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 Post subject: 100 cal/cm^2 Arc Flash Suits
PostPosted: Thu Mar 06, 2014 8:31 am 
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Just curious, has anyone worn 100 cal/cm^2 arc flash suits? I assume if you did it was because the incident energy was quite high. I have had this conversation a few times and just wonder what people's experiences where.


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PostPosted: Thu Mar 06, 2014 9:19 am 
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In the past, nowhere where I have worked has bothered with anything beyond a 40 cal suit; under the assumption that the explosive force would kill you beyond 40 cal, so there was no point in trying to work on anything that high.


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PostPosted: Thu Mar 06, 2014 12:13 pm 
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Most of the greater than 40 cal/cm2 occurances I have seen have been due to older designed systems where the interrupt timing created this problem, or where on newer installations the engineer tried to utilize to close of a working distance. This does happen, and when it does the first approach would be to work with the engineer to figure out ways to bring the incident energy level down, which could include adjustments in trip setting, some of the newer relays have this feature that alow adjusments in the tripping schem for maintenance. Oher corrections should be considered by the facility to make improvements to the design to create a safer work emvironment.


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PostPosted: Thu Mar 06, 2014 1:10 pm 
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The assumption about arc blast is baseless.

There is a theoretical equation again due to Lee for arc blast but there is a lot of evidence that it is way off.

There have been some recent efforts to look arc blast but nothing that I know of published yet. For instance arc blast takes a short period of time to occur. If you arrest the arc before that by using say one of the high speed arc termination/mitigation devices, this eliminates arc blast. Similarly, it occurs in a very quick impulsive force. After a certain period of time, it does not continue. So many of the cases of very long trip times may in fact not be a serious arc blast hazard although they may pose a serious arc flash hazard.

High levels of thermal radiation protection have been used for years in the oil/gas industry for protection against flash fires as well as in iron/steel for handling molten metals that put out excessively high amounts of thermal radiation. There isn't a significant amount of difference between those and a 40 cal suit except for...when you get into the aluminized stuff, it becomes significantly stiffer and feels a little like wearing a suit made out of cardboard because the aluminum does not move as easily.


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PostPosted: Mon Mar 10, 2014 6:33 am 
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I am a Safety Technician at a generation station and not an electrician but I have watched our guys here racking 13.8 KV breakers in and out while the bus is still energized. The rating on these breakers is higher than the HRC 4 so they do wear the 100 cal suits, and they are a bit awkward and hot. They recently bought ventilated hoods for the 100 cal suits that they say help a lot with keeping you form sweating so much that you fog up the face shield, but I have seen them used other places as well and the main idea seems to be that you do not want to be in them very long at all. Like wearing a space suit.

I hope this helps.


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PostPosted: Mon Mar 10, 2014 8:35 am 
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PaulEngr wrote:
The assumption about arc blast is baseless.

There is a theoretical equation again due to Lee for arc blast but there is a lot of evidence that it is way off.

There have been some recent efforts to look at arc blast but nothing that i know of published yet.


I think I may have posted about this before, but I would be very interested in seeing the test data.


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PostPosted: Tue Mar 11, 2014 9:56 am 
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http://standards.ieee.org/about/arcflash/afupdate.pdf

Trying to find the other one but a powerpoint was released a couple years ago. I saw only a blurry PDF of it but the interesting thing is that at least according to the power point arc blast tends to be pretty constant almost irrespective of the various inputs to it, or at least that's what the slide was saying. Unfortunately as I said, nothing has been released in the way of actual data or anything approaching it so to date, arc blast is still basically a mystery with scant documentation on it. The above PDF shows that arc blast peaks at a little under 1 PSI whereas the powerpoint I saw showed a similar peak but was closer to 2 PSI. Organ rupture occurs at over 20 PSI so unless there is evidence of a much higher blast pressure it is difficult to get there.


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