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 Post subject: Blasts with covers on?
PostPosted: Wed May 04, 2011 5:46 am 
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Is NFPA or IEEE doing any experimentation of blasts with covers on? Does anyone know of any videos that show blasts with covers on.

I'm curious to see at what IE level the doors for panelboards, MCC, FSDs, etc will fail.


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PostPosted: Wed May 04, 2011 1:07 pm 
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I would expect door failure to be more related to blast energy than incident energy. A long duration fault with low current may have the same incident energy as a short duration fault with high current, but will have less blast energy.

I would also expect that there would be so much variation in the ability of doors to withstand arc blasts that sample testing would be of little general use.


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PostPosted: Thu May 05, 2011 5:08 am 
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I wouldn't say that. Cosntruction of most electrical equipment, within its category, i.e. panelboards, FSDs, MCCs, etc is quite similar. I thinkt he info would be very representative. The statement regarding IE being a poor predictor of pressure is valid, but IE value even being a predictor of heat take in a lot of assumptions anyway. I'm looking for evidence that a 8 cal or less blast blow off covers typically found.


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PostPosted: Thu May 05, 2011 9:14 am 
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You can check WESTEX (http://www.westex.com/), at one time they had quite a few videos of arc flash testing on typical LV equipment. I've been involved in quite a few post arc flash investigations for both LV and MV equipment. In many cases (but not all) the covers or doors stayed in place and provided a lot of shielding from the actual arc energy…the gas and energy vented around the gaps, vents, cuts, etc. It’s too bad there has not been more testing of “real world” equipment, in my opinion by the manufactures, to help answer these questions.


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PostPosted: Thu May 12, 2011 4:38 am 
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Blast w/ Covers On

I ran across some pictures in power point presentation of an arc flash event that occurred with covers on when an electrical engineer closed a fused disconnect; I then later located the detailed accident investigation report which contained additional info and more pictures.

http://www.bnl.gov/qmo/linkable_files/pdf/ISMS%20Documents/BNLTypeBFinal081106.pdf


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PostPosted: Thu May 12, 2011 8:02 am 
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This is a good example. The report says the most of the blast was contained, the doors did not fail, although the person was still burned from what escaped around the openings.

It is not my intent to say that no one could ever be hurt from switching with covers on. I am looking for some reasonable threshold of energy where PPE needs to be considered. That threshold also needs to apply to equipment maintained in good condition.


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PostPosted: Mon May 16, 2011 6:00 am 
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haze10 wrote:
This is a good example. The report says the most of the blast was contained, the doors did not fail, although the person was still burned from what escaped around the openings.


From the report (page 41): "The front covers were deformed and would have failed eventually if the fault persisted beyond the 0.2-second clearing time (see Figure 2-5 and Figure 1-4)."
"The heavy-duty padlock and hasp likely restrained switch doors 2A and 3A from being forced open toward the C-AD electrical engineer."

I understand those excerpts as it wouldn't be unlikely to have a door which fails, exposing a worker to a direct blast.


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