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 Post subject: Level 0 and the 1.2 cal threshold
PostPosted: Wed Apr 09, 2008 3:49 pm 
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I am seeing on several internet sites and in some online presentations, that they are calling any Incident Energy Level of 1.2 cal/cm2 or lower as PPE Level 0.

I can not find in NFPA 70E Article 130 anywhere that says this is true.

Where is this coming from, is it in the IEEE 1584 text? Even if it is, shouldn't we be taking Level 1 as the lowest unless using the Task Matrix.


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PostPosted: Thu Apr 10, 2008 8:48 am 
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Haze10,
The flash protection boundary is defined as the approach limit from exposed live parts at which a person could receive a second degree burn. All of the info that I have seen and read establishes this level at 1.2 cal/cm2. 70E discusses the 300 kA cycles for 600 volts or less, but at voltage levels above 600 volts, places the boundary at a level where the IE equals 1.2 cal/cm2.

If you do not exceed the 300 kA cycles, it appears to be 4 ft. I believe that I am correct in saying that the boundary and IE as they relate to PPE are otherwise independent. It would seem that you would establish the limits of the flash boundary and then base your PPE on the IE level once inside the boundary.

Hopefully we can get another opinion here!

BTW....in the NESC the "action level" is placed at 2 cal/cm2 (not 1.2).

Alan


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PostPosted: Thu Apr 10, 2008 4:01 pm 
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Alan, thanks but that's not really the question. I don't believe you can just go by the 1.2 cal limit for arc flash boundry. An unqualified person outside of this boundry could be in polyester clothing as there are no PPE requirements outside of the boundary.

My specific question relates to the PPE Level versus the cal level. The table in NFPA says Level 1 to 4 cal. So that would mean a IE of 0.5 would still need a Level 1 PPE. Some sites I see that below 1.2 cal they drop the PPE level to 0. Where does this come from? I think it may be 1584 which I don't have. But even if it does, how do we conscienciously disregard the NFPA table.


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PostPosted: Thu Apr 10, 2008 5:33 pm 
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I did not intend to mean that you could only go just by the boundary...maybe I said it wrong. I think that you first establish the boundary and then once inside the boundary, and when an arc exposure exists, you would use the IE to determine PPE level required within the boundary.

Yes the table lists 1 to 4 but it also allows in certain instances to lower the level by one if the site conditions meet certain criteria. Maybe that is where the lowered levels come from?

The tables are also to be used if an analysis has not been done.

Otherwise if you do the calcs and end up with an IE of .5, I believe that one could use a .5 level PPE (if you could find it). Most I expect would go to a level 1 as you say.

Did that help any or am I still confused?
Thanks,
Alan


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PostPosted: Fri Apr 11, 2008 4:41 am 
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Hi Guys,

130.7 (5) is the hidden answer. It refers to wearing FR clothing above 1.2 calories / cm2. The idea is 1.2 is the second degree burn threshold which is generally the degree of protection that the PPE and various rules are designed to offer. So if the incident energy is greater than 1.2 (greater than the onset of the second degree burn) then PPE is required. There is a footnote that actually allows you to go to 2 calories if non melting clothing is used. I think the idea here is the clothing would offer some degree of thermal protection (until it catches fire! :eek: )

Alan, some scary news, I just met with many of the NPFA 70E people 2 weeks ago, there is a proposal (that looks like it will pass) to change the 300 kA-cycles to 100 kA-cycles. That's going to be the shot heard round the world..... or at least around the world of arc flash. That will greatly restrict the use of the 4 foot rule and more locations will fall into the category of requiring calculations. .....The plot thickens!

_________________
Jim Phillips, P.E.
Brainfiller.com


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PostPosted: Fri Apr 11, 2008 6:52 am 
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Thanks Jim, I was sure that I had seen the reference to 1.2 cal and the second degree burn in 70E but had not gone back to check. Sounds like the standards committee is intent on requiring facilities to do the calcs in the future!

Thanks Again,
Alan


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PostPosted: Fri Apr 11, 2008 9:51 am 
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Ok, got it.
130.7.5 Body Protection.
Employees shall wear FR clothing wherever there is possible exposure to an electric arc flash above the threshold incident energy level for a second degree burn (1.2 cal/cm2).

Exception: For incident energy exposures (2cal/cm2) and below, employees may wear non-melting clothing described in hazard Risk Catergory 0....


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