Arc Flash PPE Assumptions

[Kyle2022]

Good afternoon,

It has been mentioned in some seminars that I've attended that the PPE requirements of an arc flash study can be lowered by 2 categories if the switchgear door is closed (closed-door racking, etc). Is this an industry-wide assumption or the ramblings of the un-educated? If it is a legitimate assumption, can I find it in either IEEE 1584 and/or NFPA 70E?

I will go one-step further and ask what PPE a person must wear to simply enter a room containing the gear. They may well be within the arc-flash boundary, but not performing any maintenance tasks.

Thanks!

 

[JBD]

IEEE 1584-2002 is a methodology to determine the amount of incident energy in an arc flash. IEEE 1584 does not make PPE recommendations

NFPA 70E is the proper place to go for implementing PPE and other electrical safe work practices based on the arc flash incident energies.

Arc flash incident energies from calculations rarely differentiate between the state of equipment doors nor tasks that may be performed.

As long as no tasks are being performed and there are no exposed energized parts most electrical safe work practice programs allow personel to be present without additional PPE. But, the actual requirement is dependent on your safe work practice program. NFPA 70E does not specifically address this issue.

 

[stevenal]

See Table 130.7(C)(9)(A). For metal clad 1KV and above; racking with open door > 4, racking with door closed > 2.

http://nfpa-acs-01.gvpi.net:8080/rrserver/browser?title=/NFPASTD/70e04

 

[dpc]

I agree with JBD's comments. In the run-up to release of 2004 version of NFPA 70E there was consideration of allowing reduction of PPE level based on the task being performed. This did not make into the final version, but you can see something similar going on in Table 130.7(C)(9)(a),which is task-based table for determining PPE requirements in lieu of doing arc-flash analysis (and may or may not be used depending on meeting the limitations given in the footnotes of the Table.

In normal metal-clad switchgear, a closed door offers very little protection against available arc-energy while racking a breaker in. It's better than having the door open, but it isn't going to allow someone to go from PPE #4 down to PPE #2.

There are cases where workers in 100 cal/cm2 suits were killed when racking in a breaker (with the doors closed).

 

[wbd]

CAUTION! Please be aware that if there are vents cut into the switchgear this will constitute exposure to energize components since the blast can come thru the vents. This was pointed out in the October issue of NEC Digest. Here's a link:

http://www.nfpa.org/itemDetail.asp?...Magazine/Current issue/Columns/Safety Section

 

[rbulsara]

I agree to above posts.

To add to the above, it is important to remember that PPE only affords protection against burn injuries and that too only to second degree burn, which most painful but curable.

There are other potentially deadly hazards that occur due to a fault, arcing or not, such as shrapnel or flying debris and sound pressure waves. So some one standing outside of a arc flash boundary but directly in front of a breaker can still be fataly wounded if the breaker or the piece of switchgear comes flying out upon a fault.

The point is just wearing a PPE does not make one safe to wander around a live piece of electrical equipment. So all those common sense precautions and professional judgments that were taken before "advent" of this new arc flash calculation methods and standards, still have to be taken.

On the other hand, if you only are concerned about burn injuries there would not be need to wear any PPE beyond the flash boundary. Also PPE inlcudes shock preventing measures too (insultated gloves and tools etc.) that the person not working live does not have to don.

 

[ScottyUK]

For those who are still unconvinced about the risks of arcing faults, we had another accident on Teesside earlier this year.

http://news.bbc.co.uk/1/hi/england/tees/5255292.stm

This one was an MV motor control centre which suffered a major internal fault. I am not certain but I would be surprised if the workers were wearing arc-flash PPE over and above the flame-retardent coveralls which are standard at most petrochem facilities in the UK. It isn't clear whether the door was open or not, but if it was then it did little to contain the explosion. Other than in the mining industry I have not seen much UK switchgear equipped with doors which could contain an explosion - the doors would just become another projectile. I have some photographs of the board at work - I will see if I can post them on Monday.

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