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 Post subject: Associate incident energy with real world
PostPosted: Fri Mar 20, 2009 7:37 am 
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Joined: Mon Dec 08, 2008 7:52 pm
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I am in the process of developing an electrical safety program for my group.

The degreee of hazard is express in cal per cm2. Any thoughts on how I can related let's say 20 cal per cm2 to something the electricians can relate to? I want to make the point that will make the point other than a relatively sterile number i.e. 20 cal/cm2. Thanks reading my post.


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PostPosted: Fri Mar 20, 2009 8:53 am 
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Location: Quebec, Canada
1.5 cal/cm2 = 2nd degree burn.


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PostPosted: Fri Mar 20, 2009 9:16 am 
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Location: Charlotte, NC
beenthere wrote:
I am in the process of developing an electrical safety program for my group.

The degreee of hazard is express in cal per cm2. Any thoughts on how I can related let's say 20 cal per cm2 to something the electricians can relate to? I want to make the point that will make the point other than a relatively sterile number i.e. 20 cal/cm2. Thanks reading my post.


An arc flash can reach temps up to 36,000F. Steel melts around 1,800F, the surface of the sun is around 7,000F. An arc can be 20 times the temp it takes to melt steel or about 5 times as hot as the surface of the sun.

Download the arc flash testing viseos from http://www.westexinc.com and show them what a 5cal/cm2 arc flash looks like, they wont even need to see 20cal/cm2 after that.


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PostPosted: Fri Mar 20, 2009 10:41 am 
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There's also the "dynamite equivalent" approximation.

From the available fault MVA, you can get the max power of the arc (max power is half the available fault MVA). Power times time (arc duration) equals energy.

For dynamite, 1 kg contains about 7.5 MJ.

Of course it's not exactly the same feeling (the shorter the arc duration, the closer it is though), but a blast is a blast.


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PostPosted: Tue Mar 24, 2009 8:53 am 
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Joined: Thu Jul 19, 2007 7:54 am
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Location: St. Louis, MO
Try this one:

Get you a butane lighter (like a Zippo).
Light it.
Now if you hold your hand 1 inch above the blue section of the flame for just one second, that's about 1.2 cal/cm2. You should get a pretty good blister.
(NO, don't really do it!!!)

Now, multiply that by 17, and you get ~20 cal/cm.


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PostPosted: Tue Mar 24, 2009 12:39 pm 
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Location: Aurora, Ontario, Canada
The temperature 36,000F is at the origin of an arc flash, and it is less at the working distance which is usually 18in. Also, 20cal/cm2 is the IE at the working distance. Calorie is a unit to measure thermal energy, not temperature. Arc flash can deliver a very high energy in a very short period of time (ms). Much less energy, but longer time can have the same effect, i.e. if you put your hand into the fireplace for a minute you can obtain the same burn as 20cal/cm2 from Arc Flash. Yes, in most cases the temperature kills, but there are many other dangerous factors associated with arc flash: toxic gases, intense light, molten metals etc., so don’t tell about the energy (temperature) only. The best way is to show a few pictures and/or videos.


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