Arc Flash Category 4 and 4+ ?

[Eleceng01]

I was hoping to get everyones help on this. I see that several manufacturers offer arc suits up to 100 cal/cm^2 but my understanding of the NFPA70-2004, Table 130.70(c)(11) is that anything above 40 cal/cm^2 can not be worked on energized.

My understanding is at above 40 cal/cm^2 the blast itself will kill you - not necessarily the arc.

So how do I handle a location that is 85.2 cal/cm^2 until the engineering solution is implemented?

Am I confused? Any comments will be appreciated. Thanks.

 

[Zogzog]

No, you are not confused. The PPE manufactues developed those suits back before the research was done regarding the presseure effects on the human body. A 100Cal suit for your 85 cal hazard will protect the worker from 2nd degree burns, but the blast may be unsurviveable.

If you can describe the equipment maybe I can help you with your problem.

 

[Eleceng01]

Thanks Zogzog!

As I said, this was my understanding and I wanted to get a sanity check with what everyone else is being told or is telling clients about levels >40 cal/cm^2.

Our consultant has told me that no one can go near the switchgear until we reduce the levels to below 40 cal/cm^2.

 

[Zogzog]

Well your consultant should have provided a quicker (Although possibly temporary) solution, what kind of advice is "Dont go near it"?

Ther are several solutions depending on your equipment type and configuration that you could have implemented over this weekend. We would nevr leave our clients in a situation like that. What happens if you have a breaker trip tonight? I am sure the production boss would love to hear "Sorry we cant turn anything back on, the consultant said to stay away"

Scott Peterson
Training Manager
Power Plus Engineering

http://www.epowerplus.com

 

[dpc]

There's nothing improper about wearing 85 or 100 cal/cm2 PPE to work on something below 40 cal/cm2. The extra layers will provide more protection against the heat of an arc-flash event, regardless of the level.

 

[DanDel]

"So how do I handle a location that is 85.2 cal/cm^2 until the engineering solution is implemented?"

De-energize it.

 

[stevenal]

Except it must be considered energized until it is tested and found absent of potential. Who performs the test and what do they wear while doing it?

 

[Zogzog]

The key question is "85.2 cal/cm^2 at what distance?"

 

[stevenal]

Incident energy is determined at the skin or clothing surface. Distance does not matter at this point because it has already been factored in. Eleceng01 used an assumed distance to get the 85.2.

 

[rbulsara]

As in all aspects of the life, common sense must prevail. Existing guidlines and equipment are not "all problem solved" solutions but something better than we had so far. So use them to your advantage not make foolish issues out of it.

It is very simple, if you are so worried and caring about someone's life do not work live. Arrange and design redundant systems. OR some risk in life are necessary, but I would not ask someone to risk his/her life for saving anyone's any amout of money or equipment.

There are many much less risky ways to determine if the equipment are deenergized.

 

[Zogzog]

"Incident energy is determined at the skin or clothing surface. Distance does not matter at this point because it has already been factored in. Eleceng01 used an assumed distance to get the 85.2."

My point exactly. If the assumed working distance was 18", you can re-run the numbers to find the Ei at the actual working distance. For example if you want to use a remote racking system, a remote breaker operator (Like the chicken switch), or a hot stick for verifing a system de-energized you may find the Ei is less than 40 cal/cm2.

 

[Eleceng01]

The real issue right now is that the fault protection boundary is 27.6 feet and the room is only 30' x 12' (LxW). So can anyone even enter the room with the equipment energized without some PPE?

 

[dpc]

As long as the equipment doors are closed and no switching operations are underway, PPE is not required by NFPA 70E just to be in the room.

However, some companies do require PPE to be worn when entering some electrical rooms - that is a company safety policy, but not required by NFPA 70E - at least not yet.