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 Post subject: Risk assessment after Arc Flash study
PostPosted: Wed Jan 05, 2022 7:52 am 

Joined: Tue Mar 05, 2019 5:47 am
Posts: 10
Hi All

I didn't find it and this question is with me for some time. In latest revisions of NFPA70E we have Risk Assessment part where we can estimate :
- likelihood
- severity (study)

and calculate overall risk. As far I see we can use whatever method for it. This is clear but what to do next with results? NFPA say "take further safety measures" so it is not very specific. Let me make example:
- Main LV switchgear - switching (normal operation) IE=80cal/cm2 (very high), Likelihood (low) overall risk high- what next ? Do I need PPE for switching OFF/ON or I can ignore it in this case ?
- Main LV switchgear - opening doors to do infrared scan live , IE= 4 cal/cm2 (low) likelihood (low distance> 30cm) overall risk low - Do I need PPE to open energized panel to see bare copper busbars ?
- Industrial panel - automation job (not electrical but close to main switch which is fully covered with plexi) - IE 3 cal/cm2 (low) and likelihood (low) overall risk low.

For me it will make sense if I can say - overall risk for some lighting panel is low and despite it is 12 to 3 cal/cm2 we can state no arc rated PPE is needed to operate or do some replacement. And for other panels where high IE ( >40 or 65 cal/cm2) exists we can say that even for normal switching we need PPE as overall risk is too high. What you think? Any proper guideline ?

What I follow for a time being is table 130.5(C) with likelihood estimate in NFPA70E which is straight forward. In EU we have lower approach distance( called vicinity zone or live work zone) for LV it is no touch and 30cm as shock hazard distances. When it comes to arc flash it needs to be easy to understand to electricians when they have to use PPE and when not. I started once discussion about risk assessment and I saw it is too complicated. How do you approach it in recent arc flash studies ?

I saw few studies where risk was estimated in 3x3 matrix compiled with AF results and overall risk was produced for each panel but it has nothing to do with activity you do (reading meter, infrared scanning, switching or direct busbar measurements).


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 Post subject: Re: Risk assessment after Arc Flash study
PostPosted: Thu Jan 06, 2022 7:16 am 
Sparks Level

Joined: Thu Apr 18, 2019 11:42 am
Posts: 63
In my opinion, you do the assessment as follows:

1) categorize the risk with NO mitigation
2) categorize the risk with mitigation

That should point you to whether or not PPE is needed. I would say though that if maintenance has not been performed, if there are installation issues, noticeable damage, etc. then that will point you to PPE in most cases.

I really don't like the subjective procedure for risk assessment as the NFPA 70E guidance lays out. I found a very nice paper on the internet at one point, that used IEEE 493 as a means to take the subjectivity out of the risk assessment (incorporated layers of protection method). The data in IEEE 493 was later updated by the Army to include more recent failure data.

Mike


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