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 Post subject: Mixing of Tables & Analysis
PostPosted: Thu Nov 20, 2014 6:20 am 
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I understand that NFPA 70E does not allow the 2 methods to be applied to the same piece of equipment. Will labels that specify incident energy and the PPE category have to be changed? Especially if the labels were installed in 2013. Also, what is the reason we cannot mix the 2 methods, other than the fact 70E does not allow it?


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Thu Nov 20, 2014 9:46 am 
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Vica1ME wrote:
what is the reason we cannot mix the 2 methods, other than the fact 70E does not allow it?

The question of 2015!

I have been a bit vocal about this going back to around 2010 when the 2009 Edition of NFPA 70E stated that either the incident energy or category be listed on arc flash labels. It was pointed out to me the "OR" was a big deal and the debate began.
One of the older threads where this began is:

http://arcflashforum.brainfiller.com/viewtopic.php?f=8&t=655&hilit=PPE+fujita

My personal opinion and confirmed by a few others, is the problem lies in the introduction of 12 cal/cm2 PPE. 12 does not fit the old 4, 8, 25 and 40 cal categories.

An argument made in the past was HRC and incident energy do not directly correlate. I agree, HRC had risk associated with it and incident energy does not. People began to simply call it "PPE category" and continued linking PPE category with incident energy.

The 2015 edition of 70E dropped HRC and changed the reference to PPE category (basically taking ownership of the alternate language that the industry used to circumvent the silly no linking language.)

Guess what! Now you can not link PPE category with incident energy i.e. it is strictly prohibited to have both on a label. The only argument I heard in the past was HRC and Incident energy don't correlate and now that is gone but the prohibition still exists. So much for that argument.

If the reason for the "no linking" is something other than 12 cal/cm^2 not fitting the 4, 8, 25 and 40 cal/cm^2 categories, I would like to know what it is. However, so far in discussions with many including some 70E committee members, no such reason seems to exist.


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Thu Nov 20, 2014 11:14 am 
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Thanks so much. I really appreciate this website!


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Mon Nov 24, 2014 8:08 am 
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Jim Phillips (brainfiller) wrote:
The question of 2015!

My personal opinion and confirmed by a few others, is the problem lies in the introduction of 12 cal/cm2 PPE. 12 does not fit the old 4, 8, 25 and 40 cal categories.

An argument made in the past was HRC and incident energy do not directly correlate. I agree, HRC had risk associated with it and incident energy does not. People began to simply call it "PPE category" and continued linking PPE category with incident energy.


I am not sure I understand the dilemma. Either you use PPE that is greater than the calculated incident energy (In this case 12 cal/cm2), or you use category 3 which exceeds the calculated incident energy of 12 cal/cm2.

Why would this be confusing on a label? If the incident energy is 20 cal/cm2 you would just use PPE Category 3, right?

Are we going to have to start interpolating the PPE categories based on actual incident energy?
(12 cal/cm2 would then be a PPE Category of 2.2353)

or create new PPE categories for different levels of incident energy?


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Mon Nov 24, 2014 8:32 am 
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I agree that the HRC is not directly related to the incident energy because it contains an element of risk. One issue using mixing the HRC with incident energy may be liability. Let's say for example the incident energy calculation was 10 calories. You would put an HRC of 3 for this energy. So, if you have someone injured and they are wearing 12 calorie clothing, there could be an argument that they should have worn 25 calorie clothing. In my opinion there has been widespread misunderstanding and mis-use of the HRC tables. NFPA 70E 2015 emphasizes that a risk assessment is required. Usually, in the past the arc flash hazard analysis would stop at the point of the incident energy analysis without the client continuing with the risk part of the job tasks. I think we are going to have issues with firms bidding based on the old arc flash hazard analysis concept. It must be made clear by the client requesting proposals whether they want the firm to provide the risk assessment or just the incident energy analysis. Technically, it has always been important to conduct a risk assessment after the incident energy analysis. The 2015 NFPA 70E makes it very clear that you have not completed the job by just preforming the incident energy analysis. I see the potential for a lot of confusion with arc flash bids in the future. Incident Energy Analysis or Risk Assessment? Note that risk assessment includes the includes the incident energy analysis, unless you are using the table method in which case you must know the clearing time and short circuit current.


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Mon Nov 24, 2014 9:32 am 
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rdj wrote:
I agree that the HRC is not directly related to the incident energy because it contains an element of risk. One issue using mixing the HRC with incident energy may be liability. Let's say for example the incident energy calculation was 10 calories. You would put an HRC of 3 for this energy. So, if you have someone injured and they are wearing 12 calorie clothing, there could be an argument that they should have worn 25 calorie clothing. In my opinion there has been widespread misunderstanding and mis-use of the HRC tables. NFPA 70E 2015 emphasizes that a risk assessment is required. Usually, in the past the arc flash hazard analysis would stop at the point of the incident energy analysis without the client continuing with the risk part of the job tasks. I think we are going to have issues with firms bidding based on the old arc flash hazard analysis concept. It must be made clear by the client requesting proposals whether they want the firm to provide the risk assessment or just the incident energy analysis. Technically, it has always been important to conduct a risk assessment after the incident energy analysis. The 2015 NFPA 70E makes it very clear that you have not completed the job by just preforming the incident energy analysis. I see the potential for a lot of confusion with arc flash bids in the future. Incident Energy Analysis or Risk Assessment? Note that risk assessment includes the includes the incident energy analysis, unless you are using the table method in which case you must know the clearing time and short circuit current.


Using the Table method, you determine if Arc Flash PPE is required (Table 130.7(C)(15)(A)(a)) then check the table by task to determine the level (Tables 130.7(C)(15)(A)(b) and 130.7(C)(15)(B)). After which you can lower the PPE Category by 1 number, but not below 1 if certain conditions are met.

Determining if Arc Flash PPE is required would seem like it is determining a level of risk, would it not?
Personally, I don't use the tables. I do a risk assessment and calculate the incident energy.
Both of these are a means to an end.

In the end, there is an incident energy which correlated to an arc-rating the PPE needs to meet - or a PPE Category.

YOu are not really talking apples and oranges, you are talking Macintosh and Gala (types of apples)


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Mon Nov 24, 2014 12:25 pm 
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Vica1ME wrote:
I understand that NFPA 70E does not allow the 2 methods to be applied to the same piece of equipment. Will labels that specify incident energy and the PPE category have to be changed? Especially if the labels were installed in 2013. Also, what is the reason we cannot mix the 2 methods, other than the fact 70E does not allow it?


The modified NFPA 70E 2015 table method seems to be outright unusable. Fault clearing time is required in order for the method to be used. The time cannot be determined unless arcing fault current is known. Although the NFPA 70E incident method provides formula from the IEEE 1584 Guide for calculating arcing current from the IEEE 1584 Guide, the formula is an integral part of incident energy method and the new standard now SPECIFICALY prohibits mixing both incident energy and table methods. Strange as it may sound, but NFPA has rendered unusable its own method in the new NFPA 70E 2015 edition. Therefore, the equipment with existing labels made based ont NFPA 70E table method should be analyzed again using one of the engineering study methods included in NFPA 70E-2015 Annex D (with variable incident energy at arc flash boundary as explained below), and new labels should be created and applied to the equipment.

New NFPA 70E does not explain why the 2 methods cannot be mixed. In my opinion, the reason lies in industry spread wrongful approach of measuring arc flash hazards using energy units alone (such as cal/cm^2) disregarding rate of energy delivery. An argument made in the past was that representing arc flash hazard by energy units alone is incorrect if the rate is not taken into account (see this forum thread at http://arcflashforum.brainfiller.com/viewtopic.php?f=34&t=2221 for more information).

A very interesting thing to know is that the infamous 1.2 cal/cm^2 threshold incident energy for a 2nd degree burn on bare skin cited in NFPA 70E and widely accepted in arc flash industry actually comes from misinterpretation of Alan Privettes' "Progress Report for ASTM Burn Study". As a matter of fact, Privettes' work is based upon tests where the test animals were shielded with flame retardant fabrics. Assuming Privettes' findings apply also to bare skin exposure is same as having a confidence you can safely touch hot glowing metal with bare hands as long as you have managed escaping damage by touching it previously while wearing protective gloves.

Indeed, incident energy does not have any risk associated with it. But incident energy coupled with time interval, within which the energy was delivered, does. For example, bare skin exposure to 1.2 cal/cm^2 incident is generally safe and oftentimes beneficial unless the energy was delivered within one (1) second time interval. In fact, only a fraction of 1.2 cal/cm^2 is required to cause the damage when delivered within shorter than 1 second time interval. This may also explain the reason why NFPA group abandoned Category 0 and removed any references to it in new NFPA 70E year 2015 edition.


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Tue Nov 25, 2014 3:36 pm 
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Interesting discussion. Not being bound by NFPA, here in Australia we have a bit more latitude in approach to the subject.
One key factor that needs to be borne in mind is that risk is always a function of consequence AND likelihood. Ignoring the likelihood element of risk introduces all sorts of unhelpful distortions. Control measures applied in everyday life are largely a function of risk, and also take into account the impost versus benefit of available risk mitigation control measures. Overprotecting against an unlikely consequence can introduce additional risks, which is why we don't just apply a Cat 4 suit for every occasion. This is recognised by IEEE1584 for example. The problem from a legal perspective is that a prosecution lawyer has the benefit of 20-20 hindsight and doesn't have to deal with the fuzzy probabilities and competing risks that engineers can't avoid.
Tied in with the necessity to take into account a probability distribution of potential consequences (which is risk analysis) is the fact that when there is a barrier in the path of the arc, such as a closed door, incident energy calculations go out the window. Yet we know from experience that arc fault explosions can cause injury beyond a closed door. There is no basis in the standards for just ignoring the door. Yet there is also no basis for calculating an incident energy when the door is closed. The control measures are arrived at through a subjective professional judgement of risk.


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Sat Nov 29, 2014 5:43 am 
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The "H/RC includes risk" argument is the only one that previously made any sense and only from a theoretical argument. The new tables break that link once and for all. It looks like an editting holdover to me. It also begs the question of whether we can use the first table only, then substitute engineering analysis. The text seems to prohibit this. Also...what happened to the first table?? In the second draft it was readable. In the final edition it blew up with a bunch of confusing stuff that makes little sense.


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Sat Nov 29, 2014 12:39 pm 
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So, if I am reading NFPA 70E-2015 130.7(C)(15) correctly, if I don't do an incident energy analysis and I want to operate a circuit breaker or disconnect switch, I can use Table 130.7(C)(15)(A)(a) and if all the conditions are met for operating a CB or DS, then Arc Flash PPE is not required.

However, if I went to the expense and effort of having a study done to determine the incident energy level at this CB or DS then I cannot use Table 130.7(C)(15)(A)(a) to determine if Arc Flash PPE is required. For example, suppose my study shows a IE of 10 cal/cm^2 at this CB or DS and is labeled as such, what PPE is needed to operate assuming the same conditions are met as in Table 130.7(C)(15)(A)(a)? Do I need Arc Flash PPE rated a minimum of 10 cal/cm^2 to do the same task that, if an analysis was not done, could be accomplished wearing non melting clothing?

Seems absurd, so what am I missing?

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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Sat Nov 29, 2014 7:21 pm 
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wbd wrote:
So, if I am reading NFPA 70E-2015 130.7(C)(15) correctly, if I don't do an incident energy analysis and I want to operate a circuit breaker or disconnect switch, I can use Table 130.7(C)(15)(A)(a) and if all the conditions are met for operating a CB or DS, then Arc Flash PPE is not required.

However, if I went to the expense and effort of having a study done to determine the incident energy level at this CB or DS then I cannot use Table 130.7(C)(15)(A)(a) to determine if Arc Flash PPE is required. For example, suppose my study shows a IE of 10 cal/cm^2 at this CB or DS and is labeled as such, what PPE is needed to operate assuming the same conditions are met as in Table 130.7(C)(15)(A)(a)? Do I need Arc Flash PPE rated a minimum of 10 cal/cm^2 to do the same task that, if an analysis was not done, could be accomplished wearing non melting clothing?
ISeems absurd, so what am I missing?


What is missing is that the engineering study now must include a full risk assessment. IEEE 1584 only adresses the hazard. Other standards such as I recommend CCPS LOPA address risk assessments. Notice that throughout 70E the term risk assessment has replaced hazard assessment. Previously irrespective of the likelihood, one stopped halfway by only doing a hazard analysis. This left a void where knee jerk decisions were made irrespective of the risk, which is the gist of your question. Modern safety practices also look at likelihood and attempt to give equal weight to equal risk so that we don't attempt to use a rifle to kill a mosquito, or require a secretary to wear a 100 cal flash suit to plug in a coffee maker. The big learning curve now is that power engineers don't usually know anything about safety engineering. Annex F is fundamentally broken. So it will continue to get knee jerked.


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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Sun Nov 30, 2014 10:40 am 
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PaulEngr wrote:
What is missing is that the engineering study now must include a full risk assessment.


I don't quite see it that way. The purpose of the engineering study is to identify the magnitude of the incident energy taking into consideration the electrical maintenance program at the facility. The study should also make recommendations to reduce high incident energy levels.

The risk assessment is part of the electrical safety program at the facility. (NFPA 70E-2015 Article 110.1(G))

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 Post subject: Re: Mixing of Tables & Analysis
PostPosted: Mon Dec 01, 2014 11:18 am 
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wbd wrote:
PaulEngr wrote:
What is missing is that the engineering study now must include a full risk assessment.


I don't quite see it that way. The purpose of the engineering study is to identify the magnitude of the incident energy taking into consideration the electrical maintenance program at the facility. The study should also make recommendations to reduce high incident energy levels.

The risk assessment is part of the electrical safety program at the facility. (NFPA 70E-2015 Article 110.1(G))


As a general statement encompassing hazards other than electrical, valid point. However it looks odd. Shock is basically handled prescriptively. Acid burns are handled by requiring certain ppe on hand (but no requirement to wear it). Arc flash under the table method is like shock...its all prescriptive. The equipment limit practicality has been argued to death (without a practical alternative). So with tables we address risk in the tables while with incident energy analysis we let the engineers off free and just pester them on the vague definition of "properly maintained"? If it was my PE license you get a disclaimer for the latter.

Having both participated in and facilitated many risk assessments, I can say it is daunting at first to the uninitiated. But you can get new participants up to speed in 30 minutes of refresher training. Participants are supposed to be heavily weighted towards experienced hands, not engineers or outside safety consultants.

So at least in theory its a " electrical safety program" item. It allows us to address PPE for batteries more concretely (when to wear gloves). And it becomes a level above the incident energy study. But that is not the way the tables are structured. Perhaps the new task table should move to Article 110.


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