Arc Flash - NFPA 70E 3

[rconnett]

For those of you involved at plant sites, have you or are you being encourged to look at the new regulations regarding Arc Flash, and applying Personal Protective Equipment?

Are you (a)complying, (b)ignoring, or (c)stumped on how to respond? I'm trying to figure out just what kind of an impact this is having/will be having on the industry in the US. There seems to be a lot of discussion about this topic.

Thanks

 

[dpc]

Most large industrial facilities are taking the necessary steps to provide PPE and hazard assessment for arc-flash hazards. Now we're starting to see interest by municipal and commercial facilities.

It is done deal - just a question of when you will get the program implemented. If there is an arc-flash related injury right now in any facility, OSHA can and has levied fines if proper PPE and hazard assessment was not provided.

 

[rconnett]

I guess the imple,entation varies. I deal with a lot of large industrials, and their position varies according to my post - hence I ask the question.

According to OSHA, they have not directly adopted NFPA 70E (although there ared indirect incorporations of it), but they can make the case.

OSHA apparently will be adopting portions of NFPA70E directly, most likely this winter. That's not to say OSHA can't levy fines, since the safe work practices rule applies & NFPA 70E addresses this. However, OSHA 1910 does not directly reference NFPA70E at this time.

I am interested in people's experience here.

 

[Electic]

As a consultant, I am helping several plants comply with the intent, by
1) offering arc flash training
2) performing arc flash exposure calculations

It seems like a big step when first considered but at the site I am most invovled with, actual deployment has not been a hardship.

This site is an oil refinery with existing PPE requirement of nomex coveralls. Most of the switchgear we analyzed has only an arc flash exposure of '1' (NFPA designation) so we are verifying that the coveralls offer protection of 4 cal/cm sq.

There are a few locations that have exposure of '2' and for those locations an arc flash jacket and face hood is kept handy.

We are presently preparing labels for the entire complex, with modern software (e-tap) the calculations are routine, but making that many labels gets to be a big project.

I feel there are many open liabilities within NFPA 70E, and though it can be used as a consensus/guidline; should not be followed too literally. That may be a reflection on the subjective nature of arc flash phenomena, too many variables to quantify in a code book.

As an example, exposure level 1 requires 4 cal/sq cm protection but no face sheild. Personally I would rather not have my face burned up. One must hope that in an arc flash incident, the worker's face is far enough away to be out of contingency.

 

[dpc]

We are working with large fossil power plants, pulp & paper mills, assembly facilities, food processing plants and others in implementing their arc-flash assessment. These are in various stages of implementation, but they plan on compliance with NFPA-70E, at least in general. The energized work permits required in the 2004 version do not seem to gaining quite as rapid an acceptance as the basic PPE and labeling requirements.

There are certainly a lot, maybe a majority, of facilities that haven't done anything yet.

You're right that NFPA-70E is not a mandatory standard in the sense that the NEC is. But OSHA is enforcing the need for arc-flash hazard assessment and PPE already. In the regions were there have been accidents and fines, the pace of adoption has picked up.

 

[ScottyUK]

Europe is lagging behind the US in arc-flash assessment. It is something I'm interested in because we're classifying our switchgear according to risk presented to a worker carrying out 'live working' in the sense of commissioning tests or maintenance troubleshooting once all the 'dead working' alternatives have been exhausted.

Can any of the US engineers involved in this sort of classification give any guidance on how to go about assessing the risks? I'm not really interested in the legislative process because the US authorities obviously don't have any jurisdiction in the UK, but am keen to understand and hopefully apply the assessment methods developed in the US.


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

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[porf]

At our facility, rather than be confused from the “get-go”, we are encouraging the use of standard tables found in NFPA 70E, Tables 130.7(C)(9) and 130.7(C)(10). In those tables, many of the activities that an electrician will be involved with are listed along with the appropriate PPE that should be used. Thus, why have an engineer go through the calculations and possibly come up with one of three, or more, possible results for selection of PPE or arc flash protection distance?

We lean very much toward the use of tables to satisfy, in part if not entirely, NFPA 70E. We understand that labeling should be produced for equipment but this will come in due time as the engineers gather all of the pertinent equipment information to use with software programs invoking NFPA 70E and IEEE Std. 1584TM-2000.

Cheers!

 

[dpc]

Scotty,

You might want to get hold of a copy of NFPA 70E (2004) as a starting place. It's not terribly expensive (compared with IEEE 1584 anyway) This is a "consensus" standard on electrical safety in the workplace (in the US). It's use is not legally required, but our federal OSHA has said that if NFPA 70E is followed, you will meet OSHA requirements for electrical safety.

At this point, most facilities are not in full compliance with all parts of NFPA 70E, but it still serves as good reference for a "model" safety program.

 

[Electic]

Scotty,
I aggree with dpc. Start with a copy of NFPA 70E and check the hot work portion of it (there is a bunch of other material that you probably have covered with local codes and regulations).

In my case, the arc flash exposure calculations seem MUCH simpler after having reviewed the tables provided by modern software on the calculated values.

The calculations are based on fault current available, voltage, clearing time, distance from the source, etc. It sounds complicated until one sees the printout, which (from ETAP) nicely tabulates the incident radiation exposure in tables with clearing time on the vertical axis, and distance from fault on the horizontal; a unique calculation (and table) for each bus.

NFPA 70E has much empirical information and seeming inconsistencies. When questioning this, I was advised that iw will make work 'safer', a relative term. There in lies a huge liability.

 

[dbaird]

For those who are interested Bussmann has a very good document that covers this subject:

http://s51.yousendit.com/d.aspx?id=34B7ZCQN16VCS04RECPWBOSPME

David Baird
mrbaird@hotmail.com
Sr Controls Designer
EET degree.
Journeyman Electrician.

 

[RonShap]

Porf,
Notice the notes associated with most aspects of the NFPA 70E PPE selection table. Many times those notes make the table useless.
Be sure you're aware of the TIA issued by NFPA a few months back, modifying the table.

 

[Laplacian]

Scotty,

When our site went through the Arc Flash calculations (just prior to the release of IEEE-1584), we used the Duke equations for calculating incident energy and appropriate PPE levels.

Arcing fault current is calculated as a percentage of the bolted fault current; higher percentage as voltage increases. This arcing current is used with existing coordination settings to determine the actual clearing time of a purely arcing fault.

For plant level distribution voltage, this adds significant time to the flash. This is where I really disagree with the IEEE-1584 method. The incident energy (and associated flash protection boundary) increases in direct relation with time even through one minute if that's what the clearing time comes to.

Looking at the test data used by the IEEE team, all (or most) of their tests cleared between 6 and 30 cycles. There were also very few test data points. The empirical formulae were based off a very small sample size and very fast clearing times. In the real world where clearing times are significantly longer (for arcing fault current), the IEEE results yield unrealistically high incident energies and extreme flash protection boundaries.

I believe that the proper way to protect against arcing faults is to implement one of the newer technologies to detect both elevated current and photo sensing such as ABB's ArcGuard system.

As noble an idea as arc flash protection is, my peers are convinced that it was a special interest by one particular chemical company who also makes the fibers which the PPE is made of, since most of the IEEE team was from that same company.

Sorry for running off on a tangent, but is there anything in particular you want to know Scotty? The general workflow for assessing PPE requirements is the following. Once you see a trend, you can assume a worst-case scenario and base your PPE on that.

1. Have an up to date system model or relaying settings on hand
2. Know the 3-phase bolted fault for each level of the system
3. Use some methodology to determine the arcing fault (IEEE, Duke, etc.)
4. Use the arcing fault current along with other assumptions to determine incident energy and flash protection boundary. These assumptions are such things like space between conductors, distance from point where fault occurs, arc in a box or in the open, etc.
5. Label the equipment

After a while, the trends start to develop. 2500KVA (and larger) transformers with 480V secondaries are hard to protect against as there is a lot of available fault current. These are not your friends when performing an arc flash study. Older plant systems that used a lot of fuses don’t lend well to clearing arcing faults quickly. It’s easy to dictate what must be done to get the incident energy down below a point. It’s much more difficult to find the funding required to make such changes.

 

[RonShap]

I've found while doing IEEE 1584 calcs, that more bolted fault current the better. After the reduction down to arc flash fault current, you need a lot to activate an inverse time OCPD.

 

[ScottyUK]

Hi Laplacian,

Steps 3 & 4 are the stages where the UK is kinda living in the dark. Establishing which methodology to use is my first step. There doesn't seem to be much consensus in the US, so you can imagine how difficult it is over here where arc-flash hazard is not really considered.

We have a lot of 2.5MVA distribution transformers operating at 415V secondary. The available fault level at the main load centres is very large, and our equipment doesn't use current-limiting fuses. Most of the MCCBs are old thermal-mag types. We tend to do a lot of fault-finding on the boards with cubicle doors open, and while our PPE is almost certainly better than the majority of UK industrial sites, we don't use the level of personnel protection that our US colleagues would be required to use. I'm probably the first engineer at our site to start trying to quantify the risk based on something other than instinct. We have so many ultra-high energy systems at the power station that we probably don't treat distribution-level circuits with as much caution as we should.


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

One day my ship will come in.
But with my luck, I'll be at the airport!

 

[Laplacian]

There are two methods cited in the IEEE document, one is of course the IEEE equations; the other is the Duke Energy equations. Do a google search for "flux.exe"; it's a simple DOS based program for approximating incident energy.

Bottom line is that while doing troubleshooting on or near energized equipment, some protection is required. Our site provides and has standardized on full 65 cal/cm^2 suits including face shields for this purpose. We have some normally closed tie breakers that exceed 65, but we can open them before work to reduce the energy.

The IEEE document is a work in progress in my opinion and should only be used as a guideline. When OSHA incorporates this into electrical safe work practices, I hope there is some flexibility for interpretation.

Our company has had a few arc-flash injuries in the UK and a few saves in the US where arc-flash PPE prevented serious burns. The electricians hate it since it's bulky and hot.

There is no need to perform a full study to protect the technicians, just provide a suit for them to wear during "at-risk" activities. A few examples of "at-risk" activities for us are racking breakers in/out, opening and closing load break disconnects above 480V, performing voltage checks on energized conductors/bus.

 

[alehman]

There is no need to perform a full study to protect the technicians, just provide a suit for them to wear during "at-risk" activities. A few examples of "at-risk" activities for us are racking breakers in/out, opening and closing load break disconnects above 480V, performing voltage checks on energized conductors/bus.

This approach can still put technicians in danger where the incident engergy may exceed the rating of a 65cal suit. It is common for situations to arise where no level of protection is adquate and the equipment must be worked de-energized.

 

[dpc]

Just to quantify alehman's comment a little: The current version of NFPA-70E (2004) basically says that if the arc-flash level exceeds 40 cal/cm2, the equipment cannot be worked on while energized, period.

Also, the advantage of knowing arc energy levels is that in many locations, a heavy flash suit is not required. A 8 cal/cm2 coverall or shirt and pants with a face shield will suffice in many situations.

 

[NorPwr]

I am involved with a new, moderatly sized mine site in Canada. If there is anyone with knowledge of Canadian legislation/CSA standard prudent to this topic. As of now there is no reference to NFPA 70E at my site. Current procedure indicates the use of flame retardant coveralls for all live electrical work.

 

[bigbillnky]

NFPA-70E is a ridiculous document. The requirements make it nearly impossible to actually perform the work. IF some of the individuals that created 70E actually worked under the guidelines, they would start to understand that they have created a greater danger of electrocution. After just a few minutes in a 20 cal suit in moderate temperatures, the worker AND the suit are soaked with perspiration. I would much rather be burned than electrocuted! Yes, electrical work is a dangerous occupation, but how far can you go with PPE? If we all wore flak jackets while driving, there would definitly be a decrease in injuries and fatalities from auto crashes.

I have never had a single person recieve an arc flash injury on any project I have been involved with or led. Neither has my Father, and we have nearly 60 years combined experience in the electrical industry. At the same time, we have both been involved on projects where fatalities occurred from falls.

Bigbillnky,C.E.F.....(Chief Electrical Flunky)

 

[mykh]

NorPwr,
the Canadian Standards Association (CSA) does not currently have a standard equivalent to NFPA 70E. Nonetheless, when hearing a case, the court decides on the standard of care by asking what a reasonable person with same background or expertise would have done in the same circumstances. In the absence of such a document, many companies in Canada adhere to the NFPA 70E standard. Check

http://www.arcadvisor.com/faq/canadian_considerations.html

for more info.