Q: I am brand new to the safety side of contracting and need guidance on finding information about heat stress. There are lots of guides on assessing heat illness as it occurs, but what about industry practices to prevent heat stress? What do successful heat-stress prevention plans look like?
A: We have three recommendations for you. First, some state plan safety and health agencies – such as California’s – have mandatory program requirements that include trigger temperatures. When a worksite reaches such a temperature, certain site practices for heat stress must be employed. Section III, Chapter 4 of the federal OSHA Technical Manual (see www.osha.gov/dts/osta/otm/otm_iii/otm_iii_4.html) also has detailed information about heat hazard assessments and programs.
Second, call your local hospital or favorite occupational medicine specialist and review your heat-stress prevention plan with them. In the past, I have offered to pay a fee to have a doctor visit a safety meeting to talk about prevention, although doctors usually will come to speak for free.
Third, do just as you have done: Ask questions, and share information with individuals and companies that have good, effective programs.
In addition to the three recommendations above, we have identified four key components often found in high-success heat illness prevention programs:
Ultimately, the employer is responsible for providing information about and prevention of heat-related illness on the job. The recommendations above are some ideas, but the best idea is to seek medical assessment and recommendations for your specific work environment and workforce from a medical professional.
Q: I read an article from the Incident Prevention magazine archive that discussed American Electric Power (AEP) discounting the use of pole bands in creating equipotential. Doesn’t that article conflict with the general consensus that the pole band is the best practice?
A: No, there is no conflict at all. First, clamped-on manufactured pole bands are one way to accomplish bonding in between a lineworker and the structure for the lineworker’s personal protective grounding protection system, but it is not the only method used. And while it is a widely recognized method, as far as we know, pole banding is not required by any mandatory standard. AEP is a respected utility with a good test lab and people with good technical expertise operating it. Their conclusions were regarding their facilities and equipment in their region, on poles of undefined condition from their system. Their experience is of value to us because it shows that there is more than one way to bond a pole to the system. With the exception of government-operated high-voltage labs, private utilities have been hesitant to release numbers related to testing. I am not privileged to have seen the testing or results and that is understandable. Grounding for personal protection is a serious issue, and it might be easy for persons with nefarious intent to try to hold AEP accountable for conditions and outcomes that could never be duplicated or precisely explained in civil court.
Poles that are saturated wet produce good bonding results. Poles dry out, and we likely will never work on two poles with the same conductive potentials in our lifetime. The reality is that in most cases, there will be a difference in currents and voltages measured, but the questions are, is the voltage high enough to injure the worker and was the result better than not using an equipotential arrangement?
Q: We are an old municipal utility with a workforce averaging 30 years in the line trade. We are pressing on with EPZ use for wood poles, even though we climb very little, but we are at odds with the lineworkers, mostly because we can’t explain how a wood pole can be the same potential as a primary conductor during a fault. There is no explanation on the web. Can you help us explain this to our workers?
A: Yes, we can, and the explanation will probably help many of our other readers, too. Keep in mind as you read that it takes at least 50 volts to penetrate the worker’s skin to allow current to flow. If current can flow, it takes at least 50 milliamps to rise to a level of risk. These measurements are commonly accepted as shock risk criteria. Bonding the wood is not about making the wood a conductor like the phase conductor. Bonding the wood is about current and voltage in two parallel paths. Those paths are through the lineworker and the path through the parallel low-resistance bonding jumper. Read carefully here: Both paths originate on the phase and terminate on the wood. The wood pole is a high resistance, but it is an unknown quantity as a resistor. If the lineworker is the only path, and enough current can flow on the wood pole, it could be high enough to be deadly and usually is. In that case, the conductivity of the wood pole is the only limit for the current that could flow through a lineworker. More importantly, there also is a potential difference between the wood pole and the grounded phase because that wood pole is a higher resistance than the grounded phase. We say “more importantly” because the potential difference is the easiest risk to control. We can do little to limit fault current. To control potential, we put a very low-resistance jumper parallel with the lineworker between the phase and pole. The pole is now effectively bonded to the phase so that there is no potential difference between the two. If there is no – or a very low – potential difference, the voltage cannot penetrate the worker’s skin and current cannot flow, so no injury is sustained. If you have a hard time with this wood-pole-bonding concept, think about this: We do the same thing in bare-hand techniques on energized lines. The boom the worker is in limits the current flow to less than 1 milliamp, so we have a control for hazardous current. But the resistance of the boom to the bare-hand lineworker would do little to protect that worker from the voltage potential. A simple bonding jumper between the energized phase and the insulating boom eliminates the voltage difference, just like the bonding jumper between the grounded phase and the insulating wood pole eliminates the voltage difference. If the voltage cannot penetrate the lineworker’s skin, current cannot flow, and the worker cannot be injured.
One last thing: That bond between phase and wood pole is only effective for the lineworker between the pole and phase. There will still be a difference in potential between phase and neutral, so we also must bond between the pole and neutral as well as the phase and neutral. In that way, it does not matter what you touch – each of the paths is bonded to protect the worker.
Q: There are a lot of adages about line work, and we heard that the one about wind on power lines is wrong. Still, one of our apprentice training manuals states that wind causes static on lines. Do you have any information?
A: We do have information. And this is a fun adage to discuss, one that we also have been hearing for years and believed until not too long ago. It turns out, however, that it is not true, and the proof is easy to find in any physics book or on any website – try searching for “triboelectric effect” – concerning the properties and conditions necessary to create static.
Here’s some background about where this adage might have come from: In the 1950s and ’60s, helicopters began performing some external suspended-load line work operations, and lineworkers got shocked by those external loads. The assumption was that rotor-wash wind created the voltage buildup. In the late 1950s, the U.S. Army began arming helicopters with mounted remote-controlled ordinance and occasionally had an unintended launch or detonation created by transient-voltage buildup on the aircraft. The Army’s Transportation Command in Fort Eustis, Virginia, did the research in 1961 that told the story. The Army research found there was some triboelectric effect if the rotor-wash was high enough and there were sufficient contaminants in the air. But the researchers also found ionizing voltage from the exhaust blown down over the metal skin of the aircraft. There is, however, another source of voltage buildup that is more interesting. Helicopters can be charged by the natural magnetic field around the Earth through which the low-flying, isolated, conductive helicopter flew. That magnetic field makes a compass work. Coils next to a spinning magnet make electricity, also known as electromagnetic force. The Earth’s magnetic field weakens the farther you are from ground-creating gradients. A helicopter with a suspended load flies through gradients, spanning hundreds of volts in magnetic field potential that can charge the isolated but conductive helicopter skin. An insulated power line stretched 20 miles 40 feet above Earth also is in that magnetic field and attenuates an electromagnetic charge. These charges that gather might be called static. It’s more important to realize that this form of voltage is rarely deadly and should not be confused with induction. Induction is deadly, static is not.
KNOWLEDGE, INSIGHT & STRATEGY FOR UTILITY SAFETY & OPS PROFESSIONALS
Incident Prevention is produced by Utility Business Media, Inc.
© 2004 - 2019 Incident Prevention™. All Rights Reserved.