elihuiv wrote:
if you need an HRC 2 you must use that level but an HRC 2 can be anything from 8 cal protection to 24 cal protection.
So if you have a 12 cal hazard you must wear a 12 cal protection (which happens to be an HRC 2 but not any HRC 2 will work).
Hope this helps.
HRC vs. Incident Energy Calculations.
This has been a recurring issue stemming from the use of the word "OR" in 130.3(C) Equipment Labeling ...available incident energy OR required level of PPE...
I agree there can be some misinterpretation in the use of Table 130.7(C)(11) however that should not dictate that it cannot be used with calculations. I believe we all can agree you CAN NOT mix 130.7(C)(9) and the calculations. Table 9 is not the issue, Table 11 is the issue.
Like the ratings of many things, (This philosophy is not unique to just PPE), there are TWO parts to any rating. Pretty simple logic.
Number One - What is the rating (arc rating in the case of PPE)
Number Two - What is available i.e. do you exceed the rating (incident energy in this case)
Obviously the incident energy must be less than the arc rating.
The Arc Rating of Table 11 follows this very simple logic. Category 2 has a MINIMUM arc rating of the PPE of 8 calories/centimeter2 therefore if Category 2 is used, the MAXIMUM incident energy available cannot exceed 8 calories/centimeter2
I agree, as Hugh correctly pointed out that a Category 2 garment must have a MINIMUM Arc Rating of 8 calories/centimeter2 but technically speaking, Category 2 can also include garments that are rated up to 24 (just under 25) calories/centimeter2.
This does not mean that mixing Table 11 and incident energy calculations is the problem. The table simply states MINIMUM ARC RATING so if a Category 2 garment is specified, then the CALCULATED incident energy must be less than the MINIMUM ARC RATING of 8 calories/centimeter2 – even though the actual garment might be rated higher.
I also agree with Hugh as he pointed out that this could lead to an overkill where someone actually has a 12 calories/centimeter2 garment that would technically be Category 2. Listing both 12 calories/centimeter2 AND Category 2 could lead to confusion since the values of Table 11 would indicate 8 calories/centimeter2 However, the problem is not Table 11, it is the correct application of Table 11. The user must know it is the LOWER of the two values if both are used. This is why some use only incident energy but this is not the majority. Worst case scenario is this might lead to an overkill (conservative) if not properly analyzed.
I believe the ORIGINAL intent of Article 130.3(C) was to require information for selection of PPE it was NOT ABOUT the use of the word “OR” and I very strongly believe it was not intended to prohibit the use of correlating incident energy with HRCs via Table 11.
I believe what happened was when the 2009 Edition of NFPA 70E was released, people questioned the use of “OR” in 130.3(C) i.e. “Do they really mean only one OR the other?” Looking at the literal use of the word “OR” yes that is what it presently means however I believe the original intent was NOT to restrict the correlation of incident energy with HRCs of Table 11.
The “OR” issue, I believe was an unintended consequence that can happen when new proposals are introduced. The committee focuses on the real issue of the proposal (adding information on the label to assist in PPE selection) and the unintended consequence of a word or a phrase is not picked up until people begin to interpret it.
Here is some of my supporting information (there is a lot more than this):
I went back to the NPFA Report On Comments (ROC) for the 2009 Edition. It was interesting because many of the people making an issue out of the use of the word “OR” have their comments on record as part of this document. Most of the comments focus on either debating the necessity of having more detail on the label or the burden it would place on companies. There was no debate about the word “OR” or Table 11.
There were a few references to Table 130.7(C)(9) Hazard Risk Category Classification Table discussing calculations OR HRC’s from Table 9 (which we know you cannot mix), but absolutely nothing about Table 11. Table 11 is NEVER mentioned it was calculations OR HRCs from Table 9.
The “OR” issue seems to have gotten so out of hand I spoke with the Chairman of the 2009 Edition of NFPA 70E a few weeks. He also concurred it was not the intent of this article to prohibit correlating incident energy with HRCs of table 11. Although this is not an “Official” opinion from NFPA, it does shed a tremendous amount of light on this whole issue.
I have also talked with a representative of a large well respected PPE manufacturer that is involved with the proposal process. He also said it was NOT the intent to prohibit correlating incident energy with HRCs and actually seemed a little surprised about how it was being interpreted.
I have checked with a few software manufacturers and they also still correlate incident energy with HRCs.
When IEEE 1584 was developed, they based part of the equation, known as the “Calculation Factor”, on the correlation of incident energy to HRCs. With the “OR” issue, does this mean IEEE 1584 is wrong? (Rhetorical question)
I [url="http://www.arcflashforum.com/showthread.php?t=655"]conducted a survey elsewhere in this forum[/url](far from scientific but pretty overwhelming results) and the overwhelming majority still list HRC AND incident energy.
It seems the original intent was simply to require some form of information so a person could select PPE, either from the incident energy or HRC (referring to Table 9) and again we all know you cannot mix these two. However, from what I have heard from some very credible sources (including the Chairman) it was never intended to prohibit the use of Table 11 with calculations.
However as presently written, people have been splitting hairs over what the meaning of the word “OR” is – reminds me of a famous trial in the 1990’s.
In my opinion 130.3(C) should read “AND / OR” so people can use one or the other OR both if they choose. For many, this simplifies their arc flash study and PPE selection if they base the study and PPE on the ratings from Table 11 ([url="http://www.arcflashforum.com/showthread.php?t=655"]see people’s comments[/url]). For others that choose to use ratings higher than those in Table 11 (i.e. like 12 cal or something else), they do not have to use HRCs with calculations. Leave the decision up to the person responsible for the study. Keep in mind that 70E is a MINIMUM requirement but it appears that the use and interpretation of “OR” is putting limits on it.
Yes this can lead to overkill as discussed above, but many (the great majority) still use the cutoff of 4, 8, 25, and 40 calories/centimeter2 correlated to PPE selection and incident energy. The change to “AND / OR” would not require both the incident energy and HRC be on the label, but it would “officially” ALLOW it to be on the label for those that choose to use this method.
