Isolation)

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Ground-fault circuit interrupter (GFI)

Insul ation ofEl ectrical Equipment 

One of the best ways to prevent shocks

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Three functions:  –  prevent leakage of current  –  separate the conductor and worker   –  prevent overheating in conjunction with cooling

systems (blown air, chilled water, etc)

Insul ation ofPersonnel 

Ways to insulate personnel:  –  ladders and other equipment used  –  mats  –  gloves  –  shoes  –  Remove all metallic objects from body  –  Remove /secure loose clothing

Grounding 

Earth maintains relatively even charge, zero reference potential

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Completes electrical loop in most cases

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Creates electrical hazard if human is in loop

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Ground wire usually reduces this risk 

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Isolation of structures also reduces risk 

Encapsul ation 

Embed electrical units in casing

Isolates the unit from malfunction and  personnel

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Encl osure:Isol ation: 

Power to equipment shut off (LOTO)

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Temporary restraints

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Permanent restraints

Ground::Faul Ground tCircuitInterrupter :GFI: 

Provides protection against line-to-ground contact

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Detects the flow of current to the ground

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When current is detected the circuit is opened

Ground Gr ound::Faul tCircuit Interrupter:GFI:

El ectricShock 

Human body

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Electrical circuit

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Current flow

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Ground fault current

Physiol ogicalEf f ectsof El ectricShock

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Central Nervous System: contains tiny electrical voltages used as signals to brain

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Large currents freeze muscles which can:  –  Not allow victim to release the source  –  Stop breathing  –  Stop heart

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Skin provides some resistance to shock 

Currentto ShockComparison 

1 mA or less: Not felt

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3 mA - 10 mA: Painful shock 

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10 mA - 15 mA: 2.5% of population freeze

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15 mA - 30 mA: 50% of population freeze

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30 mA - 50 mA: Breathing difficulty

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50 mA - 100 mA: Possible heart fibrillation

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100 mA - 200 mA: Certain heart fibrillation

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200 mA & up: Severe burns; heart stop

:::::Vol ::: tMyth 

“ordinary 110-volt circuits are safe.”

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110-volt circuits can kill

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Statistics prove more deaths from 110-volt than 220-volt or 440-volt

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Environment and characteristics of shock usually indicate seriousness

Wiring 

A typical 110-volt circuit has 3 wires  –  “hot”  –  “neutral”  –  “ground”

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Shorting

WiringDangers  

“Jump” ground wire to neutral wire  –  create low voltages on exposed parts of

equipment 

“Reversed polarity”

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“Open ground”

Correctl ywired::::vol t circuit Electric power source

Fuse or breaker

Neutral wire (white)

Ground wire (green or bare)

Ground

Hot wire (black)

WireFires  

One of most common causes of fires of electrical origin are wires

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Wire diameters must be of proper size

Over:currentProtection Devices 

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If current exceeds a given limit, power is shut off.

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circuit breakers

Over:currentProtection Devices 

If current exceeds a given limit, power is shut off.  common devices: 

 –  fuses  –  circuit breakers  –  arc-fault protection: typically associated with

high voltage situations (new technology used in submarines) sensing light flash, or pressure surge.

Over:currentProtection arc-fault protection: typically associated with high voltage situations (new technology used in submarines) sensing light flash, or  pressure surge.

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Over:currentProtection Devices 

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If current exceeds a given limit, power is shut off.

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fuses

 TestEquipment Safety managers should have access to several  pieces of test equipment

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 –  Circuit Tester

(voltmeter)  –  Receptacle Wiring Tester   –  Continuity Tester (ohmmeter)

FrequentViol ationsofthe NationalEl ectricalCode 

Grounding of portable tools & appliances

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Exposed live parts

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Improper use of flexible cords

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Marking of disconnects

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Connection of plugs to cords

FireHazards  

Most people think electrocution when they think of electrical hazards

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Electrical codes deal with fire hazards

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Fuses and circuit breakers main purpose is fire prevention

HazardousLocations   National Electrical Code

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Class - major classification, material

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Division - relates to the extent of the hazard

Cl assesandDivisionsof HazardousLocations  

Class I - flammable gases or vapors  –  Division 1 and 2 - extent of hazard

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Class II - combustible dust  –  Division 1 and 2 - extent of hazard

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Class III - easily ignitable fibers or flyers  –  Division 1 and 2 - extent of hazard

Saf etyPrecautionsf or El ectricalHazards  

Be sure power is off 

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Proper LOTO procedures

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Properly qualified

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Proper protective equipment

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Always test the system

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Do not wear conducting material

Saf etyPrecautionsf or El ectricalHazardsCon:t: 

Proper grounding and bonding

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Inspect insulation

 Never stand on wet or damp floors

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Use right kind of fire extinguishing agent if needed

Saf etyPrecautionsf or El ectricalHazardsCon:t:

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Explosion proof devices

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Lightning protection

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Basic first aid and CPR 

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Proper enclosure for bare conductors

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Rope man to evacuate worker from source

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Use a checklist to ensure compliance