Q: Should we worry about beards in relation to arc flash? At our company, we think hair generally protects the body against extremes. Do you know of any evidence to the contrary?
A: Here is what we know: Human hair is protein fiber. It will burn when exposed to a flame but stop burning when the heat source is removed. Human hair does not melt; it becomes a fragile ash that turns to powder when crushed. This property is known as self-extinguishing. Hair is pretty much like cotton – it burns away. As such, it is not a hazard related to arc flash and actually provides some protection. OSHA does not address exposed hair any differently than the exposed body. It is up to the employer to decide if exposed hair increases employee risk as it pertains to arc flash hazards. If you were to analyze it from a practical perspective, you likely would agree with most of the safety experts we asked about it; they indicated that hair has a heat-insulating property and will not increase a burn hazard to the face provided workers abide by the appropriate arc flash standards of protection established by OSHA. However, there is an issue with some grooming products that may change the hair’s natural resistance to burning, which could be a problem for those lineworkers who use them.
Q: I am trying to find any technical and/or investigation reports that could assist me in understanding the hazards of using synthetic ropes while stringing in energized corridors. Can you help?
A: One of our consultants shared an experience he once had that relates to your question. Here’s what he had to say:
“I was asked to consult on an incident that occurred some 20 years ago in the Northeast. Crews had roped in and left the ropes up for a day or so and then lost one that broke and went into the river. I found that they had strung travelers on suspension insulators except for the break-over sheave that was near the river’s edge. Since all of the travelers were hanging from suspension insulators, the rope was isolated from any ground path except for two locations. Because they needed a short angle down to the tensioner and thought it highly stressful, they decided to steel-sling the aluminum sheave to the arm near the pole.
“That break-over was the only grounded traveler in the pull, with the exception of the far end that was caught off to the last structure on steel slings and grips. They had a nearby energized transmission circuit, rope spanned over a saltwater river, high humidity and fog. Overnight, all three ropes had been parked in the single break-over sheave that was tied to the pole top with a steel sling. During the night, the ropes broke at the sheave and fell into the river. What happened was induction. The ropes were conductive by virtue of the environment and moist air. The grounded sheaves created arcing conditions as current from the rope passed into the ground. It doesn’t take much whittling down of fibers to weaken and break a rope under strain.
“It is likely that the far end of the ropes being grounded created a ground path for current to flow once the rope got wet. There was enough magnetic induction to create a current across the ropes and enough current on the aluminum break-over sheave to heat and burn the rope in two.
“Section 126.96.36.199. of IEEE consensus standard 524, ‘IEEE Guide for the Installation of Overhead Transmission Line Conductors,’ states the following warning: ‘When installing semiconducting lines, care should be taken to prevent deterioration of lines due to excessive leakage currents that may occur at traveler or running ground locations.’”
Q: Is there a specific retrieval line for rescue when performing underground work? Does the retrieval line have to be nonconductive? Steel or non-steel?
A: The OSHA standard does not address the material used for the rescue line. We have to evaluate the exposure of the line in the work environment to decide what’s best. High-strength synthetic rope would be fine if there are no abrasive surfaces that might damage the rope, but a nylon rope under tension running against a polymer cable will cut through insulation and conduit. A jacketed steel line might be more appropriate if you want to be sure no rescue line can get or “saw” into cable or conduit. Most users prefer a synthetic line because it’s easier to work with. So, training and practice with awareness may be appropriate where concerns arise regarding synthetic ropes cutting PVC and solid dielectric insulation. In other exposures, steel or synthetics could become conductive if contaminated by floors and water. The worst thing is that if you have a flash in a hole, the synthetic rescue line could be damaged and melt. There are many considerations that ultimately rely on training and awareness coupled with inspection and maintenance of equipment to ensure you have the right equipment for rescue.
Q: What is required on the source side (feeder) of primary? How much air gap is required? If an existing dead-end is on a line arm with line hardware, do we need to insert a tested link?
A: There are no standards that define a gap installed for the purpose of isolating a section of line. We don’t believe tested links are necessary, although there is no criticism of crews or companies that want to use them. Several manufacturers now make strain links complete with grips and ratcheting mechanisms to tension, belly and cut conductors with a built-in disconnect switch and jumpers.
As to air gaps, many people mistakenly think that the gap must be the minimum approach distance (MAD) for the phase voltage, but that’s a little excessive. An open cutout is a gap usually considered an open for the purpose of isolation. OSHA has not commented, but it is reasonable to take out the barrel and tag the switch if you are not in effective control of it. Here is why an open cutout should be sufficient: A gap is the distance in air that will prevent voltage arcing over the gap. The distance in air that is required to prevent a flash-over is known as the minimum air insulating distance (MAID). It is the MAID plus the human factor of 24 inches for distribution voltages that make up the MAD calculation. The distribution voltage MAID is fewer than 3 inches for 15 kV, so any distribution switch – or an air gap the same as the gap across a switch that is cut into wire – would be sufficient to prevent a flash-over and assure isolation. Obviously, if you don’t know the MAID for the system you are on, using the MAD would be better than acceptable. There also is no reason you couldn’t create an open in the circuit with dead-end bells or a tested isolating link. All of the tables for MAID, human factor dimensions and MAD can be found in IEEE 516, “IEEE Guide for Maintenance Methods on Energized Power Lines.”
Q: Are open cutouts approved backfeed protection for transformers?
A: Yes. Most authorities agree that opening the dropout, removing the barrel and – if required by local procedures – grounding the primary are considered effective control of backfeed as a source of inadvertent energizing of a circuit. But be careful grounding the primary. Even if you close the switch after grounding it, the impedance of the transformer will not necessarily trip the fuses on a generator, so the secondary could still be hot even if the primary bushing is grounded.
Q: We have a lot of questions about using a cluster bar as a means of bonding a pole to the grounded circuit. For instance, is it required, where does it have to be and what are the exceptions? Are there any specific rules to guide us?
A: There are no rules except for Appendix C to OSHA 29 CFR 1910.269 and the IEEE 1048 consensus standard, “IEEE Guide for Protective Grounding of Power Lines.” The wording of Appendix C has put many employers at odds with the agency in a manner of speaking. The issue is that, unlike other appendices OSHA has written, Appendix C to 1910.269 lacks the introductory note that states the guidance is not mandatory. Appendix C has guidance for cluster bar use along with the wording that “the employer must ensure,” which certainly makes the guidance sound mandatory. However, that guidance was written early in the development period of personal protective grounding practices, and much testing and experience show that pole bonding can be effectively achieved without using the cluster bar. You have to make your own decision as to whether the method you choose will be compliant. Take note here that Incident Prevention is not saying that it is OK to use another method considering the wording of the appendix. But many of our experts agree that other, simpler methods that produce the same effect would likely end up as a de minimis condition, meaning the employer did not comply with a standard but no employees were exposed to risk.
One of the issues was that the cluster bar “required” by OSHA was admittedly lacking in effectiveness, so OSHA also required the employer to drive a metal spike or nail into the pole, as described in the appendix. Many questioned why OSHA – after all the years that the agency had claimed that it is not their mission to tell employers how to accomplish a safety task – was now telling them how to accomplish the task. Not only that, but they were requiring employers to add appurtenances to manufacturer devices to make them work better. Yes, OSHA is right about the spike, but the issue is that, after all this time of being an agency that writes outcome-based rules, they ventured into procedures and didn’t do it very well.
Now, credit is due. As we said earlier, we agree that OSHA was right about adding the spike, which deserves some explanation. Here is why OSHA required the spike: The cluster grips the dry exterior of the pole while a lineworker’s climbers may penetrate a more conductive part of the wet inner portion of the pole. That raises the possibility of potential differences. Bonding the cluster to the inner pole with a strap and spike (lag screw) would bond across that difference and minimize risk.
As to where the pole band goes, both OSHA and IEEE recommend as close to the work area as practicable below the lineworker’s feet. In the years that I climbed, I never had to install a pole band. I do know that sometimes it is impracticable to get a pole band close to the work or even above the communications circuits on many distribution poles. The issue is that distance increases resistance between the lineworker’s hands on the wire and the phase bonding to the pole through the pole band. The farther away the band or connection to the pole, the more voltage difference there will be. A few feet or more is not likely to develop a voltage increase that will rise to the level of risk, but it is up to the employer to decide what constitutes an acceptable location when those problems arise.
The final answer is, it’s not too difficult to bond a pole to the system you ground to. Many tests have found that simple copper pole bonds with multiple well-driven staples successfully bonded the grounding system to the pole for their purposes. The employer has to research the available information and select the method of bonding that will protect their employees from differences in potential in temporary grounding of systems. If you want to read Appendix C to 1910.269, visit www.osha.gov/laws-regs/regulations/standardnumber/1910/1910.269AppC.
© 2004 - 2021 Incident Prevention™. All Rights Reserved.