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 Post subject: Arc Flash Clothing - Use Over 40cal/cm
PostPosted: Mon Sep 20, 2010 6:32 am 
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Location: Baltimore, Maryland
I am an instructor for a utility and have to teach arc flash / electrical safety training. We have not performed an arc flash analysis at many of our facilities as of yet. I have been using the table methods to inform the plant personnel as to what level of clothing to wear and at what distances to set up their boundaries. A study was recently completed at one of our facilities and several of the low voltage switchgears (<600V) ended up with 85cal/cm ratings. The company that performed the analysis also provided the labels for each of our switchgears and MCC's. The labels on several of the swtichgears indicate Required PPE: Dangerous as well as No FR Category Found. I have noticed that their are 100cal/cm suits in the FR catalogs that I have looked through. Is it unacceptable to work on this equipment (e.g. racking breakers in or out) unless it is deenergized? Can a 100cal/cm suit be utilized or is it unacceptable to work on this equipment at all unless it is deenegized. All electrical equipment is considered energized, until proven otherwise. How do I test it, while performing the task of testing would put me in harm's way. The flash hazard boundary for this same piece of apparatus is 242 inches. I don't have a long enough pole to reach it for testing since I have to have on proper PPE to be within the boundary. Does anyone know what to do in this case?


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PostPosted: Mon Sep 20, 2010 6:45 am 
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Location: Charlotte, NC
smokegetsnureyes wrote:
I am an instructor for a utility and have to teach arc flash / electrical safety training. We have not performed an arc flash analysis at many of our facilities as of yet. I have been using the table methods to inform the plant personnel as to what level of clothing to wear and at what distances to set up their boundaries. A study was recently completed at one of our facilities and several of the low voltage switchgears (<600V) ended up with 85cal/cm ratings.


Sounds like you may have not been using the tables correctly, does your system meet the limits of the tables in the notes? With 85cal/cm2 it does not sound like it.

smokegetsnureyes wrote:
The company that performed the analysis also provided the labels for each of our switchgears and MCC's. The labels on several of the swtichgears indicate Required PPE: Dangerous as well as No FR Category Found. I have noticed that their are 100cal/cm suits in the FR catalogs that I have looked through. Is it unacceptable to work on this equipment (e.g. racking breakers in or out) unless it is deenergized?


>40cal/cm2 the issue becomes the pressure from the arc, which has been found to be un-surviable at those levels, regardless of PPE being worn. However, this is from a note in the handbook and there is not a hard "rule" about this.
smokegetsnureyes wrote:
Can a 100cal/cm suit be utilized or is it unacceptable to work on this equipment at all unless it is deenegized. All electrical equipment is considered energized, until proven otherwise. How do I test it, while performing the task of testing would put me in harm's way. The flash hazard boundary for this same piece of apparatus is 242 inches. I don't have a long enough pole to reach it for testing since I have to have on proper PPE to be within the boundary. Does anyone know what to do in this case?


The verification that systems like this are de-energized is one of those issues where you are in a tough situation. You can re-calulate youe Ei at a distance other than what was assumed based on the length of your hotsticks.

Operating and racking of breakers can be done outside that 242" boundary with remote racking and switching devices, but sounds like you need to look at mitigation solutions.


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PostPosted: Mon Sep 20, 2010 6:56 am 
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Location: Wisconsin
Above 40cal/cm², the danger is primarily from the shock wave of the blast, for which there is no PPE.

The 242" distance you quote is for dropping all the way down to 1.2cal/cm². The incident energy drops off by the inverse of the square of the distance: doubling the working distance, in the calculation, lowers the incident energy by a factor of 4. To be able to use a 40cal suite based on your 85cal/cm², you only need to be at 1.5x the original distance (40/85=.47, 1/.47=2.13, SQRT2.13=1.45). Because you mentioned 600V switchgear, the normal working distance would be 24".


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PostPosted: Mon Sep 20, 2010 9:11 am 
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Thanks

JBD and Zog, We have been using the tables, but were unaware of the actual arc flash level that was required until after the analysis. The facility that has performed the analysis is looking at various remote racking devices now. I am trying to spread the word to others in our organization and I wanted to make sure that I have my facts straight when I go to management that the equipment is unsafe to work on unless deenergized. I am unsure why they are selling a 100cal/cm suit if it is not allowable to work above 40. I am sure that these questions will come up when I present my case. I appreciate the input and look forward to some more. Thanks


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PostPosted: Mon Sep 20, 2010 5:08 pm 
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smokegetsnureyes wrote:
I am unsure why they are selling a 100cal/cm suit if it is not allowable to work above 40.


You will need that 100 cal/cm^2 suit in order to verify the equipment is deenergized. As Zog said, there is no hard rule stating 40 is the limit. Some find it acceptable to test for potential on a circuit that has been isolated when wearing FR rated for the thermal exposure.

Another thing to keep in mind, is that there is no direct correlation between incident energy and blast pressure. If your IE is high because clearing time is long, the pressure will be much less than the same IE from a high current short exposure.


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PostPosted: Tue Sep 21, 2010 5:34 am 
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We employ a 100cal option at our locations as a solution prior to mitigation or for locations or tasks where mitigation is not possible other than de-energizing. As noted above the issue of verification, after the equipment is de-energized, is still needed. Our calculations have indicated the above 40cal results are primarily a function of long clearing time. In addition, to exceed the typical 40cal PPE rating would also require the worker to remain fixed at the standard working distances (18” -36”) for the long duration.


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PostPosted: Wed Sep 29, 2010 10:22 am 
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Thank you all


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