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The calculated incident energy is 9 cal/cm2. You have 8 and 40 cal PPE available. You would:
Still wear 8 cal/cm2 PPE 13%  13%  [ 10 ]
Wear 40 cal/cm2 PPE 42%  42%  [ 32 ]
Develop an intermediate category of 12 or something similar 33%  33%  [ 25 ]
Something else (please explain) 12%  12%  [ 9 ]
You may select 1 option

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ekstra   ara
 Post subject: 2 Category PPE and 9 cal/cm2
PostPosted: Sat Aug 05, 2017 10:25 am 
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This comes up from time to time. Someone is using a typical 2 Category (Level) PPE system with 8 cal/cm2 for daily wear and 40 cal/cm2 for special situations.

Let’s say there is a location where the calculated incident energy is 9 cal/cm2 and there is no way to reduce it for the energized task at hand. With 1 cal/cm2 over, what would you do?

Wear 8 cal/cm2 PPE
Wear 40 cal/cm2 PPE
Develop an intermediate category of 12 or something similar
Something else (please explain)


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 Post subject: Re: 2 Category PPE and 9 cal/cm2
PostPosted: Sun Aug 06, 2017 9:32 am 
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Is there really a choice? The context says that there is NO WAY to reduce it.

There is a case to be made for not only developing 12 cal/cm2 PPE but simply switching over to it and abandoning the 8 cal/cm2 PPE system. With the PPE available on the market today, shirts and pants have something of a "hard limit" right at 12 cal/cm2 where stuff is available right up to that point, but that's it. After that point you can't continue to go higher with a single layer. There are "jeans" that go a little higher but the requirement for a hood instead of a face shield and wearing more than one layer in the "shirt" area whether it's an actual multilayer jacket or a tested combination of say a shirt and another shirt or a jacket means multilayer in some way. The hood though kind of is the big differentiator.

For all these reasons once you go above 12 (not 8) cal/cm2, there's not a lot of practical difference from an end user's point of view.

For those of us out in the field service world where many of our customers truly have no idea what their potential incident energy ratings are or where their local plant rules get utterly stupid about safety because they were set up by safety generalists, quite often we truly have no idea what the incident energy rating is. We have the 70E tables and that's it, and even then those are only sort of some baseline guess work. But the heartening thing is that this really means that if we go back to the "fatality chance chart" that Privette among others published way back, the survivability with under-rated PPE isn't all that much worse than properly rated PPE as long as it doesn't sustain a flame considering that the area of exposure won't be all the bad either. So even the worst case with under-rated PPE isn't all that bad.

So we come to the crux of it. Do we as professionals allow ourselves or others to dress in PPE in direct violation of existing consensus safety standards (70E, IEEE 1584, ASTM 1959) or do we sometimes make exceptions knowing that we are working to a lesser standard but this might be "good enough" for some minor situations. It's the old pragmatism vs. dogmatism argument.


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 Post subject: Re: 2 Category PPE and 9 cal/cm2
PostPosted: Mon Aug 07, 2017 8:39 am 
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I would recommend issuing the staff a pair of Arc Rated Coveralls that has been tested in combination with the 8 Cal shirt and pants. As we now know, an 8 Cal jumpsuit over 8 Cal Shirt and Pants does not necessary mean that you have 16 Cals of protection, so the combo needs to be tested. Having a jump suit available gives the electrician a bit extra light weight protection without going to the full 40 Cal flash suit.

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


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 Post subject: Re: 2 Category PPE and 9 cal/cm2
PostPosted: Mon Aug 07, 2017 9:20 am 
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Wear the 40cal coat + arc-rated gloves, and 8cal pants. What is the IE at the cuff of your 11" voltage gloves, 14cal probably.

Does anyone calculate & report alternate IE for other working distances? It's a great feature in EzP.

70E Handbook: "Normally, the hands are the most exposed part of a person’s body, since they are used to perform work. Generally, an arc flash risk assessment is based on an exposure distance of 18 in. or 36 in. Because a person’s hands are closer to the hazard than their body, the thermal exposure will likely be much greater to the hands. Additional thermal protection is warranted, since the employee’s hands may be within the actual arc’s plasma."


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 Post subject: Re: 2 Category PPE and 9 cal/cm2
PostPosted: Mon Aug 07, 2017 11:02 am 
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This is very interesting and practical question. Most of us use only two sets of PPE, the basic protection level or daily wear and enhanced protection level. Both are determined from arc flash study and sometimes we have to settle with 8 cal/cm2 as daily wear and 40 cal/cm2 as EPL. Now if we were to work on energized equipment that has incident energy of 9 cal/cm2 , the most convenient is to use one more layer of 8 cal/cm2 like Robert mentioned. We use Westex fibers and I asked them if layering of two 8.7 ATPV would provide a protection level greater than 17.4 (2*8.7) ATPV because the air gap between the layers of clothes may provide insulation. They said it can provide a protection level of 17.4 ATPV, but do not assume greater than that due to factors such as humidity, temperature, etc in the working environment (this was conversation with my vendor only. you may want to verify with your PPE manufacturer).
Now if we don't have extra layer of PPE to use, then I will look at the arc flash result. If the 9 cal/cm2 is because it protective device took 2 seconds to clear the fault and if m the one who is going to perform the work, I will use 8 cal/cm2, because that 9 cal/cm2 got built up over the period of 120 cycles. But if that 9 cal/cm2 is a result within a cycle, no matter how hot it is, I will use 40 cal/cm2, because if something happens, I want to go home as one piece to my loved ones. But if my colleague is to perform the work, I would recommend 40 cal/cm2, irregardless of the fault clearing time and how hot the weather is.


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 Post subject: Re: 2 Category PPE and 9 cal/cm2
PostPosted: Mon Aug 07, 2017 12:43 pm 
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dinkelja wrote:
Wear the 40cal coat + arc-rated gloves, and 8cal pants. What is the IE at the cuff of your 11" voltage gloves, 14cal probably.


It roughly doubles for every halving of the distance which you are pretty close to in open air. In panels, it goes up a lot faster so that puts you somewhere around 16 cal/cm2 or higher.

Quote:
Does anyone calculate & report alternate IE for other working distances? It's a great feature in EzP.


Yes. For example operating a cutout with a hot stick from the ground or from a bucket truck. This is obviously not 18" working distance.

However the most interesting thing to realize that most folks miss is that the working distance is assumed to be from the ARC. And it is always calculated from a worst-case point of view such as the bus bars in the back of the MCC or switchgear. So with bus bars about 1" off the back of 600 V rated MCC's with a 20" depth, the 18" working distance is INSIDE the enclosure...the plane of the door is outside the working distance. And until you get into starters with something like 5U of space (essentially the whole section is one starter) where it is possible to crawl inside the starter, the working distance for the face/chest area will ALWAYS be outside the working distance. Most people assume that it is from the plane of the door, projecting out another full 18" which is simply not the case.


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 Post subject: Re: 2 Category PPE and 9 cal/cm2
PostPosted: Mon Aug 07, 2017 5:43 pm 
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Hi Jim

Greetings from Canada. As much as I am a fan of the simplified 2 Category system, in addition to as popular as it has become, I have always interpreted it as something a company or organization would implement when there has been no AFRA conducted and no detailed warning labels installed on the panels. Thus perhaps to be used in conjunction with the tables or stand alone where the incident energy has not been predicted, providing the worker with at least some level of protection in the event of an arc flash. However from the information provided it seems that the incident enregy level is known (9 cal/cm2). With the 2018 editions of NFPA 70E and CSA Z462 are we not going in the direction of the worker dressing to the calculated incident energy level (when it is known)?
Thus moving table H-2 from the Annex to the main body of the standard. After the AFHA has been completed in looking at the spreadshheet, discover an incident energy level that may be very common throughout the facility that is say at or below 12 cal/cm2 where one would not require an arc flash suit hood. This would become your dailywear- shirt and pant or coverall. A combination that is going to provide the worker with sufficient protection for every day common tasks.

Thanks Jim


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