Hazard Risk Category 4

In table 130.7(C)(11) of the 2009 edition, hazard risk category 4 says that you need either a FR shirt and pants or coverall, and an arc flash suit so that the system arc rating meets the required minmums.

I take this to read that you need 40 cal cover all (or FR shirt and pants) and a 40 cal arc flash suit. Is this correct? If so, I cannot find a 40 cal coverall or for that matter a 40 cal FRshirt or pants.

Thanks for your help.

Typically the ATPV rating of FR clothing is additive. the statement you mentioned is an OR statement. you need to wear coveralls and fr shirt and pants that meets the minimum.....40cals. An FR rated cover of 15 cals plus a switching suit of 25cals will give you 40 calories of protection....OR you can wear a 40cal flash suit. The thing to remember is to meet that minimum requirement using any combination that will get you there.

Contact for arc rated clothing

You may wish to contact to source suitable clothing
Chris Ross
+44 7802 558995
www.arcflashprotection.co.uk

cross@jkross.co.uk

Layering is not an effective alternative and prohibited by most policies.

There are some results in the calculations that just results in a rating that prohibits the performance of the task.

The code talks about the advantages of layering but does not go so far as to say that each layer is cumulative. In the testing process there is a requirement for the garment to withstand the pressure wave and not break open. A garment that breaks open obviously is of no value. I remember, but don't quote me, that the testing was to 50% probability of a 2nd degree burn, or a 50% probability of the garment breaking open. Most of the time the garment rating is to the burn rather than the break open. But if you take ten 4 cal shirts to make a 40 cal suit, there is a probability that several layers will be blown open in the arc blast.

Along that line, a 40cal suit has been tested to 40 cal. You can be inf 4cal pants and shirt, or, in your underwear, the 40 cal suit is always 40 cal and not dependant on any other undergarments. Its only using the Task Table that makes you add the FR underclothing to the suit, and thats just for conformance to the Table.

Laszlo,

There has been quite a bit of discussion in this forum regarding layering of PPE to achieve the required rating. It has been my understanding that layering 25 and 15 cal PPE would be better than using a single layer 40 cal garment. I am curious why you say it is prohibited by most policies.

I have guessed it is because maybe no one has tested the combination, but the layering idea stills seems as though it should be better, especially since the fabric will be thicker. I would think 25 + 15 might be greater than 40 if it were tested as layered.

Thanks for any input.

the arc rated suit of 40 cal is designed to help protect with the scharpnel the you will encounter during a blast of this magnitude whereas the 25 and 15 cal clothing does not.

Appendix M

Appendix M attempts to address this issue in the '09 70E, but in my opinion only muddies the water. After performing examples of additive layering, the last thing they state is:

" It is important to understand that the total system arc rating cannot be determined by adding the arc ratings of the individual layers. In a few cases, it has been observed that the total system arc rating actually decreased when another FR layer of a specific type was added to the system as the outermost layer. The only way to determine the total system arc rating is to conduct a multilayer arc test on the combination of all of the layers assembled as they would be worn"

That's the clearest thing they say in the entire appendix and my read on it is if it's not tested, it doesn't add up. I'm with Haze on this one.

TxEngr

I am glad I am not a part of a group that initially states that layering has been shown to be better than a single layer, but then flips to say well....on second thought not really!

I tell my folks to get the "effective" layered rating from the clothing mfg. Then if the mfg. has completed the layered test the client has the results and recommendations to rely on.

I am clueless as to how the layered rating can reduce the initial value unless maybe they put the lower rated garment on the outside? I have also been told by the mfg. that if the rating is exceeded, the fabric will still not burn. Would seem that with enough heat, anything would burn.

Is there actually data that shows a 40 cal garment is better designed for schrapnel protection than a 15 + 25 layer?

Thanks,
Alan

According to NFPA 70E 130.7 FPN No1, PPE has nothing to do with sharpnel protection:

... Due to the explosive effect of some arc events, physical trauma injuries could occur. The PPE requirements of 130.7 do not adress protection against physical trauma other than exposure to the thermal effects of an arc-flash.

Did I miss something about new flash suits?

You answered the question: it is NOT tested in combination. Too many variants and combinations.

On the other hand if we can rely on supercomputers to simulate nuclear weapons effectiveness, why can't we do the same for many other things and insist on actual testing. I can think of one thing though: the actual testing of arc-flashes so far indicate that the actual released energy is mangitudes below the 1584 calcualtions. That tells me that the mathematical model is a failure, but it makes a lot of money for a specific segments of the industry.....

your correct in the statements from 130.7. while i was attending an arc flash trianing class they mentioned that as the arc flash increases in intensity from class 1 to 2 2 to 3 3 to 4 and above 4 the blast wave increases. these suits that are rated for the higher levels have layers woven inside to help spread out the blast and help reduce the schrapnel injuries as well.
I believed what they told me and it did make sense. Also saw pictures of the suits in comparison the higher ratings did hold up better to the flying parts.

No one is discussing the 'break open' issue. Thats part of the test to get the rating.

Your correct, arc flash PPE was never intended and will never be suitable for protection from blast sharpnel.

In reference to layering being less effective, it does happen. If you put a 4 cal shirt over a 40 cal suit how long will the 4 cal shirt last? Layering does work but the inner layers need to be the lower rated values and increase going out. In other words wear the 25 on the outside of the 15 but when it comes to a 40 cal requirement, buy the 40 cal suit, it does not cost that much more. Remember that if the 25 cal clothing fails under a 40+ cal fire, the next layer is only 15.