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 Post subject: Normal Operation of Equipment
PostPosted: Tue Dec 23, 2014 6:19 am 

Joined: Mon Jun 09, 2014 9:19 am
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In the new NFPA 70E it was passed that when you are operating equipment under "Normal Operations", there is no need for arc flash PPE. We had worked very hard in our company under the way the 2012 70E was written that anyone operating electrical equipment that had already had the arc flash analysis performed needed to wear PPE that protected them from the amount of incident energy was available per the analysis. Now with this "Normal Operation" clause in the 2015 70E, several members of our electrical safety team and management want to change our policy to make it not necessary any longer.
I know that there has been extensive research done that shows at 8cal/cm^2 covers will start to break open on MCC, switchgear, and panels, but does anyone know where that research is published? I feel that when we have done the Risk Assessment and we know that there is a hazard above 8cal, we need to protect our operators. I can't believe the committee would consider that a "Normal Operation". Our operators at our compressor stations are required to wear cotton clothing at a minimum, but we do not have an AR rated clothing policy yet. Only when working on energized equipment that requires that PPE.
Thanks!


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 Post subject: Re: Normal Operation of Equipment
PostPosted: Tue Dec 23, 2014 7:23 am 
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Normal operation is operating a switch with the doors closed. If you open the enclosure up at all, you are no longer under normal operation and need to wear the proper PPE for the shock and arc flash hazards.

That's an oversimplification, and I'm sure someone will follow up with a more verbose reply.


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 Post subject: Re: Normal Operation of Equipment
PostPosted: Mon Jan 05, 2015 3:26 pm 

Joined: Mon Feb 22, 2010 10:24 am
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Yes, doors closed and secured is one the criteria for normal operation. The others are properly installed, properly maintained, covers in place and secured, and no evidence of impending failure. Once you have done the incident energy analysis, which may be how you know it is 8 calories, you need to do the risk assessment which includes the likelihood of an event occurring. The final decision about worker safety and protection is yours. My personal opinion is that you usually cannot verify all of the criteria (maintenance or employee error such as leaving grounds on when energizing, for example). I have an Dow video that shows what happens when you leave the grounds on and still meet all of the criteria for normal operation.

Ken Jones presented some testing examples at one of PCIC meetings. He may be able to give some data. I think the amount of energy that will blow the doors open or allow energy to escape is highly dependent on the design, installation, and maintenance of the equipment.


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 Post subject: Re: Normal Operation of Equipment
PostPosted: Tue Jan 06, 2015 8:48 am 

Joined: Mon Jan 05, 2015 9:01 am
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You mention that there is a potential issue with leaving the grounds on and re-energising the equipment why should this be an issue ?

If you have fault make switchgear installed all that will happen is that the breaker will trip. As long as you haven't exceeded your trip or operational switching number of operations there should be no issue.


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 Post subject: Re: Normal Operation of Equipment
PostPosted: Tue Jan 13, 2015 8:17 am 
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lovetacycle wrote:
In the new NFPA 70E it was passed that when you are operating equipment under "Normal Operations", there is no need for arc flash PPE. We had worked very hard in our company under the way the 2012 70E was written that anyone operating electrical equipment that had already had the arc flash analysis performed needed to wear PPE that protected them from the amount of incident energy was available per the analysis. Now with this "Normal Operation" clause in the 2015 70E, several members of our electrical safety team and management want to change our policy to make it not necessary any longer.


And I agree. The issue at hand is that the likelihood of an arc flash incident in the first place is very low (about 1 in 100,000 per year), half of the rate for electrocution. This is an average. There are definitely times where the likelihood is greatly increased so the actual average during routine tasks is probably in all actuality closer to about 1 in a million or less, a number that is generally considered an acceptable injury rate for the general public. The arc flash PPE itself is only specified to work 95% of the time so there is still a 5% chance that even if you wear the PPE, it won't do any good. That's just the success rate under IEEE 1584. So the PPE is not a security blanket. It is likely to work but there are no iron clad guarantees. So the whole idea with "normal ooperations" is capturing those cases where there is simply no value in wearing the PPE in the first place And just making sure the doors are closed is not a sufficient condition. In fact just the opposite...you can easily and safely operate a lot of equipment whether the doors are closed or not, and the arc flash hazard is calculated as if the doors are not even present. To me, this criteria is neither necessary nor relevant. What is relevant and what the "doors closed" concept partially captures is whether or not there is any exposed conductors, because if there are no exposed conductors, then the likelihood of tools or bodily parts creating an arc flash is nullified. That is a far better criteria than "doors closed" because it addresses the hazardous condition.

The other criteria can be broken down into two groups. It should be possible to do a quick field inspection of some basic issues such as whether there are soot marks present, whether the equipment is damaged, whether there are liquids present where there shouldn't be (water running out of the panel), whether it has just tripped and has not been inspected (as per NEMA AB-4). These are all concerns that should be checked before performing most tasks. The rest of the criteria can be evaluated ahead of time, except for "maintenance". NETA MTS and NFPA 70B are mainenance standards but a good read of them shows they don't really give "acceptance" criteria at all. They are at best inspection, and many of the inspections they specify are suspect anyways because they are not inspections that are predictive in nature but rather can in some cases be a predictor of current condition at best, or nothing at all in some cases. For instance NETA MTS recommends IR scans, milliohm measurements, or torque testing of joints. IR scans are fine as long as the joint is a power connection and not control wiring, and its a great tool with predictive capabilities that works very well in the right circumstances. Milliohm readings have never been an established standard because they don't seem to mean much. The readings can go up, down, or sideways, and don't correspond at all to joint reliability. That is why NETA MTS gives a "+/-50%" criteria for passing. Torque testing is a proven loser and flies in the face of basic fastener engineering. Any consensus safety standard recommending this should be viewed with great suspicion. NFPA 70B has many similar issues.

Quote:
I know that there has been extensive research done that shows at 8cal/cm^2 covers will start to break open on MCC, switchgear, and panels, but does anyone know where that research is published? I feel that when we have done the Risk Assessment and we know that there is a hazard above 8cal, we need to protect our operators. I can't believe the committee would consider that a "Normal Operation". Our operators at our compressor stations are required to wear cotton clothing at a minimum, but we do not have an AR rated clothing policy yet. Only when working on energized equipment that requires that PPE.
Thanks!


No. cal/cm^2 is not part of arc blast.


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 Post subject: Re: Normal Operation of Equipment
PostPosted: Tue Jan 13, 2015 1:47 pm 
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More to the point and I posted earlier the actual formula that the CIGRE work that was done on arc blast is using. Pressure inside an enclosure is among other things directly proportional to the arcing energy being released integrated over time. Incident energy is also directly proportional to the arcing energy being released integrated over time. Thus to say that if the enclosure does NOT rupture that there is a direct correlation between incident energy and pressure inside the enclosure, this would be true. On the other hand there also would not be an arc flash injury. The point at which the enclosure ruptures is dependent on the physical, mechanical pressure that the enclosure can withstand, coupled with any openings that exist that cause the enclosure to vent. So far so good and there would potentially be a relationship between arc flash and rupture (and arc blast for that matter). However it falls apart after this point. The pressure rise occurs very quickly (milliseconds, less than a cycle).

In contrast, incident energy as we know it today is a radiant heat condition. The gases and pressure inside the enclosure or for that matter, whether there is a door on the enclosure at all, is immaterial. Incident energy will continue to rise regardless of whether the enclosure ruptures or not until the overcurrent device interrupts the arc or it self extinguishes or the victim moves or is moved from the area. In contrast once the pressure reaches the limit of the enclosure, the door ruptuers and pressure rise ceases.

Over very short time intervals before the enclosure ruptures (no more than 1 cycle) there is a direct correlation between incident energy and presssure. But that relationship ends very quickly and after that point, arc blast is fixed but incident energy continues to increase.

This is of course ignoring all of the various side factors such as working distance, enclosure size, etc., that will modify arc last and arc flash.


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 Post subject: Re: Normal Operation of Equipment
PostPosted: Fri Jan 30, 2015 9:57 pm 

Joined: Fri Jan 30, 2015 9:53 pm
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In contrast, incident energy as we know it today is a radiant heat condition. The gases and pressure inside the enclosure or for that matter, whether there is a door on the enclosure at all, is immaterial. Incident energy will continue to rise regardless of whether the enclosure ruptures or not until the overcurrent device interrupts the arc or it self extinguishes or the victim moves or is moved from the area. In contrast once the pressure reaches the limit of the enclosure, the door ruptuers and pressure rise ceases.

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