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 Post subject: incident energy > 40 cal/cm2 and PPE
PostPosted: Fri Apr 19, 2013 9:29 am 
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Recently I have found labels where a study has been completed and the Incident energy was greater that 40 cal/cm2. But the label referred back to (*N9) of the 2009 70E calling for the min of 40 cal. Since the labeling requirement have changed in 2012. Am I wrong in assuming these labels will no longer be adequate. They also do not list the incident energy on them, I had to go pull the actual study. My other question is the incident energy is listed at 70 cal/cm2, so how could (*N9) Apply? Shouldn't the PPE utilized be at minimum rated at the Incident energy lever 70 cal?


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PostPosted: Fri Apr 19, 2013 11:18 am 
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*N9 is a note generated by the study software package from SKM, it is not directly part of 70E.

The label does not need to contain actual incident energy levels. It must contain 'energy level' information that allows a qualified person to select the appropriate PPE.


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PostPosted: Fri Apr 19, 2013 12:21 pm 
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Thank you, I guess my confusion comes from
130.5 (C)
[SIZE=2][font=Times-Italic]"Labels applied prior to September 30, 2011,[/font][/size]

are acceptable if they contain the available incident energy
or required level of PPE.
The method of calculating and data to support the information
for the label shall be documented."
After reviewing the study I seen the incident energy level was calculated to 70 cal/cm2, but the PPE on the label only called for
Category D
- FR Rated Shirt and pants (min 8 ca/cm2)
- Arc Rated Flash Suit ( min 40 cal/cm2)
- Saftey Glasses and Hard Hat
- Voltage Rated Gloves
- Leather Work Shoes
- Double layer Switching Hood and hearing proection
[SIZE=2][font=Times-Roman]Electrical Safety Boundary minimum 10 feet when exposed to live parts[/font][/size]
[SIZE=2][font=Times-Roman]Since the energy is greater than 40 cal/cm2 , I found it strange that they would call out a min of only 40 cal.[/font][/size]
Granted this study was done in 2008.


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PostPosted: Fri Apr 19, 2013 3:22 pm 
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The "40 cal limit" has been in 70E for a long time. At one time there was no available PPE for the thermal energy. Another justification given was a concern about being beyond the human performance limit based on the theoretical arc blast calculation given by Lee. However, the most recent 70E edition calls for only "greater caution" and disappears at least in the first draft of the 2015 edition. I have not seen the data yet but some powerpoint slides on the joint NFPA/IEEE project suggest that arc blast may not be as severe as previously thought. It would certainly point to the approach by the 70E standards effort to drop tbe 40 cal limit. At a minimum even analysis of the Lee equation (right or wrong) suggests that the 20 PSI concussive limit developed for military explosive estimation purposes sets the arc blast limit down around 12 cal for some inputs. So I wouldn't put any faith in the theoretical result.


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PostPosted: Sun Apr 21, 2013 2:08 pm 
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TedN wrote:
Granted this study was done in 2008.

There has been a noticeable change in how 70E has been applied in the past 5 years.

130.5(C) gives several method for determining required PPE, one of which is a company's requirement - in your case Category D.

70E does not really say what PPE is need for any specific incident energy level, it it left up to each company (although there is some guidance in the current Annex H, table H.3(b).
It is common practice to work backwards from Hazard Risk Category minimum ratings, but that is not what 70E intended. This common practice led to another common practice of 'rounding up' a calculated incident energy level so that labels directly corresponded to the HRC values of 1.2, 4, 8, 25, and 40; this way there was minimal math skills need to select PPE.

Back in 2008, it was not an uncommon practice to use 'layering' to achieve higher rated PPE. This practice was often misapplied, so restrictions and clarifications were added (this can be seen in the current Annex M).


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PostPosted: Fri Apr 26, 2013 4:55 pm 
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I almost agree about layering. Have you looked at the test result on arcwear.com? Far from additive...layering seems to provide huge increases, much more than additive.


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PostPosted: Mon May 20, 2013 6:47 am 
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I am going to try and resurrect this thread. I have read through it and don't feel like the answer was forthcoming enough. I am looking into a very similar topic. Not necessarily the original questions comparing the 09' and 12' regarding over 40cal, but just in general what do you do above 40cal? "Extreme Danger" is not actually a "Hazard Risk Category" (HRC) but then again you don't have to use the "HRC" on the label, only the information needed to choose PPE.

Bottom line I have a client that has items in the facility that are labeled "Extreme Danger" due to poor power distribution design, and they want a reference in a standard why they cannot work on those items. What do I tell them, there is no standard but work at your own risk?

Any thoughts would be greatly appreciated.


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PostPosted: Mon May 20, 2013 12:24 pm 
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For incident energy that is above 40 cal/cm2[color=#000000], I list the incident energy and [color=#ff0000]"Incident Energies exceeding 40 cal/cm2 are deemed too hazardous for live work."[/color][/color]

How likely is an injury to happen? In the entire realm of electrical work, an incident is quite rare.
If it DOES occur what are the possibilities of serious injury or death? Extremely high.
What process is worth an employee's life - or more likely employees' lives?

We tend to think that we have been doing this work for 20, 25, 30 or more years without incident. So the realization of the actual danger gets pushed to the back of our minds becoming more and more insignificant with each successful encounter or near-miss. Why are we looking for excuses to ignore the very real dangers that exist and ignoring very wise counsel to NOT work on live voltage unless it is absolutely necessary?


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PostPosted: Tue May 21, 2013 6:15 am 
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McFlash wrote:
I am going to try and resurrect this thread. I have read through it and don't feel like the answer was forthcoming enough. I am looking into a very similar topic. Not necessarily the original questions comparing the 09' and 12' regarding over 40cal, but just in general what do you do above 40cal? "Extreme Danger" is not actually a "Hazard Risk Category" (HRC) but then again you don't have to use the "HRC" on the label, only the information needed to choose PPE.

Bottom line I have a client that has items in the facility that are labeled "Extreme Danger" due to poor power distribution design, and they want a reference in a standard why they cannot work on those items. What do I tell them, there is no standard but work at your own risk?

Any thoughts would be greatly appreciated.

I might have also placed this article elsewhere in the forum but it is probably worth repeating in this thread since the topic came up. The problem with the 40 cal limit is it doesn't factor in time. The IEEE equations can result in some really large incident energy values if you have long arc duration times. (slow protective devices) Although the thermal energy from a large Ei may be bad with long clearing times, it doesn't necessarily mean it is a blast which was part of the original concern.

As Larry S. points out above (as well as others throughout the forum) - it is better to work electrically safe when possible.

[url='http://brainfiller.com/library-articles/arc-blast-and-40-calories-centimeter-squared.31/']40 cal/cm^2 article[/url]

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Brainfiller.com


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PostPosted: Wed May 22, 2013 6:33 pm 
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Larry Stutts wrote:
For incident energy that is above 40 cal/cm2[color=#000000], I list the incident energy and [color=#ff0000]"Incident Energies exceeding 40 cal/cm2 are deemed too hazardous for live work."[/color][/color]

How likely is an injury to happen? In the entire realm of electrical work, an incident is quite rare.
If it DOES occur what are the possibilities of serious injury or death? Extremely high.
What process is worth an employee's life - or more likely employees' lives?


When you start looking at it this way the problem is determining an acceptable level of risk. What is the outcpme of driving a vehicle? Of walking? Of getting out of bed? Of staying in bed? I can trivially give examples of fatalities for everyone of these mundane activities. Just ask some of the kids in Oklahoma City this past week or the Russians struck dead by meteors a few months ago. So somehow we have to level the playing field...to say that the risk is too great in one case and not in another. Just because there is a significant hazard is not enough. There is a significant hazard with weather and meteor showers as well. We have to adopt a method of comparing risks so that we can rationally compare them to determine that one is acceptable and another is not. Otherwise we will be paralyzed by emotional responses (fear) and unable to do anything at all. This post is intended to make an emotional case, not a rational one.


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We tend to think that we have been doing this work for 20, 25, 30 or more years without incident. So the realization of the actual danger gets pushed to the back of our minds becoming more and more insignificant with each successful encounter or near-miss. Why are we looking for excuses to ignore the very real dangers that exist and ignoring very wise counsel to NOT work on live voltage unless it is absolutely necessary?


This is in general a problem...that the less likely the perceived negative result is, the more likely someone is to use incorrect methods and procedures and develop bad habits just because nothing bad happened the first few hundred times. This is human nature. Numerous studies have been done recently looking at how to intercept this exact problem in order to improve human performance. It is not by the way easy to do.


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PostPosted: Thu May 23, 2013 7:19 am 
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PaulEngr wrote:

When you start looking at it this way the problem is determining an acceptable level of risk.

We have to adopt a method of comparing risks so that we can rationally compare them to determine that one is acceptable and another is not. Otherwise we will be paralyzed by emotional responses (fear) and unable to do anything at all. This post is intended to make an emotional case, not a rational one.


It is not meant to induce fear.

I am just saying that if the incident energy is greater than 40 cal/cm^2 there is no reason to work on it live when it can be worked on de-energized. And persuading an employee to work it live is not rational solely based on history of it not happenning. And presuming an activity is safe just because of what has transpired in the past is faulty logic.
(Just because one has stood on a train track in the past and not been run over by a train does not mean standing on the tracks is always safe)

I am saying that working on live circuits that have incident energy greater than 40 cal/cm^2 is dangerous and you need to take proper precautions - like turning off the power and working them de-energized when it is feasible to do so.

I am also saying (I said it in another post somewhere) if an employee is afraid to do a certain task then he has no business doing it - fear is a hazard in and of itself. Requiring an employee to do something that they are afraid to do is dangerous. If the employee needs to do this task, then they need to be properly trained to do it safely.


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PostPosted: Thu May 23, 2013 10:26 am 
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PaulEngr wrote:

When you start looking at it this way the problem is determining an acceptable level of risk. What is the outcome of driving a vehicle? Of walking? Of getting out of bed? Of staying in bed? I can trivially give examples of fatalities for everyone of these mundane activities. Just ask some of the kids in Oklahoma City this past week or the Russians struck dead by meteors a few months ago. So somehow we have to level the playing field...to say that the risk is too great in one case and not in another. Just because there is a significant hazard is not enough. There is a significant hazard with weather and meteor showers as well. We have to adopt a method of comparing risks so that we can rationally compare them to determine that one is acceptable and another is not. Otherwise we will be paralyzed by emotional responses (fear) and unable to do anything at all. This post is intended to make an emotional case, not a rational one.


With the exception of the last sentance, I agree with what you are saying. I do not think your examples are trivial, but you are right - there are risks in everything we do:
[INDENT=1]Arc Flash Incident - 30,000/year - Likelihood 1 in 50[/INDENT]
[INDENT=1]Arc Flash Injury- 7,000/year - Likelihood 1 in 217[/INDENT]
[INDENT=1]Arc Flash Fatality - 400/year - Likelihood 1 in 3,800[/INDENT]
[INDENT=1](Likelihood was based on an estimation of 1,521,000 active electrical workers)[/INDENT]
[INDENT=1] [/INDENT]
[INDENT=1]Struck by lightning - 300/year - Likelihood 1 in 280,000[/INDENT]
[INDENT=1]Struck by lightning - 70/year - Likelihood 1 in 1,200,000[/INDENT]
[INDENT=1](Likelihood was based on all Americans)[/INDENT]
[INDENT=1] [/INDENT]
Being struck by a meteor is likely 10 or 100 times less likely than getting hit by lightning, and just pulling out into traffic is a risk.

There are two types of accidents - things you pretty much have no control over like lightning, tornados and meteors - and then everything else where being aware of your surroundings, being cautious in your actions, and taking safety to heart rather than just getting your annual safety ticket punched.

Safety hinges on understanding what is hazardous, assessing what risks are acceptable and which risks are not, and working in awareness of both your surroundings and what hazards exist around you that you can not perceive with your senses.


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PostPosted: Thu May 23, 2013 10:51 pm 
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ESFI reports arc flash fatalities based on BLS statistics at 1 in 100, 000/year. Shock is twice that rate. Equipment arcing fault rates are generally around 1 in 10k to 1000k depending on type. Not sure your data source but it seems extremely high from comparative data. I think using electrical workers is skewing your data high. Many arc flash incidents happen to nonelectrical workers so you'd have to look at the occupational data. For instance most electrical injuries occur in construction.


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PostPosted: Fri May 24, 2013 6:43 am 
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ESFI reports a total of 192 fatalities in 2008 and 170 in 2009, and 163 for 2010 for all industries combined from BLS statistical data on workplace injuries in their report for 1992-2010. LTA's for the same years are 2,490, 2,620, and 1,890. Carefully totalling just what appears to be "electrician" occupations, it adds up to about 33%. Contact with overhead power lines is #1 at 44% of all fatalities. Second was contact with wiring, transformers or other electrical components (27%), and third was contact with current of machine, tool, etc. (17%). Further, about 39% of nonfatal electrical injuries are burns. As few as 1 in 4 fatalities are due to electrical burns based on BLS data. ESFI has to manually check this by checking each case summary individually because arc flash injuries get classified as either "burns" (not necessarily electrical) or electrical injuries (not necessarily burns).

I just can't see any conceivable way based on BLS data at least for the U.S. to even approach 400 arc flash fatalities per year when the total number of electrical fatalities doesn't even exceed 200, regardless of what the percentage is for arc flash injuries. Similarly, nonfatal injuries are drastically less than the numbers quoted. Now, these are based on the most detailed data I can obtain which is for the U.S. only. It may be dramatically different based on statistics for the rest of the world.


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PostPosted: Fri May 24, 2013 8:06 am 
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I obviously have old data. The statistics you are quoting show we are obviously being safer. I definitely need to research the statistics again. Thanks


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PostPosted: Sat May 25, 2013 7:15 am 
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Jim Phillips (brainfiller) wrote:
I might have also placed this article elsewhere in the forum but it is probably worth repeating in this thread since the topic came up. The problem with the 40 cal limit is it doesn't factor in time. The IEEE equations can result in some really large incident energy values if you have long arc duration times. (slow protective devices) Although the thermal energy from a large Ei may be bad with long clearing times, it doesn't necessarily mean it is a blast which was part of the original concern.

As Larry S. points out above (as well as others throughout the forum) - it is better to work electrically safe when possible.

[url='http://brainfiller.com/library-articles/arc-blast-and-40-calories-centimeter-squared.31/']40 cal/cm^2 article[/url]


Jim as always thank you for the input, and all who have provided opinions and direction. The article you provided is exactly what my thoughts were in regard to the blast pressure. The specific situation I am currently dealing with is just that small current and long clearing time. This client has several disconnect switches labeled danger and no ppe but these are 30-60 amp disconnects. The IE is below 50cal but obviously greater than 40. Their concern is using the switches as a lockout device not necessarily for working on energized parts.

Could they us PPE with a rating that exceeds the calculation? I obviously as a consultant can only tell them the facts and let them decide. I just want to be sure they are not directly violating any standards, mainly NFPA 70E or OSHA. I also know the best way to do things is to die energize but as stated, that is what they are trying to accomplish. The LOTO point is the Danger spot.

Any Thoughts again would be appreciated


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PostPosted: Sun May 26, 2013 4:19 am 
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Blast pressure is very different from thermal. As I understand it, it is dependent on enclosure size for the amount of available air. It has an initial onset during which a very fast arc detection/trip can prevent it entirely. And after a very short time interval, the arc blasr is over even if thermal energy continues. However I have not seen any data publicly released except one presentation on the joint NFPA/IEEE study that said that arc bkast reaches a consistent peak under various conditions following the pattern I described and is not as big as previously thought. I think the data set will be released in the 2015 edition of IEEE 1584.

Also the reference to 40 cal was deleted out of the latest 70E edition.

Also the 2012 and draft 2015 versions make it clear that PPE is not required for switching activities in most low voltage cases. IEEE 493 survey data indicates that an arcing fault in disconnects is very rare, below the likelihood that most risk standards use for a cutoff for even a multiple fatality scenario. Thus we are not talking about an inherently risky procedure such as racking buckets off or onto an energized MCC bus.


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PostPosted: Tue May 28, 2013 6:07 am 
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PaulEngr wrote:
Also the reference to 40 cal was deleted out of the latest 70E edition.


Article 130.7 (A) Note 3. Same note that has been in previous editions. That is why the concern for the levels above 40. I do know what you are saying in regards to operating the disconnects and that is more of a risk assessment matter to understand if significant risk is present.

My question was more from the angle of is there ever a time that it is acceptable to put on PPE higher than 40 and work as long as the PPE exceeds the calculated Incident Energy. That seems to be a question with no apparent answer.


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PostPosted: Tue May 28, 2013 6:32 am 
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McFlash wrote:
Article 130.7 (A) Note 3. Same note that has been in previous editions. That is why the concern for the levels above 40. I do know what you are saying in regards to operating the disconnects and that is more of a risk assessment matter to understand if significant risk is present.

My question was more from the angle of is there ever a time that it is acceptable to put on PPE higher than 40 and work as long as the PPE exceeds the calculated Incident Energy. That seems to be a question with no apparent answer.


Are you looking for validation for working on incident energies greater than 40 cal/cm^2?
Or just asking if it is safe to do so as long as you have PPE rated greater than the calculated incident energy?
Or is your question based on acedemic curiosity? I ask a lot of those


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PostPosted: Tue May 28, 2013 6:51 am 
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Regarding the stats posted, I spent 10+ years teaching 70E at large industrial facilities across North America and nearly every facility I visited had someone that had suffered burns or a story of a arc flash fatality, there just always seemed to be at least one at every place. More often than not it was something recent and me being there was a direct result of the incident.

Back to the OP's question, the first question that needs to be asked, regardless of the Ei, is can this work be done energized per the guidelines set by the 70E.


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