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 Post subject: Risk assessment vs Table
PostPosted: Fri Dec 06, 2019 8:14 am 

Joined: Fri Dec 05, 2014 12:23 pm
Posts: 13
Normal operation of equipment that is properly maintained at which point there is very little likelihood of an arc flash in the first place and PPE is not required according to table 130.7(C)(15)(A)(a). Specifically, operation of a circuit breaker that is properly installed, properly maintained, doors closed, covers in place and no evidence of impending failure, no PPE is required. The table says nothing about IE levels, where you are standing etc. In this case we are presuming the person is standing in front of the gear.

How do we square that against Annex F (I am looking at the 2015 70E handbook) risk assessment for operating this same breaker under same conditions where, if you have IE > 40 Cal/cm^2

I would use the following parameters which would give me a 36 out of a possible 120 score.
R=SE(FR+PR+AV)
SE = 6
FR=2
PR=1
AV=3
Given that score of 36 one would presume that the statement "no PPE required" for the operation of the breaker per table 130.7(C)(15)(A)(a) is not true.
Implied in that 36 score is that there is risk in operating that breaker.


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 Post subject: Re: Risk assessment vs Table
PostPosted: Mon Dec 09, 2019 2:05 pm 
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Joined: Thu Jul 07, 2011 6:03 am
Posts: 64
Location: Netherlands
(disclaimer: I don't mean to have a go at you personally, but your question highlights an issue that I think needs attention)

There are a lot of hidden assumptions in both your choice of risk assessment method and scoring that you may need to evaluate. ISO 12100 is aimed at assessing machinery with operators performing tasks repeatedly or during a long time, both are not that applicable to most tasks that can lead to arc flash exposure. When these factors are always set to low you may end up underestimating the risk. Also, what's the basis for determining if a risk is acceptable or not? (fair warning: it is exceptionally difficult to find a straight answer on this)

In my opinion R=SE*PR is a better choice for arc flash risk assessment. But I could be wrong.

NFPA 70E has not given us a risk assessment method for use with IEEE 1584 calculation results. Appendix F only describes what risk assessment is, it doesn't give us any guidance on how to do it and what acceptable levels of risk are. Right now it's everyone for themselves and my assumption is that very few get it right. Even less get it right intentionally.

Most on this forum have an electrical engineering background and although risk assessment may have come up in some form during our education or work, occupational health and safety risk management probably hasn't. We could look for guidance from OHS professionals, but in my experience they come to us because they don't understand NFPA 70E. There's a knowledge gap between electrical engineers who can do IEEE 1584 calculations and OHS professionals who can do OHS risk management.

There is surprisingly little guidance to be found when it comes to arc flash, even though we had the requirement in NFPA 70E since 2015. The easiest way forward is to develop table 130.7(C)(15)(A)(a) into a risk assessment method using IEEE 1584 calculations. I'm not sure why the NFPA didn't do this along with the Table method.


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 Post subject: Re: Risk assessment vs Table
PostPosted: Tue Dec 10, 2019 7:28 am 
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Joined: Mon Jan 18, 2010 11:35 am
Posts: 524
Location: Wisconsin
jvrielink wrote:
The easiest way forward is to develop table 130.7(C)(15)(A)(a) into a risk assessment method using IEEE 1584 calculations. I'm not sure why the NFPA didn't do this along with the Table method.


According to NFPA 70E 130.5(A) and (B), you should first use table 130.5(C). Once you have decided the risk hazard analysis requires PPE you can then choose to follow the calculation method (i.e. IEEE1584) or use the task tables like 130.7(C)(15)(a).


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 Post subject: Re: Risk assessment vs Table
PostPosted: Tue Dec 10, 2019 8:44 am 
Sparks Level

Joined: Thu Jul 07, 2011 6:03 am
Posts: 64
Location: Netherlands
JBD wrote:
jvrielink wrote:
The easiest way forward is to develop table 130.7(C)(15)(A)(a) into a risk assessment method using IEEE 1584 calculations. I'm not sure why the NFPA didn't do this along with the Table method.


According to NFPA 70E 130.5(A) and (B), you should first use table 130.5(C). Once you have decided the risk hazard analysis requires PPE you can then choose to follow the calculation method (i.e. IEEE1584) or use the task tables like 130.7(C)(15)(a).


I must admit I never looked closely at how the Table method changed in the 2018 edition as I've never used it, it is indeed the same procedure as incident energy analysis.


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