Layering of Arc Flash Clothing

[Eleceng01]

I was having a conversation with a vendor today and he stated that you could layer FR clothing to get the desired FR rating. For instance, if the arc flash hazard is 59 cal/cm2 then you could wear 12 cal/cm2 coveralls and a 55 cal/cm2 suit (12 + 55 = 67 > 59).

I have never heard this and thought that you needed a 60 cal/cm2 suit.

I was hoping to get others opinion on 'adding cal/cm2 numbers' to get the desired protection. Thanks.

 

[tem1234]

This is true but...

60 cal/cm2 is cat > 4, so event with suit 60 cal/cm2 you cannot work there, since the suit will not protect you against the force of the explosion

But for a 40 cal/cm2 case per exemple, you can wear 2 x 20 cal/cm2 layer (event if it's not really confortable)

You must still have a hood rated 40 cal/cm2, since i think it's a little bit difficult to have two layer or more for the hood and facesheild.

 

[JTS44]

Article 130.7.12 of NFPA alludes to application of additional layers to achieve required protection level.
Also, NESC refers to the effective arc rating of a "clothing system", which can be made up of multiple layers.

 

[ichrist]

The vendors I've talked to don't endorse mixing layers from different manufacturers. In reality it's likely okay but none of the vendors will test their gear together with another's.

 

[jghrist]

There is an additive effect in layering, but you can't determine the overall rating without testing the combination.

 

[jghrist]

The vendors I've talked to don't endorse mixing layers from different manufacturers.

You would probably get a different answer if you have FR clothing from Mfg A and asked Mfg B if his coveralls could be mixed with your existing clothing!

 

[GTstartup]

I agree with Tem.

You can wear all the layers you want but a 60cal arc flash is like getting hit by a fridge at 100MPH

 

[ScottyUK]

Given the choice of working on legacy equipment with a 40 cal suit, 60 cal suit, or 100 cal suit I'd take the best protection available. With incident energy over 170 cal/cm^2 on some of our boards the blast would likely have blown us straight through the substation walls like some Looney Tunes cartoon character and maybe the only difference the heavier suit would make is between open casket, closed casket, or dustpan & brush but I'd still take the highest available providing I could still work in it. The 100 cal suit we had wasn't outrageously heavy, although very warm, but the hood wasn't much fun.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[dpc]

I agree with jghrist. Layering is effective, but you need to use a tested combination.

David Castor

http://www.cvoes.com

 

[GTstartup]

In the US I am pretty sure you cannot legally work on live equipment with incident energy of the level mentioned in the OP.

 

[ScottyUK]

GTstartup,

That is somewhere the UK lags way behind the US. It relies totally on companies developing their own policies, and individuals making a stand when necessary. Hopefully that will change over time.


----------------------------------

If we learn from our mistakes I'm getting a great education!

 

[Zogzog]

There is not really a law against working >40cal, just mentioned in the 70E as a point where the pressures from the arc may become a hazard that PPE becomes ineffective (Paraphrased). Typically systems >40cal are labeled as dangerous. Mitigation should be looked at in these cases to properly protect personel.

 

[Eleceng01]

My understanding is the same as ZogZog - it isn't illegal in the U.S., it is only not recommended.