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Power
Delivery Product News, September/October 1998
Focus
on Safety Equipment & Clothing
Software
Helps Protect Workers from Electrical Arcs
Safety
is extremely important to utilities whether it is climbing to
the top of utility poles or handling power lines. To prevent injury
to utility workers, utilities provide safety equipment, including
gloves, proper tools and fall prevention equipment. To protect
workers from dangerous electrical arcs, utilities also have guidelines
on protective clothing.
The
sudden discharge of electricity, causing an electrical arc, can
cause clothing to ignite without warning. The hazard can be prevented
with proper planning and analysis of clothing types, weight and
distance from the potential hazard. OSHA has established standards
to assist utilities in determining their clothing needs.
OSHA
Requirements
According to a Department of Energy (DOE) OSHA Technical Reference,
arc burns, caused by electric arcs, are heat burns similar to
burns from high-temperature sources. The temperatures generated
by electric arcs can melt material nearby, vaporize metal in close
vicinity and burn flesh and ignite clothing at distances up to
10 feet.
To
assist employers in protecting their employees, OSHA regulations
have made it necessary for employers to ensure that the clothing
worn by workers exposed to electrical arcs must not contribute
to the extent of an injury. OSHA requires utilities and industries
to show compliance with such regulations if there is an accident.
According
to OSHA policy, the types of clothing that are acceptable under
the rule are all flame-resistant and flame-retardant (FR) clothing
under all conditions. This includes FR cotton and wool, as well
as Nomex and PBI/Kevlar. Clothing made from 11-ounce cotton is
acceptable for employees exposed to electric arcs that are comparable
to a 3800-ampere, 12-inch arc lasting for 1/6 second at a distance
of 12 inches from the employee. It is the responsibility of the
employer to determine proper clothing for the particular circumstances
that its employees may be exposed to.
Clothing
Analysis Tool
To help utilities determine the proper clothing, HD Electric Company
has released an electric arc hazard assessment software program,
ArcPro v.2. It is a software program developed to calculate the
thermal parameters of electrical arcs and to aid in the selection
of protective clothing by defining the arc hazard for workers
who may be accidentally exposed to electrical arcs. The user can
then specify clothing that will withstand the level of predicted
arc hazards.
ArcPro
v.2 is designed to provide the user with a method to calculate
heat exposure regarding total heat flux and heat energy on a surface
at various distances from an electrical arc. The software is used
to predict the potential arc hazard in a particular work environment
and thus it can help in choosing the appropriate protective clothing.
The
computer program is based on a state-of-the-art electrical arc
model. Temperature-dependent gas properties, the electrode materials
and configuration are taken into account in the model.
According
to C. Thomas Baker, safety consultant at Detroit Edison, ArcPro
is an extremely user friendly program to use. Coming from a non-technical
background, Baker believes that the program input windows and
results are easy to learn and analyze.
Most
of the calculation results are provided in numeric and graphic
forms on the screen and can be sent to a printer. Users provide
several input parameters describing the arc and then simply click
on the menu items to run calculations and view results. The typical
input to the program includes arc current, arcing gap and distance
from the arc. The typical output from the computer program includes
the total energy available, the heat and heat flux at any location
around the arc, illustration of the zone in which a particular
fabric will ignite, radiated heat flux, convected heat flux, clothing
database, second degree burn criteria and waveforms of the arc
current, arc voltage and arc diameter.
At
Detroit Edison, Baker uses the program for hazard analysis of
FR clothing. According to Baker, the 1998 update to the program
has been extremely helpful. The new version includes clothing
updates that have been useful in Detroit Edison's hazard analysis
operations.
Protection
from any hazard is important to all utility workers. Analysis
of the hazard before actually going out in the field is critical
and, according to HD Electric Company, ArcPro provides this analysis.
Go
to the ArcPro Arc Hazard Assessment Software product page
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