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PostPosted: Mon Nov 12, 2012 11:44 am 
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You are making a lot of assumptions about other's people's knowledge and you are quite well read in a very small area of this subject. I still encourage you to attend the meetings of ASTM F18 and NFPA 70E and make your case. Both committees are quite reasonable.

My knowledge is based on much more than Dr. Neal's paper. It is based on 100,000 electric arc tests, 18 years of committee work and over 200 accident investigations. You seem to hear in everyone's comments only what supports your contention that we need to greatly expand arc flash boundaries because you have found potential theoretical evidence in papers written on testing other than arc flash. I encourage your company to do real testing and publish a paper supporting your contentions instead of trying to scare people when all the anecdotal evidence suggests this is not the case.

But fear makes a good base for consulting. Deep knowledge makes a better base. Move over to the dark side and do some real testing. An old Russian saying, "Theory appeals to theoriticians but people won't trust you, testing appeals to the masses but the testers continually question the testing to make it better." I'm a tester. You have raised a great issue to consider but you keep attacking everyone who could help you. I suggest you make phone calls instead of attacking in e-mails and public forums. Seriously. Make a phone call. It will accomplish a lot more.

I'm tired of you attacking my knowledge to try to make you look smart. If you call, you will find me a great person to work with. Otherwise you will find me silent except at the committees which can really change things.

Join us! We all want workers protected.


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PostPosted: Mon Nov 12, 2012 5:33 pm 
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This was an interesting and thought provoking discussion. It seems it is getting a bit personal for a public forum. Conspiracy? attacking? come on guys, get back to a constructive conversation.


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PostPosted: Mon Nov 12, 2012 5:59 pm 
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You have complete agreement here.


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PostPosted: Tue Nov 13, 2012 4:31 am 
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elihuiv wrote:
You have complete agreement here.


IF the Privette data is suspect is there some way to take experimental data to verify second degree burn data at times OTHER than say 1-2 seconds, say during short or excessively long intervals? Such as using samples of cadaver pig or human skin? Could it be extended upward and downward (1st and 3rd degree burns)? Is radiant heat energy the "right" way to model it? The terms plasma, hot gases, and molten metal keep coming up, and it's obvious that there are multiple phenomena going on but the distances may be wildly different to say nothing of the shape of the affected zones.


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PostPosted: Tue Nov 13, 2012 8:59 am 
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PaulEngr wrote:
IF the Privette data is suspect is there some way to take experimental data to verify second degree burn data at times OTHER than say 1-2 seconds, say during short or excessively long intervals? Such as using samples of cadaver pig or human skin? Could it be extended upward and downward (1st and 3rd degree burns)?


A. Brownell [A. Brownell, et al., “Ocular and skin hazards from C)2 laser radiation”. Joint AMRDC-AMC Laser Safety Team, Philadelphia, Pensylvania, 1972] provides test evidence supporting extrapolation of Stoll curve as proposed in [M. Furtak, L. Silecky, “Evaluation of Onset to Second Degree Burn Energy in Arc Flash”, IAEI magazine, July/august 2012]. Have a look on Figure 1 from Brownell's study:

Image
For your convenience I've imposed on it Lines A and D Figure 1 from the IAEI arc flash article (blue and green lines respectively). Observe the correlation between the ERYTHEMA (SKIN) line with the Stoll curve in around 0.5 to 10 sec time interval. Note that, according to the graph, only 0.3cal/cm2 energy dose delivered within 0.01sec time interval is required to cause same damage as from 1.2(cal/cm2) dose delivered within one (1) second.

For excessively long time intervals, consider following example. Standing on a sunny day for roughly 20 minutes makes you exposed to approx 30cal/cm2 dose of radiation emitted from Sun. If severity of bare skin burn was determined in terms of incident energy alone, you wouldn't survive such exposure without wearing PPE 4 suit.

PaulEngr wrote:
Is radiant heat energy the "right" way to model it? The terms plasma, hot gases, and molten metal keep coming up, and it's obvious that there are multiple phenomena going on but the distances may be wildly different to say nothing of the shape of the affected zones.


I strongly believe that, indeed, radiant heat energy is the right way to model arc flashes (hence the term "flash"). Laser, nuclear, pyrotechnic irradiation are all useful parallels to consider.

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PostPosted: Tue Nov 13, 2012 4:32 pm 
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arcad wrote:
...


I got that all from the original article correlating data from several different sources of non-arc flash injuries. No reason to reiterate. My thought is though that this is all correlation and conjecture with non-arc flash related data while the concern is for the effect of an arc flash. You are making the case that based on indirect evidence that heat flux and not heat energy is the correct way to model this. You also keep plotting everything on log scales which is SOMETIMES appropriate (when it's an exponential) and at other times just tends to make everything look like a straight line when in fact it may not be.

I'm particularly interested in the Privette data in particular and in duplicating similar experiments because that data seems to suggest that there is a maximum absorption rate at short time intervals and that cooling may apply at longer time intervals...thus lending credence to your idea that heat flux is important at long time intervals but drawing the opposite conclusion at shorter ones. I've heard two different versions of the Privette data. One says that it is testing a case with FR cloth and one that says that it isn't. Since it seems like a lot of folks on the various technical committees interpreted the Privette data set as being a bare skin case extrapolated to low exposure times, it would seem that somehow at least for myself, I'd like to see additional evidence. It would seem like just a couple experiments with appropriate human analogs for skin placed at several distances would answer the question pretty quickly.


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PostPosted: Tue Nov 13, 2012 9:27 pm 
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PaulEngr wrote:
I got that all from the original article correlating data from several different sources of non-arc flash injuries. No reason to reiterate. You also keep plotting everything on log scales which is SOMETIMES appropriate (when it's an exponential) and at other times just tends to make everything look like a straight line when in fact it may not be.


Sorry if I've upset you by publishing the tests resuIts from A.Brownell [A. Brownell, et al., “Ocular and skin hazards from C)2 laser radiation”. Joint AMRDC-AMC Laser Safety Team, Philadelphia, Pensylvania, 1972] but I did it upon your own most recent request for more 2nd degree burn evidence:

PaulEngr wrote:
IF the Privette data is suspect is there some way to take experimental data to verify second degree burn data at times OTHER than say 1-2 seconds, say during short or excessively long intervals? Such as using samples of cadaver pig or human skin? Could it be extended upward and downward (1st and 3rd degree burns)?


I don't quite understand your concern with using logarithmic scale in the IAEI paper. The scale seemed to working well so far with A.Stoll, A.Privette, Brownell etc. works cited in this thread, and however many more other researches using the scale. Regarding your next observation:

PaulEngr wrote:
My thought is though that this is all correlation and conjecture with non-arc flash related data while the concern is for the effect of an arc flash. You are making the case that based on indirect evidence that heat flux and not heat energy is the correct way to model this.


You could also argue that some of the Privette's tests series reported in [A. Privette, "Progress report for ASTM Burn Stufy", Duke Power Company, 1992] were conducted using a muffle furnace as the heat source and not the arc. And, yes indeed I am confident that heat flux should be factored in when evaluating threshold incident energy for a second degree burn. I'll take liberty to repeat the quote from A. Stoll [A.Stoll, "Heat Transfer in Biotechnology", Advances in Heat Transfer, v.4. Academic Press. 1967] summarizing the issue of using 1.2 cal/cm2 as a threshold incident energy to 2nd degree burn as well as any other heat dose to produce damage without regard for the speed of delivering the energy. 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."

Regarding your appeal for additional evidence from A.Privette's research:

PaulEngr wrote:
I'm particularly interested in the Privette data in particular and in duplicating similar experiments because that data seems to suggest that there is a maximum absorption rate at short time intervals and that cooling may apply at longer time intervals...thus lending credence to your idea that heat flux is important at long time intervals but drawing the opposite conclusion at shorter ones. I've heard two different versions of the Privette data. One says that it is testing a case with FR cloth and one that says that it isn't. Since it seems like a lot of folks on the various technical committees interpreted the Privette data set as being a bare skin case extrapolated to low exposure times, it would seem that somehow at least for myself, I'd like to see additional evidence. It would seem like just a couple experiments with appropriate human analogs for skin placed at several distances would answer the question pretty quickly.


Sorry I cannot provide you with my copy of Privette's report. Please contact the author or Duke Power Company owing it for your copy of the report. However, please find below the additional evidence from the report:

"Comparing the burn injury with the tests from the muffle furnace the Pbi/Kevlar produced a burn injury just less than the onset of second degree. The Green Nomex, Pbi/Cotton and Nomex Plus produces burn injury just exceeding the onset of second degree. From this data it is assumed that the onset of second degree burn injury occurs around 2.0 calories. If the Stoll Curve was extended as shown in Fig 9 then the onset of second degree burn injury would be at 4.2 calories per sq.cm.-sec.

Image
The full scale tests indicate that the range should be between 8 to 12 calories per sq.cm - sec. When you take into account the tests from the muffle furnace along with the bare skin tests you see that the Stoll curve should start to curve upward on a log-log graph as in Fig. 10.

Image
This is a proposed modification to the Stoll Curve and may require additional tests for verification".

Hope this helps.

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


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PostPosted: Wed Nov 14, 2012 7:23 am 
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Getting clarification from Alan but he indicates that he did the work on bare skin and on FR covered skin.

"We used White Sprague Dawley rats for the tests. We exposed the rats, six per group, bare skin to various arc flashes. Using these results, we also exposed the rats with fabric coverings, six per group, to arc flashes that we felt would cause a second or partial thickness burn.
At Chapel Hill we reproduced the tests based on the Stoll Curve. We used a Muffled furnace for these test. Also six per group." Alan Privette in e-mail today.

I've asked if the 2-3 cal/cm² for arc flashes was on bare skin as the standards have assumed. I'll confirm when I have the information. Seems strange that over a shorter period of time it would take the same or less heat flux when skin should have some ablation effect like clothing which has a higher arc rating with higher amperages.


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PostPosted: Wed Nov 14, 2012 6:43 pm 
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Wish I knew earlier that Alan Privette worked for Duke. It just so happens that I live about 2 hours from Chapel Hill and Duke is the major utility in my area.


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PostPosted: Mon Nov 26, 2012 7:57 pm 
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Alan is a great guy but isn't involved in this type of thing anymore due to his day job (like most of us on committees, his work was done to support the safety program at his employer to keep workers safe and give us tools to make electrical safety more practical).


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