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What arc rating would you select for incident energy of 8.1 cal/cm^2
 Use 8 calories/cm^2 (close enough) Use something greater such as 12 cal/cm^2 Jump to Category 4 - i.e. 40 cal/cm^2 Some other rating
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 Post subject: PPE for incident energy = 8.1 cal/cm^2Posted: Sun Sep 16, 2012 2:10 pm
 Plasma Level

Joined: Mon Sep 17, 2007 5:00 pm
Posts: 1637
Location: Scottsdale, Arizona
If the calculated incident energy is 8.1 cal/cm2, what arc rating of PPE would you use?
Assume the study data is as accurate as it can be, no physical changes are made such as increasing the working distance - 8.1 is as low as it gets.
• Use 8 calories/cm2 (close enough)
• Use something greater such as 12 cal/cm2
• Some other rating
Thoughts and opinions are always encouraged!

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Jim Phillips, P.E.
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 Post subject: Posted: Mon Sep 17, 2012 7:59 am

Joined: Mon Apr 18, 2011 1:43 pm
Posts: 11
Location: Denver, CO
I guess some people don't mind 2nd degree burns. Me, I'll play it safer.

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 Post subject: Posted: Mon Sep 17, 2012 6:27 pm

Joined: Wed Jul 25, 2012 6:06 pm
Posts: 1
Location: Brisbane, Australia
I vote for 8cal, as this would be the most likely to see compliance from personnel.
This would particularly be the case if everywhere else is below 8cal/cm2.

It does however depend on both the methods used in the study and the level of acceptable risk.
In our studies, the worst case incident energy requires the coincidence of a number of worst case variables.
The combined probability that all variables would be at their maximum is low.
We do not consider a study accurate to 0.1cal/cm2

On the other hand, we recommend company policies that include a buffer in the rating of PPE, to further decrease injuries.
It also depends on the duration of the arc. A 0.2s arc giving 8.1 cal/cm2, would tip the choice towards higher rated gear.
A max duration, 2s arc, would definitely tip the choice towards 8 cal/cm2 gear.

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 Post subject: Posted: Thu Sep 20, 2012 4:45 am
 Plasma Level

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
IEEE 1584 states that irrespective of the underlying estimates made according to the test bank there is a 95% confidence that wearing PPE equal to or greater than specified will result in less than a 2nd degree burn. There are several variables that have nonlinear effects on this, so a table of adjustments and confidence intervals would likely have to be calculated. Without those calculations, simulations, etc., and especially without the backing of an industry standard, in a court, there will be a huge problem. This would be a problem even if another bus with a lower cal/cm^2 rating resulted in an injury because it can be used as evidence of playing fast and loose and taking unnecessary risks.

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 Post subject: Posted: Mon Sep 24, 2012 6:54 pm
 Sparks Level

Joined: Thu Oct 18, 2007 7:10 pm
Posts: 263
Location: NW USA
If the calculated exposure is greater than risk category 2, we prescribe full risk category 3 PPE.

Trying to keep this simple and away from independent interpretations.

As mentioned in your IEEE 1584 thread, I often wonder if this whole science has been poorly handled to result in so much complication instead of simply giving the fellows HRC 4 rated flash suits for 480V hot work(with stated limitation such as transformer size) and something lesser for less than 300V hot work. Two suits to wear, don't do hot work without them (note: we've not given such advice, just question the splitting of hairs that leads folks to park their PPE).

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 Post subject: Posted: Thu Sep 27, 2012 3:43 am
 Plasma Level

Joined: Tue Oct 26, 2010 9:08 am
Posts: 2174
Location: North Carolina
Gary B wrote:
As mentioned in your IEEE 1584 thread, I often wonder if this whole science has been poorly handled to result in so much complication instead of simply giving the fellows HRC 4 rated flash suits for 480V hot work(with stated limitation such as transformer size) and something lesser for less than 300V hot work. Two suits to wear, don't do hot work without them (note: we've not given such advice, just question the splitting of hairs that leads folks to park their PPE).

We did. There are a number of problems with this:

1. Visibility is down to less than 50%. Increases risks dramatically.
2. Manual dexterity is drastically reduced. Again, increased risk when doing fine detail work such as landing wires.
3. Heat exhaustion/stroke risk drastically increased.

Overdressing is neither safer nor simpler. It's not like establishing "LOTO for everything".

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