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L. Rene’ Graves, BS, CSPSenior Safety SpecialistTexas Instruments, Inc.

Dallas, TX

Electrical Safety: Are you Prepared?

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• Certified Safety Professional• BS in Occupational Safety and Health from

Murray State University• AS in Industrial Electronics• AS in Air Conditioning and Refrigeration • Journeyman Electrician in the State of Texas• Member Group Technical Staff• Member of Texas Instruments, Inc. WW-ESH

team

L. Rene’ Graves, BS, CSP

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• Stop Electrical Events from occurring by:– Identifying what causes these events– Conducting a risk assessment through the use of

an electrical energy study– Creating a plan to reduce identified risks before

an event occurs– Implementing a plan

• Consider participation in the IEEE Electrical Safety Workshop to learn more about electrical safety

Conclusion

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• Financial Burden of electrical work• Components of an electrical event• NFPA 70E • Electrical System Equipment• Investigation Method

Overview

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• OSHA identified the following areas in electrical safety in which fines were assessed:• Wiring design and protection• Wiring methods, components and equipment for general use• Training• Failure to provide a safe work environment

• Financially the industries were cited • General Industry - $1,373,087 • Construction – $1,133,424

Financial Burden

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• OHM’s Law• Shock• Arc and Arc Flash• Blast Energy• Incident Energy• Hazard Boundary• Burns

Components of an Electrical Event

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Ohm's Law• E = I * R • or • Volts = Current * Resistance

– Volts (potential difference)– Current (ampere)– Resistance (impedance)

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Shock

Shock – a reflex response to the passage of electric current through the body.

Effect of Electrical Current flowing through the Body Men Women

Slight tingling sensation felt 0.4 ma 0.3 ma

Threshold of perception 1.1 ma 0.7 ma

Painful but able to release from electrical source 9.0 ma 6.0 ma

Painful and unable to release from electrical source 16 ma 10.5 ma

Severe pain and difficulty breathing 23 ma 15.0 ma

Possible heart fibrillation after 3 seconds 100 ma 100 ma

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• Arc and Arc Flash– An arc is an electrical current bridging an air gap– Most common manmade creations of an arc

occur during a welding procedure– Temperatures of an arc flash can reach up to

35,000°F and usually vaporize any material when extended contact occurs

– Besides heat; light, sound, and UV radiation are released by an arc

– The flash of light and other radiation produced by an arc is called an “arc flash”

Arc and Arc Flash

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Examples of Arc Flash

Open Air

Box or Enclosed

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Blast EnergyBlast Energy or Pressure – the amount of force produced from rapidly expanding air during an electrical event

Blast pressure waves have thrown workers across rooms and knocked them off ladders. Pressure on the chest can be higher than 2000 lbs/ sq. ft.These high pressures can easily exceed the ability of a worker to withstand the force causing a worker to be knocked off a ladder, or rupturing eardrums, and possibly causing the lungs to collapseCalculating potential blast effect

9.0*58.11

D

IP arc

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Blast Calculation225 KVA Transformer, 3 phase, 480V to

208/120V with Z = 3.5% Impedance

Distance (D) - 18” from source (NFPA 70E Box) Current (I – (KVA) – 18.203 KVA

ftsqpoundsP arc _./_635.1518

203.18*58.119.0

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– The amount of energy imposed on a surface, at a certain distance from the source, generated during an electrical arc event

– The unit of measurement is either calories per centimeter squared (cal/cm2) or joules per centimeter squared (J/cm2)

Incident Energy

Hazard Boundary• Hazard Boundary

– Flash Protection Boundary– Limited Approach Boundary– Restricted Approach Boundary– Prohibited Approach Boundary– Prohibited Space

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Burns

Burn Classification1° Burn – redness to the outer layer of the skin only. Healing time is normally

6-10 days2° Burn – superficial, no loss of dermis.

Healing time 7-14 days3° Burn - deep dermal burn, whole skin loss. Healing more than 21 days. (Note:

large areas where healing might not occur and debriefing will be required)

4° Burn – deep structural loss. Healing – never if area is large

• Burns – any energy caused by heat, electricity, chemicals, radiation or gases.

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Temperature as it Effectsthe Human

Burns and the Effects of Temperature on Human Skin

Skin Temperature Time to reach temperature Damaged Caused

110°F 6.0 hours Cell breakdown beginsPossible 1-degree burn

158°F 1.0 seconds Total cell destruction1st-degree burn / begin

2nd-degree burn 176°F 0.1 seconds

6 cycles2nd-degree burn

200°F 0.1 seconds 3rd-degree burn

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Questions about:Shock, Arc, or Blast

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• Using table method (NFPA 130.2(C)) to establish level of PPE– (d) For systems rated less than 1000 volts, the fault

currents and upstream protective device clearing times are based on an 18 in. working distance.

– (e) For systems rated 1 kV and greater, the Hazard/Risk Categories are based on a 36 in. working distance.

– (f) For equipment protected by upstream current limiting fuses with arcing fault current in their current limiting range ( cycle fault clearing time or less), the hazard/risk category required may be reduced by one number.

Limitations of NFPA 70E

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• Specific Notes (as referenced in the table): – 1. Maximum of 25 kA short circuit current available;

maximum of 0.03 sec (2 cycle) fault clearing time. – 2. Maximum of 65 kA short circuit current available;

maximum of 0.03 sec (2 cycle) fault clearing time. – 3. Maximum of 42 kA short circuit current available;

maximum of 0.33 sec (20 cycle) fault clearing time. – 4. Maximum of 35 kA short circuit current available;

maximum of up to 0.5 sec (30 cycle) fault clearing time.

Limitations of NFPA 70E (cont.)

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• Using Appendix D to Incident Energy– Calculates incident energy for 3-phase arc on

systems rated 600 V and below; applies to short-circuit currents between 16 kA and 50 kA

– Equations must be used only under qualified engineering supervision

Limitations of NFPA 70E (cont.)

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• Labeling of Equipment– Establish the Arc Flash Protection Boundary– Identify the Personal Protective Equipment– Equipment Labeling - Equipment shall be field

marked with a label containing the available incident energy or required level of PPE

– A review of the arc flash analysis should occur anytime major renovation is conducted or periodically, not to exceed 5 years

Arc Flash Hazard Analysis

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Equipment TerminologyTransmission

Distribution

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Electrical Equipment Components

Box or CanPanel Interior

OrGuts

Dead Front Or

Pancake

DoorOr

Hinged cover

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• Two categories of Electrical Events– Human– Equipment

• Signs of problems– Discolored metal in electrical equipment– Report of someone being shocked– Breaker tripping– Flickering of lights or power– Over heating of conductors

Electrical Events

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• Conduct a total system evaluation– Fault Current Study

• What is it?• How is the study executed?

– Training Evaluation• Are the correct people being trained?• Are the employees knowledgeable of the equipment

upon which they are performing maintenance?• What training do your suppliers have to make them

qualified to work on your equipment?

Prior to an Electrical Event

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• Securing the scene– Isolate the area– Request assistance from electrical team– Confirm the electrical panel is off– Install LOTO and verify equipment involved in the

event is de-energized• Provide support for injured employees• Gather Investigation Team• Photographs

Electrical Event Investigation

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• What information should be contained in the report?

• Who is responsible for ensuring the accuracy of the report?

• How do you limit the information and limit the distribution so that multiple copies stating different things are not floating around?

Final Report Contents

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• Stop Electrical Events from occurring by:– Identifying what causes these events– Conducting a risk assessment through the use of

an electrical energy study– Creating a plan to reduce identified risks before

an event occurs– Implementing a plan

• Consider participation in the IEEE Electrical Safety Workshop to learn more about electrical safety

Conclusion

IEEE Workshop 2011

Conference: 2011 IEEE IAS Electrical Safety Workshop Conference Dates: 24 Jan - 28 Jan 2011 Location: Toronto Ontario

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L. Rene’ Graves, BS, CSPSenior Safety SpecialistTexas Instruments, Inc.

Dallas, TX

Electrical Safety: Are you Prepared?