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 Post subject: Safety Rookie
PostPosted: Mon Jul 06, 2009 9:21 am 
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Joined: Mon Jul 06, 2009 9:06 am
Posts: 5
Hey everybody. I'm new to the forum. I am currently a safety professional working as an Air Force contractor. I am currently attending Tulane University for a greaduate degree in Safety Management. My first paper that I am writing is on Arc Flash PPE. This is a very high priority for my company right now because two of our maintenance guys got burnt pretty bad by a flash from a 480v 600 amp chiller unit.

here is my first question for you guys:

Why is PPE determination based on Volts and not Current? I always hear the 600V ideology, but never any mention of current. It's the current that does the damage. All of the safety guys that I work with say that since our guys were not working with over 600V they did not require PPE as per the standard. Now after reviewing the 2009 NFPA 70E we know different. But I still do not understand the Volts ideology when determining PPE. The only thing I can think of is that the higher the volts the better current can be transfered into an arc flash. Maybe I'm thinking too much into it. But hey thats our job right.

Thanks I look forward to coming back on a regular basis.


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PostPosted: Mon Jul 06, 2009 2:38 pm 
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Joined: Mon Jun 02, 2008 11:58 am
Posts: 1103
Location: Charlotte, NC
bfietkau wrote:

Why is PPE determination based on Volts and not Current?


It is not based on voltage at all, but rather the totoal amp-cycles of the fault and the distance from the arc to the worker.

bfietkau wrote:
All of the safety guys that I work with say that since our guys were not working with over 600V they did not require PPE as per the standard. Now after reviewing the 2009 NFPA 70E we know different.


Typically you will find higher (larger) arc flash hazards on LV equipment than you will on anything >600V.

bfietkau wrote:
But I still do not understand the Volts ideology when determining PPE.


Not sure what you mean or where you get that from, please explain.

bfietkau wrote:
Thanks I look forward to coming back on a regular basis.


We are glad to have you, may I suggest you read some old posts, get a feel for what an arc flash is, etc...


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PostPosted: Tue Jul 07, 2009 12:21 pm 
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Joined: Mon Dec 08, 2008 7:13 am
Posts: 26
Location: Quebec, Canada
Arc flash PPE is based on energy levels. Shock protection PPE is based on voltage levels.

Most arc flash labels show arc flash and shock protection PPE. Maybe that's why you asked that question?

I suggest you read NFPA 70E again.


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PostPosted: Wed Aug 26, 2009 1:18 pm 
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Joined: Thu Jan 29, 2009 2:06 am
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bfietkau wrote:
It's the current that does the damage.


Not necessarily true. Plus you still need to have voltage to push the current.


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PostPosted: Wed Aug 26, 2009 11:36 pm 
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Joined: Fri Jan 16, 2009 1:07 pm
Posts: 67
Location: North Florida
B-

I understand your confusion about PPE being based on voltage - a quick look at table 130.7(C)(9) would lead you to this since it is broken up into voltage ranges to help you determine the PPE Level. What is not said in the table is that this is simply a means to help people quickly get to a value. The table is based on 'typical' installations of equipment at a given voltage and short circuit energy level and what the expected PPE should be for the 'typical' incident energy level. So the reality is that the table is based on incident energy - how much energy for how long - but it looks like it's based on voltage.

That is also why there are limitations on the use of the table and on larger systems why it is necessary to do the Arc Flash Study - many systems don't fit the tables.

I hope this helps and good luck with your studies.

TxEngr


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PostPosted: Thu Aug 27, 2009 3:21 am 
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Joined: Sun Aug 16, 2009 8:42 am
Posts: 184
Location: Lawrenceburg KY
Training

I see safety people trying to figure electrical requirements a lot. In my opinion, the two should work together as a team. The safety person would be best to leave most of the study of short circuit, coordination and equipment duty to an electrical person knowledgeable in this field of study. I believe a safety management group can make a livable policy with assistance from an electrical authority. There is much more to electrical safety that can take person years to learn and understand. I personally find that safety management that has no background in electricity tends to be very over concretive towards PPE, creates impossible policies to live with, has no ideal about the electrical equipment and can create a hazardous work area unknown to safety management.
Just my take.


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PostPosted: Thu Aug 27, 2009 3:46 am 
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Joined: Sun Aug 16, 2009 8:42 am
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Location: Lawrenceburg KY
I meant conservative not concretive. :confused:
Sorry


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