Transcript File

High Voltage
Electrical Safety
The Shocking Truth
Course Objective
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Regulation OSHA and NFPA 70E
Qualified Person Unqualified Person
Level of Hazards (Hazard Classification and Category)
Location Planning and Procedures
Approach Limits
Lockout and Energized Electrical Permitting
Insulated Equipment and Tools
Personal Protective Equipment (Arc Flash and
Blast rating)
Objective Continued
• Special Precautions
• Electrical Diagrams
• Equipment Details
• Examples of Equipment
Arc Flash Hazards
Every year, more than 2,000 workers are treated in burn
centers with severe arc flash injuries. The flash is
immediate, but the results can cause severe injuries that
last months, years—even a lifetime. In some cases, they
may cause death.
Fortunately, arc flash hazards can be reduced by following
safety precautions and using the recommended personal
protective equipment.
What is an arc flash hazard?
Think of an arc flash as a short circuit through the air. In an
arc flash incident, an enormous amount of concentrated
radiant energy explodes outward from electrical equipment.
The explosion creates pressure waves that can damage a
person’s hearing, a high-intensity flash that can damage
their eyesight and a superheated ball of gas that can
severely burn a worker’s body and melt metal.
The pressure waves can also propel loose material like
molten metal, pieces of damaged equipment, tools and
other objects, through the air.
Where do arc flash hazards occur?
A hazardous arc flash can occur in any electrical device,
regardless of voltage, in which the energy is high enough to
sustain an arc. Potential places where this can happen
include:
Panel boards and switchboards
Motor control centers
Metal clad switch gear
Transformers
Motor starters and drive cabinets
Fused disconnects
Any place that can have equipment failure
Who is at risk?
Some of the employees at risk from arc flash hazards
include mechanics, electricians and HVAC personnel. The
most dangerous tasks include:
•Removing or installing circuit breakers or fuses
•Working on control circuits with energized parts exposed
•Racking circuit breakers in and out of switch gear
•Applying safety grounds
•Removing panel covers
•Low voltage testing and diagnostics
What are the effects of an arc flash explosion?
The effects of an arcing fault can be devastating. The intense
thermal energy can cause severe burns in a fraction of a second.
One of the major causes of electrical burns and deaths to
workers is ignition of non-fire rated clothing due to an arcing
fault. Treatment can require years of skin grafting and
rehabilitation. A victim may never return to work or enjoy quality
of life. Treatment costs can exceed $1,000,000 per case.
Other considerations include loss of life, potential litigation fees,
loss of process, potential fines and escalation of insurance
premiums.
Did you know?
The temperature of an arc flash can reach
35,000 degrees Fahrenheit – about four
times as hot as the surface of the sun.
How can we reduce the risk:
Understand how to reduce the probability of an arc
flash event and its effects.
By begin with an Arc Flash Analysis and Assessment
that includes:
•Potential arc flash incident energy levels
•Flash protection boundary distances
•Safety training
•Selecting the correct personal protection equipment
(PPE)
•Proper Electrical equipment labeling
Electrical Safety-Related Work Practices
If electrical equipment must remain energized while
servicing and maintenance is performed, electrical safetyrelated work practices must be utilized by qualified
employees as outlined by OSHA in 29 CFR 1910.331 –
1910.335. In addition to OSHA’s requirements, NFPA 70E
Standard for Electrical Safety in the Workplace 2004
Edition contains requirements for performing a flash
hazard analysis.
Flash Hazard Analysis and Flash Protection Boundary
Prior to commencing work on electrically energized conductors > 50 volts,
NFPA 70E Article 130.3 requires that a flash hazard analysis be performed
to identify work tasks that must be performed while electrical equipment
remains energized. Instead of performing a detailed analysis, however,
Table 130.7 (C)(9)(A) (Hazard Risk Category Classifications) may be
utilized to identify various job tasks and the corresponding hazard risk
category.
NFPA 70E Article 130.3 (A) requires employers to establish a flash
protection boundary – a distance from exposed energized electrical parts
at which an employee could sustain a second degree burn if an electric arc
flash were to occur. Employees performing work on energized conductors
inside this boundary must be protected with appropriate Personal
Protective Equipment (PPE). In most cases, the flash protection boundary
for electrical systems 600 volts and below will be four (4) feet.
What are the NFPA 70E
Guidelines?
An employer is required to:
•Conduct an arc flash hazard analysis of the
workplace.
•Implement qualified and general worker safety
training based on the arc flash hazard analysis
results.
•Establish shock and flash protection boundaries.
•Provide protective clothing (PC) and personal
protective equipment (PPE) that meet ANSI
standards.
•Put warning labels on equipment (see example at
right). A future edition of the arc flash safety code
may require more extensive labeling (inset) that
includes flash hazard boundary and PPE levels.
Arc Flash Marking on Field
Breakers
In addition to the flash hazard analysis and PPE
requirements specified in NFPA 70E, the 2002
National Electrical Code® (NEC) requires field
labeling of circuit breaker panels and electrical
disconnects to warn qualified employees of the
potential arc flash hazards:
Article 110.16 Flash Protection: "Switchboards,
panel boards, industrial control panels, and
motor control centers in other than dwelling
occupancies, that are likely to require
examination, adjustment, servicing, or
maintenance while energized, shall be field
marked to warn qualified persons of potential
electric arc flash hazards. The marking shall be
located so as to be clearly visible to qualified
persons before examination, adjustment,
servicing, or maintenance of the equipment."
An example of an arc flash label is shown.
Selection of Personal Protective Equipment
NFPA 70E Table 130.7 (C)(9)(A) lists various work tasks and the corresponding
hazard risk category (0 through 4). Once the hazard risk category has been
determined, Table 130.7 (C)(10) [Protective Clothing and Personal Protective
Equipment (PPE) Matrix] is consulted to determine the appropriate PPE. An
example is listed below.
Example: Employee is working on an energized panelboard
(including voltage testing) rated < 240 volts.
Required PPE: Task is listed as a hazard risk category one (1). In addition to
voltage rated gloves, Table 130.7 (C)(10) specifies the following PPE: Flame
retardant clothing (long-sleeve shirt and pants), hard hat and safety glasses.
Other Personal Protective
Equipment
•Jackets
•Hard Hat
•Shield
•Gloves Tested
•Gloves Leather
00
Insulated Tools
Meters
&
Testers
Types of Electrical Boxes
480 volt Switch Gear
1.Open/close pushbuttons permit local electrical operation.
2.Dual-purpose manual handle for charging and tripping switch operators when control power is
not available.
3.Operator targets show switch operator status (charged or discharged) and position (open or
closed).
4.Optional remote-control receptacle for attaching remote-control station. Permits open-close
operation from adjacent area.
5.Charging shaft for manual charging in the event power is lost.
6.Switch-position target indicates whether Mini-Rupter® Switch is open or closed.
7.Decoupler indicator shows whether switch operator is coupled to Mini-Rupter Switch.
8.Decoupler handle permits convenient decoupling of switch from switch operator for functional
testing of source-transfer schemes and exercising of switch operator, without disturbing power
circuit.
9.Bolted covers provide access to input connectors and receptacles, and terminal blocks.
10. Micro-AT® Source-Transfer Control
E-Vault
Dry Transformer
Power Closet
480 Switch Gear
Disconnect found during Infrared Inspection.
Failed due to loose connection inside the switching
mechanism. Switch was found to be in the
energized state
Cover Completely
Blown Off
Summary
Arc flash hazards pose a serious risk to employee safety; proper safe work
practices must be utilized. Electrical equipment > 50 volts must be
deenergized and lockout/tagout followed prior to servicing and maintenance
unless doing so would increase hazards or is infeasible. Remember,
convenience is not an acceptable reason for keeping equipment energized
during servicing and maintenance. If electrical equipment must remain
energized during servicing and maintenance, NFPA 70E should be consulted
to determine flash hazard boundaries as well as required PPE. Finally, circuit
breakers and electrical disconnects must be marked to warn qualified
employees of potential arc flash hazards.
For more information on electric arc flash hazards or assistance on
performing a flash hazard analysis, please contact W. Jon Wallace, CSP, MBA