NFPA 70 E - Eye Protection From an Arc Flash

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jmd445

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Hamilton Twp., NJ
The following quoted e-mail was circulated around work. Can anyone provide any feedback?

Thanks, Jim

Colleagues:
At a training I gave on NFPA 70 E, one contractor brought to my attention the following event that actually occurred:
Energized electrical was being performed.
All distances ? flash protection and limited approach distances were correctly calculated and area barricaded.
An arc flash incident occurred and temporarily blinded two workers in the vicinity but outside barricaded area.
His question was : How should these workers be protected?
My question to you all is, if the flash protection/limited distances are correctly calculated then is it possible to have an arc of sufficient intensity to cause injuries described above?

 
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jim dungar

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Wisconsin
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PE (Retired) - Power Systems
The anecdotal phrase "temporarily blinded" is to vague to say for sure what actually happened. Were the workers blinded for 2 days, was their vision disturbed for 2 minutes?

An electric arc flash is similar to an welding arc. I can draw all sorts of scenarios where a workers vision is affected by a welding arc even at distances measured in the 10's of feet.
 
zog

zog

Senior Member
Location
Charlotte, NC
Liek Jim said, for how long?

The intent of the 70E is to protect workers from electrical shock and 2nd degree burns from an arc flash event. There is no way to protect workers from everything (God help us if they tried :) ) so minor injuries like a 1st degree burn or what you described are still going to happen.

ANSI Z87 approved safety glasses do have some UV filtering that will minimize this type of injury.
 
joebell

joebell

Senior Member
Location
New Hampshire
were these two workers bystanders, just happening by the outter boundries? Were they affiliated with the energized work in any way?

Like Zog said the PPE for live work is supposed to protect from shock and 2nd degree burns. The face shield we have are tinted and I believe they have a UV rating, the gear does not make you invinsible. Keep in mind there is no protection available to protect from the pressure caused from an event.
 
weressl

weressl

Esteemed Member
Location
Texas by the Gulf, geat crab, great shrimp
jmd445 said:
The following quoted e-mail was circulated around work. Can anyone provide any feedback?

Thanks, Jim

Colleagues:
At a training I gave on NFPA 70 E, one contractor brought to my attention the following event that actually occurred:
Energized electrical was being performed.
All distances – flash protection and limited approach distances were correctly calculated and area barricaded.
An arc flash incident occurred and temporarily blinded two workers in the vicinity but outside barricaded area.
His question was : How should these workers be protected?
My question to you all is, if the flash protection/limited distances are correctly calculated then is it possible to have an arc of sufficient intensity to cause injuries described above?
Click to expand...

AS it has been pointed out be fore NFPA 70E provides reasonable protection from serious injuries.

It does not protect you from temporary blindness since, as somebody else pointed out, arc flash is like arc welding - and that is equated to looking into the Sun directly - and if vision protection would be provided equal to arc-welders the person would be unable to see what he is doing.

70E does not provide protection against temporary hearing loss, nor from hard or molten shrapnel that can accompany an arc-flash explosion.
 
mxstar211

mxstar211

Member
Location
Hawaii
I figured I would throw my two cents in. It is 3rd degree burns not 2nd, that arc flash hazard analysis is designed to protect. First and second degree burns are curable. This is what I had been in taught in my last two arc flash safety courses.
 
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C

Cold Fusion

Senior Member
Location
way north
weressl said:
=== and if vision protection would be provided equal to arc-welders the person would be unable to see what he is doing. ---.
Click to expand...

No, the protection is available. But, it's probably more than most want to pay. My welding hood is electronic darkening. It's about a 3 and goes to a 9 - 12 (setable) when the arc strikes - fast enough you don't see the flash.

cf
 
mxstar211

mxstar211

Member
Location
Hawaii
Cold Fusion said:
No, the protection is available. But, it's probably more than most want to pay. My welding hood is electronic darkening. It's about a 3 and goes to a 9 - 12 (setable) when the arc strikes - fast enough you don't see the flash.

cf
Click to expand...

Welding is more of a controlled arc flash though. I don't think they make one that would work in a arc flash hazard. I remember bringing this up about a year ago in a hazard analysis course, and I believe the instructor mentioned the flash observed in welding is slower than the flash you observe during a electrical arc fault, and they (engineers who design this stuff) have not been able to design a arc flash shield that auto darkens fast enough.
 
zog

zog

Senior Member
Location
Charlotte, NC
mxstar211 said:
Welding is more of a controlled arc flash though. I don't think they make one that would work in a arc flash hazard. I remember bringing this up about a year ago in a hazard analysis course, and I believe the instructor mentioned the flash observed in welding is slower than the flash you observe during a electrical arc fault, and they (engineers who design this stuff) have not been able to design a arc flash shield that auto darkens fast enough.
Click to expand...

That is correct, a friend of mine was involved in this research and they could not get an auto darkening sheild to work well enough to allow it.
 
C

Cold Fusion

Senior Member
Location
way north
mxstar211 said:
---, and they (engineers who design this stuff) have not been able to design a arc flash shield that auto darkens fast enough.
Click to expand...
Wow - I never would have expected that. I've got two auto-darkening welding hoods, a first generation and a second generation. They both really work well.

I had expected that the arc-flash application was just a research issue and it's hard to pay off the research with a small customer base.

cf
 
don_resqcapt19

don_resqcapt19

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Staff member
Location
Illinois
Occupation
retired electrician
I wonder if it is something more than just the darkening time? The new auto darking welding hood that we bought darkens in 0.00005 seconds, or 0.003 cycles. It is hard to imagine that there would be enough energy in that short of a time to cause an eye injury, especially when the hood we have says that the UV protection is the same whether or not the hood had darkened.
 
W

wtucker

Senior Member
Location
Connecticut
Light covers a wide spectrum. We normally think, correctly, that ultraviolet light, such as is emitted by sunshine or an electrical arc causes the most damage. Polycarbonate safety glasses filter 99.9% of UV light, acrylic safety glasses filter less, glass safety glasses filter almost no UV at all. So the first question is, what type of safety glasses were the blinded workers wearing? But visible light can damage eyes, too--often only temporarily. That's where tinted and polarized glass is useful. It'd be worse if the worker was looking directly at the arc source the instant the arc occurred.
 
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