Arc flash safety

[MARK WARNER]

I would appreciate any help and advice I could get regarding arc flash PPE and their use. We have just received the results of an short circuit and coordination and resultant arc flash study. This study revealed that incident energy of 63 cal/cm2 exists at our NWP's and switch gear. I have been advised that this exceeds the minimum of 40cal/cm2 of level 4 PPE and that we should not operate main or tye switches and that the stickers we are to apply to our equipment states, and I quote, " DANGER HAZARD LEVEL EXCEEDS MAX ARC FLASH PROTECTION" I have seen that there are suppliers of PPE rated at 70 cal/cm2. My question is, can I purchase the heavier PPE and have my technicians safely operate this gear and thusly continue my operations? We presently have 4 feeders and perform switching to insure redundancy whenever the utility takes a single feeder from us. We can not insure redundancy without moving those switches..I am not a degreed electrical eng. and know not who to turn to.

 

[zog]

I would appreciate any help and advice I could get regarding arc flash PPE and their use. We have just received the results of an short circuit and coordination and resultant arc flash study. This study revealed that incident energy of 63 cal/cm2 exists at our NWP's and switch gear. I have been advised that this exceeds the minimum of 40cal/cm2 of level 4 PPE and that we should not operate main or tye switches and that the stickers we are to apply to our equipment states, and I quote, " DANGER HAZARD LEVEL EXCEEDS MAX ARC FLASH PROTECTION" I have seen that there are suppliers of PPE rated at 70 cal/cm2. My question is, can I purchase the heavier PPE and have my technicians safely operate this gear and thusly continue my operations? We presently have 4 feeders and perform switching to insure redundancy whenever the utility takes a single feeder from us. We can not insure redundancy without moving those switches..I am not a degreed electrical eng. and know not who to turn to.

70Cal/cm2 rated PPE will protect from burns but not the blast pressures, 40cal/cm2 is the industry standard limit to survivable arc flash (wearing PPE) due to the pressures created. This may change in the future, IEEE is doing more resaerch on this as we speak but for now you shouldnt work on anything >40cal.cm2 no matter what you are wearing.

Hundreds of copmanies have turned to remote switching and racking solutions for this problem. Either that or mitigate the hazard using arc flash reduction systems, changing settings, etc...

My specialty are is mitigation and arc flash solutions for this exact problem. Every situation is different. Feel free to contact me if you have any questions. (PM me) I will be able to give you several solutions to your problem.

 

[ghostbuster]

There are many issues surrounding this problem.I would recommend you hire a local professional engineering group practising in this area for guidance.:smile:

 

[jim dungar]

There are many issues surrounding this problem.I would recommend you hire a local professional engineering group practising in this area for guidance.:smile:

Once the engineering has been done, it becomes a work practices issue. NFPA 70E requires you to implement a safe work practices program, it suggests including a risk analysis. So, make sure the safety department is involved. NFPA70E is not a 'how-to' book, just like the NEC is not a design manual.

 

[weressl]

I would appreciate any help and advice I could get regarding arc flash PPE and their use. We have just received the results of an short circuit and coordination and resultant arc flash study. This study revealed that incident energy of 63 cal/cm2 exists at our NWP's and switch gear. I have been advised that this exceeds the minimum of 40cal/cm2 of level 4 PPE and that we should not operate main or tye switches and that the stickers we are to apply to our equipment states, and I quote, " DANGER HAZARD LEVEL EXCEEDS MAX ARC FLASH PROTECTION" I have seen that there are suppliers of PPE rated at 70 cal/cm2. My question is, can I purchase the heavier PPE and have my technicians safely operate this gear and thusly continue my operations? We presently have 4 feeders and perform switching to insure redundancy whenever the utility takes a single feeder from us. We can not insure redundancy without moving those switches..I am not a degreed electrical eng. and know not who to turn to.

Any engineer worth their salt would include at least general recommendation to bring the facility into an operable condition.

 

[WDeanN]

This study revealed that incident energy of 63 cal/cm2 exists at our NWP's and switch gear. I have been advised that this exceeds the minimum of 40cal/cm2 of level 4 PPE and that we should not operate main or tye switches and that the stickers we are to apply to our equipment states, and I quote, " DANGER HAZARD LEVEL EXCEEDS MAX ARC FLASH PROTECTION"

There is no such rule. 70E states that additional protection should be taken over 40 cal.
Just a clarification. It is up to each company to provide work rules.

70Cal/cm2 rated PPE will protect from burns but not the blast pressures, 40cal/cm2 is the industry standard limit to survivable arc flash (wearing PPE) due to the pressures created.

I am seaching for one, just ONE, case where a guy was crushed from over pressure due to the blast while wearing a "bear suit" to perform work.
So far, no luck...

 

[cpal]

I highly recommend securing the services of a PE tomodify your system to a risk hazard level two .

This might be accomplished through current limiting fuses or series inductors, or another recognized method.

even at 40 cal the risk is tremendous.

 

[zog]

I am seaching for one, just ONE, case where a guy was crushed from over pressure due to the blast while wearing a "bear suit" to perform work.
So far, no luck...

Utilities Remote Racking of Metal-Clad Switchgear
Dec 1, 2002 12:00 PM
With two employees dead and three injured (two very seriously), Gulf States Electric Utilities (Beaumont, Texas, U.S.), now part of Entergy (New Orleans, Louisiana, U.S.), had to find a solution.

The accident occurred on Jan. 5, 1993, at the Sabine Power Station near Bridge City, Texas. Sabine personnel had racked-in a retrofitted Toshiba breaker and sent the close command, but the breaker did not close.

With the breaker indicator showing that it was still open, the operator (in a full flash suit) began racking-out the breaker to troubleshoot the problem with his supervisor standing nearby. Neither knew that the breaker received the closed command, which unlatched and began its closing operation but could not complete the close due to mechanical problems.

The breaker was still receiving the close command while it was being racked-out. As it moved, the mechanical bind was relieved, the trip-free protection failed and the breaker closed while partially racked-out. The resulting electrical arc-flash and explosion critically burned them and slammed them back against the wall; both died. The arc-flash traveled around a corner and burned three other individuals.

By wearing a full-body flash suit during racking procedures on an energized bus, the primary operator at the Sabine Station was doing everything required by “A”-NFPA A70E and OSHA 29CRF-1910-S-App. While the suit provided him with some protection, it did not save his life.

Entergy began looking for more effective ways to protect its workers. First, it quickly corrected the problems with retrofitted Toshiba breakers. Second, after considering various solutions, Entergy began to retrofit all rackable breakers (2300-V and above) with remote racking systems.

 

[ron]

This might be accomplished through current limiting fuses or series inductors, or another recognized method.

Charlie,
I've found better luck using solid state CB's than fuses especially if the fault current is relatively low.
An inductor or reactor will lower fault current and generally increase incident energy because the OCPD requires more time to trip at lower current (inverse time).

 

[cpal]

Charlie,
I've found better luck using solid state CB's than fuses especially if the fault current is relatively low.
n inductor or reactor will lower fault current and generally increase incident energy because the OCPD requires more time to trip at lower current (inverse time).

Thanks for that info Ron,

can you refer me to some literature on the CB's you are talking about???you

 

[ron]

can you refer me to some literature on the CB's you are talking about???

All of the major manufacturers have them generally in frame sizes larger than 100A.
Here's a white paper on CB's
http://www.sea.siemens.com/step/pdfs/circuit_breakers.pdf

 

[WDeanN]

Thanks zog. This is almost what I am looking for...

The resulting electrical arc-flash and explosion critically burned them and slammed them back against the wall; both died. The arc-flash traveled around a corner and burned three other individuals.

By wearing a full-body flash suit during racking procedures on an energized bus, the primary operator at the Sabine Station was doing everything required by ?A?-NFPA A70E and OSHA 29CRF-1910-S-App. While the suit provided him with some protection, it did not save his life.

It still does not say, though, that they died from concussion injuries. It makes it sound like they died from the critical burns received.

I'm not making light of the situation at all, you should know that by now. I am just questioning the justification for the 40 cal cut-off.

 

[weressl]

Thanks zog. This is almost what I am looking for...



It still does not say, though, that they died from concussion injuries. It makes it sound like they died from the critical burns received.

I'm not making light of the situation at all, you should know that by now. I am just questioning the justification for the 40 cal cut-off.

The quote DID mention that the operator fully complied with the NFPA requirement. Less than full compliance would mean that the suit's rating was not high enough for the available energy. The conclusion can be drawn from the facts as reported - despite what it states - that they have died from other causes, not related to inappropriate or inadequate rating of the PPE's. The statements (1)that they were critically burned and (2)the operator was in compliance with the regulations indicates either of two things; either it is contradictory to the facts, eg. they do not died as the result of the burn, or that the existing regulations are inadequate to protect them.

 

[WDeanN]

The quote DID mention that the operator fully complied with the NFPA requirement. Less than full compliance would mean that the suit's rating was not high enough for the available energy.

No, full compliance only means that they may have followed the tables within 70E, which are task and equipment specific, and do not estimate the actual hazard that may exist.
They may have been performing a task, for example, that only required level 2 protection (8 cal/cm), but the actual energy, had it been calculated, may have been 39 cal/cm. They still could have been in compliance with the 70E.

Look, we follow the 40 cal cutoff at my location. This is not a compliance issue, however. This is more of a liability issue. I also constantly see people saw that the resulting explosion will crush you. I have yet to see a case of this. Yes, I have run the numbers by Ralph Lee's equations in Pressures Developed by Arcs. I don't disagree that the pressures are high, and could lead to damage.
I just want to see the case...

 

[weressl]

No, full compliance only means that they may have followed the tables within 70E, which are task and equipment specific, and do not estimate the actual hazard that may exist.
They may have been performing a task, for example, that only required level 2 protection (8 cal/cm), but the actual energy, had it been calculated, may have been 39 cal/cm. They still could have been in compliance with the 70E.

Look, we follow the 40 cal cutoff at my location. This is not a compliance issue, however. This is more of a liability issue. I also constantly see people saw that the resulting explosion will crush you. I have yet to see a case of this. Yes, I have run the numbers by Ralph Lee's equations in Pressures Developed by Arcs. I don't disagree that the pressures are high, and could lead to damage.
I just want to see the case...

So you are saying that if one follows the NFPA they may or may not get killed? And we mandate such to be followed? Is anybody awake at the wheel?