Download Practical Guide to Arc Flash Hazards

SASCO NFPA 70E Training
SASCO NFPA 70E Training
SASCO NFPA 70E Training
• NFPA 70E—Standard for Electrical
Safety in the Workplace
– Title: Standard for Electrical Safety for
Employee Workplaces
– Began 1976 by NFPA. Guidance for
OSHA
Electrical Hazards Addressed in
NFPA 70E
• Shock
• Arc Flash & Arc Blast
• Fire Ignition
The Effects of Current on the Body
Burns
Two Types of Burns from Shock
• Surface Burns
– Entrance and exit
of a electrical
currents through
the body
– Can be a very small
amount of current
– 1st to 3rd degree
Two Types of Burns from Shock
• Internal Tissue burns
– From current
running through the
organs of the body
– Currents in excess of
1.5 amps
– 3rd degree burns
– Damage to internal
organs
– Often fatal
One Type of Burn From Arc Flash
• Surface Burns
– From exposure to arc flash
– Can cause more surface burns if the initial
arc ignites other material,
such as clothing
– 1st degree to third degree
burns
– Has caused death
Probability of Survival
The probability of surviving burns decreases with
age:
How to Prevent Shock?
1. Place circuits in an electrically safe working
condition by locking out and tagging out all
energy sources
– NFPA 70E-2004: Chapter 1, Section
120.2 (D)
2. Verify that no electrical energy is present
– NFPA 70E-2004: Chapter 1, Section
120.2 (D)
Exposure to Danger
• The National Electric Code (NEC) was
designed to protect individuals from shock
hazards under normal conditions.
• It is not designed to protect employees under
abnormal conditions.
• We need additional policies to
protect us under abnormal
conditions.
This is
normal
somewhere
in the world
What NFPA 70E is designed to take
into account:
• Electrical arcs produce the highest temperatures on
earth—up to 35,000ºF. That’s 4 times the temperature
of the sun.
• The intense heat from arc causes the sudden expansion
of air that results in a blast with very strong air
pressure. (Lightning is a natural arc.)
• All known materials vaporize at this temperature.
– Copper expands 67,000 times; Water expands 1670 times.
Notes From Practical Guide to Arc Flash Hazards,
By Chet Davis, P.E.; Conrad St. Pierre; David
Castor, P.E.; Robert Luo, PhD; and Satish Shrestha
Arc Flash Characteristics
• Arcs in enclosures, such as Motor Control Centers
(MCCs) or switchgear, magnify blast and energy
transmitted as the blast is forced to the open side
of the enclosure.
• Arcs spray droplets of molten metal at velocity and
pressure. Shrapnel can penetrate the body
• Blast pressure waves have thrown workers across
rooms and knocked them off of ladders. Pressure
to the chest can exceed 2,000 lbs/sq. ft.
Notes From Practical Guide to Arc Flash Hazards
Arc Flash Characteristics
• Clothing can be ignited from several feet away.
Clothed areas can burn more severely than
exposed skin.
• Hearing loss from sound blast. The sound can
have a magnitude as high as 140 dB at distance of
2 feet from the arc.
• Energy released is a function of:
– System voltage
– Fault current magnitude
– Fault duration
Notes From Practical Guide to Arc Flash Hazards
How to Protect Against Shock
and Arc Flash/Blast?
• NFPA 70E-2004
– Chapter 1, Section 130
1. Justification for Live Work
2. Work Permits Secured—If Applicable
3. Approach Boundaries Established
• Shock Protection
• Limited Boundary
Note: De-energization is
covered in Section 120
OSHA 1910.333 (a) (1) and NFPA 70E 130.1
•
Qualified electrical workers shall not be asked
to work on equipment that is “live” except for
two demonstrable reasons:
1. Deenergizing introduces additional or increased
hazards
Example: Cutting ventilation to a hazardous
location
OR:
2. Infeasible because of equipment design or
operational limits
Example: Volt testing for diagnostics
Energized Electrical Work Permit
• NFPA 130.1 (A) (1):
– “If live parts are not placed in an electrically safe
work condition (i.e., for the reasons of increased
or additional hazards of infeasibility per 130.1),
work to be performed shall be considered
energized electrical work and shall be performed
by written permit only.”
Exemptions to Work Permit
• “Work performed on or near live parts
by qualified persons related to tasks such
as testing, troubleshooting, voltage
measuring, etc., shall be permitted
without energized electrical work permit,
provided appropriate safe work practices
and person protective equipment in
accordance with Chapter 1 are provided
and used.”
Approach Boundaries to Live Parts
Picture From Practical Guide to Arc Flash Hazards
Approach Boundaries
NFPA 70E-2004 Chapter 1, Sect. 130.2
• Flash Protection Boundary
– Linear distance at which no more than 2nd degree burns
possible from potential arc flash (typically 4 feet).
• See table 130.2 (c)
• Limited Approach Boundary
– Entered only by qualified persons or unqualified persons who
have been advised and are escorted by a qualified person
• Restricted Approach Boundary
– Entered only by qualified persons required to use shock
protection techniques and P.P.E.
• Prohibited Approach Boundary
– Enter only by qualified persons requiring same protection as if
in direct contact with live part
Shock Hazard Analysis
• How to Comply with NFPA 70E
– 3. Determine Personal Protective
Equipment
a. Determine Risk Category from Table
130.7 (C) (9) (a) on NFPA 70E-2004
b. Determine Specific PPE & Clothing
from Table 130.7 (C) (10) of NFPA
70E-2004
Shock Hazard Analysis
Determining Risk Category from Table 130.7
(C) (9) (a) on NFPA 70E-2004
Determining PPE from
Table 130.7 (C) (10) on
NFPA 70E-2004
Flash Hazard Analysis Example
Task: An electrician is to remove the covers to measure the
voltage on a panel board operating at 480 V.
Solution: Table 130.7 (C) (9): Hazard/Risk Category=2*
(V-Rated Gloves & V-Rated Tools Required)
Table 130.7 (C) (10) Specifies the following:
•
•
•
•
•
•
•
•
Untreated Natural Fiber T-Shirt & Undergarments
FR (8 cal/cm2) Long Sleeve Shirt and Pants
Hard Hat
Safety Glasses or Safety Goggles
Arc-Rated Face Shield w/ Flash Hood
Hearing Protection
Leather Gloves
Leather Work Shoes
No Fabric
Softener or
Bleach
Shortcut (2) to ppe arc flash portion.wmv.lnk
Common PPE Terms
• Incident Energy: Measurement of thermal energy at a
specified distance for the arc (normally 18”). Energy is
typically measured in cal/cm2.
• Arc Thermal Performance Exposure Value (ATPV): The
incident energy level (in cal/cm2) that would cause the onset
of a second-degree burn.
• V-rated: Tools and gloves tested for the line-to-line voltage
at the area where the work is to be performed.
• Flame-Resistant or Flame-Retardant: A term referring to
fabric and its ability to limit severity of burning.
• Break-open Threshold Energy (EBT): The highest incident
energy level which did not cause flame resistant (FR) fabric
break-open and does not exceed second-degree burn
criteria.
Review:
Determining PPE by using NFPA 70E
NFPA 70E Table 130.7(c)(9)(a)
1. Determine common work task from table that
matches work to be performed.
2. Identify Hazard/Risk Category of task (0-4).
3. Refer to NFPA Table 130.7(c)(10): Protective Clothing
and Personal Protective Equipment Matrix.
4. Read all applicable “Notes” that may apply.
Note: Any task not covered in tables or exceed assumptions are
required to have a Flash Hazard Analysis performed in
accordance with NFPA 70E 130.3
0
•
+
1
Or
2
+
Or
2*
+
Or
+
3
+
OR:
+
+
+
•
4
+
+
And now you know the rest of the story…
National Safety Council Hierarchy of Controls
Elimination/Substitution & Engineering Controls
•Substitute for hazardous materials/reduce energy or speed
•Machine guarding/sound enclosures/circuit breakers
Warnings
•Signs/placards/alarms/back-up beepers/labels
Training/Procedures
Administrative Controls
•Lockout-Tagout/Job Hazard Analysis
•Rotation of workers
P.P.E.
Other Protective Equipment: Insulated Tools
•• Insulated
tools and
1.
equipment must be rated
for the voltages on which
they are used
• Insulated tools—
designed and constructed
for the environment and
manner in which they are
used.
Alerting Techniques
• Physical barricades
• 1.
• Signage
• Attendants
– “If barricades and signage
fail to provide sufficient
warning and protection
from electrical hazards, an
attendant shall be stationed
to warn and protect
employees.”
2002 NEC
• § 110.16 Requires Arc Flash Labels
Response to an Electrical Accident
• Personnel who are trained to
perform First-Aid/CPR should be
identified and available when work
near or on energized part is being
performed
Response to an Electrical Accident
The first step must be to
TURN OFF THE POWER
Steps to Take if an Electrical
Incident Occurs
If power cannot
be turned off,
break victim’s
contact with
electricity
Steps to Take if an Electrical
Incident Occurs
• Remove the
immediate hazard:
Turn off the power
• Remember speed is
essential
• Extinguish flames
• Call for help (911)
• Begin First-Aid &
CPR
• First Aid
– Cool the burn with
water
– DO NOT attempt to
remove burnt clothing
– Elevate burned limbs
– Handle the victim with
care
– Treat for shock
• Maintain body
temperature
• Do not give anything by
mouth
`
Any Questions?