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 Post subject: Confusion Arc Labels <1.2cal/cm^2
PostPosted: Mon Apr 29, 2019 4:54 am 

Joined: Mon Aug 04, 2014 5:19 pm
Posts: 13
It seems that when the results of a study show less than the 1.2cal/cm^2 and the labels from say SKM say "no arc rated PPE required" is causing much confusion for the end user and raising many questions.
So it seems to me that if one is doing a arc flash study for a plant, the optimum solution is to recommend that the plant have a policy of their qualified electricians to have some minimum PPE such as 8 calorie clothing?
Are others seeing these same questions arising?

thanks Jimmy


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 Post subject: Re: Confusion Arc Labels <1.2cal/cm^2
PostPosted: Mon Apr 29, 2019 9:48 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 520
Location: Wisconsin
jimmy wrote:
It seems that when the results of a study show less than the 1.2cal/cm^2 and the labels from say SKM say "no arc rated PPE required" is causing much confusion for the end user and raising many questions.


In my opinion SKM is a software company with expertise in performing calculation.
Theyare safety experts and should not be used as the default for PPE selection. NFPA 70E clearly puts the responsibility on the employer, who should create an Electrical Safe Work Practices (ESWP). If no ESWP existis then the default language should be that of NFPA 70E.


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 Post subject: Re: Confusion Arc Labels <1.2cal/cm^2
PostPosted: Mon May 13, 2019 11:48 am 
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Joined: Tue Oct 26, 2010 5:00 pm
Posts: 187
Location: Maple Valley, WA.
Quote:
....it seems to me that if one is doing a arc flash study for a plant, the optimum solution is to recommend that the plant have a policy of their qualified electricians to have some minimum PPE such as 8 calorie clothing?


Yes, we and many other safety professionals recommend that electricians and anybody else who work on or around electrical equipment wear arc rated clothing rated 8 cal/cm2 clothing for daily wear.

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Robert Fuhr, P.E.; P.Eng.
PowerStudies


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 Post subject: Re: Confusion Arc Labels <1.2cal/cm^2
PostPosted: Mon May 13, 2019 3:48 pm 
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Joined: Tue Jul 01, 2014 8:40 am
Posts: 93
Hi Jimmy

As per the other comments. Anyone who places any reference to "No PPE Required" or any reference to PPE on a detailed warning label for arc flash and shock is going down a slippery slope of liability. An engineer wants to limit their liability so this reference to no PPE required could come back to haunt someone. The "Everyday Wear" PPE Cat 2, minimum 8 cal/cm2 has become very popular not only in industrial facilities but for contractors performing work there


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 Post subject: Re: Confusion Arc Labels <1.2cal/cm^2
PostPosted: Wed May 22, 2019 2:25 pm 
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Joined: Sat Nov 21, 2009 10:23 pm
Posts: 107
Location: Ohio
Did anyone else notice that the 2018 70E removed all clothing recommendations for <= 1.2 cal


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 Post subject: Re: Confusion Arc Labels <1.2cal/cm^2
PostPosted: Sat Oct 19, 2019 8:19 am 
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Joined: Wed Jun 10, 2009 5:00 pm
Posts: 263
Location: Toronto
Flash wrote:
Did anyone else notice that the 2018 70E removed all clothing recommendations for <= 1.2 cal


Is the NFPA 70E trying to distance itself from 1.2 cal/cm2 threshold incident energy level for a second degree burn first introduced in year 2012? NFPA 70E year 2012 stated that "a second degree burn is possible by an exposure of unprotected skin to an electric arc flash above the incident energy level of 1.2 cal/cm2 ( 5.0 J/cm2 )". The NFPA 70E-2018 Specifically revised the definition of arc flash boundary and no longer uses the term "second degree burn" but instead "at which incident energy equals 1.2 cal/cm2". Although NFPA 70E has informational note referencing the Stoll skin burn injury model, its notion of 1.2 cal/cm2 as some kind of a magic number contradicts the Stoll model. A quote from A.Stoll "Heat Transfer in Biotechnology" summarizes the issue of using a critical thermal load approach in determining arc flash boundary. The quote reads:

"Serious misconceptions have crept into this field of research through adoption of rule-of-thumb terminology which has lost its identity as such and become accepted as fact. A glaring example of this process is the “critical thermal load.” This quantity is defined as the total energy delivered in any given exposure required to produce some given endpoint such as a blister. Mathematically it is the product of the flux and exposure time for a shaped pulse. Implicit in this treatment is the assumption that thermal injury is a function of dosage as in ionizing radiation, so that the process obeys the "law of reciprocity," i.e., that equal injury is produced by equal doses. On the contrary, a very large amount of energy delivered over a greatly extended time produces no injury at all while the same "dose" delivered instantaneously may totally destroy the skin. Conversely, measurements of doses which produce the same damage over even a narrow range of intensities of radiation show that the "law of reciprocity" fails, for the doses are not equal."

Be mindful of the pressure to join the crowd (can't get tired repeating it to myself and kids over and over again :D ). Incident energy alone has no impact on thermal damage and blast pressure. One can expose himself to any arbitrary incident energy and suffer no damage as long as the energy is delivered at slow enough rate. On the other hand, an exposure to only a fraction of 1.2 cal/cm2 may result in incurable burn provided that the energy has been delivered fast enough. Google Evaluation of onset to second degree burn energy in arc flash hazard analysis for more information. There is also a free online resource available capable of determining time to 2nd degree burn and onset to 2nd degree burn energy as a function of heat flux (measured in cal/cm^2/sec)

Image


The issue of using incident energy as a measure of damage alone and without regard to the rate of the energy release has been raised to NFPA 70E committee before year 2015 edition was published but unfortunately it was never appropriately addressed by the group.

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Michael Furtak, C.E.T.
http://arcadvisor.com


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