Arcs Above 40 Calories

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big john

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Does anyone have some links to arc-flash studies or test results for greater than 40 cal?

I know people often say that's the upper end of the blast that can be survived without serious injury, but I'm hoping to find some hard data on that.

I know that 70E removed the "HRC 5" category for this reason, but what's the deal with 65 cal and 100 cal suits being labeled "HRC 4"? Seems like when you're more than doubling the minimum arc rating it's a cheat to keep it in the same category.

-John
 
Above 40 cal/cm?, the concern is with blast (shock wave and shrapnel) which requires a true bomb suit.

A 40ATPV suit does not guarantee no major injury, so going to a 65 or 100 is kind of like using 1000V insulated tools at 480V.
 
Here is what 70E says 130.8

Informational Note No. 1: The PPE requirements of 130.8 are intended to protect a person from arc flash and shock hazards. While some situations could result in burns to the skin, even with the protection selected, burn injury should be reduced and survivable. Due to the explosive effect of
some arc events, physical trauma injuries could occur. The PPE requirements of 130.8 do not address protection against physical trauma other than exposure to the thermal effects of an arc flash.

Informational Note No. 2: When incident energy exceeds 40 cal/cm2 at the working distance, greater emphasis may be necessary with respect to de-energizing before working within the Limited Approach Boundary

When you get to the higher Ei's the pressure from the blast becomes the limiting factor for the PPE, but calculating pressures is different than heat. A 50cal/cm2 arc flash that resulted from a low arcing current and long clearing time in open air won't produce much pressure. A 50 cal/cm2 arc flash in a cubic box (Like a breaker cell) from a high current and fast clearing time will have tremundous pressure produced. The best reference is Ralph Lee's "other" paper "Pressures developed from arcs", which I can send you if you want. (Too large to attach here)
 
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