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 Post subject: Electrical Safe Work - Scenario rather than condition
PostPosted: Thu Mar 15, 2012 11:07 am 
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Joined: Thu Mar 15, 2012 10:57 am
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Location: Toronto, ON, Canada
Has anyone been able to define Electrical Safe Work, rather than simply condition? As I'm writing my company's Energized Electrical Safety Program and am currently trying to define electrical safe work - the environment scenario of the worker rather than the condition of the equipment.

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PostPosted: Sat Mar 17, 2012 4:09 am 
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Although this is not very well stated, the overall point of 70E (and NESC) is that you should be doing a risk assessment of every task and determining what the hazards are. This is true in a greater sense not only for electrical tasks but for all tasks. Based on the assessment it determines what sort of work practices and methods should be required (the work rules) to mitigate the hazards that are present down to an acceptable level.

Just because there is a potential hazard does not automatically mean that it must be mitigated in any way. Take for instance just walking by electrical equipment that has all the doors closed with nothing exposed and no work going on. In responses to proposals that have been submitted, the 70E committee has stated over and over again that there is no hazard in this condition. If that were so, I'd have to put everyone in 40 cal/cm^2 suits over a wide area in a certain part of the operation where I work and there would be a fence put up around some of the equipment where no work of any kind could actually occur. This is common for the secondary side of transformers, especially very large ones.

70E in the task tables contains a pretty good list of tasks to get you started, and they have even provided a partial list of which tasks have relatively speaking more or less risk. The only issue with the task tables is that they reduced the arc flash PPE requirement with several tasks but did not give any footnotes explaining the logic behind the change. The "0"'s are pretty easy to figure out if you assume that for those tasks, the likelihood of an arc flash hazard is very low regardless of the incident energy. But the ones where the PPE has been reduced by "1, 2, or 3 categories" (their terminology) leaves one without any idea of what the reasoning is.

If you do not already have an established risk assessment methodology, don't look to 70E for help. The one in the appendix is very incomplete. I can see the intent because I'm familiar with more than one of them, but this one doesn't work. I would suggest you consider adopting ANSI RIA R15.06. This is not as popular as ANSI B11.TR3 in the U.S. or IEN 951-4 (or IEC 61508) elsewhere but has the advantage that it is very simple to use, has the definitions already coded into it, and has the risk matrix coded into it. Others leave it up to discretion to define terms such as "severe" or "moderate", or "frequent" and "infrequent".

These risk assessment methodologies help avoid knee-jerk reactions to perceived risk especially for the "borderline" cases. For instance if you read through many threads on this web site, it becomes obvious that there is definitely some risk in someone opening or closing a disconnect or a circuit breaker with the doors closed and latched. 70E recommends that there is essentially no need for PPE in this case if the equipment is properly installed, operated, and maintained, for 600 V or less equipment. The rules change somewhat for 1 kV or larger class equipment but the 1 kV+ situation is one of those "1, 2, or 3 category" reductions. If you do an arc flash hazard analysis without doing the full risk assessment, you would likely require arc flash PPE for most simple switching exercises. If you do the risk assessment, you will find that the likelihood of an arc flash during a switching task is very low with some types of equipment (pretty much everything except draw out gear and some but not all air switches) and not for others.

In a similar way, the knee jerk reaction to opening up an enclosure that contains 480 VAC components and some 120 VAC control circuits may be considered subjecting yourself to both shock and arc flash hazards which is true. However, if there are no exposed components or if the exposed components are outside the restricted approach boundary, there may be no appreciable shock hazard. The arc flash hazard strongly depends on what you are doing and whether for instance you stand a chance of accidentally shorting across two phases of the 480 V side if you slip with a screwdriver while working on the 120 VAC control wiring. The situation would be drastically different if the whole bucket was energized compared to if the disconnect or circuit breaker is thrown and the only energized part is the incoming feeds way at the top of the bucket and they not likely to be touched. The risk may also be different if you are sticking wires or fish tape blindly out into the trough in that same MCC while everything is energized.

Anyways...just food for thought. It is not only conditions that have to be considered. The tasks themselves (activities) clearly have to be a part of an electrical hazard policy.

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PostPosted: Wed Mar 21, 2012 6:00 am 

Joined: Mon Nov 19, 2007 5:25 am
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Location: Titusville, Fl.
Well written, and will be reading the suggested, "ANSI RIA R15.06 ," and "ANSI B11.TR3 in the U.S. or IEN 951-4 (or IEC 61508) ," for risk assessment of electrical work activities at our sites/centers...

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