Arc Flash Boundary during Dead Check

[jcy123]

My company uses either Incident Energy Calculations or Arc Flash Category for PPE Selection.

The Incident Energy Calculation method for selecting appropriate PPE starts at 1.2 cal/cm^2. So far so good.

During a dead check of a piece of equipment, the incident energy was calculated to be 0.6 cal/cm^2 at the nominal working distance of 18" in SKM. The Arc Flash Distance is 12" per SKM.

A Fluke meter will be used with the normal leads in place. The technician will have on appropriate shock rated gloves and leather covers (Class 00, 480V). His hands, by nature of the equipment (just a box with some terminals inside) will cross the "Arc Flash Boundary" while doing the dead check.

What PPE is required to do the dead check on the equipment?

 

[hillbilly1]

My company uses either Incident Energy Calculations or Arc Flash Category for PPE Selection.

The Incident Energy Calculation method for selecting appropriate PPE starts at 1.2 cal/cm^2. So far so good.

During a dead check of a piece of equipment, the incident energy was calculated to be 0.6 cal/cm^2 at the nominal working distance of 18" in SKM. The Arc Flash Distance is 12" per SKM.

A Fluke meter will be used with the normal leads in place. The technician will have on appropriate shock rated gloves and leather covers (Class 00, 480V). His hands, by nature of the equipment (just a box with some terminals inside) will cross the "Arc Flash Boundary" while doing the dead check.

What PPE is required to do the dead check on the equipment?

The same as live. Once it’s verified dead, then the PPE can be reduced to what is used around dead equipment (safety glasses, etc.

 

[jcy123]

The same as live. Once it’s verified dead, then the PPE can be reduced to what is used around dead equipment (safety glasses, etc.

Yes I understand that.

What about within the arc flash boundary of 12 inches. We are not required PPE at the working distance of 18 inches. However part of the arm is going past the arc flash boundary.

So is one required to suit up entirely for the job since it is a dead check and requires crossing the 12 inch arc boundary, or are we not required?

Also, since it is a dead check and we'll be well within the boundary, do we do analysis closer and closer to the terminal, say 4 inches out, or do we dress for the 1.2 cal level?

 

[jim dungar]

This would be part of the risk analysis required by NFPA 70E.

I have performed this type of distance evaluation, but once you get too close the incident energy climbs pretty fast.

 

[jcy123]

This would be part of the risk analysis required by NFPA 70E.

I have performed this type of distance evaluation, but once you get too close the incident energy climbs pretty fast.

Right, in an inch by inch assessment, the energy climbs very quickly.

So realistically is there no situation wherein you can do a dead check, above 120/208/240 without PPE? I'm sure there are cases, but it seems as though when doing a physical check and not a proximity check, you'll almost always cross the boundary. We have some 0.09 cal/cm^2 equipment where the boundary is right at five or four inches where you'd be outside of the boundary with some Fluke leads. But anything higher than that, at least a finger will be in there!

I'm questioning both our posture on not providing written rules for this situation, and also what OSHA/NFPA cares about during a dead check. Are we only required to protect chest/head? That's the whole point behind the 18" rule for incident energy, correct? Otherwise, what's the point in standardizing 18"? Why not just report the arc boundary where 1.2 cal/cm^2 exists?

None of this should be considered "gotcha" questions. I'm genuinely curious as to why this situation exists and how to proceed. I'm an EE at 17 years post graduation and still find myself questioning everything!

And as it pertains to the arc boundary in my case, do I instruct our technicians (or myself really) to dress for 1.2cal/cm^2 since they'll effectively be crossing the boundary or do all analysis at the length of a Fluke lead and go with that value?

 

[jim dungar]

Yes. The industry practice is pretty much based on accepting the risk of severe injury to the extremities while saving the torso and head. 18" is a typical hand to elbow distance, so it has become the industry standard distance. We know the incident energy is roughly inversely related to the square of the distance, so having a common starting point makes it easier to make comparisons of different scenarios.
Remember arc flash PPE does not prevent injury, it only minimizes it.

I have seen many labels that list a working distance of 18" while having a 1.2 cal/cm² distance of only a few inches.

 

[hillbilly1]

The industry practice is pretty much based on sacrificing the extremities while saving the torso and head. 18" is a typical hand to elbow distance, so it has become the industry standard distance.
Remember arc flash PPE does not prevent injury, it only minimizes it.

Open casket vs closed casket.

 

[jim dungar]

Open casket vs closed casket.

That assumes arc flash events are not survivable.

 

[hillbilly1]

That assumes arc flash events are not survivable.

That assumes arc flash events THAT are not survivable. Fixed it for ya!

 

[David Castor]

We are not required PPE at the working distance of 18 inches.

It going to come down to what your goal is. If you are trying to find a reason to avoid using PPE, you can make this argument, but do you really want electricians to be finding reasons to avoid the PPE that is called out on the label? The required PPE would be minimal - the should probably already be wearing most of it. The face shield will provide valuable protection from whatever might get shot towards them if there's a fault. Consistency is really important in safety. I'd just tell them to wear what is on the label until it's proven dead, even when the risk seems pretty low, like in this case.

Also, in most cases, PPE should be worn to remove the covers to expose the live parts you are testing.