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 Post subject: Cotton underwear/undershirt
PostPosted: Sat Dec 21, 2013 5:03 am 
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I was discussing with someone the other day cotton underwear under arc rated clothing. This person had just been at a meeting with a company that sells arc rated clothing and was told that the cotton undershirts should not be worn as it could melt. They were also told that what needs to be worn is an arc rated undershirt (at a cost of $$).

My position is that cotton undershirts are acceptable as long as they are 100% cotton and are not t-shirts with emblems on them that can melt. I also feel it is a sales pitch to sell clothing.

I welcome other opinions/comments.

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PostPosted: Sat Dec 21, 2013 5:59 am 
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I heard the same BS from a trainer. First, cotton does not melt. Cotton, silk, wool, and several other materials char as they heat, or ignite. Cotton in particular begins to break down at 600 F. This means it chars...it does not lose its insulative properties unless it ignites (adds heat). It is definitely possible (proven) that the underclothjng is affected during an arc flash, just as bare skin would be. A second degree burn on bare skin occurs at 140 F after 1 second. The time required decreases at higher temperatures and increases at lower temperatures. Synthetic fibers, particularly polypropylene, melt as low as 134 F. They don't really ever char but just go straight to ignition after melting, and jgnition temperatures are lower. When they are molten, they tend to stick to the skin. This traps heat and imparts heat into the skin much mkre efficiently. The result is a very nasty burn because the melted clothing has to be removed, most often with attached skin, even if the skin did not reach second degree burn status. This is larticularly problematic lately because the market has been flooded with all kinds of underarmor cold/heat products, polypropylene cold weather shirts and long johns, and all kinds of work dry products. All of them are made from meltable fibers or blends of meltable and charring fibers. Some may actually be acceptable if the melted stuff does not penetrate the surface (or name tags or reflective stripes), but this has to be tested. The bonus with even cotton undergarments is that the trapped air between the arc rated clothing and the cotton adds significantly more protection to the ensemble. The amount would have to be tested but is more than just 1 cal. Several documents on arcwear.com show tested combinations of arc rated layered clothing, but I have not seen any tests with just cotton. Based on the burn literature that shows that burns up to 25% of total body surface area have a very high survivability, I put in a proposal on the last 70E cycle to quantify the "negligible" rule with say no more than half of that or 12.5% of body surface area. Hugh Hoagland submitted something similar based on a new ASTM test that would look at whether the meltable material penetrates a backing layer. This amount is quite large and would allow for reflective stripes meeting NFPA requirements for turnout gear, ANSI level 1 and 2 as well as emergency services high visibility clothing, in addition to name tags. These were all rejected.


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PostPosted: Mon Dec 23, 2013 10:23 am 
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Cotton undergarments are safe to wear when you have the properly rated ATPV arc rated clothing covering over them. Also the elastic material as in the waist bands on underwear and leggins on cotton socks are considered acceptable, when worn under properly rated ATPV rated clothes.


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PostPosted: Mon Dec 23, 2013 11:41 am 
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In NFPA 70E section 130.7(C)(12) there is an exception which specifically addresses this issue of underwear. It says "Nonmelting, flammable (non-arc rated) materials shall be permitted to be used as under layers to arc-rated clothing clothing....."As an FR manufacturer we do produce arc rated under layers for those who desire some additional protection.It is not uncommon to see folks wearing a heavy arc rated shirts with most of the top buttons undone which exposes their upper chest to a potential burn. While this is not allowed by code, and not something we advocate, it is unfortunately what we see out in the field. We believe if we can replace that 100% cotton t-shirt with a comfortable, lightweight FR under garment it is going to help by removing some of the fuel in the event of an arc flash. So while 100% cotton which is not arc rated is allowed there are also options for those who want to go above code minimums. Mr. Donovan would you mind sharing the who misinformed you claiming arc rated under wear was required by code?


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PostPosted: Mon Dec 23, 2013 1:31 pm 
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For confidentiality reasons, I can't disclosed the company. The company that asked me about it is a client and a salesman from a company that sells arc rated clothing made the statement during a visit as my client company is purchasing some AR clothing now that the arc flash analysis has been completed. I had quoted the same section of the NFPA 70E to the client. I thought might be an interesting discussion here on the forum and see if others have had the same experience. I am glad that a manufacturer provided some input also.

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PostPosted: Tue Dec 24, 2013 5:50 am 
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Benchmark FR wrote:
It is not uncommon to see folks wearing a heavy arc rated shirts with most of the top buttons undone which exposes their upper chest to a potential burn. While this is not allowed by code, and not something we advocate, it is unfortunately what we see out in the field.


In regards to the above, I wonder why they are dressed in such heavy AR clothing all the time. Is it really necessary? Are they constantly working on equipment that requires that? Is most of the equipment rated much less than what they have on and would be better with lesser AR clothing but have a AR coverall with higher rating to put on when needed? Was a study done or are their AR clothing needs from the tables in NFPA 70E? Do they button up their shirts prior to working on the equipment and unbutton for walking around?

As you can see a host of questions on your statement.

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PostPosted: Tue Dec 24, 2013 8:49 am 
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Non-arc-rated fabrics can not be used to augment any layered clothing withstand calculations under NFPA 70E.


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PostPosted: Tue Dec 24, 2013 9:05 am 
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sparksmore wrote:
What you think you heard was most likely incorrect if you got this information from an EHAZARD seminar. Hugh Hoagland has all his trainers working off the same script and NONE of those people would have told you that cotton melts! Non-arc-rated fabrics can not be used to augment any layered clothing withstand calculations under NFPA 70E.


It was a salesman that made the comment.
Not sure what you mean by your last sentence. If you meant trying to increase the AR of the combined clothing that is not what I was originally discussing. The comment was made that you have to have AR undershirt on under the AR clothing. Currently the standard does not say that only that non melting, non flammable garment be worn

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PostPosted: Fri Dec 27, 2013 7:12 am 
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The old 'layering' standard in 70E has been gone for years. Layering can be used but the combinations must be tested. There is nothing preventing one of the layers from being cotton in the test. When you read the labels I'm not entirely sure whether untreated materials might not be used anyways. In the kiln jndustry multilayer brick assemblies are common. As refractoriness (abrasion and temperature resistance) goes up, so does density. As a consequence, insulative properties go down. Thus it is very common to see say a 3500 degree magnesite brick backed by an alumina or even common fire clay brick when the temperatures on the back side of the magnesite brick are low enough to allow a much more jnsulative brick to be used. The same strategy is used in firefighter turnout gear, especially the aluminized stuff where the aljminum is mkstly there to decrease emissivity. There is no reason that the same strategy would not work in multilayer flash suits. From the ones we have it is clear that the manufacturer is varying the materials in each layer (Salisbury). 70E is silent on the precise makeup of arc rated clothing. As long as jt passes the ASTM test, the precise makeup of the clothing js immaterial. Wearing multiple layers is not specifically disallowed. Just that you cannot simply add ratings. In fact it turns out that actual tests show that layers provide more than additive protection. Many of the tests are with Westex treated cotton (Indura Ultrasoft) which seems to hit 8-12 cal/cm^2 on its own. Since the ammonka treatment mostly just increases the jgnition temperature and disables flame propagation then if tests were done where the outer layer imparted enough protection that the inner layer no longer require treated material then there is nothing in 70E disallowing this as a rated combination. Granted the layered rating is most likely only going to impart a small bump before the untreated material becomes the limiting factor of the combination.


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PostPosted: Fri Dec 27, 2013 9:19 am 
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Thanks PaulEngr for the additional information. The main point is that a salesman was trying to say that cotton could not be worn since it would melt and one needs AR undershirt. Which I think is BS also.

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PostPosted: Mon Dec 30, 2013 8:45 am 
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I think we all agree that is BS


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PostPosted: Tue Dec 31, 2013 9:08 am 
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wbd, the salesperson is wrong. This is pretty common. Cotton does not melt.

Non-FR Cotton t-shirts DO NOT melt but they have two issues:

1. They can ignite.
This is most common in higher voltage contact injuries where cotton can ignite UNDER the arc rated shirt with as low as a 1.5 cal/cm2 calculated exposure (see our new paper in February 2014 at the IEEE-ESW for details of this last December research).

2. They hold moisture and allow ratings to be reduced due to water conducting the heat in form of steam to the body reducing protection levels. (see last year's and 2010 IEEE-ESW papers on effect of moisture).

The main concern is ignition. If you aren't working greater than the calculation in 480V there is little risk. But in higher voltages there is a real hazard but the standard still allows you to wear them.

What is clearly not understood above is that while cotton might raise the level of protection when it is dry, at some point before or slightly after the ATPV of the system with cotton, the cotton will ignite (this has occurred at the ATPV of the outer shell in some cases but happens right past the EBT of the outer shell in almost all cases). Ignition and burning of a shirt will kill a 50 year old worker about 40% of the time (American Burn Association Data).

The sales person is wrong on cotton but right on AR t-shirts. We aren't anti cotton but it carries a risk that the NFPA 70E committee recognized (ignition). I like AR t-shirt to be worn all day and wear a long sleeved AR shirt when working exposed. Makes the normal life cooler and gives extra protection when working energized without adding risk. That is what we think, but cotton is allowed as long as you don't count it as extra protection. Once that protection is at the inflection point, you go from protected to 20-40% probability of dying. That is what we warn of and I think the salesperson was trying to get across.


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PostPosted: Mon Jan 06, 2014 8:34 am 
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A couple of observations:

Some of the highest arc flash exposures we've calculated, originate on 480V systems. It may be misleading to state that some protection is not needed unless working voltages greater than 480V. I believe HRC is a single dimension number without the need for further interpretation based on voltage.

Wearing an AR T shirt all day long might suit your work environment, but would not necessary conform to other industrial environments. In refineries there is a non-electrical requirement to wear flame resistant full coveralls to enter the plant. These are now obtained with Arc Rating so the electricians working in the plant have this on at all times, whether or not they are doing electrical work or electrical work with arc flash exposure.


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