Electrical Arc-Flash Hazards

1. Electrical Arc-Flash Hazards
IEEE IAS Distinguished Lecture
Peter E. Sutherland, IEEE Fellow, IAS Distinguished Lecturer, 2012-2013

2. Discussion Highlights
The Bigger Picture of Electrical Safety
Arc-Flash Risks and Effects
Arc-Flash Approach Boundaries
Arc-Flash Hazard Calculations
NFPA 70E Tables
IEEE Standard 1584-2002
Arc-Flash Mitigation
Arc-Flash Categories & Protective Clothing
Arc-Flash Labels and Permits

3. Worker Safety is Important
Why?
– In addition to being the right thing to do it is intrinsically
connected to productivity, worker morale and liability costs
– Machinery, processes & facilities usually designed with worker
& machine safety as key consideration from start...
– However, electrical safety often handled differently… Late, after
base system design is finished, sometimes after equipment is
purchased . . .
It should not be !
– Electrical safety can best be optimized by being part of the
initially defined mission for the facility’s power distribution
system and being considered at every decision point in the
design, purchasing and installation process.

4. Hierarchy of Hazard Control
Measures
1. Elimination of the hazard
2.
Substitution for less hazardous equipment,
materials or process
3.
Engineering control for less hazardous
exposure or severity
4. Warnings, signs, and other communications
5.
Administrative controls including safe work
practices
6. Personal protective equipment
From ANSI Z10-2005 American National Standard for
Occupational Health and Safety Management
Systems
Thinking through this
table allows assigning
value to different
potential solutions to Arc-
Flash & shock hazards
PPE is the last resort!

5. Hazards Involved in Working On or Near
Energized Electrical Equipment
Dangers associated with working on or around exposed energized
conductors or parts:
Electrical shock - Becoming part of the circuit.
Arc-Flash - The violent release of superheated gases caused by
an electric arc.
Arc Blast - The blast effects from the pressure wave associated
with an Arc-Flash occurrence.
Shrapnel - Ejection of projectiles or bits of metal.
Noise - From initial explosive expansion of air.

6. Standards for Electrical Safety and Arc-Flash
Hazards – Industrial and Commercial
NFPA 70E -2012, “Standard for
Electrical Safety in the Workplace”
– AC Systems Table <240 V - 38 kV
– DC Systems Table 100-600 V
IEEE Std. 1584-2002, “IEEE Guide
for Performing Arc-Flash Hazard
Calculations”
– 3-phase AC Systems 208 V-15 kV,
CSA Z462-12, “Workplace Electrical
Safety”
NFPA 70-2011, “National Electrical
Code”
OSHA 29 CFR 1910 Subpart S -
Electrical

7. Standards for Electrical Safety and Arc-Flash
Hazards – Electric Power Generation,
Transmission and Distribution
IEEE Std. C2-2012, “National
Electrical Safety Code”
– 3-phase AC Systems 1 – 500 kV
– Single phase-ground arc in open air.
– Tables 410-1, -2, -3 for Clothing and
Clothing Systems.
– Arc-Flash Hazard Analysis may be used
in place of tables.
OSHA 29 CFR 1910 Subpart R
Section 1910.269 - Electric Power
Generation, Transmission and
Distribution
– No reference to Arc-Flash Standards

8. NEC References to NFPA 70E
NFPA 70-2011 “National Electrical Code (NEC)”
– NEC Article 100, Definitions: Qualified Persons has NFPA 70E
referenced for electrical safety training requirements.
– NEC Article 110.16 requires that Electrical equipment such as
switchboards, panelboards, industrial control panels, meter socket
enclosures, and motor control centers shall be field marked to
warn qualified persons of potential electric Arc-Flash hazards.
– NEC Article 240.87 requires that when a circuit breaker is used
with a non-instantaneous trip one of the following means shall be
provided: zone selective interlocking, differential relaying or
energy-reducing maintenance switching with local status indicator.
– NEC Article 430.102 refers to Lock-Out Tag-Out procedures for
Motor Disconnecting Means.
– NEC Article 490.1 Scope Statement for Equipment Over 600 Volts.

9. OSHA References to NFPA 70E
OSHA regulation 29 CFR 1910 Subpart S –
Electrical, Appendix A: Reference Documents
– NFPA 70E-2000 is the basis for most of the OSHA final
rule. However, there are some parts based upon the 2002
and 2005 NEC and even some selected parts of NFPA 70E
2004 Edition.
– OSHA can, and has enforced lack of Arc-Flash protection
under the "general duty clause".

10. Arc-Flashover Incident
Description: A routine voltage check at a 480V
terminal board inside the GAC resulted in an Arc-
Flash burning the hand of the person checking the
voltage. The check consisting of placing one meter
lead on a single phase and measuring the other 2
phases with the second meter lead. The employee
was treated and released to return to work.
Direct Cause: The terminal board was delivered with
incorrect long terminal lugs that were also not
insulated. The terminal points of the meter were
exposed clamps too large for this small equipment.
Root Cause: The equipment being used and the
equipment being checked was not carefully evaluated
prior to conducting the voltage check.
Contributing Factors: Terminal board delivered with
incorrect terminal lugs that were also not insulated.
Corrective Actions:
– Use of a different style leads, the use of pointed
leads instead of clip leads
– Replace the terminal board with a new component
Broken Insulator and extra long terminal
lugs
Clips across
two phases

11. What May Happen with a
Slow Protective Device

12. Worker’s Flame-Resistant Shirt and
Insulating Gloves

13. Arc-Flash Effects
Temperature of the arc can reach 20,000°C
(35,000 °F) – about 4 times the temperature of
the sun!
In US, 5-10 Arc-Flash incidents requiring
hospitalization per day.
1 – 2 deaths per day from electrical events,
(shock, flash & blast).
More than 2,000 workers treated in burn
centers per year with severe Arc-Flash injuries.
(This does not include injuries in other hospitals
and clinics which go unreported.)

14. Examples of Activities which Involve
Arc-Flash Risks
Racking in or out of draw-out
circuit breakers.
Removing or installing circuit
breakers or fuses.
Working on control circuits with
exposed energized primary parts.
Applying safety grounds.
Removing panel covers for
inspections or other activities.
Low voltage testing and
diagnostics.

15. Arc-Flash Standards
Simplified Tabular method presented in:
– NFPA-70E -2012, “Standard for Electrical Safety in the
Workplace”
– In Canada Z462-12, “Workplace Electrical Safety”
More sophisticated calculated methods suitable for low
voltage and higher voltages developed in:
– IEEE Std 1584-2002, “IEEE Guide for Performing Arc-Flash
Hazard Calculations.”
– Amendment 1 issued in 2004 as IEEE Std 1584a-2004,
(changes were relatively minor.)
– Sometimes combination of these two documents referred to as
Std 1584-2004.
– Amendment 2: Changes to Clause 4 issued in 2011 as IEEE Std
1584b-2011. Clarifications to clause on analysis process.

16. NFPA 70E Approach Boundary Fig. C.1.2.4

17. Shock Protection Approach Boundaries
Fixed Live
Part
Prohibited
Approach
Distance
Restricted
Approach
Distance
Limited
Approach
Distance
@15,000 Volts 5 ft, 0 in2 ft, 2 in0', 7"
@480 Volts 0', 1" 1 ft, 0 in 3 ft, 6 in
Limited Approach Boundary – Distance from an exposed live
part within which a shock hazard exists.
Restricted Approach Boundary – Distance from an exposed live
part within which there is an increased risk of shock, due to electrical
arc over combined with inadvertent movement, for personnel
working in close proximity to the live part.
Prohibited Approach Boundary – Distance from an exposed live
part within which work is considered the same as making contact
with the live part.

18. Arc-Flash Protection Approach
Boundaries
Flash Protection Boundary – Distance from an exposed live part within
which a person could receive a second-degree burn if an electrical Arc-Flash
were to occur. This second-degree burn results from the minimum Arc-Flash
energy of 1.2 cal/cm2, (5 joules/cm2). This boundary is determined by
calculating the distance at which an Arc-Flash energy of 1.2 cal/cm2 exists.
Working Distance - Dimension between the possible arc point and the head
and body of the worker positioned in place to perform the assigned task.
Value selected for the application – minimum 18 in (48 cm).
Flash
Protection
Boundary
Working
Distance
Fixed Live
Part
@15,000 Volts
@480 Volts 18" (Typical)
36" (Typical) (Must be calculated)
(Must be calculated)0.48 m (18 in.) (typical)
0.96 m (36 in.) (typical)

19. Combined Shock & Arc-Flash Boundaries
Fixed Live
Part
@480 Volts
@15,000 Volts
Limited
Approach
Distance
Restricted
Approach
Distance
Prohibited
Approach
Distance
0', 1"
0', 7"
1 ft, 0 in
2 ft, 2 in
3 ft, 6 in
5 ft, 0 in
(Arc Flash)
Working
Distance
18" (Typical)
36" (Typical)
Flash
Protection
Boundary
(Must be calculated)
(Must be calculated)
Usually > than the
Limited Approach
Distance but not always
25 mm (0 ft 1in)
0.2 m (0 ft 7 in.)
0.3 m (1 ft 0in)
0.7 m (2 ft 2 in.)
0.48 m (18 in.) (typical)
0.96 m (36 in.) (typical)
1.0 m (3 ft 6in)
1.5 m (5 ft 0 in.)

20. Safe Approach Distances
Unqualified persons - Safe when maintaining a distance from exposed
energized parts equal to the Limited Approach Boundary or the Flash
Protection Boundary, whichever is greater.
Qualified persons - Appropriate Arc-Flash protection shall be utilized if
flash protection boundary crossed.
To cross the Restricted Approach Boundary, the qualified person must:
– Have a documented work plan approved by management.
– Use appropriate protective equipment for work near exposed conductors and rated for voltage
and energy level.
– Be certain no part of body enters prohibited space.
– Keep as much as body as possible out of restricted space.

21. Safe Approach Distances
Qualified persons
Appropriate Arc-Flash protection shall be utilized if flash protection
boundary crossed.
To cross the Prohibited Approach Boundary, which is considered the same
as making contact with exposed energized conductors or parts, the
qualified person must:
– Have specific training for working on energized parts
– Have a documented plan justifying the need to work that close approved by management.
– Perform a risk analysis approved by management.
– Use appropriate protective equipment for work on exposed conductors and rated for voltage and
energy level.

22. Other Key Arc-Flash Definitions
Incident Energy – The amount of energy impressed on a surface, a
certain distance from the source, generated during an electrical arc event.
Measured in joules/cm2 or cal/cm2. (1 joule/cm2 = 0.24 cal/cm2).
Flash Hazard Analysis – A method to determine the risk of personal
injury as a result of exposure to incident energy from an electrical Arc-
Flash.
Arcing Fault Current – A fault current flowing through an electrical arc
plasma, also called arc fault current and arc current.
Bolted Fault Current – Resulting from a short circuit or electrical contact
between two conductors at different potentials in which the impedance or
resistance between the conductors is essentially zero.
Arc Duration – The total time it takes system protective devices to detect
and interrupt a fault current.

23. Operating Company Responsibilities
1. Conduct an Arc-Flash analysis of the power system.
2. Establish shock & protection boundaries and determine incident energy
levels at working distances.
3. Put warning labels on equipment.
4. Implement qualified and general worker training.
5. Provide necessary personal protective equipment, (PPE)
6. Require outside engineering consulting firms involved in
upgrades/expansions to provide 1, 2 and 3.
7. Require outside contractors to meet 4 & 5.

24. Steps in Performing an Arc-Flash Hazard
Analysis
1. Collect power system data.
2. Determine the system modes of operation.
3. Determine the bolted fault currents.
4. Determine the arcing fault currents.
5. Find protective device characteristics and arc durations.
6. Document system voltage levels and equipment classes.
7. Select the working distances.
8. Determine the incident energies for all equipment
9. Determine the flash protection boundary for all equipment.

25. Performing an Arc-Flash Hazard Analysis
Methods
– NFPA 70E-2012 Table 130.7 (C)(15)
AC systems
DC systems
– Power System Analysis Software
Arc-Flash calculation modules (AC and DC) can be obtained
with commercially available comprehensive power system
modeling software.
Steps in Arc-Flash Hazard Analysis:
1. Short-Circuit Study
2. Protective Device Coordination Study
3. Arc-Flash Hazard Analysis (Per NFPA 70E and IEEE 1584)

26. Do not do locally, on live equipment, what
can be done remotely outside Arc-Flash
boundary.
Substitution and Engineering Controls
Remote Racking, Remote Controls, Remote Metering

27. • “Arc Resistant Switchgear”
• Common in MV systems
• Moving into LV systems in US
• Contains arc safely
• Containment system between
person & arc
• Must be fully assembled
• Plenum needed to exhaust
May be solution for operators, but not
for maintenance
Substitution and Engineering Controls
Containment method – passive arc resistance

28. Transfer energy to alternate current path
Crowbar method
• Remove arcing fault via bolted fault
• Energy goes to lowest impedance path
• Protection provided even if equipment
doors are open
• Not reusableMain LV
Breaker
Feeders
. . . . .
XFMR
52
MV
Breaker
B
C
A
Substitution and Engineering Controls
Arc Fault Diversion – Crowbar Method

29. Containment method
• Triggered fault in containment vessel
• Lower resistance arcing fault
• Lower energy than bolted fault
• < 8 ms transfer
• Reusable, maintainable
Substitution and Engineering Controls
Arc Fault Diversion – Containment Method
Protected
Zone
Containment
Vessel
Arc
Diversion
Relay

30. Arc-Flash Categories & Protective
Clothing
Arc
Rating
Hazard/Risk
Category
Description of Required Clothing
cal/cm
2
(HRC) and Personal Protective Equipment (PPE)
-- 0 Nonmelting or Untreated Natural Fiber (Weight ≥≥≥≥ 4.5 Oz/yd
2
) Pants and
Shirt + Safety glasses or goggles + Hearing protection + Heavy
duty leather gloves (AN)
4 1 AR Shirt & AR Pants or AR Coverall + AR AF Suit Hood or AR Face
Shield & Balaclava + AR jacket, parka, rainwear or hard hat liner
(AN) + Hard Hat + Safety glasses or goggles + Hearing protection +
Heavy-duty leather gloves + Leather work shoes (AN)
8 2 AR Shirt & AR Pants or AR Coverall + AR AF Suit Hood or AR Face
Shield & Balaclava + AR jacket, parka, rainwear or hard hat liner
(AN) + Hard Hat + Safety glasses or goggles + Hearing protection +
Heavy-duty leather gloves + Leather work shoes
25 3 AR Shirt & AR Pants + AR Coverall + AR AF Suit Jacket, Pants and Hood
+ AR Gloves + AR jacket, parka, rainwear or hard hat liner (AN) +
AR = Arc-Rated, AF = Arc-Flash, AN = As Needed
Source NFPA 70E-2012 Table 130.7(C)(16) and Clause130.7(C)(10)(b)

31. Arc-Flash PPE by HRC
HRC 2
8 cal/cm2
HRC 1
4 cal/cm2
HRC 3 = 25 cal/cm2
HRC 4 = 40 cal/cm2
HRC 0
1.2 cal/cm2

32. AF Hazard Analysis & Protective
Clothing
Location
Incident
Energy
Description of Required Clothing*
Arc-Flash
Boundary
cal/cm
2
and Personal Protective Equipment (PPE)
Outside ≤≤≤≤1.2 Nonmelting or Untreated Natural Fiber (Weight ≥≥≥≥ 4.5 Oz/yd
2
) Pants
and Shirt + Safety glasses or goggles + Hearing protection +
Face shield for projectile motion (AN) + Heavy-duty leather
gloves or rubber insulating gloves with leather protectors
(AN)
Inside >1.2 to 12 AR Shirt & AR Pants or AR Coverall or AF Suit + AR Face Shield &
AR Balaclava or AR AF Suit Hood + AR jacket, parka or
rainwear (AN) + Hard Hat + AR hard hat liner (AN) + Safety
glasses or goggles + Hearing protection + Heavy-duty leather
gloves or rubber insulating gloves with leather protectors +
Leather work shoes
Inside >12 AR Shirt & AR Pants or AR Coverall and/or AF Suit + AR AF Suit
Hood + AR gloves or rubber insulating gloves with leather
protectors + AR jacket, parka or rainwear (AN) + Hard Hat +
*Arc-Rating must be ≥≥≥≥ Incident Energy from AF Hazard Analysis.
AR = Arc-Rated, AF = Arc-Flash, AN = As Needed
Source NFPA 70E-2012 Table H.3(b)

33. Arc-Flash PPE by Incident Energy
>1.2 to 12 cal/cm
2
>12 cal/cm
2
Arc Rating must be ≥≥≥≥ Incident Energy from AF Hazard Analysis.

34. Notes on AF Hazards & Protective
Clothing
Source: NFPA70E-1012 130.7 (A) Informational Notes (IN) 1 – 3,
130.7(C)(15) IN2 and 130.7(C)(16) IN 2
1. PPE Requirements of NFPA 70E-2012 130.7 do not protect
against effects of explosions such as physical trauma injuries.
2. Normal operation of enclosed electrical equipment is “not likely”
to present an electrical hazard when it is
a) 600 volts or less
b) Properly installed by qualified persons.
c) Properly maintained by qualified persons.
3. However, closed equipment doors do not remove the
requirement to wear PPE.
4. These tasks are Category 0 in Table 130.7(C)(15)(a).
5. For Incident Energy > 40 cal/cm2 it is recommended to de-
energize the equipment before working on energized parts or
equipment. There is no HRC greater than 4.

35. Typical Arc-Flash & Shock Equipment
Label

36. Typical Shock & Arc-Flash Work Permit
(1)

37. Typical Shock & Arc-Flash Work Permit
(2)

38. Thank you!
Any questions?