bvadams wrote:
Paul, NFPA 130.7(C)(1) says that you need to wear protective clothing and other personal protective equipment when working within the arc flash boundary. Is there a requirement to wear nonmeltable clothing when you are outside the arc flash boundary? Or, are you talking about best practices rather than 70E requirements when you say that nonmeltable clothing is still required?
70E says that, but there are two caveats to this.
First, the arc flash hazard boundary is not fixed. It can easily change. For instance if I adjust the overcurrent protection device, I can easily move the arc flash boundary. This is commonly done with "maintenance switches" or equivalent breaker settings.
Second, read the definition of an arc flash hazard carefully. With shock hazards, there are no shock hazards if the doors are closed and latched. Similarly you may not have an arc flash hazard (and thus no boundary) if the doors are closed and latched because the arc flash has been provably diminished in the area in front of the equipment.
As to nonmeltable clothing, this is one area that is extremely grey. Clearly 70E does not require an arc flash PPE, even nonmeltable clothing, outside of the arc flash hazard boundary. Clearly though there are many cases within 70E that default back to nonmeltable clothing as a minimum standard. Given that the arc flash hazard at the boundary is 1.2 cal/cm^2 and since we have not done testing or proven what the cutoff for nonmeltable clothing is (is it 0.5 cal? 0.1 cal? 0.01 cal?), best practice would dictate nonmeltable clothing in all cases except when the likelihood of an arc flash hazard is so low that making it a requirement would be silly. As of the 2012 edition though at least, we are still focussed entirely on quantifying the hazard and there are only one or two sentences which allude to looking at likelihood, one of which is the definition of arc flash hazard itself.