Download Electrical Hazards and Arc Flash Awareness

Electrical Hazards and Arc Flash
Awareness
Instructor: Brian Terry
Class Outline
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Welcome/Overview
Accident Statistics
Electrical Terminology
Introduction to Electrical Hazards
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Electrical Shock / Electrocution
Electrical Burns
Arc Flash
Arc Blast
Class Outline
• Arc Hazard Boundary
• Four Approach Boundaries
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Limited Approach Boundary
Restricted Approach Boundary
Prohibited Approach Boundary
Flash Protection Approach Boundary
• Qualified and Unqualified Persons
• Energized Electrical Work Permit
• Arc Flash Hazard Marking Requirements
Class Outline
• PPE / FR Clothing
• Safe Work Practices
• Identifying Other Electrical Hazards
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Inadequate Wiring Hazards
Overload Hazards
Grounding Hazards
Identifying Disconnects
Clear Spaces
Ground Paths
Guarding Live Parts
Clues that Electrical Hazards Exist
Accident Statistics
National Safety Council Statistics
• 30,000 electrical shock accidents occur each
year.
• 1,000 fatalities due to electrocution occur
each year.
• 5 to 10 arc flash explosions occur in
electrical equipment every day.
• 2,000 workers are sent to burn centers with
severe injuries each year.
Introduction to Electrical
Hazards
Hazards of electricity
• There are five main types of electrical
injuries:
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Electrical shock
Electrocution (death due to electrical shock)
Electrical Burns
Arc Flash
Arc Blast
Electrical Shock
• Received when current passes
through the body
• Severity of the shock depends on:
– Path of current through the body
– Amount of current flowing through
the body
– Length of time the body is in the
circuit
• LOW VOLTAGE DOES NOT
MEAN LOW HAZARD
Dangers of Electrical Shock
• Currents greater than 75 mA* can cause
ventricular fibrillation (rapid, ineffective
heartbeat)
• Will cause death in a few minutes unless a
defibrillator is used
• 75 mA is not much current – a small power
drill uses 30 times as much
* mA = milliampere = 1/1,000 of an ampere
How is an electrical shock received?
• When two wires have different potential
differences (voltages), current will flow if they are
connected together
• If you come into contact with an energized (live)
wire, and you are also in contact with a Neutral,
grounded wire, a conductor with a different phase
voltage, current will pass through your body and
YOU WILL RECEIVE A SHOCK
How is an electrical shock received?
• If you are in contact with an energized wire or any
energized electrical component, and also with any
grounded object, YOU WILL RECEIVE A
SHOCK!
• You can even receive a shock when you are not in
contact with a ground
– If you contact both wires of a 240-volt cable, YOU
WILL RECEIVE A SHOCK and possibly be
electrocuted
Electrocution
• Accidental death by
electric shock.
• An average of one
worker is electrocuted
on the job every day.
• NSCS states that
1,000 fatalities due to
electrocution occur
each year.
Electrical Burns
• Most common shock-related,
nonfatal injury
• Occurs when you touch
electrical wiring or equipment
that is improperly used or
maintained
• Typically occurs on the hands
• Very serious injury that needs
immediate attention
Arc Flash
• Arc flash occurs when an electrical current
passes through air.
• It creates temperatures up to 30,000 o F
• It burns skin and ignites clothing causing
additional burns.
• It can create an explosion
• It can create dangerous vapors
Arc Blast
• Arc blast occur when the extreme
temperatures of the electrical arc cause
explosive expansion of both the surrounding
air and the metal in the arc’s path.
• It creates extremely high air pressure
• A very loud sound
• The force sends flying shrapnel and molten
metal in a 270o outward radius.
What happens during an Arc Flash /Blast?
• An Arc Flash is the result of a rapid release of
energy due to an arcing fault between a phase bus
bar and another phase bus bar, Neutral or a Ground.
• During an arc fault, The ionized air is the conductor.
• After the short burns away, the arc fault is then
sustained by the establishment of highly conductive
plasma.
• This massive energy discharge burns the bus bars,
vaporizing the copper, expanding rapidly into an
explosive volume of approximately 40,000 to 1.
• This explosion devastates everything in its path,
creating deadly shrapnel as it dissipates.
Laboratory Controlled Arc Blast
Short Circuit
A
B
Arc Fault
A
B
Electrical Arc Flash
35,000 °F
Molten Metal
Pressure Waves
Sound Waves
Shrapnell
Copper Vapor:
Solid to Vapor
Expands by
67,000 times
Hot Air-Rapid Expansion
Intense Light
Results
Sound
P1
141.5 db @ 2 ft.
>2160 lbs/sq.ft
T2
T1
>225°C / 437°F
T3
> 225°C / 437°F
50°C / 122°F
> Indicates Meter Pegged
Arc Flash PPE
What about Circuit Protection?
• The arc fault current is usually much less
than the available bolted fault current and
below the rating of circuit breakers.
• Unless these devices have been selected to
handle the arc fault condition, they will
NOT trip and the full force of an arc flash
will occur.
Are there any circuit protection devices
that can suppress fault currents during
arc flash conditions?
• The answer is Yes!, some companies incorporate
transformers and other arc fault suppression
devices in there circuit breakers that limit the
amount of fault current available during an Arc
flash condition.
• These are being developed and may be available
for certain applications.
• But by NO means, this takes the complete arc
flash hazard away.
Industry Standards for arc flash
prevention
• OSHA 29 Code of Federal Regulations
(CFR) part 1910 Subpart S
• NFPA 70 National Electrical Code
• NFPA 70E Standard for Electrical Safety
Requirements for Employee Workplaces.
• IEEE Standard 1584 Guide for Performing
Arc Flash Hazard Calculations.
Compliance with OSHA involves
adherence to a six-point plan:
• 1. A facility must provide, and be able to demonstrate,
a safety program with defined responsibilities.
• 2. Calculations for the degree of Arc Flash Hazard.
• 3. Correct personal protective equipment (PPE) for
workers.
• 4.Training for workers on the hazards of Arc Flash.
• 5. Appropriate tools for safe working.
• 6. Warning labels on equipment. (provided by the
owner of the equipment, Not manufacturers)
Qualified vs Unqualified
• Qualified Person. A qualified person shall be trained
and knowledgeable of the construction and operation of
equipment or a specific work method and be trained to
recognize and avoid the electrical hazards that might be
present with respect to that equipment or work method.
• One who has skills and knowledge related to the
construction and operation of the electrical equipment
and installations and has received safety training to
recognize and avoid the hazards involved.
• A person can be considered qualified with respect to
certain equipment and methods but still be unqualified
for others.
Qualified vs Unqualified
• Unqualified Persons. Unqualified persons
shall be trained in, and be familiar with, any
electrical safety related practices necessary
for their safety.
• A person who is not a qualified person.
Why a Safety Program
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Safer work environment
Personnel Safety
Fewer work related injuries
Fewer days missed due to work injuries
Lower insurance rates
Fewer medical cost to employee and employer
A more confident workforce
The saving of lives of qualifies and unqualified
personnel
Hazard Video
• http://www.youtube.com/watch?v=4bBvmP
Rqfmo
130.4 Approach Boundaries to Energized
Electrical Conductors or Circuit Parts
130.4 Approach Boundaries to Energized
Electrical Conductors or Circuit Parts
130.4 Approach Boundaries to Energized
Electrical Conductors or Circuit Parts
Approach Boundaries – NFPA 70E
Limited Approach Boundary
• Unqualified persons must stay a safe distance call
the Limited Approach Boundary.
– 3.5 ft. for fixed circuit parts ( 50 to 750 volts)
– 10 ft. for exposed movable conductors ( 50 to 750 volts)
– Boundaries increase as voltage gets higher to more than
23 ft in some cases.
Minimum Required Labeling
!
WARNING
Arc Flash and Shock Hazard
Appropriate PPE Required
24 inch Flash Hazard Boundary
3
cal/cm2 Flash Hazard at 18 inches
480
42
12
1
VAC
inch
inch
inch
Shock Hazard when Cover is removed
Limited Approach
Restricted Approach - 500 V Class 00 Gloves
Prohibited Approach - 500 V Class 00 Gloves
Date: 6/28/2001
Bldg. ECR #1
Equipment Name: Slurry Pump Starter
!
WARNING
Arc Flash and Shock Hazard
Appropriate PPE Required
24 inch Flash Hazard Boundary
3
cal/cm•2 Flash Hazard at 18 inches
1DF
PPE Level, 1 Layer 6 oz Nomex ®,
Leather Gloves Faceshield
480 VAC Shock Hazard when Cover is removed
36 inch Limited Approach
12 inch Restricted Approach - 500 V Class 00 Gloves
1 inch Prohibited Approach - 500 V Class 00 Gloves
Equipment Name:Slurry Pump Starter
Courtesy E.I. du Pont de Nemours & Co.
Hazard Category One
• Clothing with a minimum Arc Rating: 4 Cal/cm2
• 100% cotton Jeans min weight (12 oz/yd2) or FR
rated pants.
• FR rated Shirt or FR rated coveralls.
• Electrically rated Hard Hat.
• Non-conductive safety eyewear.
• Example: Removing bolted cover to expose live
parts on panel boards rated 240V and below.
Hazard Category Two
• Clothing with a minimum Arc Rating: 8 Cal/cm2
• Under layer of 100% non-melting natural fiber
(cotton/wool).
• FR rated shirt / pants or coveralls.
• FR rated Face shield or flash suit hood.
• Electrically rated Hard Hat, Eye protection, Boots and
gloves.
• Example: Performing diagnostic testing or voltage
measurements on 600V switchgear.
Hazard Category Three
• Clothing with a minimum Arc Rating: 25 Cal/cm2
• Two Under layers of 100% non-melting natural fiber
(cotton/wool) rated at 15 Cal/cm2 which will give a
combine protection of 30 Cal/cm2 or a multi-layer flash
suit rated at 40 Cal/cm2.
• FR rated flash suit hood.
• Electrically rated Hard Hat.
• Eye protection.
• Boots with dielectric overshoes.
• Electrically insulated FR rated gloves.
• And hearing protection for exposure to 200 dB or better.
Hazard Category Four
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Clothing with a minimum Arc Rating: 40 Cal/cm2
40 Cal/cm2 Flash suit.
FR rated flash suit hood.
Electrically rated Hard Hat.
Eye protection.
Boots with dielectric overshoes.
Electrically insulated FR rated gloves.
And hearing protection for exposure to 200 dB or
better.
So, What Do I Do If I’m
(Way) Above 40 cal/cm2
Solutions
• Above 40 cal/cm2
– Label equipment warning that no PPE is available
– Refer to safety procedures
– Must use engineered solution
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Current limiting fuses
Arc Resistant switchgear
Remote racking
Remote operation through Smart Equipment
Zone Interlocking
IP20 shrouding
Re-coordinating protective devices
Increasing distance
Enabling instantaneous function
De-energizing before operation
PPE / FR Clothing
Personal Protective Equipment
(PPE)
• Anytime your body crosses the Restrictive
Approach Boundary or the Flash Protection
Boundary, You Must wear PPE to protect
you from Arc Flash and Electrical Shock.
Depending on the task, you may need:
• Rubber insulated gloves and insulated tools to protect
against electrical shock.
• Leather hand and arm covers ro protect against arc flash
burns and flying debris.
• Head, face, neck, chin, eye and body protection.
• Hearing protection
• Dielectric overshoes
• A full multi-layer flash suit, including hood, face shield and
suplied air may be needed for higher risk.
Prohibited Clothing
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Polyester
Nylon
Rayon
Any blend of the above fabrics
Any metallic or conductive clothing.
Metal/ Plastic Jewelry
Category One Clothing
5 Cal/cm2
Category Two Clothing
11 Cal/cm2 kit
Category Three Clothing
25 Cal/cm2
Category Four Clothing
40 Cal/cm2
100 Cal/cm2 FR rated Clothing
Safe Work Practices
Safe Work Practices
OSHA 1910.333 (a) (1) & NFPA 70E 130 (A) (1)
not to work “hot” or “live” except :
1. Deenergizing introduces additional
or increased hazards
2. Infeasible due to
equipment design
or operational
limitations
Wearing Proper PPE?
Safe work Practices
• Remove conductive articles.
• Wear natural fibers (100% cotton/100%
wool).
• Clothing should be loose-fitting and FR
rated.
• Wear eye protection – safety glasses or
goggles under Face shields or hoods.
• Get an Energized Electrical Work Permit.
Safe work Practices
• Double check tools and equipment voltage
ratings.
• Keep tools and equipment from accidentally
coming in contact with live parts.
• All parts are considered Live until you test
to make sure.
• Work in adequate lighting.
Safe work Practices
• Never reach blindly into equipment.
• Never be put into a position where you could fall
into live parts.
• Keep vehicles and mechanical equipment 10 feet
from energized overhead lines.
• Do not touch Vehicles that could accidentally
become energized without proper PPE.
Safe work Practices
• Keep unqualified persons out of the area
beyond the Limited Approach Boundary.
• Use attendants to keep unqualified people
out of the area.
• Attendants may be needed to observe the
qualified worker for safety reasons.
Identifying Other Electrical
Hazards
Inadequate Wiring Hazards
• A hazard exists when a conductor is too
small to safely carry the current
Example: 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
Overload Hazards
• If too many devices are plugged into a
circuit, the current will heat the wires to a
very high temperature, which may cause a
fire
• If the wire insulation melts, arcing may
occur and cause a fire in the area where the
overload exists, even inside a wall
Grounding Hazards
• Frequently violated OSHA standards
• Metal parts of an electrical wiring system that we touch
(switch plates, ceiling light fixtures, conduit, etc.) should
be at zero volts relative to ground
• Housings of motors, appliances or tools that are plugged
into improperly grounded circuits may become energized
• If you come into contact with an improperly grounded
electrical device, YOU WILL BE SHOCKED !
Grounding Path
• The path to ground from circuits,
equipment, and enclosures must be
permanent and continuous
Identifying Disconnects
• Each disconnect
must be labeled
indicating its
purpose, unless
located and
arranged so the
purpose is evident
Clear Spaces
• Must have access to
working space around
electrical equipment.
• Must have at least 3’ in
front of switch boards
or motor control centers
Guarding of Live Parts
• Must guard live parts of electric
equipment operating at 50 volts
or more against accidental
contact by:
– Approved cabinets/enclosures, or
– Location or permanent partitions
making them accessible only to
qualified persons, or
– Elevation of 8 ft. or more above the
floor or working surface
• Mark entrances to guarded
locations with conspicuous
warning signs
Guarding of Live Parts
• Must enclose or guard
electric equipment in
locations where it would
be exposed to physical
damage
• Violation shown here is
physical damage to
conduit
Clues that Electrical Hazards Exist
• Tripped circuit breakers or blown fuses
• Warm tools, wires, cords, connections, or
junction boxes
• GFCI that shuts off a circuit
• Worn or frayed insulation around wire or
connection
Conclusion
• Arc Flash Awareness is an important part of any
electrical workers training.
• The standards used are to protect qualified
electrical workers and the Unqualified.
• Proper PPE should always be used for the Hazard
Category established for the equipment.
• Safe work practices should always be followed on
and off the Job… Your life may depend upon it.
End of Lecture