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 Post subject: 70E 2018 No restriction for clothing for less 1.2 cal/cm2?
PostPosted: Fri Oct 20, 2017 5:16 am 
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If the AFIE calculation method is used, there appears to be no restrictions on the type of clothing to be used if the AFIE is below 1.2 cal/cm2. Before, when the PPE table was in Appendix H, there was a range between 0 and 1.2. That range has been eliminated in 2018.

The old range allowed for non treated clothing but had some restriction like it couldnÔÇÖt be flammable or meltable.

Are those restrictions eliminated? If the calculated AFIE is, for example, 1.1 cal/cm2, can I use flammable or meltable clothing? What about safety glasses? All references to clothing and equipment below 1.2 cal/cm2 seemed to have been deleted.


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Sun Oct 22, 2017 7:46 pm 
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No restrictions.

Keep in mind most untreated clothing hits ATPV 6-10 (just like the treated version) until it melts or ignites. ATPV by itself has to do with thermal properties. FR just keeps it from sustaining a flame.


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Mon Oct 23, 2017 8:28 am 
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These were deleted due to the philosophy of "risk assessment". The issue is that IF there is NO hazard, there is NO risk but if there is a small hazard, the risk must still be assessed. Companies which have operators who only operate equipment less than 1.2 cal/cm┬▓ equipment MAY do the risk assessment and decide clothing is not an issue and provide a glove and sleeve to protect the hand and arm which will enter the AFB since the calculations may be done at 18 inches. However, risk assessment doesn't mean we don't have to look at the issue and assess risk when the calculation is below 1.2 cal/cm┬▓

Another thing to consider is if SOME equipment is >1.2 cal/cm┬▓. Then do I want people in melting clothing since they will have to change to natural fibers for garments UNDER AR gear? Probably not. HRC 0 is long gone but non-melting clothing should always be required for those who operate anything >1.2 cal/cm┬▓ and AR gear should be the rule for electrical workers.

Remember 1.2 cal/cm┬▓ is second degree burn onset at the distance calculated (theoretically) so closer distances should still be considered.

Not a fan of melting or ignitable clothing but some conditions don't justify AR for non-electrical workers. Companies using this change to get rid of AR clothing or cotton may wind up with a huge issue if something doesn't go "according to calculations".

Hugh Hoagland
Sr. Managing Partner
e-Hazard | http://www.e-hazard.com




RECS wrote:
If the AFIE calculation method is used, there appears to be no restrictions on the type of clothing to be used if the AFIE is below 1.2 cal/cm2. Before, when the PPE table was in Appendix H, there was a range between 0 and 1.2. That range has been eliminated in 2018.

The old range allowed for non treated clothing but had some restriction like it couldnÔÇÖt be flammable or meltable.

Are those restrictions eliminated? If the calculated AFIE is, for example, 1.1 cal/cm2, can I use flammable or meltable clothing? What about safety glasses? All references to clothing and equipment below 1.2 cal/cm2 seemed to have been deleted.


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Mon Oct 23, 2017 8:33 am 
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Technically there is NO ATPV, in the standards, for ignitable or meltable clothing, due to the requirement to ONLY test fabrics passing a vertical flame test. Some want to remove this but it would be confusing in the market. ASTM F1506 (in the new 2018 notes) requires vertical flame AND Arc Rating (either ATPV or EBT). Never trust an ATPV of non-FR materials since ignition is much more affected by current than arc rating. Raise the current in an open arc test or put the garment in a box test and ignition will occur at a much lower incident energy. You have the concept right Paul but there is more to it unfortunately.

Dang this science stuff is hard. No one told me when I started 23 years ago!

Hugh Hoagland
e-Hazard.com

PaulEngr wrote:
No restrictions.

Keep in mind most untreated clothing hits ATPV 6-10 (just like the treated version) until it melts or ignites. ATPV by itself has to do with thermal properties. FR just keeps it from sustaining a flame.


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Tue Oct 24, 2017 5:09 pm 
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I just switched over from incident energy since we are talking about fabrics. ATPV means passes vertical flame test...noted.

My basic problem with arc rated / non-arc rated fabrics and the concept of non-meltable fibers is simply that when we do the calculation or look at the arc flash boundary or any of that, there is the issue that the definition of the working distance looks at the distance to the face/chest area. So just because my face/chest is outside of that boundary, my hands and arms aren't. Not only that but the 18" rule seems kind of screwy in terms of anatomical considerations which is why OSHA in 1910.269 moved it back to 15" to match the normal "working distance" between the hands and the body. It's only 3" but if you are working near the 1.2 cal/cm2 threshold, it's pretty easy to be over/under it. So I'm probably just making the nonmeltable clothing argument here in reality. As I sit here and write this I just took off my arc rated work shirt and pants and got comfortable but I'm still wearing a cotton undershirt. I specifically avoid anything that is meltable when I'm doing electrical work. Besides it's a lot cheaper than Under Armor!!

Second Hugh I get your idea that it is somehow connected to current but I think that gets into the hot gas issue. I know it has been called plasma and just due to the temperatures and what I would expect to happen I'm not sure that we can call the hot gas cloud "plasma" but there is definitely something going on with that. It has completely different effects when it comes to textiles especially with regards to permeability for instance, and it is much more affected by equipment configuration. Let me just throw this out there. Heat transfer by radiation is proportional to the fourth power of the temperature difference. Thus relatively small increases in temperature result in dramatically increased heat transfer.

As I recall from the physicists working on arcs, basically the things that are going on inside the arc column are pretty much well settled science at this point and the diameter of the arc column which 100% contains the plasma that does exist is also well defined because there is a magnetic force pulling the plasma in towards itself which drastically restricts the rate of growth of the arc column, and the arc column is very small on the order of a few millimeters under the most extreme circumstances. So this is the reason that I'm not buying arguments about effects of "plasma" at all. The arc column temperature is around 20,000 K, and that number can be calculated from the physics equations. So there is a definite boundary between the plasma that does exist and the rest of the air around it. You can't have huge glowing clouds of plasma because it would be magnetically attracted to itself and form columns which we refer to as arcs. Plasma itself is really strange stuff because it is highly conductive and magnetic. The electrons are completely blown out of the outer "shell" or shells and the electrons and nuclei simply float around in a cloud-like structure. The concept of a molecule or even semi-ordered molecules that we see in liquids and gasses is gone.

But then we enter a huge amount of relatively unknown territory outside the arc column itself which is simply not well understood. None of the physics studies on arcs attempt to do anything to understand it. It even has a lot to do with upper atmosphere physics which is also not understood at all. Air begins to dissociate at only 4,000-6,000 K at surface pressure (1 atmosphere) so somewhere close to the arc we can expect the normal forms of O2, CO2, N2, and H2O to crease to exist and replaced with O-2, CO+2, H+, and N-. Since it is chemically and physically different I would not be surprised to see different physical heat transfer effects since other than CO (carbon is the one element that actually gets more aggressive towards bonding with oxygen as temperature increases), there won't be any diatomic molecules. Needless to say, thermal as well as electrical conductivity will get a lot better but nowhere near the metal like state of plasma. Convective heat transfer also obvious gets better with increases in temperature as well. But the big reason that above 4,000-6,000 K vs. below it is important is that air has to absorb energy in order to break chemical bonds so this process is inherently endothermic and will limit temperatures from increasing much beyond this point as well as being kind of unstable and rapidly reverting back to under those temperatures whenever there is not a source of energy driving it (the arc). I don't know about air molecules either but metals are generally luminuous only above about 800-1,000 F and people that work around kilns use this as a reference point for visually detecting where temperatures in the structure have gotten excessive. So I'd expect that somewhere in that temperature range, the air would tend to "glow" which explains what you see in arc flash videos and has been attributed to "plasma" although I'm going to contend that this is not what it is. Rather it is simply air or other fumes that are hot enough to emit light.

Sorry...I had 3 physics majors as house mates in college. I learned a lot about physics and a lot about why I don't want to be a physicist. But it comes in useful sometimes. One of my housemates was specifically studying how nitrogen's excited states operate in the 1990's such as how quickly they recombine/reform after you use a laser to blow away an energy state...something you would think would be well known but can't be determined mathematically.


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Mon Oct 30, 2017 11:02 am 
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I agree with you Paul, nothing melting EVER for electricians (unless AR in blends).
Distance of 18 in. is a problem ESPECIALLY when looking at ignition.
Plasma RARELY reaches a worker in normal equipment and will destroy anything, pretty much.
Hot gas balls can ignite and cause burn under AR garments in a small area but are in a focused area and not life threatening (IF clothing doesn't ignite).

The physics of plasma is very well understood but arc flash is a combination of several issues and I don't think this was an improvement by removing PPE for IE <1.2 but we have to live with it.

i think risk assessment will be successful most of the time as long as people consider what enters an AFB. Just takes a little more thinking with this removal.


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Fri Nov 10, 2017 12:43 pm 
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I find this discussion most elucidating. As a poor hillbilly engineer, I want to make sure I understand the 2018 NFPA 70E requirements. Are you gentlemen intimating that I can now do energized work on equipment under 600 volts with a total energy exposure of less than 1.2 cal/sq cm while wearing a polyester short sleeve shirt, polyester shorts, flip-flops and no safety glasses?


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Fri Nov 10, 2017 2:34 pm 
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As a fellow hillbilly engineer, I think that doing work on any three phase equipment whatever the calculation is in polyester or even cotton is evidence of a Darwin Award Nominee. Just MHO.

Hugh Hoagland
ArcWear/e-Hazard


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 Post subject: Re: 70E 2018 No restriction for clothing for less 1.2 cal/cm
PostPosted: Sun Nov 12, 2017 11:00 am 
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I've got no claims on family relations in the Appalachians so not a hillbilly. Just an ordinary redneck I guess.

In 2009 two rednecks from Georgia that were in flip flops and tank tops according to the accounts on the story were there to remove a temporary construction panel. They didn't want to wait for the lineman to get there so they started taking the panel apart live. One died and one was hospitalized in a burn unit. No shock/electrocution mentioned at all only burns so this was pure arc flash. It doesn't say but I think it goes without saying that this was clearly a 240/120 panel just based on what it is so I think we can conclude that it's rare but possible to die from arc flash at 240 V. Not sue if the tank tops contributed to their injuries or not either.

Yesterday I spent most of the day working on a 25 HP DC starter fed from a 125 VDC battery power system at a utility generating station. Incident energy wasn't posted but is probably under 1.2 cal/cm2. I had on an FR welder's shirt over a cotton long sleeve undershirt, cotton insulated long johns, and jeans. The plant was deep in the hills about an hour's drive from Charlottesville, VA.


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