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 Post subject: Hazard Risk Category Help
PostPosted: Wed Nov 11, 2009 7:25 am 
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Currently, i do the arc flash calculation based on calculation method in IEEE1584-2004. However, the calculated incident energy is too high beyond 40cal/cm2. How can i define the PPE for that device?NFPA 70E table only proposed less than 40cal/cm2. Please throw me a light.

Thank you. :confused:


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PostPosted: Wed Nov 11, 2009 7:53 pm 
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You could label the PPE by specifying the calculated IE, which would require clothing with a rating in excess of the IE. A more common approach would be to label the equipment "Dangerous! Do not operate energized" or something to that effect.

It is possible to get PPE rated higher than 40 cal/cm┬▓, but with this high an IE, the blast hazard is probably high and high IE PPE won't be protect against the blast.


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PostPosted: Thu Nov 12, 2009 11:38 am 
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You specify adequate for the energy calculated.

But, as jghrist suggested, the industry consensus is that over 40 cal/cm2, the blast hazard is sufficient to significantly injure the person, regardless of the flash hazard PPE worn, most will label the equipment as Dangerous, and require that the equipment be deenergized before any work is performed.


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PostPosted: Thu Nov 12, 2009 1:08 pm 
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The guy would need to know how to verify de-enerigized. I would recommend a non-contact voltage detector on a pole maybe according to the situation.


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PostPosted: Thu Nov 12, 2009 1:50 pm 
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How long is the clearing time? Often incident energy becomes quite large because of a low fault current causing the upstream protective device to take a long time to trip. The result is low current X long clearing time = high incident energy which may not be explosive.

What I am still holding out for is a cut off of energy per time. That would help define how explosive an event is. In your case did you try cutting the time of at 2 seconds per IEEE 1584? Did you try to see what happens if you lower the protective device setting? (assuming it is adjustable).

Just a few ideas and thoughts for you.

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PostPosted: Thu Nov 12, 2009 1:55 pm 
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brainfiller wrote:
How long is the clearing time? Often incident energy becomes quite large because of a low fault current causing the upstream protective device to take a long time to trip. The result is low current X long clearing time = high incident energy which may not be explosive.

What I am still holding out for is a cut off of energy per time. That would help define how explosive an event is. In your case did you try cutting the time of at 2 seconds per IEEE 1584? Did you try to see what happens if you lower the protective device setting? (assuming it is adjustable).

Just a few ideas and thoughts for you.


I do believe, that is a good catch.


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