Given the video presented here:
http://www.arcflashforum.com/showthread.php?t=216
I would like to see the NFPA/IEEE study group perform some testing on long time arcing faults.
The current 1584 assumes time to be a linear component of the arc fault hazard. But looking at this video, the fault appears to last for nearly 4 seconds before extinguishing.
In the past, I have been in favor of the 2 second cut-off, but after seeing this video I may question it. My assumptions in favor of the 2 sec cut-off were that a number of things could happen:
1) The victim would be blown out of the area.
2) The material needed to continue the arc would vaporize and be blown out in this time.
3) If the material didn’t vaporize, the magnetic and pressure forces would be enough to separate the materials to such an extent that the arcing would extinguish.
Now, in the video, the victim does appear to have been blown clear of the cubicle, although it is hard to see because he is behind the door. But the arcing does continue for nearly 4 seconds.
However, even though the arcing continues, it seems to come and go in pulses. This would seem to imply, from strictly a measurement standpoint at a distance from the arc source, that the energy measured would is not instantaneous (or nearly so), and so may not result in the extreme calorie measurements that you would get from an application of the formulas, where time is a linear component.
So, what I am now wondering is this:
Is there a time value where the output of the event essentially levels off due to one or more of the things listed above occurring? If so, what is the maximum time that should be used? Is this value voltage dependent, as I suspect?