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 Post subject: Five Year Review of Arc Flash Hazards
PostPosted: Wed Sep 24, 2014 8:46 am 
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NFPA 70E states that Arc Flash Study should be updated whenever there are major changes in electric system and that the entire study shoud be reviewed every 5 years. Is the 5 year review an OSHA requirement, does this apply to electric utilites and what does a "review" involve? Thank you


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 Post subject: Re: Five Year Review of Arc Flash Hazards
PostPosted: Thu Sep 25, 2014 5:00 am 
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NFPA 70E does not apply to utility facilities used for generation, distribution and transmission of electricity, so it is separate from OSHA 1910.269 which applies to utilities. Unless I missed it, there is nothing in OSHA about when to do a review of the assessment.

I would say the review would consist of:
1. Update of utility available fault current.
2. Update of any changes made to the facility
3. Any changes due to NFPA revision since last study
4. Issue new labels

I'm sure I missed something.


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 Post subject: Re: Five Year Review of Arc Flash Hazards
PostPosted: Thu Sep 25, 2014 9:39 am 
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My review items would be (I'm in the middle of one now):

1. Review the standards and assumptions. For instance, are you using the 125 kVA "rule" and is it still valid? Should you be using IEEE 1584 or something else? As an example for the 22.9 kV equipment that we have we previously relied on the tables in 70E. Now that the tables have been cut off at 15 kV, we need to come up with a new standard for how to rate 22.9 kV equipment.
2. As another example, check the standard. The 2015 edition includes lots of references to equipment in good working condition where previously this was a footnote. If that is important to you (and it should be), did the previous study address it? Is the existing maintenance program adequate? What is the equipment condition? This may need a full blown top-to-bottom inspection/audit.
3. And as a final example of reviewing changes to standards, 70E-2015 introduces the concept of doing a risk assessment. Previously it only required a hazard assessment. This means that likelihood as well as worst case have to be considered as part of the arc flash study. This means things like assessing the likelihood that a particular piece of equipment may or may not have an arcing fualt during a particular task, and whether or not this meets any particular standard of concern. In this regard although I prefer fault trees, the CCPS LOPA manual collections a lot of data suggesting reasonable targets for risk benchmarks. Essentially it comes down to 1 in 1 million per year is more or less an industry standard for fatalities, and major injuries requiring a visit to a burn unit would be about 1 in 100,000 per year. At the current time according to statistics collected by the ESFI (www.esfi.org), U.S. average injury rates due to arc flash are pretty close to these values, so it's a reasonable standard. This means that for instance when considering published failure rates for equipment, breakers are right on the line. Disconnects are far more reliable than the requirements call for, and "just walking by" should not be considered for arc flash reasons. Note that the way that the text is written if you do your own study (such as IEEE 1584), then you can't use the tables in 70E and have to do your own risk assessment as well. The tables in 70E-2015 though are a pretty good starting point but I like the tables in the annexes to the new 1910.269 standard even better as they are more clear.
4. Do an audit, either paper or field. Are there areas where the power system analysis is deficient necessitating field verification, either partly or completely? Even something as simple as doing an inspection of fuses and breakers to ensure that the settings have not been changed is in order, though you have to decide whether to check them all or check a percentage.
5. Is the mitigation that is in place adequate or is more work needed here? This one is important to consider because essentially most arc flash studies don't put enough money in it for mitigation plans. So on each succeeding update, it's probably a good idea to continue to knock out more of the "hot spots" in terms of doing hazard mitigation.

I do not subscribe to going through ALL the equipment and redoing the entire field study unless you know there are errors/omissions in it. I recommend doing a thorough review of all the assumptions that are baked into it as well as looking at how the standards have changed over time. Then and only then, a field verification should be done but may be only a sampling if there are no known changes that would invalidate the study. However, engineers that make money doing studies would rather spend as many hours as possible doing field verification because there are a lot more billable hours in that effort.


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 Post subject: Re: Five Year Review of Arc Flash Hazards
PostPosted: Tue Mar 03, 2015 9:24 pm 
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Thank you for the insight PaulEngr.

I'll use it as a guide as I complete a 5 year review.

David


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