Hello,
My site has completed an updated power system study and are affixing new arc flash labels. The engineering company provided us labels that say either WARNING or DANGER at the top depending if it is was 40 cal/cm2 or less or above 40. It then identifies the incident energy, working distance, (shock hazard) voltage, PPE level, and upstream feeder ID. This label is consistent with the formatting in ANSI Z525.4

I am confused if this is the only label we need on the cover of a 480V 400A load center to meet codes or standards. For example, there is a field applied sticker that says "DANGER HIGH ENERGY" but the arc flash label says WARNING as it is under 40 cal/cm2. There is another 480V load center that has a sticker that says "WARNING - ELECTRICAL HAZARD" and again, we are separately affixing the arc flash warning label.

Does just affixing the arc flash hazard label meeting the requirements for equipment labeling under NFPA 70E satisfying the labeling requirements for the panel such that site does have electrically qualified (& trained) - electrical workers on-site at all times?

Can we remove the other stickers and just have the arc flash label?

If the panel is 208/120V fed by a 15kVA transformer and no arc flash analysis was performed, what electrical label is required?

If we did not have a qualified electrical worker on-site at all-times, what additional labeling is required? I believe that's where the NEC says you need "DANGER" signs over 600V.

Thanks!

By your own statements it is not ANSI Z535.4 compliant. There is nothing magical about >=40 cal/cm2. According to ANSI Z535.4, it must use the signal word WARNING. DANGER is reserved for equipment where you are in imminent danger by accessing it. That is definitely not the case for any electrical equipment especially considering the low incidence rate for shock and arc flash. This is for cases like opening a door which directly releases poisonous gas for instance. I'm not exactly sure how and why this happened but one of the software vendors for the arc flash software started defaulting to "DANGER" stickers for >=40 cal/cm2 and "WARNING" stickers for everything else and pretty soon all the other software vendors copied this. It's dead wrong, it's not compliant, and it takes a bit of effort to go into the software and fix it so that it is ANSI Z535.4 compliant. I've managed to do it with some effort in SKM. Not sure what the level of difficulty is in the others.

This all stems from a single line in 70E that stated that greater caution is required for >=40 cal/cm2 but did not actually specify any additional requirements. It is believed (lost to history here) that the 40 cal/cm2 "barrier" came out back in the 1990's because the available PPE at the time was technologically limited to <=40 cal/cm2. There are arc flash suits that are rated for 100 cal/cm2 and higher and they have been available for almost 20 years. As of the 2018 edition of 70E this ridiculous "requirement" that was not a requirement has been completely eradicated. Now it is truly only a screw up with the software vendors and even less valid than ever.

Furthermore, it's clearly not NFPA 70E compliant either. 70E requires EITHER a "PPE Level" or an incident energy number, but not both. At this point this is something of a historical note but PPE levels come from a table-based method which incident energy comes from an engineered approach. To be in 70E compliance you can use either one but not both. You can of course create your own "PPE level" system but I don't recommend it for two reasons. First off if as you stated there are no qualified personnel in your plant and you create your own system that has a level of say 10 cal/cm2, I might come into your plant as a contractor and I have 12 cal/cm2 PPE so I'm compliant but the local utility that comes into your plant and has say 6.5 cal/cm2 knit linemens shirts isn't compliant so it bumps them up into some crazy high arc flash PPE. Plus if the PPE standards change, you don't have to go all over your plant changing all the labels again just because the PPE changed. Think it won't happen? What is known as PPE level 2 changed with nearly every new edition of 70E for several years straight and the headgear part keeps changing on nearly every Code cycle (every 3 years) as well.



"DANGER HIGH ENERGY" is made up. "WARNING -- ELECTRICAL HAZARD" is, too. Can you tell me what the hazard is and what specific action you would take to avoid it? If not, it's not ANSI Z535.4 compliant. ANSI Z535.4 requires you to identify what the hazard is, and instructions on how to avoid it. It should say something like "ELECTRICAL SHOCK" or "ELECTRICAL BURN" followed by an action to take such as "KEEP OUT" or "DO NOT OPEN". The existing signs would be akin to having a door on a fan that read "DANGER -- FAN"...see? It's meaningless a sign. It might as well be a sign on a beach that reads "DANGER -- SUN". On a panelboard of course this should not be on the outside. It should be either on the outer panel or the inner panel which exposes the conductors, not the access door that covers the breaker handles since obviously there is no hazard there and it is designed for unqualified workers to access for instance to lock out equipment.

There are a bunch of scattered label standards all over the NEC and this isn't one of them. What NEC does require is a label on covers that expose energized conductors to inadvertent contact. In the past everything electrical used to be "wide open" with literally just the outer door or a fence protecting unqualified personnel. Today even utility substations are no longer typically the outdoor, "overhead" type construction and are tending more towards closed sheet metal panels at least for distribution substations. So you can definitely see why a sign would be required at the fence or the locked door. Today NEC requires a "DANGER HIGH VOLTAGE ..." sign where the fence/door/panel is at which prevents access to exposed (to inadvertent contact) energized conductors if it is over 600 V, and it requires some kind of mechanism to prevent access that requires some kind of tool (key, screwdriver, wrench, etc.) to keep "the public" out. Below 600 V the tool access requirement disappears and the sign is not specific but a warning sign is still required. Obviously the "DANGER HIGH VOLTAGE" sign is inherently an ANSI Z535.4 violation since the signal word would be WARNING and not DANGER but they grandfather it by stating that specific signage requirements in other standards supercede ANSI Z535.4.



There are quite literally dozens of signage requirements in NEC and the warning sign requirement got exponentially worse in the last few years. ANSI Z535.4 does have a requirement of no more than 3 warning signs per task and at this point I'm pretty sure that in some circumstances NEC violates this one, too. It really has gotten that bad and I'd hesitate to try to capture everything. I was working on a signage standard for a former employer a couple years ago and with the then 2014 update it was getting almost impossible to keep track of it all.



Neither of the existing labels are NEC compliant nor 70E compliant nor ANSI Z535.4 compliant so obviously they can all be removed. There is a requirement to have a sign for exposed conductors as I stated earlier. Below 600 V you can use whatever you feel appropriate (NEC does not spell it out) and so if your arc flash sticker includes shock information that would do it, as long as you fix all the ones that say DANGER instead of WARNING if your goal is to be ANSI Z535.4 compliant. If your goal is to be software company made up rule compliant, then just ignore this and put whatever you want on the panel. I don't think very many people have actually read ANSI Z535.4 because a lot of signage out there is totally noncompliant. So...sticking with the signage you mentioned yes you can simplify it down to one label. That doesn't mean that there aren't other label requirements but in terms of shock and arc flash you should be covered.



IEEE 1584 states that an arc flash hazard analysis need not be done because the incident energy is below the point where PPE would be necessary. There is obviously still a shock hazard if the panels are removed because it's above 50 VAC. The problem is that there are likely to be lots of things all over your plant that aren't labeled so it's hard to tell if a panel was simply not intentionally labeled or if it was looked at but determined not to be a hazard. So in this case many plants use some kind of generic label like "NOTICE -- NO SIGNIFICANT ARC FLASH HAZARD" or "NOTICE -- <1.2 cal/cm2 arc flash" and then a voltage label with appropriate information. That way it is labeled but not with a hazard label since there isn't one and it won't get confused with stuff that has a hazard but doesn't have a label. Motor peckerheads for instance aren't typically labeled but there is usually a hazard present. But they aren't usually opened except with the power off so no label is needed.



NEC doesn't distinguish on the danger signs based on whether or not qualified workers are present. It only gives more lenience for certain installations like how certain types of grounding are handled or removing the requirement to have a disconnect switch within sight of a motor.

Also be aware that 70E as well as OSHA do NOT remove all training requirements if there are no qualified workers present. It's simply that the type of training changes. Qualified workers must be trained to recognize hazards and the work methods used to avoid them while being exposed to them. Unqualified worker training still involves recognition of hazards although it's a lot more simplified (are there signs? Is there a damaged electrical cable?) and how to avoid them altogether (stay 3'6" or 10 feet away depending on what it is, call an electrician if you see signs of defective electrical equipment such as downed lines or burned spots or a breaker that has tripped).

Great feedback! Thank you so much for taking the time to work through my questions.

PaulEngr, great reply. Thank you for this. I can fill in some of the gaps...

The 70E committee believed that blast can occur above 40cal/cm2. It was one of those claims that could not be proven or refuted so it made its way into the standard. Some equipment manufacturers supported this as it help sell internal arc classified switchgear.

We have since undertaken research in this area and we have demonstrated that blast is more a function of short circuit current and less so influenced by incident arc flash energy. In fact, we have blown off doors at 6cal/cm2; 16kA at LV. With published papers in hand, we attended the NFPA 70E meetings and presented this data. We are glad that the "limit" of 40cal/cm2 has since been removed - now we need to get engineers performing the modeling to understand and create awareness of where/when blast is a hazard.

I run several arc flash studies across the country and or some of our clients are open minded and support the label change. I have labeled above 65cal/cm2 all the way up yo 90cal/cm2 (mainly because of low fault currents and longer clearing times). Above those values, I find that the short circuit currents get to dangerous level creating a possibility of blast. i will then use a danger label.

I find our training classes a good platform to discuss these concepts. Some listen, others are just too stuck in old ways to change. At one of my classes, an operator approached me offline and mentioned that they operate >40cal/cm2 but don't tell the safety department. The plant will not label above 40cal/cm2. How unsafe in the name of safety!!! Hopefully now you may understand why I DON'T support the 40cal/cm2 limit?

Kind regards,
Zarheer Jooma Pr Eng SMIEEE, SMSAIEE

E-Hazard has published a couple papers on arc flash and there are some misconceptions here. I'm sure you've measured pressures inside a sealed panel up to around 10 PSI. That's about the highest pressures I've found spanning all the reports out there on arc flash. But what pressure did you measure outside the panel? And what pressure is lethal? And more importantly, how did you arrive at a relationship between arc blast pressure and current?

Answer 1: using purely theoretical math Lee came up with maybe 2 PSI maximum in open air and even then, it's questionable. Nobody has measured anything above 1 PSI except a microphone experiment that has been discredited the to the method of measurement, despite years of attempts. Remember...it's outside the panel that matters. Inside actually doesn't matter because pressure would be equal in all directions.
2. 1 PSI blows ear drums. 20-100 is lethal, depending on the source and whether you are looking at a threshold chance or say a 50% chance.
3. There is no relationship between arc blast and current. The pressure rise is the to heated air. So the rate of rise will be proportional to arc power which is roughly the normalized incident energy which is strongly dependent on current and weakly on voltage and arc gap by simple inspection of arc flash equations. If we stop the process at a definite time interval while varying current, we will see a pressure variation. But for a given enclosure exposure occurs when the enclosure ruotures. If the venting process is slow further rise could occur just like an undersized pressure relief valve but electrical enclosures are not that strong. Thus the rupture pressure is a constant for a given enclosure and surveying the available literature shows maximums around 8-10 PSI. We don't really care about pressure rise because if the box does not rupture then there is no arc blast.
Outside the enclosure the pressure wave raoidly dissipates. Standard chemical engineering literature such as Lees covers this condition well. Suffjce to say oressure falls off with the cube of dustance since its volumetric expansion. Thus the arc blast for practical purposes (what we must protect against) is actually a function of box construction, and falls off within inches of the box theoretically but as mentioned previously we haven't yet measured it in experiments above 1 PSI.

Further, there is no concussion wave trauma in the medical reports on arc flash that I've seen. Perhaps you can point me to An OSHA report on it?

I have seen reports of people "blown back". But given that the timing on arc blast tests shows peak pressure 1 or 2 cycles in, we should see the bodies fly through the air in 3 frames or less single stepping through. Actual jerking and similar motion is around 250+ milliseconds or roughly 20 cycles later, WAY past the arc blast. This appears to be nothing more than fight/flight reflexes.

I'll support the notion that arc blast can rupture ear drums but unless you can produce evidence of a pressure rise (remember...equalized pressure doesn't count...ask any diver) outside an enclosure, arc blast by itself is not a hazard.