arc flash boundary for synthetic fabric
arc flash boundary for synthetic fabric
(OP)
So the arc flash boundary is usually put at 1.2 cal/cm^2, although the implication of the new NESC rule puts it at 2 cal/cm^2. Either way, the boundary is meant to minimize rather than prevent injury. Since injury can occur, OSHA 1910.269(l)(6)(iii) requires only clothing that does not increase the extent of injury be worn at that boundary. So where must I stand while observing the work while wearing my best disco polyester? Is there a recognized incident energy level where synthetics will not melt?






RE: arc flash boundary for synthetic fabric
RE: arc flash boundary for synthetic fabric
NFPA 70E requires any clothing worn to be "Non-melting or untreated natual fiber"
RE: arc flash boundary for synthetic fabric
NFPA 70E Typical Thermal Performance of Various Fabrics in Cal/cm^2
Material Total Weight (oz/yd^2) Rating (Cal/cm^2)
Bare Skin (Clean) - 0.5
Bare Skin (Dirty) - 1
Untreated Cotton 4 2
Single Layer FR cotton 7.5 6
Single Layer FR cotton 12.5 13.8
PBI Fiber Blend 4.5 6.1
Nomex III 4.5 9.1
Nomex III 6 13.7
Nomex III A 4.5 9.2
Nomex III A 6 13.1
Cotton (4oz) under FR cotton (8oz) 12 12.5
Nomex (2 layers) 12.2 22.6
Nomex (8oz over FR cotton (8oz) 16 31.1
Switching suit of FR coverall 24-30 40.0+
RE: arc flash boundary for synthetic fabric
Jweav33,
Bare skin is preferable to the polyester. The polyester (and other synthetics) melts into the skin, trapping the heat inside for maximum injury. From your chart, I'm looking for a value somewhere between 0 and 0.5. Any ideas?
RE: arc flash boundary for synthetic fabric
By NFPA 70E approach, beyond the flash hazard boundary defined by 1.2 cal/cm2, no special protective clothing is required.
The goal of NFPA 70E is not to eliminate injuries due to arc-flash, but rather to keep the injuries relatively minor and recoverable. The approach is reducing risk, not eliminating risk.
RE: arc flash boundary for synthetic fabric
On a wet day in a substation, worker A is doing some switching with a hook stick. Arc flash analysis has been performed, and A is wearing FR clothing covered with FR rain gear that adds up to a value exceeding the calculated incident energy at his assumed distance from a possible arc.
Meanwhile worker B is digging a hole to replace a fence post some distance away. Since FR rain gear is expensive and his work is likely to destroy it anyway, he is wearing disposable PVC, non-FR rain gear. Arc flash analysis shows an incident energy level of 0.25 cal/cm^2 at this location if A's actions were to cause an arc. According to Jweavs chart, worker B would be fine if he was naked. But B is not to keen on this idea, and neither are the neighbors. Will B's PVC gear melt into his skin in the presence of the arc generated by A causing an injury that more than minor?
Meanwhile the general manager is taking the board on a substation tour. Hard hats and safety glasses are handed out by their qualified escort, and they stand under their nylon umbrellas observing the action from a 0.2 cal/cm^2 distance. Their suits are made of -- who knows???
Coward that I am, my disco polyester and I are outside the gate at 0.15 cal/cm^2.
Safe situation? OSHA or NESC violation? Hope this clears up my question.
RE: arc flash boundary for synthetic fabric
RE: arc flash boundary for synthetic fabric
Is it "safe"? I guess that depends on your definition of "safe". I wouldn't be concerned about it.
Tours inside a substation by "unqualified" personnel is a little different situation. There are a lot of reasons why I'd be concerned about that, with arc-flash being only one. At least one industrial client we have required PPE to be worn by anyone to walk into a substation.
There a plenty of gaps in NFPA 70E and probably the new NESC. But we know how to deal with a good majority of normal work activities. And we probably can't wait for a "perfect" set of guidelines before we do something.
RE: arc flash boundary for synthetic fabric
RE: arc flash boundary for synthetic fabric
Got a reference #? I never saw the prohibition against being in the sub. 1910.269(l)(6)(iii) speaks only of exposure making no reference to a fence line. 1910.269(u) speaks of substations with no reference to clothing.
Although I used a substation is in my example, the scope of my original question extends beyond any such boundary.
RE: arc flash boundary for synthetic fabric
1910.269(l)(6)"Apparel."
(l)(6)(ii) The employer shall train each employee who is exposed to the hazards of flames or electric arcs in the hazards involved.
(l)(6)(iii) The employer shall ensure that each employee who is exposed to the hazards of flames or electric arcs does not wear clothing that, when exposed to flames or electric arcs, could increase the extent of injury that would be sustained by the employee.
Note: Clothing made from the following types of fabrics, either alone or in blends,is prohibited by this paragraph, unless the employer can demonstrate that the fabric has been treated to withstand the conditions that may be encountered or that the clothing is worn in such a manner as to eliminate the hazard involved: acetate, nylon, polyester, rayon.
RE: arc flash boundary for synthetic fabric
RE: arc flash boundary for synthetic fabric
RE: arc flash boundary for synthetic fabric
RE: arc flash boundary for synthetic fabric
Extending this reasoning, for an industrial application I'd proceed with anyone within the room containing exposed energized parts shall not be wearing clothing which can contribute to the severity of an injury (keep the janitor or mechanic out when energized equipment is exposed). Hard barriers such as walls and doors would reflect heat and thus contain the heat from arc-flash hazards to the space within that particular room.
This would be a good question for a code interpretation - OSHA perhaps? I would think this line of reasoning, if it were included in a facility's safety manual, would pass a review given my past experiences with OSHA investigators.
RE: arc flash boundary for synthetic fabric
You have a problem with your fences being within the FHB, however the proballity of an arc flash occuring is slim in a static state compared to when work is being done in the switchyard. I think you have found a loophole here and you might want to email your situation to the 70E commitee.
My personal recommendation would be to post the FHB when work is being done in the switchyard if the FHB would cross the fenceline. Sorry I cant give you something more concrete than my opinion, I dont think there is a concrete answer. My experence with OSHA inspectors is in a situation like this, they are looking for an effort to be made to protect persons exposed to electrical hazards.