# Arcs Above 40 Calories



## Zog (Apr 15, 2009)

Big John said:


> 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.
> 
> ...


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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## don_resqcapt19 (Jul 18, 2010)

Big John said:


> ...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. ...
> -John


 You could look at the ROP and ROC for that change on the NFPA website. That will give you some information.


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## Big John (May 23, 2010)

don_resqcapt19 said:


> You could look at the ROP and ROC for that change on the NFPA website. That will give you some information.


 Good idea, I'll take a look.

-John


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## Mshea (Jan 17, 2011)

I think the simplest explanation is over 40 cal and it is a bomb suit. A 100 cal suit can be made but the wearer is still dead and just not crispy.


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## ralpha494 (Oct 29, 2008)

To explain informational Note 1 from 130.8 I usually say that the 40 cal suits keep you from getting 2nd degree burns on your torso, but nothing to keep your sternum from touching your backbone from the blast.


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## Big John (May 23, 2010)

As best as I can tell so far, the reluctance to include any categories above HRC 4 actually comes from a lack of data.

The substantiation for removing HRC 5 was basically that we don't know enough about how the blast will effect a person to safely include that category.

I still need to re-read that study on pressure waves that Zog spoke of.

-John


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