wilhendrix wrote:
I think there are a couple of things to consider. First, the voltage. Not many people have to work on more than 480 volts. However, they are expected to routinely do testing, measuring or troubleshooting. If this is the case, then the person is crossing the 12" restricted boundary and "should" be wearing insulated gloves and probably leathers over the insulated gloves.
So you would totally ignore and never use the insulated tool work method? Despite the fact that it is a tool and not PPE? Despite the fact that ANSI Z10 (Hierarchy of Controls) makes it pretty clear that PPE should be your LAST choice and not your first choice for dealing with a hazard? Remember you only have a very thin piece of rubber which is pretty fragile protecting you while you have a big hunk of plastic or fiberglass protecting you while doing insulated tool work, including meter probes and similar tools.
This is where 70E is somewhat confused/confusing on the issue. ALL shock protection procedures in 70E actually come from IEEE 516 which is the standard for work on outdoor, overhead lines. In that standard there are basically 4 work methods: cover up (install temporary insulation), live-line/bare-hands which is pretty impractical below 69 kV so no reason to consider further, insulated tools, and rubber gloves. The one curiosity is that IEEE 516 allows for use of EITHER rubber glove work method or insulated tool work method. In the East linemen adopted wearing gloves while using a stick while in the West it's either stick or gloves but not both. In fact there are valid arguments AGAINST gloves+sticks because both the glove and stick must be rated for the primary voltage due to the way that dielectrics work (depending on the properties of the material, ALL of the voltage drop can be on the glove) so that for instance you should not be wearing class 2 gloves while using a stick (rated at 100 kV per foot) to work on a 35 kV line, but this is getting off into the weeds.
Getting back to 70E, it makes it very clear that you MUST wear gloves IF there is a shock hazard. If you have cover up in place or you are using insulated tools then obviously unless you are concerned about for instance inadvertent contact with something that is not protected, the rubber glove is not necessary and indeed given the loss of dexterity, high propensity for failures, the hierarchy of controls which is now prominently featured in 70E, etc., there are strong reasons for not using them MOST of the time. There are certainly reasons though when glove work would be preferred to stick/tool work. For instance if I'm trying to reach down to pick something up or digging into a bundle of cables, gloves are preferred to sticks. So keep in mind that there are very strong glove proponents on the 70E Committees but there are in fact two different work methods and 70E is not and should not be written to limit you to just one. The way that I'm interpreting it to a certain degree too is that this is similar to the whole section on batteries with the various PPE (gloves, aprons, face shields, etc.) that are required in that section. It gives a list of tools that are necessary to do the job around batteries but nowhere in there does it say when and where the PPE needs to be worn, only that it needs to be available. This gets very task specific from here and that is where 70E stops because specific tasks frequently involve an understanding of the specific equipment in use. You can't just write a generic procedure that covers everything in many cases.
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Seems that if an organization is not doing this minimal safety step, the chances are none of the other safety steps would be considered. In the time I've been an electrician, I've heard of a few shock deaths. Most would not have been saved by a hook. For example, I know of a death where a person was working through a drop ceiling space and was shocked by a 277 volt lighting circuit. He was found on the ground unresponsive. He died shortly after that accident. I assume he was shocked and was thrown or fell off the ladder. I don't believe the fall caused his death. This was back in the 60's before AED's or CPR were common.
This is more common than you think. Both arc flash and shock have been shown to not be the reason for fatalities in many incidents but rather the fall. Even without an arc blast or a jerk from muscle spasms while being shocked may not be as bad as simply being startled and "jumping" back. Being "startled" is a very instinctive reaction which might not be a completely voluntary motion but is instead triggered int he cerebellum which is responsible for "instinctive" reactions and short circuits the brain when immediate action is necessary. Potentially lethal currents occur at around 100 mA. Using a 1000 ohm resistance for a human body (the standard used in IEEE Standard 80 for substations), this can occur at as little as 100 VAC. With regards to arc flash fatalities the lower limit hasn't been exactly determined but there is a documented OSHA incident at 240/120 VAC on a temporary construction panel which caused a fatality in 2009.
Taking these together it should be pretty clear why 70E sets a lower limit at 50 VAC/100 VDC. Comparatively "safe" voltages that we all work around every day are not nearly as safe as most electricians assume. Under the right circumstances, bad things can happen. The circumstances under which we can get shocked or burned remain the same at every voltage and the only difference from one condition to another is that sometimes the magnitude of the shock or burn changes to the point where it might not be fatal or not even noticeable.
As to when emergency release becomes necessary, there are really three circumstances. The first one would be if someone is "trapped" such as if they are stuck on a large energized surface or entangled in a cable. The second is if it's DC...unlike AC, DC locks your muscles up and you physically can't release your muscles with very little current necessary to cause this. The third case would be if it arced and burned into the flesh to the point where someone is "welded" to the equipment. Under normal circumstances working around AC power the propensity is either that the "startled" reaction happens and the individual rapidly retreats away from the equipment, or the current causes muscle spasms that jerk the limbs away and/or magnetically propel things apart from each other. Getting "stuck" is relatively rare at least with AC equipment. With that in mind I'm mostly going to be working around 125, 250, and higher voltage DC equipment in a power plant today...
