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Incident Energy and ATPV or Hazard Risk Category?

Discussion in 'Personal Protective Equipment (PPE)' started by Jim Phillips (brainfiller), Feb 19, 2009.

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  1. Just thought I would kick this one out there for discussion and debate.

    At the IEEE 1584 meeting a few weeks ago, the discussion came up that some people are moving away from the Hazard Risk Categories and going with just making sure the Arc Rating (ATPV) of clothing and associated PPE is greater than the incident energy. Basically ATPV > I.E. This is really all that is needed for compliance but everyone is still in the HRC mindset and this comment caused a bit of a stir in the room.

    My understanding is the HRC method was tied to the original development of the HRC / Task tables before we had good calculations methods of incident energy. Now that we have had the IEEE calculations for a while, it seems the study practices continue to evolve.

    I can see both advantages and disadvantages of going with I.E. only. One obvious advantage is if you have a location of let's say 12 cal/cm2, instead of going to category 3 and 25 cal/cm2 PPE, you just need to exceed 12 cal/cm2. (or what every your actual study indicates). This disadvantage is this could cause even more confusion with software generated labels and create an even greater disconnect between calculation studies and NFPA 70E tables.

    Just curious on what thoughts the arc flash forum gang had.
  2. Zog Sparks Level

    In a perfect world I would say using the ATPV>Ei is ideal, however this makes it confusing for the operators and harder for safety managers to have the correct PPE available at say a large industrial plant. How many sets of PPE can each person be assigned?

    I dont think there is a best answer here, it depends on a case by case basis. An operator, that has been trained to do a specific task, and has limited equipment they are required to operate may be best suited (No pun intended) to have specific clothing with the appropriate PPE for that task, but a maintenance electrician at an industrial plant or an electrical contractor would need a whole wardrobe with them, using the HRC method would be best for them. In fact, usually a simplified 2 catagory system seems to be best here (HRC 2 and HRC 4).
  3. WDeanN Sparks Level

    I can see the basis for the HRCs, but, having performed the calculations, I now ABHOR the categories.

    We are issuing PPE to our electricians and others, and have gone with an 8 cal minimum for PPE. With that, they can work on and operate ~80% of the equipment. (We've analyzed and posted over 1500 locations at my site alone. Granted, this also includes small motor disconnects and the like.)
    The only thing that the categories provide at this point is that if it is over 8 cal/cm, they now have to put on additional clothing, and they also have to go to a full hood for head protection. (We don’t have any face shields > 8 cal.) In the past, the only difference for us between Cat 1 and Cat two was the inclusion of hearing protection, but I see that that is now included in the PPE for all categories with the 2009 70E.
    With nearly all the requirements the same, what is the point of the HRC if you have performed the calculations? If you know the rating of your clothing, and the rating is posted on the equipment, you don’t care what the Category is, as long as you are wearing equipment that is rated for the incident energy.

    Get rid of the HRC if you have performed the calculations. They are a source of confusion.

    As for the disconnect between calculations and the tables? I could care less. The tables are pretty worthless given all the restrictions and footnotes applied to them, anyway. In my humble opinion, they make matters worse.
  4. WDeanN Sparks Level

    Zog,
    There is really no need for several sets of clothing. Stick with one minimum, say 8 cal ATPV. This can still be comfortable to wear on a daily basis. Anything above that requires a bear suit of 40 cal or more.
    Even a contractor travelling to many sites can do this. If his people are trained well (ok, few are…) they could even spot locations that are unmarked that may require the bear suit. 480V Substations, for example. MCC’s could fall to either side. Most small disconnects will be on the 8 cal side. Panelboards are most likely to be below 8 cal.

    This utilizes the 2 Category system, without relying on “categories.” (Which I abhor, by the way…)
  5. Zog Sparks Level

    You sure you read my post?
  6. haze10 Sparks Level

    I think going to a ATPV>IE is acceptable. The solution to the HRC table is to substitute the 1,2,3,4 Levels with 4,8,25,40 cal/cm2. That would solve that problem.

    We wouldn't see the advantage for the 'in between' the 8.1 to 24.9 cal situations until we get further developement in face shields. If you have to wear the HRC-3 face shield, you might as well wear the suit. We also have clothing manufacturers that are presently designing to the interval categories. That will probably continue to minimize inventory unless there was some supreme market demand for an inbetween value. Which I don't see.

    But, like must codes I work with, the greater the flexibility the more I like it and the more industry comes forth to fill niche products.

    The HRC task table is also of limit value because of the 2 cycle clearing time NFPA decided to use. This rules out a high percentage of users right out the gate. The rest still have to perform a limited analysis to see if they can even use the table.

    I also agree with the concept of minimums, but I find HRC 1 to be a more acceptable minimum. Level 2 in Houston or Tampa could be a harsh summer attire.
  7. Terry Becker Sparks Level

    I hope I am not confused, but here is the way I believe 70E was set up orginally:

    1. You can only officially use the HRCs if you use the Table Method for arc flash hazard analysis.
    2. If you cannot comply with the notes you need to calculate incident energy at the working distance and use this value and get ATPV rated FR clothing that is has a ATVP value greater than the calculated incident energy at the working distance.

    That's it. But, everyone still uses the HRC system even when the incident energy at the assumed working distance is calculated, I have seen it referenced on detailed Arc Flash & Shock Warning labels, etc...

    In reality we can only use the HRC classification system if we use the Table Method. Yes everyone is using HRC 2 and HRC 4 to define a simple arc flash clothing 2 category program, which is fine, but you still have to review the ATPV rating on the collar tag or other tagging on the clothing worn and ensure its value of ATPV is greater than the anticipated calculated incident energy at the working distance.

    That said people do not understand that the HRC system can only officially be used if you use the Table Method.

    Regards;
    Terry Becker, P.Eng.
    www.esps.ca
  8. Lots of good discussion on this one. Terry, I believe you are correct in that origionally the Hazard Risk Categories were set up to be used with the tables. Table 130.7(C)(11) Protective Clothing Characteristics equates the HR Categories to the minimum arc rating of PPE that is required and people tend to use these values when performing calculation studies.

    HRC 1 = 4 cal/cm^2 minimum
    HRC 2 = 8 cal/cm^2 minimum
    HRC 3 = 25 cal/cm^2 minimum
    HRC 4 = 40 cal/cm^2 minimum

    Early on, most people only used the tables - calculation studies had not fully evolved yet. I heard from Ray Jones some time back, that the HRC / Task Tables of 130.7(C)(9) were based on a lot of judgement at the time. Now that we have reasonable calcualation methods, people focus more in the incident energy but still try to equate it to the equivalent HRC.

    At the 1584 meeting in St. Louis a few weeks ago, someone (left their name out) brought up that when you perform a calculation study, you really do not need to use the HR Categories but that you only need to have the PPE's ATPV > Incident Energy. Although this is a true statement, I was curious how many people actually use this approach and do not use the HRC in calculation studies.

    My thought was it would be confusing but there might be cases where a calculation is something like 11 cal/cm^2. Using the HRC would bump you up to Cat 3 - 25 cal PPE when in fact you just need PPE > 11 cal.

    Thanks for everyone's input!
  9. keraunos Junior Level

    The ultimate goal is to protect the worker from the flash/blast. So I would agree that ATPV > IE is acceptable. However, as previous posts suggest, a practical method is to provide personnel specific HRC level PPE. We use HRC's 0, 2 & 4 specifically. This may be especially relevant in our case because of stipends and step-discipline for non-compliance may be necessary in a bargaining-unit environment. We find providing levels as Zog suggested, the simplest method to administer and we seem to have better compliance by the crews.

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