Many in the electrical industry use "daily wear" which includes arc rated clothing often of 4, 8 or 12 calories/cm^2.

Here is this week's question:

Do you feel it is appropriate to wear arc rated clothing when working around arc flash hazards less than 1.2 cal/cm^2?

• Yes
• No
• It Depends

As always, your comments are always welcome and encouraged!

My answer was yes because for the most part, many places it is a uniform that is rated appropriately so most people are already in some form of AR clothing.

Two answers. First, I specified it when I worked where flame retardant clothing was already a minimum standard (molten metal present). Second, the 1.2 cal/cm^2 threshold is based on Alicia Stoll's work on human skin. Has actual testing been done on various forms of nonmelting clothing similar to that done for rubber gloves to verify the ATPV rating of the material? I would hate to find out that a cotton shirt ignites at less than 1.2 cal.

Of course it is appropriate to wear protection that exceeds the hazard. Not sure how one could answer any other way. It would only be inappropriate if the hazard exceeded the protection.

I believe that arc rated clothing should be worn when working around arc flash hazards less then 1.2 cal/cm2 due to two reasons:

1. You risk getting 2nd degree burn or worse with a fraction of 1.2cal/cm2 only when delivered to bare skin in less than one (1) second. Check http://arcflashforum.brainfiller.com/threads/2221/ for more information.

2. Natural fiber clothing, as recommended by NFPA 70E for hazard risk category one (HRC 1), will not necessarily withstand 1.2cal/cm2 and may burn through or set on fire when charged with 1.2 cal/cm2 or less in short enough time interval.

My problem with evaluating HRC and selecting PPE using NFPA 70E methodology is that the methodology is based only on the amount energy delivered without regard to how fast the energy was delivered. The problem was concisely summarized by Allice Stole, the pioneer in arc flash research and testings, in [1]:



1. A.Stoll, "Heat Transfer in Biotechnology", Advances in Heat Transfer, v.4. Academic Press. 1967

I have always liked the idea of daily wear - always wearing PPE even below 1.2 cal/cm2. The only exception I could think of is if you are in hot environment and it is not necessary.

I concur and think the question should be: Should personnel working on electrical equipment wear arc-rated clothing all the time? We've been implementing an ARC Flash/Electrical Safety program for the last 3 years and one of the very first questions was whether or not E&I techs were going to be required to wear Arc rated clothing all the time or could they put it on only when working on energized circuits? 99% of the electricians wanted to be able to put it on when working on energized circuits only as they said it was too hot in the summer. The problem with that is: one does not always understand/identify an energized circuit correctly. We've had two Arc flash incidents in the last two years and in both instances the electrician didn't "think" they were working on an energized circuit. In the latest incident the electrician was working on a 120 volt circuit in a mini power zone and he had locked out the main breaker removing the power to all the 120 volt circuits. After terminating the wires to the breaker he was working on he noticed a loose lock-nut on a fitting coming into the panel. Since he couldn't get couldn't get his pump pliers in the tight spot he did what every good electrician does: he took out his "beater" screwdiver and used his pump pliers as a hammer to knock the lock-nut tight. Of course the screwdriver slipped and hit/penetrated the 480VAC feed to the mini power zone which he didn't realize was routed right behind the lock-nut he was banging on. The result was a small arc flash and undamaged, though blackened hand. When asked why he didn't have his gloves on he said he had de-energized the circuit he was working on so he didn't think the Arc Flash PPE applied (this panel has an 8.3 cal/cm2 incident energy). He also stated that he assumed the feed was routed up higher in the top of the panel and never verified where it was. We have re-iterated to all of our E&I personnel that unless a panel is completely de-energized and verified Arc Falsh PPE per the arc flash analysis will be worn. A bit wordy and not directly on the subject of whether or not one should wear arc rated clothing when working around hazards at less than 1.2 cal/cm2 but, yes I think E&I personnel should wear arc-flash PPE all the time. Our techs daily "uniform" consists of: 8.6 cal shirt and 20.7 cal pants, leather gloves.

I voted yes because a category 0 can become much worse if the protective device upstream fails completely or opens sluggishly.

It depends.

Too often I hear the comment 'our daily wear is Cat 2, because our techs never know when they will be called upon'. Upon further examination, the arc rating of the cloth fabric is where PPE stops. Turns out the techs rarely carry all the rest of their PPE with them. If they need to 'go back to the shop' to get their face, head, and neck protection, then they can put on a jumpsuit at that time.

That's what you should do if your policy is to get to 8 cal/cm2 using a jumpsuit. If they use shirt and pants, it is probably a good idea to wear the shirt and pants all the time (and definitely a good idea to wear the pants and a cotton T-shirt as a bare minimum in that case.)

Where I work now electricians are allowed to wear short sleeve shirts and just have to put an arc-rated (8 cal) long sleeve shirt on over it at the same time they put on their balaclava, face shield, and arc-rated gloves.

Where I used to work, workers were required to wear long sleeves in many parts of the mill anyway, so all electrical workers were required to wear 8 cal/cm2 long sleeves all of the time on the job.

Well, that depends - For the most part it does not hurt to have higher rated clothing than what is required, but
wouldn't you consider wearing a suit rated for an HRC 4 a bit of an overkill when there is only a danger of 4 cal/cm^2?

I realize that is a rather extreme example. I don't think that -just- because the clothing is rated at a higher level of protection it is automatically better for a given situation. I think it depends on how restrictive the clothing is. If the higher protection does not cause a greater hazard, then it is appropriate.

But, I do agree it is entirely inappropriate if the hazard exceeds the protection

Yes that would be overkill. That's why I refered to hazard rather than incident energy. When the PPE itself becomes part of the hazzard, that must be factored in.

I would strongly argue AGAINST wearing PPE that is rated higher than the minimum necessary for the task at hand for several reasons:

1. PPE that is damaged or soiled with grease has a lower rating. Better to keep the good stuff for when it is needed.
2. Arc rated PPE frequently increases risks heat related risks.
3. The face shields reduce visibility which in turn increases the likelihood of mistakes being made.
4. Gloves reduce dexterity which increases the chances of dropping parts or tools (and causing the thing that was intended to prevent).

However, these statements should be taken with the recognition that there are certain "break points" in the clothing systems. 1.2 cal/cm^2 is the first point where arc rated clothing is required. 4 cal/cm^2 is the point where face shields and balaclavas are required. Somewhere around 8-12 cal/cm^2 is the point where leather gloves give way to rubber or arc rated, and where either multilayer flash suits or layered PPE (assuming testing is done) become required. There is not a large difference in terms of additional safety risks when moving from a 25 to 40 or even 60 cal/cm^2 multilayer flash suit but there are major differences in moving from 1.2 to 4 to 8-12 cal/cm^2.

I understand the arguments that "PPE can fail". Indeed that is the primary reason to follow ALARP in the first place and not make PPE the primary solution. IEEE 1584 has a statistical analysis that shows that at the threshold (ASTM ATPV rating is exactly equal to calculated incident energy) that there is a 5% chance of failure which is a combination of the reliability of the ATPV calculation (assume that the raw pass/fail data is gaussian distributed when it clearly is not) and the inherent accuracy limits of the current IEEE 1584 calculation method. However, I cannot personally identify a single case where IEEE 1584 was used to determine incident energy, ASTM 1959 was used to determine properly rated PPE, PPE was worn correctly, and yet despite going "by the book", a second degree burn occurred. This lends credence to the idea that if everything is done properly, failures are largely theoretical.

To the arguments that equipment, especially circuit breakers, can and do fail: yes, agreed. For this reason some folks around here argued that we should just wear the maximum PPE available and that would prevent an injury due to an arc flash even if breakers fail. However, there is a huge fallacy with this argument. The assumption is that the increase in incident energy does not exceed the maximum PPE available (40 cal/cm^2 in our case).

I actually looked at this statistically. After doing a data dump of all 1100 buses, I found that statistically, fully 25% of the buses exceed 40 cal/cm^2 in the first place. These we can safely ignore because we know about them. Similarly although fuses can also fail, the likelihood of failure to trip is very small and thus we can ignore all fuses. For the remaining buses if a breaker fails, the incident energy will increase. Now a 2nd level breaker MIGHT trip but this argument gets overcomplicated very quickly and for the sake of simplicity, I ignored it. Also there are arguments that the "2 second assumption" may not be true but again, I'm trying to just get to a practical solution here. So I did a simple calculation in a spreadsheet that recalculated the incident energy for all buses assuming that the "2 second assumption" is valid and that 2nd level (backup) breakers also fail: new incident energy = old incident energy * (2 seconds) / (original arcing time in seconds).

The result is that we went from 25% of buses exceeding 40 cal/cm^2 to around 60% of buses. That is, if we subscribe to the premise that breakers can fail at ANY time for reasons such as not doing proper maintenance, and we tell our people to just wear a 40 cal/cm^2 suit to mitigate the risk, fully 50% of the time, they will be severely burned or killed due to an arc flash without any warning whatsoever because 35% of the risk will be due to equipment that was not labelled as exceeding 40 cal/cm^2. Coupled with the alarming statistics about the reliability of breakers if maintenance is not performed, and the idea of "overprotecting" seems to be a crap shoot at best.

Now granted this is all theoretical, and the fact that I did the statistics on a "per bus" basis knowing full well that many buses are internally and that the exposure rates are significantly different means that this is a pure thought experiment in the end, but I doubt that going the extra step would change the conclusion significantly. Properly maintained, arcing faults on breakers are at a rate of about 1 in 100,000 to 1 in a million PER YEAR. Current BLS statistics as reported by ESFI is that arc flash fatalities occur at a rate of about 1 in 100,000 per year, OVERALL, with no consideration to who is wearing PPE and who isn't, and what the PPE is rated for.

My conclusion from this is that if you are not going to PM the breakers, don't even worry about PPE for arc flash either because odds are about dead even that it won't do you any good. If you are doing proper maintenance on the equipment, then don't bother "overprotecting" out of some perceived value because first off, there is no value there (better than even odds that the victim is dead anyway), and second there are far more negatives from hazards other than arc flash than there are positives.

So the question is about wearing low rated FR clothing for IEs less than 1.2 cal/cm^2. Presumably it is safe to wear untested natural fibers or bare skin for this type of work. Safe in this case means being at the threshold for receiving a second degree burn. If given a choice, I'd opt for no burn, second degree or otherwise. But also remember no one tested your particular garment, so there's still a chance it will continue to burn after the arc extinguishes, especially if soiled as Paul points out above. The (clean) low rated FR will not continue to burn when the arc extinguishes. It is entirely appropriate to use low rated FR as daily wear for less than 1.2 cal/cm^2 exposures.

No, safe meaning that with 95% confidence (5% chance that the calculation fails), and assuming that the overcurrent protective device works (if time is dependent on one), that the burn is survivable. The second degree burn threshold is somewhat arbitrarily set at 50% at the face/chest area which is what produces the working distance assumptions. Burns at the hands/arms will clearly be much worse. Essentially what the standard as it is today implies is that should an arc flash occur, 95% of the time it will be survivable. There is no guarantee whatsoever that life altering injuries, skin grafts, etc., won't be required. Practical experience so far has suggested that this somewhat arbitrary threshold is highly conservative as the injuries so far have been minor or nonexistant.



The only practical way to get there is without PPE of any kind, arc rated or not. This means don't work energized if not required, maintain equipment properly, remote access/control, etc. PPE can and does fail for a variety of reasons. That is why the hierarchy of controls of hazards puts PPE at the bottom, not the top.



You are assuming that the garment reaches the ignition point. The threshold for ignition for cotton is 600 degrees. For skin to reach a second degree burn at 1 second, it's 140 degrees. Leather is nothing more than skin from an animal, usually one that is far more abrasion resistant than human skin. Without actual test data, I don't buy the idea that untested natural fibers will necessarily ignite before the 2nd degree burn threshold. I will easily concede that burn rates are significantly different even for the same material such as cotton but this is more dependent on the openness of the weave, how frayed or "flocked" the material is, and so forth.