Common Electrical Hazards
in the Workplace Including
Arc Flash
Introduction
This material was produced under grant number SH-16615-07-60-F-12 from the
Occupational Safety and Health Administration, U.S. Department of Labor. It does
not necessarily reflect the views or policies of the U.S. Department of Labor, nor
does mention of trade names, commercial products, or organizations
imply endorsement by the U.S. Government.
This material was produced by the Workplace Safety Awareness Council, a
501(c)(3) not-for-profit organization dedicated to safety in the workplace.
For further information about the council or upcoming safety related training,
please visit our website at www.wpsac.org or call us at (863) 537-4053.
What’s New
In February 1972, OSHA incorporated the 1971 edition of
the National Fire Protection Association's (NFPA) National
Electrical Code (NEC), NFPA 70-1971
On January 16, 1981, OSHA revised its Electrical standard
with Part I of National Fire Protection Association's (NFPA)
70E - 1979
On August 13, 2007, OSHA revised its Electrical standard to
reference National Fire Protection Association's (NFPA) 70E
- 2000
Common Hazards
Common hazards when working with energized electrical
equipment include:
• Electric Shock / Burns
• Blast
• Arc Flash
Fast Fact: It doesn’t take much for human skin to burn – in fact
an exposure of 203 F for just one-tenth of a second (6 cycles) is
enough to cause a third degree burn!
GFCI Protection
1910.304(b)(3)(i)
Receptacles installed in bathrooms or on rooftops shall have
ground-fault circuit-interrupter protection for personnel.
GFCI Protection
1910.304(b)(3)(ii)(A)
Receptacle outlets (including cord sets) that are not
part of the permanent wiring of the building shall
have ground-fault circuit-interrupter protection for
personnel.
Note: A cord connector on an extension cord set is
considered to be a receptacle outlet if the cord set is
used for temporary electric power.
Flexible Cords – Permitted Use
1910.305(g)(1)(ii)(A)-(L)
• Pendants;
• Wiring of fixtures;
• Connection of portable lamps or appliances;
• Portable and mobile signs;
• Elevator cables;
• Wiring of cranes and hoists;
• Appliances to permit removal for maintenance and repair
Pendant, or
Fixture Wiring
Portable lamps,
tools or appliances
Stationary equipment to
facilitate interchange
Flexible Cords – Permitted Use
1910.305(g)(1)(ii)(A)-(L)
• Connection of stationary equipment to facilitate their frequent
interchange;
• Prevention of the transmission of noise or vibration;
• Appliances where the fastening means and mechanical connections
are designed to permit removal for maintenance and repair;
• Data processing cables approved as a part of the data processing
system;
• Connection of moving parts; and
• Temporary wiring as permitted in paragraph (a)(2) of this section.
Prohibited Uses of Flexible Cords
1910.305(g)(1)(iv)(A)-(F)
• As a substitute for the fixed wiring of a structure;
• Where run through holes in walls, ceilings, or floors;
• Where run through doorways, windows, or similar openings;
• Where attached to building surfaces;
• Where concealed behind building walls, ceilings, or floors; or
• Where installed in raceways, except as otherwise permitted in this subpart.
Substitute for
fixed wiring
Run through walls,
ceilings, floors, doors,
or windows
Concealed behind or
attached to building
surfaces
Flexible Cords
1910.304(b)(3)(ii)(C)(3)
Extension cords must be visually inspected before each
use on any shift. Examine the cord for
• Missing grounding pin
• Damaged other jacket (tear in insulation)
• Possible internal damage (pinched cord)
Grounding Pin
1910.304(b)(3)(ii)(C)(4)(i) – (iii)
Ensure that grounding pin on extension cords is in place and
operable
All equipment grounding conductors shall be tested for continuity:
• Before first use
• Before return to service (repairs)
• Before use after an incident that may have caused damaged and
• Intervals not to exceed three (3) months
Splices
1910.305(g)(2)(ii)
Flexible cords may be used only in continuous lengths
without splice or tap.
Note: Black electrical tape does not provide suitable insulation and is not acceptable
Flexible Cords
1910.305(g)(2)(i)
• Durably marked as to type, side, and number of
conductors
• Strain relief must be provided
Inadequate Wiring Hazards
Using a portable tool with an
extension cord that has a wire too
small for the tool:
• The tool will draw more current
than the cord can handle,
causing overheating and a
possible fire without tripping the
circuit breaker
• The circuit breaker could be the
right size for the circuit but not
for the smaller-wire extension
cord
Wire Gauge
WIRE
Wire gauge measures
wires ranging in size from
number 36 to 0 American
wire gauge (AWG)
Minimum Depth of Working Space
1910.303(g)(1)(i)(A) Table S-1
Minimum clear distance for condition2 3
Nominal voltage to
ground
Condition A
m
ft
Condition
B
m
ft
Condition C
m
ft
10.9
13.0
10.9 13.0
0-150
0.9
3.0
Condition A -- Exposed live parts on one10.9
side and13.0
no live or1.0
grounded
151-600
3.5parts on
1.2the other4.0
side
Condition B -- Exposed live parts on one side and grounded parts on the other side
Condition C -- Exposed live parts on both sides
Labeling of Breakers
1910.303(f)(2) –(3)
Overcurrent devices or disconnecting devices:
• shall be legibly marked to indicate its purpose
• shall be of sufficient durability to withstand the
environment involved.
Cabinets, Boxes and Fittings
1910.305(b)(1)(i)
• Conductors entering shall be protected
• Openings shall be effectively closed
• Cable is fastened within 12” from box or raceway
Cabinets, Boxes and Fittings
1910.305(b)(1)(i)
• Conductors entering shall be protected
• Openings shall be effectively closed
• Cable is fastened within 12” from box or raceway
Cabinets, Boxes and Fittings
1910.305(b)(1)(i)
• Conductors entering shall be protected
• Openings shall be effectively closed
• Cable is fastened within 12” from box or raceway
Cabinets, Boxes and Fittings
1910.305(b)(2)(i)
In completed installations, each outlet box shall have a
cover, faceplate, or fixture canopy.
Arc Flash Event
A dangerous release of energy created by an electrical
fault
 Release will contain:




Thermal energy
Acoustical energy
Pressure wave
Debris
Arc Flash Intensity
Variables that effect the size and energy of an electric arc
flash:
 Amperage
 Voltage
 Arc Gap
 Closure time
 Distance away from arc
 3 phase v single phase
 Confined space
Arc Energy Basics
 Exposure energy expressed in cal/cm2
 ½ to 1 cal/cm2 = hottest part of lighter in 1 sec
 1-2 calorie exposure will cause second degree burn on human skin
 Typical non-FR workwear can ignite @4-5cals
 Arcs typically release 5-30 cals - energies of 30-60 cals are not
uncommon
Arc Flash Events
 Can reach 35,000 F
 Fatal burns >10 feet
 Majority of hospital
admissions are arc flash
burns, not shock
 30,000 arcs and 7000
burn injuries per year
 Over 2000 people
admitted to burn centers
yearly with severe arc
flash burns
What Is Important
Three factors are critical when discussing burns:
 Extent (% of body burned – related to
survivability)
 Severity (linked to quality of life)
 Location (linked to quality of life)
What Is a Burn?
A chemical process which
progressively injures skin; severity
relates to depth
 1st : redness, pain – not permanent
 2nd: blistering – skin will
regenerate
 3rd: total skin depth destroyed.
Will not
regenerate – requires
grafting
 4th : Underlying muscle damaged
Burn Survival
 Burn percentage, more than severity, predicts survival
because skin is infection barrier
 2nd and 3rd degree break skin, providing an infection
pathway
 Most hospital deaths 2-4 weeks post-exposure are
infection (gram-neg staph)
Burn Survival Factors
 Odds of survival fall with total % burn
 Odds of survival fall precipitously above 50% burn
 Odds of survival fall as age increases
Burn Injury
 Burn treatment requires approx. 1.5 days hospitalization per %
burn
 Average hospitalization is 19 days, at costs exceeding
$18,000/day
 Total hospitalization cost typically ranges from $200,000 to
$750,000, with many over $1,000,000 USD
Deenergized Equipment
The most effective and fool-proof way to eliminate the risk
of electrical shock or arc flash is to simply deenergize the
equipment. . .
Lockout / Tagout
A lock and a tag shall be placed on each disconnecting
means used to deenergize circuits and equipment on
which work is to be performed.
Note: Electric equipment that have been deenergized but have not been
locked out or tagged shall be treated as energized.
Working Live
OSHA has also made allowances for not deenergizing
electrical equipment when it would increase current
hazards or create additional hazards, for example:
• interruption of life support equipment,
• deactivation of emergency alarm systems,
• shutdown of hazardous location ventilation equipment,
• removal of illumination for an area.
Working live is also allowable due to infeasibility of
deenergization (i.e. testing of electric circuits)
Hot Work Requirements
Employer must develop and enforce safety-related work practices
to prevent electric shock or other injuries resulting from either
direct or indirect electrical contacts.
These safety related work practices could include:
•
•
•
•
•
•
•
Energized Electrical Work Permit
Pre-work Job Briefing
Personal Protective Equipment
Insulated Tools
Written Safety Program
Qualified Person Training
Flash Hazard Labeling
Definitions
A number of “approach boundaries” exist and both
qualified and non-qualified persons must understand
these definitions.
Flash Protection
Boundary
Flash Protection Boundary (outer boundary): The flash
boundary is the farthest established boundary from the
energy source. If an arc flash occurred, this boundary is
where an employee would be exposed to a curable
second degree burn (1.2 calories/cm2)
Limited Approach
Boundary
Limited Approach: An approach limit at a distance from an
exposed live part where a shock hazard exists.
“Working Near Live Parts”
Occurs when any activity inside the Limited Approach Boundary is undertaken
Restricted Approach
Boundary
Restricted Approach: An approach limit at a distance
from an exposed live part which there is an increased
risk of shock.
Prohibited Approach
Boundary
Prohibited Approach (inner boundary): A distance from an
exposed part which is considered the same as making
contact with the live part.
“Working On Live Parts”
Occurs when coming in contact with live parts, including test equipment, body,
PPE, tools etc. . .
Flash Protection
Labeling
Arc Flash Hazard labeling must be posted which identifies:
• Approach boundaries
• PPE required
How to Determine Boundaries
NFPA Tables: Refer to NFPA 70E – 2000 Table 3-3.9.1 or
Table 130.7(C)99)(a) NFPA 70E – 2004.
Pro: Easiest and quickest method
Con: Provides the least amount of accuracy. Limited
tasks are covered in tables
How to Determine Boundaries
Formula Method: NFPA 70 E and IEEE Standard 1584
provides formulas that can be used to accurately
determine the approach boundaries.
Pro: More accurate and all inclusive than NFPA tables
Con: Is time consuming, requires an engineer level of
expertise and is subject to human error.
How to Determine Boundaries
Approach Calculator: IEEE and others have provided a
spreadsheet based calculator to assist in determining
approach boundaries.
Pro: Quicker than formula method
Con: Still requires detailed information about the
equipment and circuit often requiring the use of an
electrical engineer.
How to Determine Boundaries
Software: There exists on the market various software
products that can simplify and expedite the approach
boundary calculations.
Pro: Creates one-line diagrams and arc flash labels
based on data entered
Con: Cost and equipment / circuit knowledge is still
required often requiring an engineer.
Qualified Persons
Qualified person: One who has received training in and
has demonstrated skills and knowledge in the
construction and operation of electric equipment and
installations and the hazards involved.
Qualified Person Training
1910.332(b)(3)(i) – (iii)
Qualified persons shall at a minimum be trained in the
following areas:
• The skills to distinguish exposed live parts from other parts
of electric equipment.
• The skills to determine the nominal voltage of exposed live
parts, and
• The clearance distances specified in 1910.333(c) and the
corresponding voltages to which the qualified person will be
exposed.