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 Post subject: NFPA70E-2012 PPE Selection Methods and Tables
PostPosted: Thu Oct 25, 2012 4:07 pm 
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Can anyone comment on my following understanding of
NFPA70E-2012 Section 130.6 (B) “Protective Clothing and Other PPE for Application with an Arc Flash Hazard Analysis”.

I am confused by the combination of arc-flash hazard ( as calculated by the NFPA70E and IEEE1584 formula ) and risk which includes consideration of activity ( not mentioned in IEEE1584 or in PTW Arc-flash program ).
For work within the arc-flash boundary, the required PPE clothing can be selected by either of the two following methods :
(1) Incident Energy Analysis – NFPA70E-2012 / IEEE1584-2002 formula
(2) Lookup Tables 130.7( C )(15)(a) and 130.7( C )(16)

In method (2) tasks performed on various types of equipment, Table 130.7( C )(15)(a) allows a range of HRC depending on the activity, doors open/closed etc. which would determine the risk of an arc occurring.
In method (1) the arc-flash analysis ( see NFPA 130.5 ) using the formulas of NFPA70E / IEEE 1584 - in programs such as PTW Arc Flash - the risk is not considered.


Another question concerns NFPA70E-2012 “informative” Table H.3(a) which appears to be recommended when above method (1) ( “hazard analysis” ) is used to calculate the incident energy exposure.
Table H.3(a) does not categorize incident energy exposure by harzard risk category.

My conclusion from the above is that if above method (1) is used to calculate incident energy exposure, then Table 130.7( C )(16) should be used for PPE selection as Table H.3(a) is only “informative”.



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PostPosted: Sat Oct 27, 2012 10:02 pm 
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Congratulations. Few people have actually read 70E closely enough to catch the distinctions between risk and hazards. Fewer still have caught the distinction between the PPE table when goes with the risk assessment table and the calculation method which does not have a corresponding PPE table.

If you use method (1), you do not use the tables. You have calculated the incident energy and must use the clothing manufacturer as reference. Annex O explains this. You can theoretically read the PPE table "backwards" and this is commonly done but is not correct usage.

More to the point that you've made...development of the tables was done by performing a risk analysis. First the incident energies were quantified using IEEE !584. Then the 70E Technical Committee performed a risk analysis and reduced the clothing requirement based on the risk analysis. Here is where my judgement differs significantly from theirs. The hazard is not being reduced. In other words, incident energy is not going down. Only the likelihood of injury is reduced. Thus the rankings given in the tables should be either the required PPE as calculated by the incident energy result, or "none" if the likelihood is sufficently low.

If you are performing your own risk analysis, in other words, method (1) as referred to above, then you are calculating the hazard. Then you need to look at the likelihood that the hazard will occur. This determines the PPE required. Since we only have one result fo rthe hazard using IEEE 1584 (either a life threatening injury or not), then we have only a binary decision to make...either the likelihood is low enough that PPE is not required, or sufficient PPE is required. If you are using a semi-quantifiative approach to risk assessments, then IEEE 1584 is very specific in calculating that the likelihood of no injury if wearing PPE as calculated is 90%. So you get a 1 category reduction if wearing the PPE.

The actual likelihoods depend on the task. This is pretty well stated in the definition of an arc flash hazard in 70E-2012. Humans generally tend to have a reliability rating of 90% in low risk scenarios with well defined procedures and outcome, and thus low stress. There have been tons of studies that have reiterated this point. Still, since in reailty even though IEEE 1584 is calculating the threshold for a 2nd degree burn, it's flirting with the line between a life threatening injury (death) and not. Most risk assessment models require a likelihood of less than 10^-5 for this to be an acceptable risk. So we can automatically rule out ALL scenarios where the reliability of a human directly dictates whether or not an injury is likely, even if we involve the acts of two or more. So tightening a screw for instance automatically requires PPE.

There are however a variety of situations that depend on the reliability of the equipment alone. For instance, opening or closing a disconnect, or racking out a breaker. IEEE 493 (Gold book) gives a wealth of information on equipment reliability. Opening and closing disconnects, circuit breakers, and most other scenarios have failure rates which result in an arcing fault (493 gives both failure rates and failure modes) less than 10^-5. The one activity that is well above this threshold is racking breakers in and out. So for this one instance, PPE would definitely be required when it comes to normal operation of the equipment. This point is reiterated in the definition of arc flash hazard as I stated earlier.

When it comes to working on the equipment though there are lots of scenarios where this is not an issue. If you are working on equipment in an unknown state...e.g. the breaker just tripped so now you know that something may be amiss, then obviously this would be a scenario where PPE would be required. However simply opening the door to do an IR scan, though there is a risk that wires are laying against the door (and closing the door has an even higher risk), doesn't exceed 10^-5. And if you have the probe tips in place on a voltmeter and ENFORCE THIS so that it is highly unlikely that taking a voltage measurement for instance would cause a phase to phase, or phase to ground fault, even if the electrician accidentally slipped and poked something with the probe tips, then this would also be a potential scenario where PPE would not be required, unless there is another reason to suspect that something could happen.

So as you can see and have correctly realized, a "risk analysis" does not stop with simply quantifying the hazard itself. That's a hazard analysis. A risk analysis must also look at the likelihood of an injury. IEEE 1584 and the equations in the annex of 70E only quantify the hazard and do not quantify the risk. There is a risk assessment method in the annex of 70E as well, but it has a lot of problems and isn't really a complete system because for instance it does not give a risk ranking matrix where it defines an acceptable level of risk.

Am I making sense here? IEEE 1584 is not enough. Both the hazard and likelihood have to be considered in order to do a risk assessment. There are a number of risk assessment methodologies out there but since in the case of arc flash hazards the hazard is a binary one, the likelihood side of the equation is the only part not being addressed by many people.

Finally, there is also a glaring problem with the approach given in 70E. The principle of ALARP is being ignored. When you do a risk analysis and find that the risk is unacceptable, then the next step is to look at a hierarchical approach to addressing the risk. You look first to whether or not you can engineer out the risk entirely, then to engineering controls such as adjusting the breaker setting or fuse sizes, or extending the handles or using remote operators to increase the working distance, or perhaps something more exotic such as differential protection, arc flash detectors, arc "termination" devices, or arc flash blankets. Then you look at admnistrative controls such as using an EEWP or procedures to limit exposure. This aspect is written into 70E but not really noted as an administrative control. Then finally if you cannot find any other method to address the risk, then and only then, you use PPE. 70E doesn't even hardly mention using any other method to address the risk EXCEPT using PPE.

If on the other hand you approach this using the framework of a risk assessment methodology such as the 2 or 3 ANSI methods, or IEC 61508, IEC 61511, etc., then these frameworks address the risk side of things and IEEE 1584 fills in the gap on hazard analysis.

In my company's own policies, we have a list of tasks that we list as "normal operation of equipment". These tasks can all be performed unless the equipment is known to have faulted or is known to not be in good condition with only "standard PPE". We have not yet gone to looking at likelihoods of tasks while equipment is being serviced except for IR scans because too many electricians will attempt to split hairs on when equipment is in good working order and when it isn't. So we are conservative when it comes to servicing equipment but take a different approach when it comes to operating equipment.


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PostPosted: Mon Oct 29, 2012 7:01 am 
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PaulEngr wrote:
...development of the tables was done by performing a risk analysis. First the incident energies were quantified using IEEE !584.


Where did you hear that this?
My understanding is that 'IEEE1584 results' were not considered during the development of the 'task table', at all.


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PostPosted: Mon Oct 29, 2012 11:42 am 
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The NFPA 70E May 2003 ROP has a proposed Annex J Hazard/Risk Category Selection Table that is the precursor to the current task tables. The Annex J table includes a column for each task that has the incident energy and risk assessment (low, extremely low, moderate, etc.). A substantiation column shows how much the hazard category was reduced for low risk.


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PostPosted: Mon Oct 29, 2012 4:05 pm 
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jghrist wrote:
The NFPA 70E May 2003 ROP has a proposed Annex J Hazard/Risk Category Selection Table that is the precursor to the current task tables. The Annex J table includes a column for each task that has the incident energy and risk assessment (low, extremely low, moderate, etc.). A substantiation column shows how much the hazard category was reduced for low risk.

The * note to that table, effectively says the incident energy was calculated per methods presented in 220.2(B). 220.2(B) says to use either IEE1584-2002 or the formulas in Annex B.

In the 2003 ROC, #70E-151 acknowledged there were some issues between the original tables values and results which would have been derived using IEEE1584-2000. It appears their recommendation was to revise the allowable fault current values in order to maintain the HRC limits.

But this Annex never made it into the final 70E-2004, so what method was used to derived the incident energy level vs. HRC relationship?


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PostPosted: Mon Nov 05, 2012 12:38 pm 
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The inconsistency between the NFPA70E prescriptive table PPE that includes "risk" and the calculated "hazard" has been noted since about 2005. It is nice to acknowledge that some tasks may be less risky, however; less risky by itself does not translate into a lower level of hazard (and PPE). Plus it seems unlikely that any individual would be willing to venture the liability to assign risk factors. For these reasons we generally recommend full PPE per calculated available hazard for any work that might disturb an exposed energized conductor.

There are some specific exceptions such as European style with-drawable motor starters built with solid dielectric that by design absolutely prevent the chance of drawing an arc; it would seem silly to suit up to operate these devices per manufacturer's recommended operation even though we can calculate a Hazard level.


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PostPosted: Mon Nov 05, 2012 7:06 pm 
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I totally agree with PaulEngR. If a company has an Electrical Safety Progam in place it will provide the mechanism to quantify the hazard and then assess the risk. Hazard analysis and risk assessment procedure should be included in the ESP. I have a matrix based on NFPA 70E/CSA Z462 Annex F. I like to quantify work tasks as low risk and high risk, and with all preventive and protective control measures applied a high risk work task can be reduced. Without any arc rated clothing 1.2 cal/cm2 if incident energy or greater will cause the onset of a second degree burn or worse. With arc rated clothing we can limit the harm to the onset of a second degree burn, trying to keep the consequences or exposure to an arc flash to as low risk as possible.

Another item that isn't in the content above is the consequences of shock and applying shock hazard analysis managing the risk of exposure to shock. The risk assessment procedure must include both hazards.

FYI the HRC tables are all calculated to 40 cal/cm2 I believe except for the 240V work tasks, then as PaulEngR outlines based on risk the HRC # was reduced from HRC 4 to the HRC # listed.

PaulEngR, can you email me offline or call me, would like to touch base. My logistics are terry.becker@espsi.ca, 403-465-3777.


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