POWER August 2015 - 57

SAFETY
the preamble and supporting material, OSHA
went to great lengths to explain what " reasonable "
meant. It compared four methods
of estimating incident energy and indicated
where these methods could or could not be
used. Note 1 in 1910.269(l)(8)(ii) directs
the user to Appendix E (Table 1) for more
guidance on assessing arc flash hazards, and
selecting arc-rated clothing and personal protective
equipment (PPE).
Note that some methods are considered
reasonable for under 600-V exposures,
some are reasonable for up to 15-kV exposures,
but only one method-Arc Pro-was
found by OSHA to provide reasonable estimates
when the voltage is above 15 kV. For
OSHA to specify a commercial product is
very unusual, but the other available methods
were never intended for use above 15
kV, except for Ralph Lee's equations, but
he had limited resources to develop them,
and OSHA considers his equations to be
too conservative. The Lee method and the
Doughty, Neal, and Floyd methods are not
generally used, as the Institute of Electrical
and Electronics Engineers (IEEE) standard
1584 superseded them.
There is another software-based model
available called " Flux.exe, " which uses equations
developed by Duke Energy. This is an
older program that does not run in newer
versions of Windows, but was designed to
calculate the incident energy (heat flux) generated
by a single-phase overhead power line,
much like Arc Pro does. OSHA states that it
is willing to consider other methods companies
may want to use for calculating incident
energy, if the estimates are reasonable. According
to OSHA, each task does not have to
be analyzed, and companies can make broad
estimates, but I think any company desiring
to use a different methodology should get
OSHA approval first.
Arc-Rated Clothing
The first new requirement-1910.269(l)(8)
(vi)-that went into effect on April 1, 2015,
is that the outermost layer of clothing must
be arc-rated if any of the following four conditions
are met:
■ The employee could contact energized
conductors or circuit parts rated greater
than 600 V.
■ An electric arc could ignite flammable
material in the work area that could also
ignite the worker's clothing.
■ Molten metal from an electric arc could
ignite the employee's clothing.
■ The incident energy exceeds 2.0 cal/cm2
.
The requirement applies to rainwear, parkas,
jackets, safety vests, fall-arrest harnessAugust
2015 | POWER
© 2014 The Lubrizol Corporation, all rights reserved. All marks are the property of The Lubrizol Corporation.
The Lubrizol Corporation is a Berkshire Hathaway company.
GC 140681
CIRCLE 26 ON READER SERVICE CARD
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57
es, or any other clothing worn as the outer
layer. Arc-rated clothing is not designed or
rated to resist heat for substantial periods of
time. Although the incident energy from an
arc flash can be very high, the time of exposure
is short-usually less than six cycles
(0.10 second). Meltable, or ignitable, clothing
or materials worn on top of arc-rated
clothing can cause it to fail.
The worker must wear arc-rated clothing
when the incident energy exposure is estimated
to be above 2.0 cal/cm2
. The arc-rated
clothing and PPE selected must have a rating
equal to or greater than the estimated incident
energy. This arc-rated clothing and PPE
must cover all parts of the worker's body, except
for hands and feet, which have their own
requirements (covered later in this article).
A 2-cal/cm2
exposure on bare skin would
cause a more serious injury than one at 1.2
cal/cm2
, but the latter is still within the lesser
second-degree burn injury category. As
a point of reference, 5.0 cal/cm2
produces
wide-area second-degree burns, while apIntroducing
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POWER August 2015

Table of Contents for the Digital Edition of POWER August 2015