Arc Flash SafetyArc Flash SafetyMurray State University

Arcing Fault EventsArcing Fault Events

An arc is produced by flow of electrical An arc is produced by flow of electrical current through ionized air after an initial current through ionized air after an initial flashover or short circuit.flashover or short circuit.

Arcs produce some of the highest Arcs produce some of the highest temperatures known to occur on earth – temperatures known to occur on earth – up to 35,000 degrees F. This is four times up to 35,000 degrees F. This is four times the surface temperature of the sun.the surface temperature of the sun.

All known materials are vaporized at this All known materials are vaporized at this temperature.temperature.

Arc Flash EffectsArc Flash Effects

Average of 1,710 (reported) electrical Average of 1,710 (reported) electrical burns per year in USAburns per year in USA– Burn from intense heatBurn from intense heat– Trauma from blast pressureTrauma from blast pressure– Toxic gases from vaporized metalToxic gases from vaporized metal– Sprayed molten metal dropletsSprayed molten metal droplets– Hearing damage from sound pressure waveHearing damage from sound pressure wave– Eye damageEye damage

Electrical Safety RequirementsElectrical Safety RequirementsOSHA 1910.333 (a)(1) & NFPA 70E 130.1OSHA 1910.333 (a)(1) & NFPA 70E 130.1

Qualified electrical workers shall not be asked Qualified electrical workers shall not be asked to work on equipment that is “hot” or “live” to work on equipment that is “hot” or “live” except for two reasons:except for two reasons:

1.1. De-energizing introduces additional or De-energizing introduces additional or increased hazardsincreased hazards Such as cutting ventilation to a hazardous locationSuch as cutting ventilation to a hazardous location

2.2. Infeasible due to equipment design or Infeasible due to equipment design or operational limitationsoperational limitations Such as doing voltage testing for diagnosticsSuch as doing voltage testing for diagnostics

Elements of Arc Flash SafetyElements of Arc Flash Safety

Defined responsibilitiesDefined responsibilities

Calculation of degree of arc flash hazardCalculation of degree of arc flash hazard

Personal protective equipmentPersonal protective equipment

TrainingTraining

Tools for safe workTools for safe work

Warning labels on equipmentWarning labels on equipment

ResponsibilitiesResponsibilities

MSU will provide:MSU will provide:– PPEPPE– TrainingTraining– LabelingLabeling– Insulated toolsInsulated tools– Lock out/tag out Lock out/tag out

devicesdevices

MSU employee will:MSU employee will:– Follow safe work Follow safe work

practicespractices– Use appropriate Use appropriate

insulated toolsinsulated tools– Wear PPE when Wear PPE when

requiredrequired

Arc Flash Hazard AnalysisArc Flash Hazard Analysis

Determines flash protection boundary and Determines flash protection boundary and PPE requirements as a function of location PPE requirements as a function of location and work activity.and work activity.Arc flash hazard and flash protection Arc flash hazard and flash protection boundary varies with:boundary varies with:– Type of equipment and configurationType of equipment and configuration– Available short circuit currentAvailable short circuit current– VoltageVoltage– Predicted fault duration – protective devices Predicted fault duration – protective devices

upstream on the arcing fault and their settingsupstream on the arcing fault and their settings

Flash Protection BoundaryFlash Protection Boundary

Linear distance from exposed live parts Linear distance from exposed live parts within which a person could receive within which a person could receive second degree burns resulting from an arc second degree burns resulting from an arc flash.flash.

Flash Protection BoundariesFlash Protection Boundaries

Limited Approach BoundaryLimited Approach Boundary– Entered only by qualified persons or unqualified Entered only by qualified persons or unqualified

persons escorted by qualified personpersons escorted by qualified person

Restricted Approach BoundaryRestricted Approach Boundary– Entered only by qualified persons required to use Entered only by qualified persons required to use

shock protection techniques and equipmentshock protection techniques and equipment

Prohibited Approach BoundaryProhibited Approach Boundary– Entered only by qualified persons requiring same Entered only by qualified persons requiring same

protection as if in direct contact with live partsprotection as if in direct contact with live parts

Prohibited shock boundary: Qualified persons only - PPE as if direct contact with live part

Restricted shock boundary: Qualified persons only

Limited shock boundary: Qualified or unqualified persons*

*only if accompanied by qualified person

Note: shock boundaries dependent on system voltage level

Flash Protection Boundary (FPB)Must wear appropriate PPEFPB dependent on fault level and time duration.

Flash Protection Boundary (FPB)Must wear appropriate PPEFPB dependent on fault level and time duration.

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Approach BoundariesApproach Boundaries

Each boundary is a Each boundary is a sphere to be sphere to be observed in all observed in all directions three directions three dimensionally.dimensionally.

LabelingLabeling

Switchboards, panel boards, industrial Switchboards, panel boards, industrial controls, etc. that require examination, controls, etc. that require examination, adjustment, or maintenance while adjustment, or maintenance while energized shall be labeled.energized shall be labeled.

LabelingLabelingLabels shall be designed to warn of Labels shall be designed to warn of potential arc flash hazardspotential arc flash hazards

MSU will classify arc flash hazard labels MSU will classify arc flash hazard labels into two types:into two types:– Low voltage below 680 voltsLow voltage below 680 volts– High voltage above 680 voltsHigh voltage above 680 volts

Insulated ToolsInsulated ToolsFlame retardantFlame retardant

Double insulated. A first hi-visibility yellow Double insulated. A first hi-visibility yellow layer provides the insulation for the tool, and layer provides the insulation for the tool, and the outer hi-visibility orange layer protects the the outer hi-visibility orange layer protects the lower yellow layer. lower yellow layer. NOTE: If the yellow layer can NOTE: If the yellow layer can be seen through the orange be seen through the orange layer, the tool should be layer, the tool should be removed from service.removed from service.

NFPA 70E 120.1NFPA 70E 120.1120.1 Process of Achieving an 120.1 Process of Achieving an Electrically Safe Work ConditionElectrically Safe Work Condition

– An electrically safe work condition shall be An electrically safe work condition shall be achieved when performed in accordance achieved when performed in accordance with the procedures of 120.2 and verified by with the procedures of 120.2 and verified by the following process:the following process:

Electrically Safe Work ConditionElectrically Safe Work Condition

1.1. Determine all electrical sources using up-to-Determine all electrical sources using up-to-date information, drawings, diagrams, etc.date information, drawings, diagrams, etc.

2.2. After properly interrupting the load current, After properly interrupting the load current, open the disconnecting device(s) for each open the disconnecting device(s) for each source.source.

– At this point, the equipment or circuit is simply At this point, the equipment or circuit is simply de-energized, not in an electrically safe work de-energized, not in an electrically safe work condition.condition.

Electrically Safe Work ConditionElectrically Safe Work Condition

3.3. Visually verify that disconnecting Visually verify that disconnecting means fully open if possiblemeans fully open if possible

4.4. Apply lockout tagout devicesApply lockout tagout devices

5.5. Test for absence of voltageTest for absence of voltage Verify proper operation of test Verify proper operation of test

equipmentequipment

6.6. Ground phase conductors if there Ground phase conductors if there is a possibility of induced is a possibility of induced voltages or stored energyvoltages or stored energy

Electrically Safe Work ConditionElectrically Safe Work Condition

Until these six steps have been executed, Until these six steps have been executed, some exposure to an electrical hazard still some exposure to an electrical hazard still exists and proper PPE is required.exists and proper PPE is required.

Safe Work PracticesSafe Work Practices

For open box work where the circuit can For open box work where the circuit can not be de-energized, safe work practices not be de-energized, safe work practices will include:will include:– Use of insulated toolsUse of insulated tools– Use of personal protective equipmentUse of personal protective equipment– Not working aloneNot working alone

Safe Work PracticesSafe Work Practices

If the box is open and the circuit can not If the box is open and the circuit can not be de-energized personal protective be de-energized personal protective equipment is required; for 120 volts:equipment is required; for 120 volts:– Safety glassesSafety glasses– Cotton shirt and pantsCotton shirt and pants

*Note: NFPA recommends cotton under *Note: NFPA recommends cotton under garments for use when an arc flash hazard is garments for use when an arc flash hazard is present.present.

Safe Work PracticesSafe Work PracticesIf the box is open and the circuit can not If the box is open and the circuit can not be de-energized, personal protective be de-energized, personal protective equipment is required; for 120-680 volts:equipment is required; for 120-680 volts:– Safety glasses, ear plugsSafety glasses, ear plugs– Cotton shirt and Indura pants Cotton shirt and Indura pants

(MSU work uniform)(MSU work uniform)– Category 2 face shieldCategory 2 face shield– Category 2 Indura coatCategory 2 Indura coat– Low voltage insulated glovesLow voltage insulated gloves

Safe Work PracticesSafe Work Practices

If the box is open and the circuit If the box is open and the circuit can not be de-energized, personal can not be de-energized, personal protective equipment is required, protective equipment is required, for high voltage of 680V or higher:for high voltage of 680V or higher:– Safety glasses, ear plugsSafety glasses, ear plugs– Cotton shirt and Indura pantsCotton shirt and Indura pants– Category 4 hoodCategory 4 hood– Category 4 Indura coat and pantsCategory 4 Indura coat and pants– High voltage insulated gloves with High voltage insulated gloves with

leather over glovesleather over gloves

PPE – NFPA 70E Table 130.7PPE – NFPA 70E Table 130.7

Typical Protective Clothing Systems

Hazard/Risk Category

Clothing Description (Typical number of clothing layers is given in parentheses)

Required Minimum Arc Rating of PPE

[(J/cm2(cal/cm

2)]

0 Non-melting, flammable materials (i.e., untreated cotton, wool, rayon, or silk, or blends of these materials) with a

fabric weight at least 4.5 oz/yd2 (1)

N/A

1 FR Shirt and FR pants or FR coverall (1) 16.74 (4)

2 Cotton underwear - conventional short sleeve and brief/shorts, plus FR shirt and FR pants (1 or 2)

33.47 (8)

3 Cotton underwear plus FR shirt and FR pants plus FR coverall, or cotton underwear plus two FR coveralls (2 or 3)

104.6 (25)

4 Cotton underwear plus FR shirt and FR pants plus multi-layer flash suit (3, or more)

167.36 (40)

SummarySummaryEquipment should be placed in an electrically Equipment should be placed in an electrically safe work condition prior to servicing the safe work condition prior to servicing the equipment.equipment.

Safe work practices should be followed to Safe work practices should be followed to reduce the hazards associated with an arc reduce the hazards associated with an arc flash.flash.

If necessary to work on live parts:If necessary to work on live parts:– 120 volts - safety glasses & cotton uniform120 volts - safety glasses & cotton uniform– 120-680 volts – Category 2 arc flash suit120-680 volts – Category 2 arc flash suit– 680 volts and above – Category 4 arc flash suit680 volts and above – Category 4 arc flash suit