Is it ever ok to work on exposed live parts per 70E?

don_resqcapt19 said:
The arc flash labeling starts at 1000 amps and the arc flash reduction rule starts at 1200 amps,

It is my opinion that the "applicable industry practice" will require the actual incident energy level and arc flash boundary on the equipment. The NEC wants to require you to use the 70E label, but the NFPA rules do not permit on NFPA document to require the use of another NFPA document, hence the "applicable industry practice" part of the rule. If there is another "applicable industry practice", you could use that, but I don't think that there is another.

110.21(B) does not require any specific information. It simply provides requirements as to the type and installation of labels that are required by other code sections.
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But NFPA 70E does not require incident energy levels, it still allows PPE selection only by Task being performed.
 
it still allows PPE selection only by Task being performed
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NFPA 70E allows two different methods - The incident energy method (calculations) or the Categories method. The Categories method involves using a series of tables in 70E based on type of equipment voltage level. There is also a table of various common tasks with a determination of whether or not "Additional Protective measures are required". That means PPE. So first you determine if PPE is required, then based on the type of equipment, the Category of PPE is determined.

BUT the big gotcha is in the notes in these Category tables. Use of these Categories is only valid up to a stated maximum fault current and a stated maximum clearing time. So in theory, in order to use this Category method you need to have an idea as to the fault current and the fault clearing time.
 
jim dungar said:
But NFPA 70E does not require incident energy levels, it still allows PPE selection only by Task being performed.
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I guess I just don't see that as an arc flash label and 110.16 requires an arc flash label. However, I don't think there is a definition of an "arc flash label"
 
Interesting thread/discussions. I’d like to weigh in please.

The labeling references in the discussions convolute the 70E labeling requirements with the NEC labeling requirements.

The NEC is predominately an installation specification requirement standard and 70E is predominately a safe work practice standard.

I’ve always contended that the NEC 110.16 is specifically related to safe work practices and does not belong in an installation specification standard (NEC). Further the NEC states 90.2 A this standard is not for “untrained” persons, substitute qualified electrical wireman. I’ve always contended that if a qualified wireman needs to be warned of an arc flash/arc blast hazard then perhaps they shouldn’t be considered qualified. So why is such a hazard warning label needed for trained, qualified wiremen? No disrespect intended. It’s just logic.

OSHA does NOT require any arc flash/arc blast labeling, either per the NEC or per 70E. There aren’t any OSHA arc flash/arc blast label requirements in OSHA’s Electrical Safety Related Work Practices Standard to satisfy. While it certainly may make work easier by specifying the appropriate levels of PPE for a wireman working at that location for protection it’s not required by OSHA.

From a historical perspective, my recollection was that several code cycles ago in NFPA 70E there was a proposal to add an “arc flash PPE category” (formerly hazard risk category) above category 4, to include the 100 cal suit. At that time the Technical Committee rejected the proposal and at the time stated the rationale being if such an arc flash/arc blast would occur at a level requiring that level of burn protection or anything over 40 cals the pressure wave would be lethal. That came from the NFPA 70E Technical Committee.

BTW I always try to use/say arc flash/arc blast together because it’s not possible to have one without the other, they go together.

Be safe out there.
 
oshaprofessor said:
At that time the Technical Committee rejected the proposal and at the time stated the rationale being if such an arc flash/arc blast would occur at a level requiring that level of burn protection or anything over 40 cals the pressure wave would be lethal. That came from the NFPA 70E Technical Committee.
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They made this decision with very little, if any, real world data.
We still have no way to relate the amount on arc blast versus arc flash.
High Arc Flash Incident Energy is usually due to extended exposure while an Arc Blast occurs in micro to milli seconds. I believe you could have conditions of extreme arc blast with low and moderate levels of incident energy.

We should be teaching safety with today's knowledge base instead of relying on outdated hysteria from decades past.
 
jim dungar said:
They made this decision with very little, if any, real world data.
We still have no way to relate the amount on arc blast versus arc flash.
High Arc Flash Incident Energy is usually due to extended exposure while an Arc Blast occurs in micro to milli seconds. I believe you could have conditions of extreme arc blast with low and moderate levels of incident energy.

We should be teaching safety with today's knowledge base instead of relying on outdated hysteria from decades past.
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I agree with you. I’ve been saying for years that the Technical Committee has made a great many (bad) decisions on the content of the Standard without real world data. They know me and my criticisms are probably why I’m persona non grata. Lol

There are several key factors related to available incident energy. While limiting the duration/time would certainly limit the magnitude I’m not sure the blast and flash can be individually dissected or calculated. They do occur together.

The temperature of the electric arc are as high as 35,000 degrees which exceeds the temperature of the sun. When ambient air is heated to those high temperatures in such a short time it expands violently creating the pressure wave (blast) that can be as high as 15 tons per square meter. I believe that limiting the duration of the event limits the magnitude of both the blast and the flash. Perhaps there is some esoteric distinction that contains individual variables however I’m not aware that this has been established or quantified as of yet.

Heck, the Incident Energy and Arc Flash Boundary Calculation Methods published in Annex D of 70E are by NFPA’s own admission are invalid at the high and low ends of the spectrum. According to NFPA they were working with IEEE to correct this and I’m not sure it has been fully resolved yet. The original calculations were developed by Dr. Ralph H. Lee who is deceased now. His calculation methods were extrapolated, resulting in the inaccuracies.

All I know for sure is I don’t have all the answers, and never will.
 
oshaprofessor said:
I believe that limiting the duration of the event limits the magnitude of both the blast and the flash.
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And I believe the blast happens then the flash burn, based on the times used in the incident energy formulas.

How many injuries have been reported as being from arc blast, not counting those from lower level pressure waves that 'blow people off their feet'? Aren't the vast majority of documented fatalities from the burns rather than the pressure wave?
 
jim dungar said:
And I believe the blast happens then the flash burn, based on the times used in the incident energy formulas.

How many injuries have been reported as being from arc blast, not counting those from lower level pressure waves that 'blow people off their feet'? Aren't the vast majority of documented fatalities from the burns rather than the pressure wave?
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You present some good points. Regrettably the fatality statistics collected by the Labor Dept. - OSHA don’t make those distinctions. In fact there aren’t accident/fatality distinctions made between electrical burns and arc flash arc blast. On the arc blast/arc flash fatalities where the ME report crossed my desk I didn’t look closely if the report addressed internal injuries caused by pressure wave/blast. I guess I either didn’t think of it at the time or thought it was moot under the circumstances.

So what are you proposing from a pragmatic standpoint and how does it apply or translate to something practical that a wireman can apply to protect themselves from arc flash/arc blast?
 
oshaprofessor said:
The NEC is predominately an installation specification requirement standard and 70E is predominately a safe work practice standard.
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Keep in mind some version of the NEC is enforceable as law most places in the US, 70E is not.
Also the I think arc flash labeling falls with the purpose of the NEC, which includes "practical safeguarding of persons";
90.1 Purpose.
(A) Practical Safeguarding. The purpose of this Code is the
practical safeguarding of persons and property from hazards arising
from the use of electricity.
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oshaprofessor said:
So what are you proposing from a pragmatic standpoint and how does it apply or translate to something practical that a wireman can apply to protect themselves from arc flash/arc blast
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Follow the current NFPA70E, it has proven itself as an industry standard.
Stay current with safety training courses. Stay away from instructors that primarily teach using outdated scare tactics.
Learn to how properly perform a risk analysis rather than just looking at the potential hazard (like the risk of a gallon of gas being spilled versus being in a sealed metal container). Driving to work And falling off of ladders are still more likely to injure a 'wireman' than an arc flash incident is.
 
David Castor said:
NFPA 70E allows two different methods - The incident energy method (calculations) or the Categories method. The Categories method involves using a series of tables in 70E based on type of equipment voltage level. There is also a table of various common tasks with a determination of whether or not "Additional Protective measures are required". That means PPE. So first you determine if PPE is required, then based on the type of equipment, the Category of PPE is determined.

BUT the big gotcha is in the notes in these Category tables. Use of these Categories is only valid up to a stated maximum fault current and a stated maximum clearing time. So in theory, in order to use this Category method you need to have an idea as to the fault current and the fault clearing time.
Click to expand...
Let me add. It is best to calculate the incident energy first and then choose the appropriate PPE after. Slight differences in locations means the incident energies can be different and using tables could lead lead to misuse. For voltages 208V up to 15 kV, IEEE 1584-2018 can be used. Above 15 kV, Ralph Lee equations is appropriate, IMO.
 
Interesting thing about all this. Last time i checked, over half of the pages in 70E deal with working things energized. Short answer, yes, you have to work things energized. Why do i say that? The absence of voltage check is energized work
Testing and diagnostics (working on definition) is also energized work
I think, most times "energized work" is mentioned it refers to the "repair" portion of the 'working on' definition.
Eric's definitions for working on
1 - diagnostic. Intentionally contacting stationary energized surfaces. (e.g. with meter probes)
2 - repair. Intentionally contacting and manipulating energized surfaces. (e.g. tightening a lug that is energized)
 
There is no process or business that is worth taking a risk on my life by working hot. Being a cowboy is stupid and dangerous. Companies that put profit above life are not were I would have ever worked, or anyone should have too. Also, remember the PPE is to try and avoid unrecoverable injuries. Doesn't mean you won't be severely injured, just that you should recover from them. No thanks.
 
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