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 Post subject: Hearing Aids
PostPosted: Thu Mar 28, 2013 4:14 am 
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If a worker enters the arc flash boundary and is troubleshooting equipment, what happens if he is wearing hearing aids and needs the aids to determine if the equipment is operating properly? Does he take the hearing aids out, and is no longer able to hear?


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PostPosted: Thu Mar 28, 2013 5:20 am 
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Some more details may help narrow down answers. For instance, just because you are entering an arc flash boundary does not necessarily mean one needs to have PPE on. As an example, reading the panelboard meters on the front of switchgear, one most likely is inside the AFB but is not interacting with the equipment in such a manner as to potentially cause an arc flash incident.

In your case, is he listening for bearing noise, an alarm, etc.?

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PostPosted: Thu Mar 28, 2013 6:16 am 
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wbd wrote:
Some more details may help narrow down answers. For instance, just because you are entering an arc flash boundary does not necessarily mean one needs to have PPE on. As an example, reading the panelboard meters on the front of switchgear, one most likely is inside the AFB but is not interacting with the equipment in such a manner as to potentially cause an arc flash incident.

In your case, is he listening for bearing noise, an alarm, etc.?

Yes, he has exposed energized parts, and is listening for proper operation of the sequencing.


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PostPosted: Thu Mar 28, 2013 7:14 am 
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What is the arc flash hazard in that location? Sounds like it is maybe an old relay panel and listening for the sequence of relays? So there is 3 phase power coming into the cabinet? What voltage? Fed by what size transformer? Is the upstream protective device a MCCB or fuse? Has a study been done or are you going by the tables in NFPA 70E for this task? As I said the more details you can provide the more likely someone can help you on this forum.

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PostPosted: Thu Mar 28, 2013 9:05 am 
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wbd wrote:
What is the arc flash hazard in that location? Sounds like it is maybe an old relay panel and listening for the sequence of relays? So there is 3 phase power coming into the cabinet? What voltage? Fed by what size transformer? Is the upstream protective device a MCCB or fuse? Has a study been done or are you going by the tables in NFPA 70E for this task? As I said the more details you can provide the more likely someone can help you on this forum.

This worker is in an HRC 2. 480V The study has been done and the calculated incident energy is 5.75 cal/cm


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PostPosted: Thu Mar 28, 2013 9:05 am 
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This worker is in an HRC 2. 480V The study has been done and the calculated incident energy is 5.75 cal/cm


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PostPosted: Thu Mar 28, 2013 9:26 am 
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Ok, so did the study look at anyways to lower that? Is there another way accomplish verifying proper operation of sequencing? Is this the way it has always been done? Could some engineering be applied to verify sequencing without exposing an employee? For example, if it is a relay cabinet, could that be replaced with a PLC?

Per NFPA 70E the PPE required for that level includes hearing protection. So yes he would have to either remove hearing aids and put in plugs or maybe ear muff style. Either way it would defeat the reason he is in the cabinet.

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PostPosted: Fri Mar 29, 2013 6:36 am 
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Is the employee actually interacting with the equipment or just standing there observing/listening? The definition of "arc flash hazard" in 70E is quite clear on a task which does not involve interacting with the equipment in such a way that it could cause an arc flash. Visual observation and IR scans are good examples of cases where there is flat out no interaction with the equipment and thus no arc flash RISK. The word "hazard" in 70E-2012 is used incorrectly. The definition has been fixed in the 1st draft of 70E for 2015, but this won't come out for a couple more years. In the mean time, reference to virtually any risk assessment procedure will clarify the differences between "hazard" (the bad thing that could happen), "likelihood" (the chance of it happening), and "risk", which is a combination of hazard and likelihood in which we want really bad stuff to happen really rarely, but that the minor bad stuff should not receive the same aggressive treatment that may be necessary to make it happen extremely rarely as well...in other words, it becomes a tolerable risk. For instance we probably want to limit the number of times that we kill someone to "one in a million" odds (that's the standard for EPA), but that we may want to limit ourselves to one or two "band aid" cases a year at the most, say 1 in 1,000 or 1 in 10,000.


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PostPosted: Mon Apr 01, 2013 6:19 am 
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Interacting does make it worse, however the NFPA 70e is very clear on the PPE needed for a risk of 2. That means from 18-36 inches away from the source, you will have enough power to light non FR clothing up in less than a second! (above a 4 cal/cm^2). The PPE for this level clearly states that one must wear ear PLUGS along with an 8cal/cm^2 balaclava under a hard hat, 8 cal/cm^2 face shield, 8 cal/cm^2 coveralls or shirt and pants, and leather shoes. (All natural underclothes as well). So if the employee doesn't wear ear PLUGS working around this open panel, he and the company would be in violation. The task table has a different view on things, but is only used when an arc-flash study has not been done. Clearly one has been done in this case so the table that has to do with jobs and risk (Table 130.7c in the NFPA 70e 2012 version) shall not be used. I would err on common sense, obviously he is in a open energized panel and should have a second trained qualified person working with him, are they both wearing hearing aids? If an electrician is colorblind, he would need a second person to help him wire a panel, obviously we need to accommodate and not discriminate people with disabilities so if I was the plant manager, I would give the man (or woman) some help when working on this panel. It would be cheaper and safer (than a fine or lawsuit) in the long run.


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PostPosted: Mon Apr 01, 2013 6:54 am 
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I have tested a hearing aid in arc flash up to about 20 cal/cm2 and it did fine. The NFPA 70E standard requires ear insert hearing protection and MOST modern hearing aids would suffice (check with the manufacturer and your CIH) as they will usually limit dangerous noise to a safe level. Most of the thoughts above are important but it is VERY unlikely that you will get a hearing aid melted into the ear in the worst arc flash event. Under a hood it will never happen. We include the data we have on arc flash testing of several common inserts in our training (which about 500 trainers use). Image

Let me know if we can assist. I don't have data to release on the hearing aid. It was one from a specific company I tested for.


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PostPosted: Thu Apr 04, 2013 11:12 am 
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wbd wrote:
Some more details may help narrow down answers. For instance, just because you are entering an arc flash boundary does not necessarily mean one needs to have PPE on. As an example, reading the panelboard meters on the front of switchgear, one most likely is inside the AFB but is not interacting with the equipment in such a manner as to potentially cause an arc flash incident.

In your case, is he listening for bearing noise, an alarm, etc.?

I realize that 70E bounds the requirement for PPE when within the APB if interacting with the equipement. We have to also consider those components that operate automatically that could also be the source for an arc flash. In that case they have the same potential result as if one were interacting with the equipment.


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PostPosted: Fri Apr 05, 2013 5:15 am 
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While it is possible an automatic operation could cause an arc flash, the probability of that happening is much, much lower than thelikelihoodof human interaction causing an arc flash. I read an[url='http://atmae.org/jit/Articles/spezia041510.pdf']article[/url]once by Dr. Carl J. Spezia in which he states that a review of OSHA incidents shows up 80% of electrical incidents are caused by human error and cites a[url='http://ieeexplore.ieee.org/xpl/articleDetails.jsp?tp=&arnumber=1430429&contentType=Conference+Publications&sortType%3Dasc_p_Sequence%26filter%3DAND%28p_IS_Number%3A30848%29']paper[/url]by Inshaw and Wilson from the Protective Relay Engineers 58thAnnual Conference.


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PostPosted: Sat Apr 06, 2013 4:17 am 
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I put together a discussion of this in the articles section based on published reliability data. Spontaneous failure rates of equipment during operation is at least an order of magnitude lower than arc flash incident rates published by esfi.org in analyzing BLS data. Again assuming proper installation and proper maintenance, that places spontaneous equipment failures in a minority at best, well below accepted risk assessment limits for tolerable risk.

Some equipment is inherently below this threshold anyways. In particular from IEEE Gold book data, knife blade disconnect switches fall into this category. This is in spite of the fact that obviously for almost every failure mode even if the device fails while in operation, the failure would only be discovered while switching.

Another device that stands out is draw out circuit breakers, while their bolted cousins have an order of magnitude lower failure rates. It has been reported by ABB that 80% of failures in draw out switchgear are due to the drawout mechanism itself, which corroborates why the difference in failure rates, especially given that 80% of those are arcing faults. There are a number of identified problems with doing this task to the point where I would always treat it as a possible arc flash incdient no matter what.

In comparison when humans are performing tasks the reported failure rates are task and situation dependent but vary between around 1% for the very, very, very best conditions to around 40% for the worst conditions with most practitioners taking 10% failure rates as something of an "average". With this kind of failure rate, any time that human performance is a factor, the risk becomes unacceptable and a task redesign is required.

For instance let's say that I have to make an adjustment to a "dial" that is common on electronic overloads and circuit breakers. For the sake of argument lets say that this particular equipment uses uninsulated bus with a bus gap of around 1 inch so that it is clearly exposed. If I use a "stubby" screwdriver to turn the dial, then I'm placing myself within the restricted approach boundary, which not only means that there is a shock hazard but also definitely an arc flash hazard if I happen to slip while I'm doing this if the dial is "sticky". This is clearly an unacceptable risk.

If I put on rubber gloves and get out rubber blankets and insulated clothes pins, I can insulate the uninsulated bus. Since everything is insulated, I am no longer able to interact with the equipment in a way that would cause an arc flash.

Or, I could switch to a long handled screwdriver that is insulated except for the tip so that it does not pose a danger to causing either a phase to phase or phase to ground fault. Again, I've taken the human interaction part out of the equation.

Now in either case I'm assuming here that the bus bars are the only risk. This happens to be a real case in a piece of equipment I help maintain where 3 insulated case circuit breakers are mounted on the side of a dry transformer enclosure where the incident energy is well over 100 cal/cm^2. The real danger here is not making adjustments. The real danger is that the cover is held on entirely by bolts. So if in the process of removing the cover, someone accidentally slips and drops a bolt into the bus bars or accidentally angles the cover back into the bus bars, the resulting arc flash incident would be very, very bad. For all practical purposes there is no way to remove the cover unless we redesign it with a hinge and a different fastener system.


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PostPosted: Mon Apr 08, 2013 6:40 am 
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It might be prudent (at least in the case of sequencing relays) to provide a visual clue, such as relays that incorporate a neon indicator or if the relays you are using do not come with that option to add indicator lights. This way the employee can use the proper PPE and see if the sequence is operating properly.


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