Arc Flash Boundary Information

Aug 6, 2018
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#1
ON some of the labels I have reviewed, the arch flash boundary was consistently listed as 18" regardless of the Incidence energy level which was less than 1.2 cal/Cm2.

Why wouldn't the actual distance calculated be used rather than a "default" 18"? I understand that the 18" distance is the working distance used for calculations but the hands and arms are going to be closer.
 

Hugh Hoagland

Moderator
Staff member
Dec 30, 2016
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Louisville, KY
www.arcwear.com
#2
Re: Arc flash Boundary information

The AFB is often listed as a default distance or as the minimum in the table. This however sounds like "the working distance" and NOT the AFB. Almost all LV work has a working distance of 18 inches per IEEE 1584 or from the tables.

The AFB of a 1.2 cal exposure would be by default 18 inches since the AFB is that by definition.

Post a photo (if it doesn't compromise anyone) to let us see what it says.
 
#3
I understand your point about the hands being closer, however, 70E - 2018 definition of the working distance is the "distance to the face and body" and hands are intentionally excluded. Firstly, at those energy levels, the hands will always be more protected if the worker is using electrically rated gloves (ASTM D120) with Leather overprotectors. Secondly, (and this isn't always the case!) the tool or test instrument adds distance between the hands and the live part.

Now, bear in mind that not all studies are specified the same. My last project requested that we label directly from the software. So the arc flash boundary was 0.01" in certain cases. What practical value does that add? So instead of guessing several positions that a workers body and face would be positioned, we make the arc flash boundary equal to the working distances when the incident energy (IE) is less than 1.2cal/cm2 (As Hugh mentioned - these are not the same). The study before my last required that the we use standardized (generic) labels for less than 1.2cal/cm2 at 18" working distance wit the AFB = 18". Call us if you are interested in seeing the both types of labels, make a decision on which suits your plant best, then go back to your engineer/consultant and request that they update the label if this adds value. There are ALWAYS pros/cons to these types of decisions. We recommend that it be kept simple and generic for all workers and contractors and support the generic label below 1.2cal/cm2.
 
#5
Greetings Zarheer and Hugh,

As you guys are well aware, the 2018 NFPA 70E contain subscript c in Table 130.5(G), subscript d in Table 130.7(C)(15)(c) and an Informational note in article 130.7(C) (10)(d)(2) which essentially states rubber insulating gloves with leather protectors provide adequate arc flash protection of the hands even though their primary function is shock protection.

A question always seems to come up from time to time asking "But how much arc flash protection do the rubber insulating gloves with leather protectors actually provide for my hands?"

I teach our guys to wear AR clothing and PPE that have an APTV that's greater than the incident energy of the equipment but when it comes to the hands that's a little bit more challenging, especially in context of article 130.5(G) where any part of the body that's closer than the working distance will require additional PPE which obviously cover the hands. We allow our technicians to wear AR gloves under the same requirements as other AR PPE (AR greater than the IE) but only if their hands will not cross the Restricted Approach Boundary of exposed energized parts. This really doesn't pose a problem when racking breakers in low and medium voltage switchgear since there are no exposed parts for the type of gear we have.

However where the challenges lies is if the hands will cross into the RAB, then they have to wear rubber insulating 'VR' gloves with leather protectors to protect them from accidental electric shock. This mainly occurs with our 480V motor control centers, panel boards similar low voltage equipment where there are lots of exposed energized parts when you open or remove a panel or door to perform tasks like taking voltage reads or to remove the bucket from the cubicle. In such cases they're exposed to both hazards the arc flash and electric shock. We use the red colored Class 0 gloves made by Salisbury with standard leather protectors with this type of exposure.

One of your e-Hazard trainers was telling me Hugh has performed a lot of arc flash testing of the various brands and classes of rubber insulating gloves with leather protectors and they have performed quite impressively for providing arc flash protection of the hands.

This leads me to my question, while I understand the testing results varied quite a bit between the same classes of gloves based on things like the color and make up of the rubber material, the manufacturer and other factors, what prompted the 70E committee to add this information but without any supportive documentation in the standard (at least that I know of)?

I'm thinking you guys can shed some inside light on the topic and it was great seeing you guys at the ESW in Reno.

George Cole
Palo Verde Nuclear Generating Station
Phoenix, AZ