Q:    (Do you know) of any studies / documented history conducted on the effects of arc flash events and the medical impact from the pressure associated with the blast?  For example, we have a client who has a 100 cal suit available for use. While it would “protect” from the 100 cal arc flash, the impact to the body from a close proximity blast could be severe.   

   
A:    I do not want to imply that arc blast is a myth but there is a  myth traveling around that you might as well not wear arc flash gear past 40 cal because the blast will kill you.  I have heard this hundreds of times and it simply is NOT true.

There are really no full studies of arc blast pressure.  IEEE 1584 now has additional data and this should be published in 2012 or 2013 but for now the data is VERY limited.  Only one paper below has data and that data has been shown to be based on a microphone which washed out at about 1 PSI.  I know of NO deaths from pressure wave.  Many knockdowns.  All the deaths I know of are from thermal burns from clothing ignition or lung burns from breathing in the hot gasses (usually from the clothing fire or subsequent fires from burning oil [oil filled cables and transformers]).  The pressures could be big but anecdotally it isn’t very convincing that there will be lots of deaths from blast alone.  I do believe pressure waves can be an issue but it isn’t half as bad as we are currently led to believe by some salespeople. I have done about 100,000 arcs and we can knock a mannequin down but we don’t usually destroy them (I did break an arm off once by putting it across a disconnect).  We are not against equipment that eliminates the arc blast, but last month I learned of a group of workers who refused to wear 100 cal suits for a potential 100 cal event because the equipment company trained them and pushed this idea that the blast will kill you and the suit will “leave a nice corpse”.  This has NO evidence to support it and leads people to doubt the real science.  I challenge the equipment manufacturers to donate – as some have – to IEEE 1584 so real science can be done on this and help to answer a very complicated question without fear and trembling, but with knowledge and integrity.  Again, always ask what they are selling. “) “Ignorance isn’t what you don’t know,it’s what you know’; wrong, Yogi Berra.

Here are the papers I have read. There are probably more but this is a good start.

[1] R. H. Lee, “Pressures developed by arcs,”  IEEE Transactions on Industry Applications, vol.  IA-23, no. 4, pp. 760-764, July/Aug. 1987.

[2] D. Sweeting and A. D. Stokes, “Energy transfers within arcing faults in electrical systems,” Proceedings of the 8th International Conference on Electric Fuses and their Applications (ICEFA), Clermont-Ferrand, pp. 169-178, Sept. 10-12, 2007.

[3] B. Koch, principal investigator for IREQ, CEA No. 046 D 549  Characterization of Secondary Arcing Faults Part 3: General Summary and Guidelines for Protection against Arcing Fault Effects. Quebec: Canadian Electrical Association, 1991.

[4] J. E. Bowen, M. W. Wactor, G. H. Miller, and M. Capelli-Schellpfeffer, “Catch the wave,” IEEE Industry Applications Magazine, vol. 10, no. 4, pp. 59-67, July/Aug. 2004.

[5] R. L. Doughty, T. E. Neal, T. A. Dear, and A. H. Bingham, “Testing update on protective clothing & equipment for electric arc exposure,” IEEE Industry Applications Society Magazine, vol. 5, no. 1, pp. 37-49, Jan./Feb. 1999.

[6] Neal, T. E. and R. F. Parry, “Shrapnel, pressure, and noise,” IEEE Industry Applications Society Magazine, vol. 11, no. 3, pp. 49-53, May/June 2005.

[7] R. A. Jones, etal., “Staged tests increase awareness of arc-flash hazards in electrical equipment,” IEEE Transactions on Industry Applications, vol. 36, no. 2, pp. 659-667, Mar./Apr. 2000.

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Q: Fred (not his real name) wrote with this question: “We’ve done an Arc Flash Study, and we have disconnects labeled as < = 1.2 cal/cm², Category 0 PPE required. Can we operate them outfitted with a hard hat, safety glasses, hearing protection, short sleeved cotton shirt and no gloves?”

A: 1.2 cal/cm² is the threshold for 2nd degree burn. As such, 70E, Table 130.7(C) 16 defines the clothing requirements for this level of protection to include, in addition the items you have listed, a long sleeved 100% non-melting natural fiber shirt and heavy duty leather gloves. If you were testing for the absence of voltage, you would need to include voltage rated gloves due to the shock hazard.

The rationale behind this is that, while the 1.2 cal/cm² of exposure is calculated at 18″ to the torso, the workers hands and bare forearms would be much closer and, therefore, exposed to a higher incident energy. Thus, the likelihood of a 2nd degree burn is significantly higher.

If we use a test case of 42 Ka of fault current and a clearing time of .015 seconds @ 480v, this would yield 1.1 cal/cm2 of energy at 18″. Using the same parameters at 9″, where the workers exposed hands and bare forearms would likely be, would result in 3.0 cal/cm² of energy. Exposed skin will certainly burn at 3.0 cal/cm², but I cannot speculate if a burn at this exposure would require a skin graft or external medical treatments.

I would recommend following the PPE requirements of this exposure level per the NFPA 70E table definition as listed.

Thank you,

Lee Hale

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1. Arc Rated vs. Flame Resistant (FR) The NFPA 70E committee, being an work practice standard, has sought to end confusion over the misuse of the term “FR”. FR is a very generic term which only has meaning in the framework of the hazard. Flash Fire clothing should meet a flash fire standard (such as NFPA 2112), electric arc hazard clothing should meet an arc standard (such as ASTM F1506), and firefighter clothing should meet a firefighter standard (such as NFPA 1975 or 1971). NFPA recently provided a clear statement against misusing NFPA 701 in garments. NFPA 701 is not allowed in garments and such use is a misuse of the standard opening the company to liability when labeling garments as flame resistant per that standard since it is only for “wall coverings”, “curtains”, “furniture” and other building uses NOT clothing. ASTM F1506, F1891, ASTM F2733 and NFPA 2112, NFPA 1975, NFPA 1971 are applicable for clothing in arc, flash fire, wildland firefighting, and structural firefighting respectively.
   Bottomline: Don’t buy FR, buy by the proper standard.
2. No increase in arc-rating for adding cotton, wool or silk under arc rated clothing.
   While still allowed for use, the NFPA 70E committee clearly prohibits using cotton undergarments for increasing arc rating — though this is allowed by NESC and by ASTM F1506. This more conservative approach has been justified by NFPA 70E due to the variability of undergarments (since no one has tested every undergarment) and by the variability of arc exposures (since calculating an 8 cal/cm² for a label does not mean you will never have >8 cal/cm² in a real life event). Preventing non-FR t-shirt ignitions will save a few lives per year. This can be accomplished by using an arc rated undershirt or ensuring that the outer suit is always at the arc rating required for the work. For layering data, see your garment manufacturer or check out ArcWear.com’s arc rated layer data.
   Bottomline: Consder arc-rated t-shirts.
   
3. Non-melting zippers, findings and logos. NFPA 70E 130.7(C)(11) states that AR clothing must meet certain performance characteristics beyond those in ASTM F1506. “Clothing consisting of fabrics, zipper tapes, and findings made from flammable synthetic materials that melt at temperatures below 315°C (600°F), such as acetate, acrylic, nylon, polyester, polyethylene, polypropylene, and spandex, either alone or in blends, shall not be used. Informational Note: These materials melt as a result of arc flash exposure conditions, form intimate contact with the skin, and aggravate the burn injury.” This is a poorly worded section since it may not make garments safer but could make them more costly. There are flame resistant zipper tapes, but when normal zipper tapes are covered properly, they can comply with ASTM F1506. While I might prefer flame resistant zipper tapes, there is a danger in using them without thinking. Exposed zipper tapes can breakopen earlier than the fabric, making the garment unsafe at exposures below the garment rating. If these garments are worn UNDER a high level of protection or if sufficient arc rated materials are worn underneath, they might be unsafe but the end user should evaluate. Non-FR zipper tapes could work well if the garment is properly designed but they do make open the garment to a little more risk in some events. ASTM F1506 should be the guide, but we have seen some zipper cover designs which are in the market which are dangerous. Arc tested zippers (NOTE: Zipper tapes are not arc rated but can be evaluated in a garment form) can solve issues of ignition if a zipper is not properly protected in the garment design.

   Reading the informational note, it could be understood that the committee did not intend to eliminate the use of common zipper tapes unless they could form intimate contact with the skin. This is yet to be cleared up. This is what ASTM F1506 would be interpreted to require today. The key is that zipper design and installation should not make garments less protective than their arc rating and the zipper must be operable for removal after an arc event.
   Logos are not included in findings because NFPA 70E refers the user to ASTM F1506 which allows non-FR logos as long as their design does not increase the extent of an injury. See NFPA 70E 130.7(C)(13)(d) which points to ASTM F1506 for trim and logos.
   Bottomline: Watch out for exposed zippers in arc rated clothing.
   

4. New Arc Ratings based on ASTM F1959-06 with two layer “pre-ablation burn” measurements. Some clothing systems have been down-rated due to a phenomenon often called the “double hump”. Some clothing systems, specifically heavy layers over lighter layers, will sometimes allow burns on skin BEFORE the outer shell begins to “ablate” or open up to allow cooling immediately after the arc. The committee made a change to the test methods in 2005-2006 addressing this, but NFPA 70E pointed to the 1999 version of the standard F1959 which did not address this, so some system ratings were artificially higher than those tested since 2005. This applies to hoods and flash suits also, even though these systems are not inherently unsafe because of this phenomenon. The real issue is when arc flash suits are worn with no clothing underneath as substantial research by ArcWear.com for ASTM F18 and Westex shows that the pre-ablation burns do not occur when any additional garment is worn underneath the fabrics (hoods should be excluded since they do not touch the body at the fabric and are tested to > the arc rating of the fabric). A coverall tested over a shirt would potentially display this effect and could allow second degree burns in some odd cases. New systems should have a ASTM F1506-08 or new label.
   Bottomline: Do not throw away an old arc flash suit due to the new pre-ablation burns change.
   
5. Proper rounding of arc ratings now done at the ASTM F1959 level. Starting in 2012, ArcWear at Kinectrics now round ASTM F1959 arc test ratings to the proper level for ASTM F1506. F1959 does not require rounding since it is a test method, but to avoid confusion in the market, all test reports will be rounded as required in the labels per ASTM F1506. Many labels have ratings to the 0.1 place which is not technically correct beyond 9 cal/cm². Ratings from 10 cal/cm² and greater will be to the nearest cal/cm². This is helpful for end users as 11.9′s are 39.9′s are now 12 and 40 cal/cm² respectively. This is what the ASTM F1506 standard has required for several years but was not being implemented at the garment labeling level.

Q: My staff are digital instrumentation technicians who will never see any voltages greater than 120VAC. What entity requires training for these type individuals (right now, we’re going to the training because our Electrical group says we need to, but can’t prove a basis for the training, and because it makes sense from a safety point-of-view)? What is the training actually required for these type individuals? Does initial training differ from refresher training? How often is refresher training required?

A: Instrument techs are normally “exposed to” voltages higher than what they commonly “work on”. This is the key. The first issue is shock and understanding when they might be “exposed to” 480V shock exposures; (usually older equipment is the culprit where there is supply and control voltage in the same compartment).

The second issue is 480V arc flash. We have several instances where workers are working on control wiring in MCC’s and a 120V minor arc flash turned into a major 480V arc flash when it ionized air gap in the 480V.

OSHA requires training of all “recognized hazards”. Shock on 120V kills more than 12,500V according to NIOSH. Arc Flash hazards are greatest on 480V systems. There is likely little or no arc flash exposure on 120V systems unless the worker is also “exposed to” 480V. I’m for meeting OSHA requirements on training and not over doing it, BUT I have investigated a few incidents of dead IE/I&C techs who thought they knew everything and had a 480V arc flash, so this work is a hazard. Even 120V control wires can kill in the right conditions. Safety training is law, not just an internal (company) compliance requirement.

Working on 120V is a hazard often ignored. Specific training is required for ALL “qualified persons” by OSHA. It doesn’t spell out what you have to train on specifically but they must be trained.

We worked a case of an untrained and unqualified supervisor in Arkansas forcing an electrician to do work unsafely which resulted in the electrician’s death. That supervisor had not attend training. He lost his job and was also investigated for homicide charges.

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