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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: 13
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: 80
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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 Post subject: Re: Risk assessment after Arc Flash study
PostPosted: Mon Jan 24, 2022 10:40 am 

Joined: Mon Feb 23, 2015 10:19 am
Posts: 10
I find the 70E committees assessment of Normal Operation of 600v equipment to be most instructive as to a risk assessment.

If the equipment meets the 5 criteria (installation per NEC, no impending danger, etc.):
Even though the AF IE might be high, if these 5 criteria are met, then it is not considered an arc flash hazard.

The only way they can make that assessment is knowing that normal operation of 600v equipment has such a low probability of failure, in an AF fashion, that no PPE is required.


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 Post subject: Re: Risk assessment after Arc Flash study
PostPosted: Mon Jan 24, 2022 12:01 pm 

Joined: Fri Sep 24, 2021 7:17 am
Posts: 24
I love this discussion. It drives home the point that an arc flash analysis (i.e. incident energy study) is a different animal than an arc flash risk assessment. The IE data is used to determine severity when performing the arc flash risk analysis

The 2021 NFPA 70E Handbook has a graphic listed as Exhibit 130.4 on page 137.....and it begins with "If PPE will be employed as a risk control, the level of PPE necessary must be determined from ONE of these two methods: Arc Flash PPE Category Method OR Incident Energy Analysis Method.

PPE is used to mitigate the remaining risk after you've tried to eliminate it, substitute other equipment or methods, apply engineering controls, increase awareness, or apply administrative controls. This risk control hierarchy is required in NFPA 70E 110.5(H)(3)

In your example: "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?".....the answer is YES unless you've found a way to decrease the incident energy to less than 1.2 cal/cm2 @ 18" using some sort of control. This action, named "Opening hinged door(s) or cover(s) or removal of bolted covers (to expose bare, energized electrical conductors and circuit parts)......is listed as an activity that has "YES" in the likelihood of occurrence column.

In your 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 ?".......the answer is YES unless you can say it's in normal working condition. The answer is surely YES if it's being used for the first time. When I question people about that they will often say "yes it's in normal working condition" until I ask them specifically if the equipment has been maintained correctly in accordance with NFPA 70B or the manufacturer's instructions. Most often it's not been properly maintained at that level, so for most cases PPE would be required when using the breaker. Does your likelihood determination include an assessment if it's under load or not, or if a reduced energy let through (RELT) device is installed?

Is there a distance that your calculations of incident energy differ from the US norm? We are normally at 18" for 480VAC


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 Post subject: Re: Risk assessment after Arc Flash study
PostPosted: Mon Jan 31, 2022 1:59 pm 
Sparks Level

Joined: Thu Jul 07, 2011 6:03 am
Posts: 69
Location: Netherlands
In my opinion, the main difficulty in managing arc flash risk is that it covers the fields of both electrical engineering and occupational safety and health. The average electrical engineer has little knowledge of occupational safety risk management, the average occupational safety engineer is a generalist because they need to control all workplace risks. This is not an impossible combination, but it is an unlikely one to find in anyone entering the field. Coming from either side (and I guess this board has mostly electrical engineers) you will need to familiarize yourself with the other.

A second difficulty is that arc flash can be incredibly dangerous without being obvious to a lay person. If you regularly work at heights of 10 ft and suddenly get a job working at 500 ft, it's immediately clear that the risk increases by a lot and you need to take additional measures. To make the same distinction for arc flash, specific knowledge is required.

I was lucky enough to enter a position as part-time EHS manager for one of my clients for about 3 years and gained some insight in the typical user experience on the receiving end of my arc flash studies. It has radically changed the way I conduct business - I'm putting a lot more focus on the practical aspects of implementation and less on technical study details that I might find interesting. I realized that most, if not all, of my customers cannot do a proper risk assessment and evaluation for arc flash. This means that without the right support the process will stall somewhere. Maybe they will apply the labels, maybe they will buy the right PPE, maybe they will get specific training for their qualified employees. Most will not make sure that the highest risks are adequately controlled.

NFPA 70E requires a risk assessment and determination of additional protective measures including the use of PPE. My personal hot take: only doing a hazard calculation and then selecting PPE to go with it indicates a fundamental misunderstanding of what occupational safety risk assessment is about. It also is the most common approach I encounter. Combining hazard calculation with Table 130.5(C) to come up with measures based on the risk of the task is already a lot better, but still misses the point. If you're unsure where I'm going with this, I have two simple questions:

- what is an acceptable level of arc flash risk for workers exposed to it? Is it 1 death per 10 thousand workers per year? per 100 thousand ? per 1 million?
- how do you determine if a certain task performed at certain equipment is above or below this acceptable level?

NFPA annex F can help you with the second one. No one (including OSHA) will tell you the first one, you can only deduce it. It's 1 death per 100 thousand workers per year if you were curious and you can find it in any risk matrix that's used for occupational health risk assessment in most industries. Why is it that number? Because that's the residual risk level for most work hazards with currently implemented measures and it's industry consensus that means it's acceptable. As an employer, putting it at 1,000,000 would be prohibitively expensive and putting it 10,000 would at some point get you in serious trouble with OSHA.

In The Netherlands, according to my estimation, the risk level for electrical workers is exactly 1 death per 100,000 workers per year. Great right? Except that exposure is not evenly divided among all electricians. If you do residential/office installation or maintenance you might never see any exposure above 1.2 cal/cm². If you're part of a team that de-energizes equipment so that contractors can do their work under electrically safe work conditions you might have potential exposure to 12 cal/cm² or larger multiple times per day. For the latter, arc flash risk is unacceptably high and needs to be controlled. Of course there's a lot in between and a properly performed risk assessment can tell you exactly where you need to focus your efforts.


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 Post subject: Re: Risk assessment after Arc Flash study
PostPosted: Fri Feb 11, 2022 5:48 am 

Joined: Tue Mar 05, 2019 5:47 am
Posts: 13
jvrielink

I'm on the same side as you. My experience is the same that people don't understand nor can do proper risk assessment. And I'm not really surprised as it is tricky with points you highlighted. My cases above are test cases and I like to keep things simple so I'm not actually implementing risk assessment matrix as in NFPA70E. It have sense but it complicate arc flash a lot. Instead I like to refer to 130.5 (C) table which is straight forward. I think it might be simplified to three points :
- if live parts are accessible ( use PPE if >1.2 cal/cm2 or in zone)
- if not accessible (covers, doors, plexi covers in palce) no need for PPE
- abnormal situations or conditions - use PPE

As you said I also like to focus on AF results + recommendations + actions for improvements + PPE + upgrading procedures+ training

For me biggest advantage of risk assessment might be to evaluate risk for specific task, document it and implement so risk is low and we can say it is acceptable risk but as you point out it will be hard to defend why I think 1 on 100000 is acceptable without national or global guide.


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