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 Post subject: Where does exposure begin per 1910.269 regarding syn fabric?
PostPosted: Wed Feb 11, 2015 10:07 am 
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The question keeps coming up, and I cannot provide a very good answer. I have yet to see any kind of incident energy boundary for meltable fabric. The personnel in question are not interacting with the circuits in any way, and are nowhere close to the minimum approach distance; but may be observing from a distance when a worker is interacting in some fashion. Where do you draw the line on synthetic clothing? At the substation fence? (Chain link of course, so the fence itself provides no protection.) Further in? Further away? Same town? County line? The standard only speaks of hazard exposure without providing a clue where that exposure begins. How do others handle this? Thanks.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Thu Feb 12, 2015 10:11 am 
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There is no standard for it. At this time the standard is to ignore anything past either the limited approach boundary or the arc flash boundary, whichever is greater. In fact there is very little in the way of standards for unqualified personnel.

Under 70E-2015, there is no longer an "H/RC 0" requirement so the requirement to wear nonmelting clothing only applies to underlayers when PPE (>1.2 cal/cm^2 condition) is required.

Under 70E-2012, H/RC 0 shows up. It is required whenever either the limited approach boundary or arc flash hazard boundary exists. The outer limit would be whcihever boundary is greater.

So it depends. Following 70E-2015, it becomes just a recommendation, not a requirement, if PPE is not involved. Alternatively under 70E-2012, there is no "H/RC -1" or whatever is below zero so the nonmelting fiber rule extends out to infinity, or alternatively since there are no rules beyond the boundaries (limited approach boundary, and arc flash boundary, whichever is greater), then the nonmelting fiber rule is also dropped.

Your point is valid that at the arc flash boundary as it exists today, there is still a ahazard. This would be akin to division 2, or zone 2 under hazardous location rules. But it does not exist today.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Thu Feb 12, 2015 5:58 pm 
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This is T&D so 70E does not apply. I believe the 1910.269 prohibition on synthetic fabric does apply, but only when there is a hazard exposure. Easy to determine after the fact, not so easy before. I'm wondering what rules others have established in this regard.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Fri Feb 13, 2015 10:11 pm 
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Missed the .269 reference. If you read the massive commentary leading up to the new .269 rules most of it references 2 cal. It seems to be up in the air. NESC still says 2 cal where they consider the hazard to begin. So thats you arc flash boundary. Reason I say this is when OSHA states that everything is under 2 cal then arc flash need not be considered. This has been an argument between the IEEE and NFPA camps. The difference is on the Stoll curve. NFPA looks at 1 second and NESC looks at around 2 seconds. Who is right? Its time dependent.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Mon Feb 16, 2015 7:05 am 

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The 1910.269 standard requires you to do an arc flash analysis to your TD&T equipment now. Meaning you need to perform the study to your substations on site. Once that has been performed you will have the approach distance for the arc rated PPE. At a bare minimum you are not allowed to be near the energized equipment with less than cotton clothing. Some of our substations have arc flash boundary distance of 22ft to exposed equipment, we do not allow anyone near them without the required PPE, even to spray weeds.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Tue Feb 17, 2015 9:44 am 
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lovetacycle wrote:
The 1910.269 standard requires you to do an arc flash analysis to your TD&T equipment now.

I know. Just don't know how to perform such a study for meltable fabric.
lovetacycle wrote:
At a bare minimum you are not allowed to be near the energized equipment with less than cotton clothing.

How close is near? Thanks.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Thu Feb 19, 2015 1:44 pm 
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stevenal wrote:
The question keeps coming up, and I cannot provide a very good answer. I have yet to see any kind of incident energy boundary for meltable fabric. The personnel in question are not interacting with the circuits in any way, and are nowhere close to the minimum approach distance; but may be observing from a distance when a worker is interacting in some fashion. Where do you draw the line on synthetic clothing? At the substation fence? (Chain link of course, so the fence itself provides no protection.) Further in? Further away? Same town? County line? The standard only speaks of hazard exposure without providing a clue where that exposure begins. How do others handle this? Thanks.


The level of intensity and duration of exposure result in a received thermal radiation dose TDU that can be calculated and used to estimate these progressive effects from the following equation:

TDU = I^(4/3) * t * 10^-4, (W/m^2)^(4/3) * sec; Equation 1

where I is radiated heat flux in W/m^2 and t is exposure time in seconds.

The TDU for melting of nylon and polyester fabrics is ranging from about 1500 to 3000 according to [1].

Threshold incident energy for melting of nylon and polyester fabrics can be calculated from Equation 1 above as:

Em = I * t = TDU^0.7 * t^0.3 * 10^3, J/m^2; Equation 2

As an example, assuming TDU = 1500, substituting different time intervals into Eq. 2 and converting the calculated onset incident energy for melting of nylon to J/cm^2 and cal/cm^2 (incident energy units commonly used in arc flash analysis):

time, s | Em, J/cm2 | Em, J/cm2
1 | 17 | 4
0.1 | 8.5 | 2
0.01 | 4.3 | 1

While the TDU value depends on type of material, it is important to note that the threshold incident energy for melting synthetic fabrics, as well as igniting clothing or causing an other degree of damage such as 2nd or 3d degree burns for bare skin exposure, roughly decreases by a factor of 2 when the exposure time is decreased by a factor of 10.

1. "Thermal Radiation: Physiological and Pathological Effects" by Ian Hymes, Warren Boydell, Belinda Prescott.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Thu Feb 19, 2015 5:42 pm 
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Where would one find the TDU value? For that matter what about the onset of 1st or 3rd degree burns?

Also at least for skin, there is an "area of effect". Heat flux focussed on a smaller area gives a different result, which explains why different experiments with burns yields different results.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Fri Feb 20, 2015 7:53 am 
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PaulEngr wrote:
Where would one find the TDU value? For that matter what about the onset of 1st or 3rd degree burns?

Also at least for skin, there is an "area of effect". Heat flux focussed on a smaller area gives a different result, which explains why different experiments with burns yields different results.


The TDU value for melting of nylol, polyester fabrics, 2nd, 3d degree burns to exposed skin and more can be found in "Thermal Radiation: Physiological and Pathological Effects" by Ian Hymes, Warren Boydell, Belinda Prescott publisehd by Institution of Chemical Engineers in 1996:

Melting of nylon, polyester fabrics: from about 1500 to 3000
Threshold 2nd degree blistering of exposed skin: from about 210 to about 700
3d degree burns to exposed skin: about 2600

I'm not sure of the "area of effect" but factors such as skin color (light-colored or dark) and skin condition (clean or dirty) have been proved to have an effect on the TDU by means of different absorption coefficient (the coefficient is equal to about 0.5 for light-colored skin and it is nearly unity for dark or dirty skin). This explains why different experiments result indeed yield different results.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Mon Feb 23, 2015 6:24 am 
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lovetocycle has it right. The 2 cal/cm2 point is the 'arc flash boundary" even though there is no such term in 1910.269. Paul's reference for nylon and poly is in fire and not useful for high heat flux exposures like arc flash. Heat flux makes a substantial difference on the effect of mleting on the human body. The transfer of the heat will occur when the melting point is reached. If we could control the arc in equipment or outside of equipment it would make the life of protection easier but for now. Use non-melting, materials up to the arc flash boundary and match to hazard inside that boundary. The good news is that the calculations are close to worst case and the arc could go away from you in MV equipment depending on electrode geometry.

Hugh Hoagland
e-Hazard.com


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Mon Feb 23, 2015 9:44 am 
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Thanks Hugh,

The question still remains though. Somewhere between the non-melting 2 cal/cm^2 arc flash boundary and infinity there must be place where meltable fabric is okay to wear. Note that at some point this becomes a public safety issue as well as an employee safety issue, and we have no control over what the public wears outside the fence. Should we therefore use the fence as the meltable fabric boundary for employees as well?


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Mon Feb 23, 2015 10:03 am 
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In NFPA 70E the 1.2 cal/cm2 boundary is all that is regulated. In NESC/OSHA 1910.269 the 2.0 cal/cm2 "boundary" is regulated. Anything below those levels does not require any PPE.

Would I EVER recommend electricians wear meltable clothing (no way). Same with operators (operating equipment) in installations with high AF energies. Just bad practice to ask, "How close can I get to a hazard without getting hurt?" If there is a risk, suit up. In acceptable risk, document and move on.

Not easy but the levels help.

Hugh Hoagland


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Tue Feb 24, 2015 3:31 pm 
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Hate to disagree Hugh but 269 stance on arc rated clothing or actually FR in this case is that its required even outside a boundary unless the incident energy at working distance is under 2 cal. The reasoning behind this is that it protects against sparks and traveling arcs. So unlike 70E, this “gotcha“ means that below 4-8 cal (depends on single or 3 phase), all qualified employees have to wear arc rated PPE for virtually all tasks. As this extends well beyond the 2 cal boundary, application for unqualified employees (269 does not even allow this) is confusing at best.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Wed Feb 25, 2015 3:24 pm 
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Confusing for sure. That's why I'd like to back up from what's the minimum we can get away with under 1910.269, and look at more from a general duty/good practice point of view. What nice simple and non-confusing company rules do others employ?


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Fri Feb 27, 2015 12:38 pm 
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Where I work, we have about 70 miles of overhead line. We step down from 230 kV to internal distribution of 23 kV. We have a little over 50 MW of cogeneration, and 90 MW of total load operating a large mining operation and multiple chemical plant facilities. We have our own port, our own runway, our own locomotives, our own tugboats, ship, fire department, etc. So basically if there's a regulation or a Code out there, it probably applies to at least some part of the facility.

Up until the recent refresh of 1910.269 prior to 70E-2015, we just used 70E-2012 tables for the 23 kV system and NESC-2012 for the 230 kV system. In fact we even mix and match and I used NESC for <300 V even for utilization equipment for cases where the transformer exceeded the IEEE 1584 "125 kVA cutoff". Now that OSHA has weighed in, I've already initiated an arc flash study on the 23 kV and 230 kV systems. We'll use ArcPro once that is done. Outside of the arc flash boundary of 1.2 cal/cm^2 (even if NESC/OSHA use 2 cal/cm^2) for consistency among all the various regulations, we'll not require anything special for PPE. For workers that are qualified to work on anything over 10 kV, we'll discuss options but I believe in the end that we'll be requiring a minimum of 4 cal/cm^2 PPE for all tasks, regardless of where they are working at. This only affects something like 4 people (out of almost 1,000) and our contract linemen are already required to follow this. We use Mastec which is one of the largest utility contractors in the country and they switched to requiring at least 4 cal/cm^2 PPE for all crews following Duke's requirements.

1910.269 is very clear that all personnel are to be qualified workers. So the "peanut gallery" needs to stay outside what is effectively the "limited approach boundary" (using 70E terms) or roughly 10 feet of clearance, although it increases with line voltage above 50 kV. OSHA doesn't define this.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Fri Feb 27, 2015 4:17 pm 
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Very interesting take on clothing Hugh. Dovetails well with the TNO Green Book model which effectively assumes that clothing is an insulator up to a certain point and if it ignites, death is 100%. Ignition is assumed to occur between V=2.5x10^4 and 4.5x10^4 (kw/m^2)^2-s where V is integral(q'')^2 dt) and q'' is the heat flux in kw/m^2. This integrates if q'' is constant (what is assumed in most arc flash models) to simply (q'')^2*t. Lees has a slightly different formula where V=K*integral((q'')^(4/3) dt), and this form seems to be more common in general. The factor K is 0.5 for normal clothing or 1.0 when clothing ignites and clothing ignition is assumed at V=1800. Lees does not assume that a fatality is guaranteed and the function V is used in a complicated integral to estimate the probability of a fatality but suffice to say that once clothing ignites, it gets ugly from there so we don't really need to go any further other than to assume that ignited clothing = bad. Granted Hugh is talking about only melting clothing, not ignition. This can be calculated via a fairly simple linear formula if we know the heat flux (kw/m^2), time, heat of fusion of the clothing, and so forth. The trouble is that I'm having problems finding the assumed values except for bulk samples of material but I believe that this would underestimate the melting point.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Mon Mar 02, 2015 10:44 am 
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PaulEngr wrote:
1910.269 is very clear that all personnel are to be qualified workers. So the "peanut gallery" needs to stay outside what is effectively the "limited approach boundary" (using 70E terms) or roughly 10 feet of clearance, although it increases with line voltage above 50 kV. OSHA doesn't define this.


Now we're getting closer to my question. So your peanut gallery individual (remaining beyond the limited approach boundary) may wear Speedos underneath his polyester and nylon outerwear?


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Mon Mar 02, 2015 7:54 pm 
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stevenal wrote:
PaulEngr wrote:
1910.269 is very clear that all personnel are to be qualified workers. So the "peanut gallery" needs to stay outside what is effectively the "limited approach boundary" (using 70E terms) or roughly 10 feet of clearance, although it increases with line voltage above 50 kV. OSHA doesn't define this.


Now we're getting closer to my question. So your peanut gallery individual (remaining beyond the limited approach boundary) may wear Speedos underneath his polyester and nylon outerwear?


Yes and no. To date my pole lines are either 13.5, 23, or 230 kV. At these voltages incident energy only gets excessive near transformers. Generally at 8-10 feet (hot stick distance) incident energy is under 1-2 cal/cm2 so I don't have to consider arc flash if using hot sticks or operators at ground level. Since its a mine I aim for 24 feet of clearance to grade everywhere. So by design I'm outside the 1-2 cal/cm2 with a peanut gallery. As voltage goes down though, incident energy tends to increase, so at utilization levels a 480 V, 2500 kva transformer is well over 40 cal/cm2 at working distance and bpundaries generally extend out of the room, but 1910.269 no longer applies. In commercial/residential, this problem would be very real for a utility.


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Tue Mar 03, 2015 9:49 am 
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PaulEngr wrote:

So by design I'm outside the 1-2 cal/cm2 with a peanut gallery.


1-2 cal/cm^2 is generally the cutoff between natural fiber and FR PPE. Would you really allow meltable fabric wearing peanuts to be near such an exposure? Or does 24 feet to grade translate to a much lower IE?


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 Post subject: Re: Where does exposure begin per 1910.269 regarding syn fab
PostPosted: Tue Mar 03, 2015 4:04 pm 
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stevenal wrote:
PaulEngr wrote:

So by design I'm outside the 1-2 cal/cm2 with a peanut gallery.


1-2 cal/cm^2 is generally the cutoff between natural fiber and FR PPE. Would you really allow meltable fabric wearing peanuts to be near such an exposure? Or does 24 feet to grade translate to a much lower IE?


I guess I was too quick with the note. What I mean is that I'm well below 1.2 cal/cm^2 but since the discussion is in a distribution context where the generally accepted limit is 2 cal/cm^2 (under both NESC and OSHA 1910.269), I stated it as BELOW 1-2 cal/cm^2. The 10 foot minimum distance estimate comes from looking at mast configurations on portable substations. This is the closest distance of approach that anyone, even unqualified personnel, would get outside of doing rubber glove work from a bucket truck.

So I'm well below "natural fiber clothing" but similarly I haven't yet seen any calculations suggesting where the "synthetic clothing" cutoff should be. Seems like it is reasonable enough to calculate it but the data I've uncovered always referenced flash fires.


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