I just returned from the 2014 IEEE/IAS Electrical Safety Workshop where there was a lot of discussion (and presentations) regarding upcoming changes to NFPA 70E.

Arc Flash Labels - Incident Energy AND PPE Categories - going, going, .....?
One topic that generated a lot of discussion (as it always does) regarded arc flash labels. Many of you have followed the posts from a while ago about grouping calculated incident energy by category. i.e. category 1 needs a minimum PPE rating of 4 cal/cm^2, category 2 is 8 cal/cm^2 etc. [url='http://arcflashforum.brainfiller.com/threads/important-survey-correlating-incident-energy-to-hrc.655/#post-3514'](See Here for Past Discussions)[/url]

The 2012 edition of NFPA 70E even had a last minute change that continued to permit linking calculated incident energy to categories (it originally was going to be prohibited).

It is well understood by most people that you should not link Hazard Risk Categories (HRC) with the calculated incident energy. As a result, most people simply began to use the term PPE category or PPE level.

2015 Edition of NFPA 70E
Guess what! The proposed 2015 edition of NFPA 70E is doing away with the term HRC and will now uses the term PPE Category. And you CAN NOT link PPE Category with Incident Energy. i.e. if the incident energy is 6 cal/cm^2 for example, you can not also refer to it as needing Category 2 PPE as in the past.

4, 8, 25 and 40 - Becoming Obsolete?
Prior to the final stages of the 2012 Edition of NFPA 70E, I made a comment that not allowing the use of categories and incident energy together could be due to the introduction of 12 cal/cm^2 PPE into NFPA 70E. The 12 cal/cm^2 rating does not fit the standard 4, 8, 25 and 40 cal/cm^2 that the industry is used to. This reason makes sense about why it is better to not link the PPE categories, HRC, whatever you want to call them with incident energy. It may be because new arc ratings are being created that don’t fit the old model. (just speculation but I have discussed this with several people)

Arc Rating - One Option
Personally, I prefer to just list the arc rating since it is much easier and can accommodate other new arc ratings as they are developed. However, a total ban on listing categories AND incident energy, a practice that has successfully been used for over a decade seems a but much. There are still many that like to use the category/levels not to mention the countless labels with the incident energy and category out there.

The Question:
With all of that stated, here is a variation of a question that surfaces on the forum from time to time.

Does it matter to you that the 2015 NFPA 70E won’t allow linking incident energy to categories?

• ·Yes it matters, Linking categories and incident energy is easier
• ·No, I think the 2015 edition has the right idea
• ·I don’t really care either way

As always, your thoughts and comments are always welcome!

I do not understand the problem, my head hurts, I’m confused and after reading the old thread I got even more confused.

But if I can recall another thread correctly, don’t they want to go to a full risk assessment not only a hazard assessment? And isn’t the table based on hazard and risk, where as a calculation is only based on hazard?

And as rdj states in the old thread

Quote:

Some folks are equating HRC with the level of PPE required on the label. The level of PPE as intended in NFPA 70E refers to the calorie rating of the PPE, not the HRC. See the Handbook. There is a lot of confusion about how the HRC relates to the Arc Flash Hazard Analysis. If the label says the incident energy is 10 calories/ cm2 and also says it is a HRC 3 there is a dilemma. If there is an incident and the employee is properly dressed in 12 calorie clothing the protection would be adequate as far as calories are concerned, and 25 calorie clothing would not be required. The HRC ratings provide some good information about the type of PPE such as face shields, hoods, etc. beyond the calorie rating. HRC tables are task related and different tasks require different PPE even though the incident energy may be the same. Also, the tables only apply for the bolted fault current and clearing time

I can imagine a worker would prefer a 12 cal suit above a 25 cal if he knows the danger is 9 or 10 cals.

And I am sorry if I misinterpreted the issues completely and my message makes no sense what so ever..

I'm not seeing the practical "do this" solution right now. Are we going to have to start labeling for task specific PPE? At the end of the day what we need is for the worker to know that if he does task A to equipment B he needs to use PPE C.

Just a simple question. If you can not list a category and a calculated incident energy, what will be on the garment label?

Think about it for a minute.

Don't they still need to have both an arc rating and the category for people that use the 70E tables and for people that perform calculations studies?

C. Marsh wrote:

Just a simple question. If you can not list a category and a calculated incident energy, what will be on the garment label?

C. Marsh wrote:

Well that is up to my boss, personally if I had to choose I would put the incident energy on the label not the PPE class. If in the next update they would decide to revamp the classes then you still have the correct incident energy labelled. Plus if you see that the energy is 20 cals you can select your appropriate PPE’s relatively easy I guess, if the label only shows the PPE or HRC class well then you need to rely on the class system on the label to still be up to date with the current classification. (you did actually calculate the hazard in cal/cm2 so why not put it on the label?) I’m not really a big fan of the HRC table, so if the NFPA 70E says I can’t put the HRC or PPE class on the label because my hazard assessment is based on the IEEE1584 calculations then I won’t put them on. In that case someone reading the label always knows if I used the NFPA70E table or actually calculated the incident energy.

The existence of this question warns me that the code writers suffer from tunnel vision.

I don't often wear arc flash PPE, but if I encountered a label with both HRC and Cal/cm2, and the two did not agree, that is good information.
1) somebody might have made a mistake.
2) If it was verified proper, I would like to know the basis for higher recommended HRC which might be plant policy.
3) Having both printed on the labels is a nice field check for Quality Assurance. We print voltage on the labels also and when installing labels this has provided a field check that we are on the proper location.
4) I am not aware of any "liability" in having both printed if the worker simply chooses the worst case of both. Such interpretation would make this a non-issue.
5) Lower HRC allowed in the tables for chores with lower probability of exposure, seems problematic from a theoretical point of view. Dead is dead, even if the event that contributed is very rare.

Sorry, I'm also confused by the question. What is the alternative to linking? We also seem to risk confusing garment labels (arc rating) with equipment labeling. We need to be able to compare the garment label to the equipment label without confusing the two things. I'm not a fan of categories, whether they are termed HRC or PPE category.

Few companies actually implemented the 4/8/25/40 system IN TOTAL because it led to even more confusion. There is almost no reason to use the 25 cal system and I have never seen it implemented anywhere since the differences between the 40 and 25 cal levels are relatively small. The question then becomes whether or not to implement the 4 or 8 cal clothing systems. If FR clothing is already required then implementing 4 cal as a "minimum" instead of 1.2 is very simple to do. Going to 8 cal from there is also a relatively minor change in the typical PPE that is already available and in service. Moving up to the 10-12 cal range is a very simple change from the 8 cal system (usually "for free"), and some companies have actually done this following the current 70E (2012) edition's recommendations and moving up to a higher cal level.

Mind you, there are PPE levels that fall out "naturally". The "protect the back of the head" rule makes 4 cal a natural trigger point. And the point where leather gloves and face shields give way to rubber or arc flash gloves and hoods is another "natural" breakpoint that occurs at around 12 cal. There is arguably little difference from a practical point of view of the clothing from 6 to around 12 cal. Similarly there is little practical difference from an end user point of view between 25 and 40 cal.

Every plant that I've been in so far has as a result done some sort of adaptation of the existing H/RC table to suit the PPE systems that they actually have one hand. They may adopt the existing H/RC levels, or they may (and frequently do) come up with a plant-specific level system such as identifying them as "A, B, C..." to get away from any confusion with existing standards.

The advantage of having SOME kind of "standard" is that PPE manufacturers don't get inundated with everyone having their own slightly different standard, which also keeps costs down to a certain degree. It also avoids problems where one would get locked into the "levels" chosen by one PPE vendor and not being able to migrate easily to another vendor. Thus I would argue to having SOME kind of levels. I think that this is exactly where 70E is going towards since the natural levels seem to be shaking out as 4, 12, and 40, with 40 still being somewhat arbitrary in nature. But I do agree that the "levels" should be a site specific decision and not dictated externally. On newer stickers I've been dropping the "H/RC" or "PPE level" requirement altogether and just giving a cal rating to avoid changes in standards.

Imposing a total ban on listing categories AND incident energy by NFPA group does not make sense to me but it does not surprise me at all. I am more a fan of linking categories and incident energy but with certain reservations explained below.

I believe that using calculated incident energy as a measure of HRC alone while disregarding the rate at which the energy was delivered is wrong. Existing NFPA 70E standard assumes that thermal injury is a function of incident energy alone and that that equal damage is produced by equal energy doses. Hence, dose (cal/cm2) based hazard risk categories in NFPA 70E. Unfortunately, this assumption is wrong as the same dose will produce different damage depending on the rate the dose is delivered. The issue was clearly and concisely summarized by Alice Stoll in [A.Stoll, "Heat Transfer in Biotechnology", Advances in Heat Transfer, v.4. Academic Press. 1967]:



[M.Furtak, L.Silecky, "Evaluation of Onset to Second Degree Burn Energy in Arc Flash". IAEI July-August 2012] presents a method for calculating threshold incident energy for a second degree burn on bare skin reflecting the above observation and field studies. Check this forum thread at http://arcflashforum.brainfiller.com/threads/evaluation-of-onset-to-second-degree-burn-energy-in-arc-flash.2221/ for more information.

Unfortunately, getting rid of incident energies and introducing the term PPE Category by NFPA group does not fix the problem. Arc rated PPE does not actually warrant the PPE will perform as expected. According to [Jim Pollard, "Do you know where your arc flash suit has been?". EB Magazine, January 2012]:



Selecting a PPE based only on its arc thermal performance value (ATPV) is very much as dubious as selecting a fuse or a breaker based only on device current carrying capabilities while ignoring the device interrupting and voltage ratings. While improperly selected protection device may serve for many years without exposing its deficiencies, the problem will arise and reveal itself only the day the device is called to clear the fault. Likewise, arc rated PPE impressive look may be deceptive without knowing how the PPE was really tested and what heat flux and for how long it was charged with during the test.

A look into test summaries (such as ASTM F1959 "Standard Test Method for Determining the Arc Rating of Materials for Clothing") from a reputable lab reveals materials exposed to relatively low heat flux for relatively long time interval (around 16 60HZ cycles, or approx 250msec) and still being rewarded with the arc ratings. It is uncertain and very much dubious whether the same material would be able to withstand even a fraction of its ATPV rating if all of the energy was delivered within 10msec time interval (the arc flash duration minimum set in IEEE 1584 and used to calculate incident energies).

I disagree. First, in order for any PPE to provide a thermal barrier, the relative rate of conductive heat transfer from one side to the other is very important. Conductive heat transfer is linearly related to temperature differences, and is relatively poor compared to radiant heat transfer which transfers heat from the arc to the garment. Radiant heat transfer is proportional to the 4th power of the temperature difference. Arc temperature is relatively fixed. What happens as arc current increases is that the size of the arc column itself increases, allowing more efficient energy transfer through the arc. In effect it is similar to the heating effect on a wire. This is quite clear when looking at the IEEE 1584 empirical equation that shows that the first term of the polynomial for current is proportional to the 2nd power, not the 4th power. Since conduction (unlike radiant heat transfer) is linear, then doubling the heat flux while halving the time results in the SAME constant amount of energy transferred from the surface of the PPE to the inner layer facing the occupant.

This is all assuming that there are no chemical or physical changes to the PPE. This would occur if the temperature of the outer layer of the garment exceeds a limitation of the material. This occurs when the amount of heat absorbed exceeds a threshold. Again, we are given that the energy density (cal/cm^2) is fixed and only that the amount of time over which it is being transferred is changed, thus heat flux (cal/cm^2/time) is increasing but total time is correspondingly reduced. If the transfer mechanism were something other than linear for conduction I would be inclined to agree that it would be possible to have a higher rate of heat transfer to the surface of the PPE and allow for localized heating on the outer surface that is not transferred to the inner surface. This would then cause a physical or chemical change that would ABSORB the heat and dissipate it through a phase change or chemical change, which again gets us right back to the same point where energy transferred as measured by a calorimeter shielded by a sample of the material that the PPE is made out of performs identically when exposed to an arc.

If that were not the case then we would see some sort of trend where the data is nonsensical in the way that the ASTM 1959 test is done...samples closer to the arc would perform differently from those farther away and the threshold that is clearly visible in the full ASTM 1959 report would be much more broad, thus indicating that a variable is missing.

[QUOTE=PaulEngr]This is all assuming that there are no chemical or physical changes to the PPE. This would occur if the temperature of the outer layer of the garment exceeds a limitation of the material. This occurs when the amount of heat absorbed exceeds a threshold. Again, we are given that the energy density (cal/cm^2) is fixed and only that the amount of time over which it is being transferred is changed, thus heat flux (cal/cm^2/time) is increasing but total time is correspondingly reduced. If the transfer mechanism were something other than linear for conduction I would be inclined to agree that it would be possible to have a higher rate of heat transfer to the surface of the PPE and allow for localized heating on the outer surface that is not transferred to the inner surface. This would then cause a physical or chemical change that would ABSORB the heat and dissipate it through a phase change or chemical change, which again gets us right back to the same point where energy transferred as measured by a calorimeter shielded by a sample of the material that the PPE is made out of performs identically when exposed to an arc.[/QUOTE]

I am not convinced that exceeding thermal threshold in garment material would cause a physical or chemical change that absorbs the heat and dissipates it through a phase change or chemical change. As a matter of fact, the evidencial material I seen shows that exceeding garment's thermal threshold could quickly ruin the material integrity and cause it to char, set on fire and break open in very short time. Perhaps, there are garments that behave the way you've described and only become stronger due to phase change or chemical change similar to hardened and tempered steel. I am yet to see them. Until that time I would rather trust actual test results proving PPE is capable to withstand its ATPV rating in time intervals as short as 10msec. To my knowledge, none of the available ASTM standards address this time domain and I can only pray in hope that arc rated garments available on the marker will adequately protect personnel relying on it.

OK now I'm really confused.

Garment labels will still need:
PPE Category 1, 2, 3, 4 etc. so people can use the 70E tables

AND ALSO

Arc Rating cal/cm2 for people that perform calculations

So it's OK to have cal/cm2 linked to categories on the garment label
but NOT on the arc flash label?

What kind of silliness is this? (I actually had a different term than silliness but this is a public forum)

There is absolutely no need for HRC categories on clothing.
Yes,there are minimum cal/cal² that correspond each are associated with each HRC. But those are easy to memorize or look up in a table by qualified individuals.

Technically the HRC is a list of many PPE items, some of which are fabrics and some that are not.
So wearing a shirt that says "HRC2" does not mean you are using all of the required PPE for that category. However saying you are wearing an 12 cal/cm² is simply a statement of fact that applies on to that item.

Yes, we would probably be better served if each piece of equipment (clothing and other PPE) listed the actual value in cal/cm2, rather than listing some other category. The shirt and pants I am wearing right now both say HRC 2 on them. It'd be more useful for me if they said 8.2 cal/cm2 or 12.6 cal/cm2 or whatever the values might be. I can find out, it'll usually be printed on a tag, or short of that I can go to the manufacturer's website, or call them to find out what it is.

Right now we have the plant broken out to three values - less than 1.2 cal, less than 8 cal, and less than 40 cal. If the equipment and clothing would support it, changing 8 cal to 12 cal would allow me to eliminate a blast suit from several areas currently requiring it. But the table values being used of HRC 2 and HRC 4 don't allow me that flexibility.

If a garment is rated for HRC 2, doesn't that mean that it is rated for at least 8 cal/cm2?
or could a garment that is rated for 6.5 cal/cm2 be labelled as HRC 2 as well?

The only advantage I see to the HRC listed on the garment is that you wouldn't have to check the table, a minor convenient at best, but as long as both the label and the garment have cal/cm2 it shouldn't be a problem.

HRC 2 (Hazard/Risk Category 2) means that the equipment is all greater than 8.0 cal/cm2.

Yeah, that's what I thought. Then I got to thinking (That's usually where I get into trouble).

So, if the clothing was actually 6.5 cal/cm2 it would be labelled as HRC 1

But the problem is that the clothing (shirt and pants) alone is not sufficient PPE for meeting HRC2, yet in practice, this seems to be the goal of many ESWP programs.

Are hard hats listed with an HRC?, What about face shields? I know my boots do not have an HRC rating.

I'm not sure about the specific HRC of these parts of the PPE. Of course, OSHA, ANSI Z133, and some other ANSI articles do refer to them though (Hard hats are compliant with ANSI Z89.1-1986, Face shields are compliant with ANSI Z87, and boots are compliant with ANSI Z41-1991)

Boots and hard hats don't come listed with HRC values or cal/cm2. Face shields that are designed for arc flash usage do.

For boots and hard hats, you just have to use ones that are compliant with the applicable ANSI standards. I believe all hard hats are assumed to have the same value, and 70E just specifies that you wear leather boots without any other guidance. Some day we'll probably have testing done on them, but that's not where things are now.