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When switching equipment, do you believe it better to face the equipment or face away.
Face equipment
Face away
Doesn't matter
Something else
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 Post subject: Face equipment or face away during switching?
PostPosted: Sun Nov 27, 2016 3:01 pm 
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This week's question was submitted from one of our forum members. I will post it here

When locking out or resetting a tripped breaker on a CAT 4 system (actually extreme danger), I have one electrician that says he feels more comfortable facing the distribution than facing away. He argues that the shield will protect him better than the Balaclava. He also says that the force needed to reset a tripped (1200 Amp) breaker is easier when facing the breaker. Our lockout rules say to face away, close your eyes and hold your breath (and pray), using your left hand. Which is safer?

To summarize, here is this week's question:

When switching equipment, do you believe it better to face the equipment or face away.
Face equipment
Face away
Doesn't matter
Something else


If you have a question you would like to see submitted as a "Question of the Week" pass it along to me and I'll get it posted! - Jim


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Sun Nov 27, 2016 8:27 pm 
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The old rule for arc flash (and arc blast) is to stand to one side. There are two reasons for this. First it stands to reason that some of the thermal energy (radiation) will be considerably less if you are not standing directly in front of the arc. We do this all the time in the thermal processing industries (iron & steel, kilns, etc.), where you stand behind a wall or a heat shield (piece of sheet metal) to avoid the heat radiating off the equipment.

The second reason is to avoid shrapnel from an arc blast...more specifically, if the door comes flying off. Hugh Hoagland has a great video somewhere that has a dummy placed in front of the panel and one interesting one where the dummy is standing on the hinged side (theory is that the door will fly open and provide a blast shield) and the door simply flies off and takes the arm of the dummy with it. As to the "force of the blast" itself, I've published a paper on this subject and others have actually tried to measure the pressure from an arc blast and failed miserably at it. The danger here is pretty much shrapnel and there is a possibility of rupturing ear drums but that's about it. The idea that you can be crushed/thrown around like a rag doll, and the like, is pure unproven theoretical nonsense based on a bunch of tests using a microphone as a pressure measurement device which gives incorrect readings.

So...there is some practical value here from what I've seen in standing to one side with your body including your arm not in the "line of fire" if something goes wrong. With a hinged door and a handle on one side this is pretty easy to figure out but if the door is open or some configuration other than that such as with very large breakers where the handle is actually in the center of a cutout, the rule becomes kind of meaningless. Also there is the obvious problem that if the equipment is positioned against a wall on the non-hinge side, there really isn't any physical way to stand anywhere except either directly in front of it or on the hinged side.

And the electrician also makes the second valid point. I've had an electrician totally destroy a 35 kV overhead switch because he was so scared of it that he very gently opened the handle instead of taking hold of it firmly and rapidly and smoothly opening it. You get the same thing with kids (and some adults) that slowly open a light switch and burn it out by opening it too slowly. It is generally a good practice to attempt to open/close any kind of electrical switch as rapidly as possible as long as it doesn't damage the equipment and the larger the equipment, the more important this rule is. And if you've ever personally attempted to operate ANY circuit breaker rated 800 A or larger that doesn't use some kind of spring charging mechanism, it requires a lot (50+ lbs.) of force to get it to open or close. You simply can't stand to one side arms length away where the best you can do is maybe 10-20 lbs. of force to do the job.

As to all that stuff about face shields vs. balaclava's, all I can say is that the text refers to a category 4 condition. Balaclavas (with a face shield) are only rated to 12 cal/cm2, not 40 cal/cm2. At 40 cal/cm2, a hood with a face shield is required so neither the face shield nor the balaclava is sufficient. But then we get to the "Facing towards vs. away". The whole purpose of the balaclava is to protect the face from hot gases coming around the edges of the face shield from the sides and to offer some protection to the back of the head. When in a <12 cal/cm2 condition using a balaclava and face shield, the face shield is clearly intended as primary protection or else it wouldn't be required (and in some cases the face shield ONLY is required, not the balaclava). So the electrician is right on this point and facing away definitely kind of defeats the face shield altogether.

However I don't have quotes right in front of me right now but it is my understanding that one of the primary benefits of arc rated PPE is that it doesn't propagate a flame and make a bad situation worse. So if it is rated high enough although theoretically there is a 5-10% chance of a 2nd degree or greater burn in practice so far there are no known cases of "failures". If it is under-rated then if we look at the "survivability" chart that 70E is based on, we still significantly reduce the percentage of the body that is burned and this drastically increases the survivability compared to wearing non-arc rated clothing that can not only burn but can sustain a flame (such as untreated cotton). So chances of survival are very good even with under-rated PPE.

This is particularly important in my line of work. Right now I'm a field service engineer. I go to customer plants all over the place and generally if I'm called, it's because something is not working right in the first place. Let's just say "normal operation" is simply not the case if I'm working on site. Many customers are small operations so they simply haven't done anything about arc flash, nor even have any idea why my work shirts and pants have an arc rated label on them. So there is pretty much almost no chance that I can find out the incident energy for anything that I'm working on. I'm going to go out on a limb and suggest that some (unknown) fraction of the time, my PPE is probably under-rated but there is no way of knowing what that fraction is. I'm the guy that the much maligned "table method" is geared towards.

I'm not arguing against best practices here by the way. I'd love to do arc flash studies for many of my customers and implement best practices. I carry a 3 level system on the truck (4 cal/cm2, 12 cal/cm2, and 40 cal/cm2), so its not like I don't have the equipment to do the job. It's just convincing the customers of the value of doing it that is missing.


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Nov 28, 2016 8:22 am 
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Joined: Fri Apr 15, 2011 7:43 am
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Location: Colorado
It depends on the safety equipment you have. If you have a face shield you probably want to face the equipment other wise the blast material could be channeled into the shield. I agree with Paul about standing to the side, Hugh's video of the flying door tells us this only makes sense.

If you have little safety equipment, use the tried and true - stand to the side, face away, use your non-dominate hand.


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Nov 28, 2016 8:30 am 
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Joined: Thu Oct 18, 2007 7:10 pm
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Location: NW USA
appreciate the writeup by Paul Engr.


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Nov 28, 2016 9:39 am 

Joined: Sun Dec 12, 2010 5:00 pm
Posts: 24
Location: Idaho
Thanks for the write-up Paul. Being that I asked Jim to submit this question this week, I will answer some of the questions brought up. We use 40 cal hoods with built in balaclava from Salisbury as a norm. We quit using the face shield and balaclava a few years ago. I used Jim's idea of throwing an object at the electrician and we talked about his response to throw his arms up to block the "shrapnel"!! I still have not convinced him that it is better to turn away, but being that is our policy, until it is changed he will turn away. I am in the process of having CBS arcsafe come in and do an assessment to remote reset our switchgear breakers, but have not purchased equipment yet. One of our other plants have had issues with the equipment that they bought. We need a little better coordination so mains do not trip, but our secondary breakers are not set up electronically to trip quicker than the mains on a locked rotor situation. Does anyone have a link to Hugh's video. I cannot find it although I thought I had all of his videos. Thanks in advance to all the responses. It looks like turning away has always and still remains to be the best practice in the industry.


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Nov 28, 2016 10:19 am 
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gastoor wrote:
Thanks for the write-up Paul. Being that I asked Jim to submit this question this week, I will answer some of the questions brought up. We use 40 cal hoods with built in balaclava from Salisbury as a norm. We quit using the face shield and balaclava a few years ago. I used Jim's idea of throwing an object at the electrician and we talked about his response to throw his arms up to block the "shrapnel"!! I still have not convinced him that it is better to turn away, but being that is our policy, until it is changed he will turn away.


This does not apply. There are tons of studies on human response rates that show that the response is around 0.3 seconds. This type of test means that for instance a light turns on and the person pushes a button. It will obviously take considerably longer to throw your hands up. According to an extensive set of tests conducted by CIGRE that were used to develop equations to design arc resistant gear and numerous other studies on the subject, the arc blast occurs in about 1 cycle or 0.017 seconds. So arc blast is over and done with before someone can throw their arms up.

Quote:
I am in the process of having CBS arcsafe come in and do an assessment to remote reset our switchgear breakers, but have not purchased equipment yet. One of our other plants have had issues with the equipment that they bought.


That has been my experience as well but keep in mind...I haven't tried to keep track but my experience is that having problems with the drawout mechanism on a circuit breaker is common. It seems like I'm trying to get it to work either to remove or insert a breaker more often than not. With my hand on the wrench, I can feel wen something is binding up or popping or just not acting right. Put me on a button located 10 feet away and that "feedback" goes away.


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Nov 28, 2016 11:15 am 
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PaulEngr wrote:
gastoor wrote:
Thanks for the write-up Paul. Being that I asked Jim to submit this question this week, I will answer some of the questions brought up. We use 40 cal hoods with built in balaclava from Salisbury as a norm. We quit using the face shield and balaclava a few years ago. I used Jim's idea of throwing an object at the electrician and we talked about his response to throw his arms up to block the "shrapnel"!! I still have not convinced him that it is better to turn away, but being that is our policy, until it is changed he will turn away.


This does not apply. There are tons of studies on human response rates that show that the response is around 0.3 seconds. This type of test means that for instance a light turns on and the person pushes a button. It will obviously take considerably longer to throw your hands up. According to an extensive set of tests conducted by CIGRE that were used to develop equations to design arc resistant gear and numerous other studies on the subject, the arc blast occurs in about 1 cycle or 0.017 seconds. So arc blast is over and done with before someone can throw their arms up.

My original comment was about wearing a balaclava. About 10 years ago while developing an arc flash practice in Europe, there was a debate about wearing a balaclava. One person believed the face shield alone would protect a person's head/face from the thermal energy - it wasn't so much about shrapnel or blast. I pointed out that a person's typical reaction is to quickly turn their head/upper body sideways and block as a "fight or flight" response and the side of the face would be exposed. (although not instantaneously) after a bit of debate, I threw a wad of paper at their head (unexpectedly to them) and they turned side-ways. They recognized a balaclava is important and was included. Keep in mind this was about 10 years ago.


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Nov 28, 2016 12:50 pm 

Joined: Sun Dec 12, 2010 5:00 pm
Posts: 24
Location: Idaho
Thanks Jim,
The reaction I got was besides putting his hands up, it made him back up. If he is facing the distribution and an actual arc flash event occurred, then it would blow him backwards and I still think that the human response would be to throw their hands up and turn their head, besides losing their balance. Even if it was not in the same time frame as the blast itself. I tried giving him the scenario of a parachute jumper. They land and travel in the forward direction. Has anyone ever seen them land backwards?? I know that in an actual arc blast event that there is no way to react quick enough to stay out of the blast, but the after effect may or may not cause more injury depending on how the person is facing, not facing, left or right hand, in front of or to the side.

Thanks, again....


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Tue Nov 29, 2016 4:24 am 
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Watch this arc flash video at the beginning when the incident occurs:

https://youtu.be/2SopsQEfoc4

The person is clearly not "thrown' but rather turns sideways and more o less jumps/crouches/cowers out of the way. Although there are few actual incident videos based on pressure measurements made with either open doors or with doors blowing off I really don't believe that anyone is going to be "thrown" or "blown" around.

Agreed with Jim though that once the concern becomes arc flash, then the balaclava applies.

Keep in mind that "flight" is processed in the cerebellum and somewhat the brain stem, NOT the main parts of the brain itself. The biological advantage is that it's much faster (under 0.3 seconds). The downside is that this part of the brain is limited to very basic things like breathing or pumping the heart. "Look before you leap" simply isn't possible, and complicated acrobatics like jumping backwards aren't going to work very well either. There are a lot of "shock fatalities" where the fatality is that someone fell off a ladder or out of a man basket when they were startled by the shock (or arc flash) and died from a fall when the cerebellum took over.

It might make more sense to describe what happens in terms of being "knocked back" but the physics don't agree and it may be more of a physiological issue.

http://www.medicaldaily.com/fight-or-fl ... nse-279176


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 Post subject: Re: Face equipment or face away during switching?
PostPosted: Mon Dec 12, 2016 8:04 am 
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Sorry to say, my personal experience with an arc flash in an mcc cubicle was that I was immediately sitting on the floor as I heard and saw the flash. It was definitely an automatic response as the calculated flash value was 2.0 cal/cm² and occurred right at eye level. So the blast did not push me down. Safety glasses were ruined and I did suffer a small degree of permanent vision loss.


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