Arc Flash over 40 cal/cm2
Arc Flash over 40 cal/cm2
(OP)
I have some equipment that is listed as "dangerous" and over 40 cal/cm2. My unsderstanding is that NFPA 70E-2012 does not
explicitly prohibit work at locations with energy levels above 40 cal/cm2. Is that true that although dangerous per code it's not a problem so long as i have the proper PPE? Is there PPE that can be purchased to work on equipment over 40 cal/cm2? Is
Thanks.
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explicitly prohibit work at locations with energy levels above 40 cal/cm2. Is that true that although dangerous per code it's not a problem so long as i have the proper PPE? Is there PPE that can be purchased to work on equipment over 40 cal/cm2? Is
Thanks.
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RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
The main arc blast hazard is the pressure wave that occurs - basically it is an explosion. However, since the incident energy is directly related to the duration of the arcing fault, not all 40 cal/cm2 incident energy events are the same. 40 cal/cm2 released in 0.02 seconds is an explosive event. 40 cal/cm2 released over 2 seconds much less so. But at this point, in the interest of safety and simplicity, the NFPA 70E committee elected to use 40 cal/cm2 as a cut-off, since arc-blast injuries start to become a major concern above this level.
Bottom line, wearing arc-rated clothing over 40 cal/cm2, although it is available, is not a guarantee of protection against arc-blast events. Although NFPA 70E is a consensus standard, not a legal requirement, allowing work with incident energy over 40 cal/cm2 would also present a huge liability risk if anyone was injured.
Also, NFPA 70E-2015 is due out in a couple of months - there will be some significant changes.
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
Yes, you are probably correct. It's definitely gone now, but you can still buy 100 cal/cm2 arc-rated PPE.
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
RE: Arc Flash over 40 cal/cm2
Can anyone refute this theory? I would be interested to see literature supporting either case.
RE: Arc Flash over 40 cal/cm2
I think this is basically correct. It is generally believed that arc-blast presents a safety hazard for very high-energy arcing faults. Pressure data was recorded during the testing used for developing the IEEE 1584 equations. High pressures were noted. I think based on this and whatever was known about blast pressure injuries they established 40 cal/cm2 as the upper limit, regardless of fault duration.
It may be overly conservative, but it would be somewhat difficult to come up with a different number that could be justified. Particularly from a liability standpoint.
The two second maximum fault duration is suggested in the Annex of IEEE 1584. It is simply a suggestion. It makes sense to set some maximum duration rather than just relying on the protective device TCC.