It is currently Tue Dec 07, 2021 5:28 pm



Post new topic Reply to topic
Author Message
 Post subject: Arc Flash Risk Assessment Methodology
PostPosted: Mon Apr 09, 2012 7:14 pm 
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
The attached file may give some insight to others as a way of addressing the likelihood question of arc flash risk assessments. I've worked several examples to show a way in which it can be done.

As stated in the file itself, this is food for thought. I highly encourage others to comment or even whole sale rip off the idea. I have not gone to the point of revising the tables in NFPA 70E yet but this would be a purely mechanical exercise. In addition the methodology trivially allows for expansion such as taking resistance grounding systems or worker experience into account as I've described. No doubt countless other variables which affect likelihood can be inserted as well.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Apr 16, 2012 1:19 pm 

Joined: Mon Nov 19, 2007 5:25 am
Posts: 33
Location: Titusville, Fl.
As by my call name (given to me by Jim), I work at the NASA Safety Center as an Analyst and Electrical Safety rep. We have an NASA Electrical Safety Working Group (NESWG), of which John T. Inge is a member from the Langley Research Center. We have been trying to realize teh risk not only for tasks as they are listed in the NFPA 70E Table 130.7(C)(9) (we work to an older version), but for those outside of this listing (i.e. cable splices/terminations/demolition/installation/repair inside of confined spaces). So this risk effort would help greatly for those cases. We also have PRA experts, one of which would be willing to help you, who has experience in the space/petroleum/nuclear assessments. If you are willing, I would like to arrange a team (3-Electrical Safety and 2 PRA experts), from NASA to help you during your peer review. Please contact me, if you would like to take opportune of such at ph#321-867-5097.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Apr 27, 2012 9:38 am 
User avatar

Joined: Fri Apr 27, 2012 6:49 am
Posts: 40
Paul,
Great paper, it really got me thinking. I may have some content questions for you after I digest the article, but today I just have a typo question.

From the Worked Example section:
Assume that the risk ranking matrix requires a maximum likelihood of 0.0000001 for major personnel
injuries (1 in a million) ...

Should 0.0000001 be changed to 0.000001?


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sun Apr 29, 2012 5:17 am 
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
MattB wrote:
Paul,
Should 0.0000001 be changed to 0.000001?


Yes.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu May 03, 2012 5:17 pm 
Sparks Level

Joined: Tue Apr 03, 2012 1:28 pm
Posts: 53
Location: Louisville KY
Paul,
Great info! Really appreciated. This answers so many debates that I have had, even with fellow arc flash instructors, concerning this idea of lowering PPE values because of various reasons. With permission, I would love to forward your paper to about 25 fellow arc flash instructors for their review...

Ken


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri May 04, 2012 3:12 am 
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Go for it. As the paper states...I'm looking to generate the discussion to bridge the gap between the tables (which incorporate likelihood) and engineering calculations which so far do not.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon May 07, 2012 4:30 am 
Sparks Level

Joined: Mon Jul 09, 2007 11:43 pm
Posts: 61
Location: Sheffield, England
Great paper Paul, I've taken the liberty to pass the document on myself. This is just the sort of risk based approach that needs to be explored in my view to stop some of the obvious anomolies in the selection of PPE for very low risk tasks. Not sure how the failure data sets would transport to this side of the Atlantic though.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue May 15, 2012 4:13 am 

Joined: Mon Aug 03, 2009 10:22 pm
Posts: 12
Location: North Carolina
Very good paper. I plan to implement something along these lines in our electrical safety policy. Thanks.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu May 17, 2012 10:35 am 

Joined: Wed Sep 15, 2010 2:41 pm
Posts: 3
Location: San Diego
Great paper.
In our Electrical Safety Program the Hazard Risk Assessment examples and text I used when I wrote it was very general and not specific to electrical activities (I lacked specific task examples and quantitative data about the hazard/failure rates). The use of this generalized material has come to be seen by me as ineffective at causing our staff to actually include any form of risk assessment when planning their approach to energized work. The paper, even though you wrote to begin a discussion, contains data that I will use to improve this teaching manual.
Thanks!


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu May 31, 2012 5:46 am 

Joined: Thu May 31, 2012 5:33 am
Posts: 1
Location: United states
Great job. This is a good post. I liked the risks you mentioned here in a very general way. I found this risk assessment methodology really very useful. Thanks for sharing this post.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Jun 11, 2012 7:12 am 

Joined: Fri May 18, 2012 4:09 am
Posts: 3
Thanks for a more detailed idea for risk assessment. I developed an excel file with simple drop down menus based on the rish assessment categories from the Annex F. It still appears to me that it doesn't cover LOTO. Example is the Frequency table. it is based on > 10 minutes which is confusing for a < 1 minute task such as LOTO.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Jun 12, 2012 3:59 am 
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
The frequency of exposure table in the back is based on how frequently an employee is exposed, not necessarily the duration. It is adapted from an IEC 61508/ANSI B11.TR3 type method. The difference would be that for instance in a production welding shop everyone working in the shop area would have nearly continuous exposure to welding flash. A fork truck driver that delivers materials once an hour to the area would have a lower frequency of exposure and a duration of only perhaps a couple minutes. Warehouse workers that have to walk through the area during shift change only would have even less exposure and very short durations.

Exposure to a potential arcing fault hazard would be for the duration of the task if working live while it is very short (seconds) for a LOTO activity. The frequency of exposure could be almost nonexistent to every day or even more depending on how job tasks are designed. In one operation I'm aware of production is responsible for doing ALL lockouts and they use a lockbox (complex lockout) system for ALL tasks. Generally only one or two production employees in an area are responsible for ALL equipment lockouts. In this condition their exposure frequencies are quite high while electricians (usually the high risk group) are relatively infrequently exposed except during troubleshooting tasks where the equipment is energized.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Fri Jun 15, 2012 12:47 pm 

Joined: Mon Nov 29, 2010 5:02 am
Posts: 2
Thanks, this is a great article and seems to be a more practical approach. I hope this shifts the direction of how the arc flash hazard and protection is approached in the future.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Jul 18, 2012 8:01 am 

Joined: Mon Jul 16, 2012 11:22 am
Posts: 1
Excellent paper. I also have always been bothered by the way NFPA 70E reduces the HRC based solely on likelihood. I strongly encourage you to submit this to the IEEE for publication and conference presentation in order to stimulate more discussion on this issue.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Sun Sep 09, 2012 7:13 pm 
Sparks Level

Joined: Thu Jul 19, 2007 7:54 am
Posts: 201
Location: St. Louis, MO
You may also like to see another paper I had the pleasure to review by Lynn Hamrick which appeared a couple of years ago in NETAWorld.

http://www.netaworld.org/files/neta-journals/Niche%20Market-Hamrick-P51.pdf


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Mon Sep 10, 2012 11:45 am 
User avatar

Joined: Fri Apr 27, 2012 6:49 am
Posts: 40
WDeanN wrote:
You may also like to see another paper I had the pleasure to review by Lynn Hamrick which appeared a couple of years ago in NETAWorld.

[url='http://www.netaworld.org/files/neta-journals/Niche%20Market-Hamrick-P51.pdf']http://www.netaworld.org/files/neta-journals/Niche Market-Hamrick-P51.pdf[/url]


The paper posted by PaulEngr takes the position that the paper posted by WDeanN is inherently flawed; "The inherent fallacy with this methodology is that again, a reduction in likelihood does not mean that the injury is reduced if an incident occurs."

Without reading through every post in this thread, I was expecting to read a paper that corresponded with PaulEngr's methodology, but these papers are quite different.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Wed Oct 10, 2012 7:59 pm 

Joined: Sun Jun 17, 2012 11:59 pm
Posts: 1
The paper does not state any details about the protection coordination exercise which plays an important role in determining the arc flash energy at busses. The definite time and Instantaneous settings play an inetgral role in the
operation of the breakers.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Thu Oct 11, 2012 6:51 pm 
Plasma Level
User avatar

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
MattB wrote:
The paper posted by PaulEngr takes the position that the paper posted by WDeanN is inherently flawed; "The inherent fallacy with this methodology is that again, a reduction in likelihood does not mean that the injury is reduced if an incident occurs."

Without reading through every post in this thread, I was expecting to read a paper that corresponded with PaulEngr's methodology, but these papers are quite different.


Lynn Hamrick's paper is one of the ones that specifically got me to thinking in this direction. Yes, I disagree with the approach taken in that paper. Numerically an order of magnitude reduction in likelihood is treated the same as reducing the severity of an injury by one from a qualitative point of view such as moving from a recordable injury to a first aid case in the published quantitative risk assessment methodologies. Where this falls down however is that PPE for protection against arc flash is a pass/fail condition. I am not aware of an equivalent to ASTM 1959 for instance that predicts the onset of a 1st degree burn so that we can look at decreasing the degree of protection from 1st degree burns to 2nd degree burns (no injury to a first degree case). Until that sort of test becomes available (and H/RC levels are based on equivalent thresholds), the approach Hamrick uses cannot be used.


Report this post
Top
 Profile Send private message  
Reply with quote  
 Post subject:
PostPosted: Tue Nov 27, 2012 1:51 pm 
User avatar

Joined: Mon Jul 21, 2008 5:00 pm
Posts: 14
This is a great paper. I hope it gets people thinking. Just looking at calculations as absolute does not seem like the best approach when you consider some tasks may create a very very remote possibility of an arc flash. Thanks!


Report this post
Top
 Profile Send private message  
Reply with quote  
Display posts from previous:  Sort by  
Post new topic Reply to topic  [ 19 posts ] 

All times are UTC - 7 hours


You can post new topics in this forum
You can reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot post attachments in this forum

Jump to:  
© 2019 Arcflash Forum / Brainfiller, Inc. | P.O. Box 12024 | Scottsdale, AZ 85267 USA | 800-874-8883