Arc Flash Requirments in HV manholes 2

[jtinge]

We have a complex underground medium and high voltage distribution system to distribute power to more than 200 facilities at our center. 6.9 kV and 22 kV cables are routed via ducts and manholes to intermediate distribution switchgear and then on to unit substations at each facility. It has been common practice for our high voltage maintenance crews to work in manholes with energized cables with proper shock barriers on the cables. Based on arc flash hazard analyses in several of our typical manholes, many of the energized cables have calculated incident energy levels of over 100 cal/cm2. NFPA 70E classifies work in manholes and confined spaces as a hazard/risk category 4, requiring multilayer flash suits. While it is our practice to work only on de-energized cables, to de-energize cables in close proximity to the work, and barrier off the non affected energized cables, this does not seem to address the arc flash issue in NFPA 70E. It is often not practical to de-energize all the cables in the manhole when doing work on a specific de-energized cable. I have been receiving many comments from our workforce that outside utilities and other industrial complexes do not wear multilayer flash suits when doing work in manholes with high voltage energized cables. I have not been able to find any guidance from NESC (ANSI C2) or any standard lineman, cableman, or engineering handbooks on the matter. How are utilities or industrial complexes dealing with the arc flash PPE requirement when they have to do work in manholes with energized cables? Because it is not atypical for the distribution cables to have incident energy levels over 40 cal/cm2, how can workers safely do the work when NFPA 70E does not address PPE for over 40 cal/cm2?

 

[dpc]

https://www.ieeecommunities.org/ieee.esafety?go=t909636

If you haven't already, you might want to join the forum above and post your question there as well.

It's an interesting question. NFPA-70E-2004 Table 130.7 does specifically list "insulated cable examination" as a Hazard Risk Category #4. On the other hand, maybe there are no exposed live parts and if workers will not contact the energized conductors you might make a case for a reduced level of PPE.

I think I know what the NFPA-70E committee members would tell you - you need to suit up.

 

[rbalex]

If you have a flash hazard analysis that indicates exposure greater than 40 cal/cm2, “suiting up” with any level of PPE will not be considered adequate. I can’t offer an NFPA Formal interpretation, but I can say with a very high level of confidence that the 70E Technical Committee would not permit such exposure in the absence of justifying “life or death” necessity for working on or near the equipment.

 

[dpc]

rbalex,

Yes, I agree, but the question is when does a hazard exists. Are there exposed live parts or is there some type of switching going on that would constitute a hazard? I don't know. Perhaps it is necessary to wear PPE just to walk within 100 feet of the manhole under any conditions?

I can calculate the arc energy for any location, but that does not mean that a hazard is always present.

Actually, Table 130.7(C)(9)(a) in NFPA-70E can be used "in lieu of" a flash hazard analysis and it says Hazard Risk Category #4 for this task. Just one of the many inconsistencies in this standard.

 

[rbalex]

dpc,

There was a subtle, but major set of redefinitions in the 2002 NEC, “Energized” and “Live Parts.” "Exposed" is not necessarily a criterion any longer. They had a very significant effect on 70E. They were a major reason 70E was delayed a year. Its cycle is supposed to be one year after the NEC’s. The 70E reformatting was also largely a result of the redefinitions, reworking incident energy calcs and a few philosophical issues over multi-employer sites and “construction” versus “industrial” for temporary power applications.

Without confirming the available fault current and clearing times in the notes at the end of Table 130.7(C)(9)(a), the Table is essentially a list of examples of applications – not an alternate to hazard analysis (See the introductory text to the Table in Section 130.7(C)(9)(a). It can't be assumed lower available faults will automatically result in lower incident energies; in fact, they may result in sufficiently longer clearing times to create higher incident energies.

IEEE/NFPA have created a new Join Task Group to review these calcs once again. There is still fierce debate on determining maximum incident energies rather than relying solely on maximum available faults.

 

[jtinge]

rbalex,

I agree with everything you've said and understand the nuances and inconsistancies with 70E regarding arc flash, and the confusions on shock and arc flash bondaries resulting from misinterpretations of "energized" and "exposed energized". What I don't understand is how utility workers are dealing with arc flash PPE when they have to work in manholes with energized cables. Does 70E apply to them? Is the coverage of 70E to utilities limited like the NEC. ANSI C2 (NESC) does not address arc flash PPE for utility workers when working in underground manholes, although they permit this type of work. This seems to be a similar activity to working on live overhead conductors, which the utility companies do on a regular basis. It's hard to imagine that utility companies would deenergize all cables in a manhole to work on just one, especially if the cables feed power to large areas of a downtown business district or a hospital area.

 

[rbalex]

jtinge,

Read the "Not Covered" Section of the 70E Scope in 90.1(B), especially 90.1(B)(5)b and c.

FedOSHA has similar limitations in 29CFR1910.302(a)(2)(v).

The assumption is utilities know what they're doing. In truth they usually do and their training is better than most. Before deregulation they also often had fewer financial restrictions and didn't hesitate to thoroughly conduct hazard analyses. In my opinion they are now in something of an unfair position with regard to “general” industrial practices.

 

[dpc]

rbalex,

I certainly agree that lower fault currents do not necessarily result in lower arc-flash energy - I see this all the time. I understand the restrictions placed on the use of Table 130.7(C)(9)(a), but it is still widely, if incorrectly, used. I have a lot of problems with the entire logic of the table, but that's another story.

Maybe you could elaborate on how the changes to the definition of "live parts" has an influence on interpretation of NFPA-70E? How does an employer determine when a hazard exists? If someone is just walking along a line-up of metal-clad switchgear where all doors are closed, is PPE required by NFPA-70E in your opinion?

dpc

 

[jtinge]

rbalex,

After talking with our local utility, they confirmed the scope limitation of 90.1(B), (5)b and c in that they don't apply the 70E arc flash guidelines per se to their utility work. Although OSHA requires PPE they aren't explicit like 70E on what to use. However, I have seen some articles indicating utilities are being proactive in the use of arc flash PPE, although most of what I've seen relates to overhead live line work. I'm still in the dark on what they do in manholes. It has been argued to me that the use of a full flash suit in a manhole may be more hazardous in other ways than the arc flash you are trying to protect against. I'm on the fence on this one.

I would have no problem arguing that arc flash PPE is needed in a manhole when working on a deenergized cable in direct proximity to other energized cables (ie. blankets and barriers used around the energized cables for shock protection and prevent cable damage). In this case, your work is close enough to inadvertantly damage energized cables resulting in an arc flash. But if the deenergized cable is isolated, and there is no chance that your work will involve other energized cables (ie. energized cables are located on an opposite wall from cable being worked on), seems like common sense could be applied here. If you are not working on the energized cables, and they are barriered off so there is no possibility that they can be damaged, what would be the cause of an arc flash event on one of those cables. Is is reasonable to think that one of those cables will just up and fail when no work is being done on it? I did see where the IEEE and NFPA have formed a joint committee to revist arc flash and OSHA is updating 1910.269 regarding arc flash as it applies to utilities. It will be interesting to see what develops. I'm still interested on what utilities do in manholes regarding arc flash PPE.

 

[rbalex]

dpc,

The critical words that disappeared were: “…and a shock hazard exists.” Other methods of protection, such as guarding or elevation above the work space, apparently disappeared with it as "automatic" safety techniques, as did simple insulation or enclosing.

Personally, I agree that there are still many open issues with accurately determining the maximum practical incident energy; hence the NFPA/IEEE Joint Task Force. There are so many criteria to consider, the recommended calculation methods change almost every 70E adoption cycle. In fact, if you review the Task Force’s current Scope they are still only trying to establish how to accurately determine incident energy based on generalized criteria. Determining "reasonable" MAXIMUM incident energy for a given installation is still a way off.

The current 70E philosophical bent is that “Management” be required to acknowledge they realize it when they are placing workers at risk. They have the right to manage. They have the right to determine the criticality of potentially dangerous work they are asking workers to do. They have the right to establish their own criteria for declaring a worker “qualified” to do the work they are asking. They have the right to make "judgment calls" that the work can be done safely. They DON’T have the right to disavow those decisions.

The 70E Tech Committee is trying to offer Management the best available basis for making reasonably informed decisions without saying, “Since we don’t know everything, we’ll ignore it.” The TC is saying “Here are worker safety issues you need to consider when deciding to ‘work live’. You can make the call, but be prepared to defend your decision without claiming ignorance. Realize you may be held personally responsible for your employee's safety.”

The data and safety determination techniques will improve over time, and even better informed decisions made, but hazards can’t be ignored (or whined about) simply because we don’t know everything now.

 

[jtinge]

After reeviewing NFPA 70E for the umpteenth time, I realized that the Flash Protection Boundary definition is an approach limit at a distance from exposed live parts (not just energized parts)....

Also the requirements in 70E, Art. 130.6(F) for Confined or Enclosed Spaces is based on the confined or enclosed space having exposed live parts.

That being said, why does Table 130.7(C)(9)(A) list so many tasks with covers on as having a flash protection boundary? Seems like the table is based on a flash protection boundary from energized parts rather than exposed energized parts. Where are the exposed live parts with the covers on? Back to my manhole issue, are insulated, grounded, and relay protected cables considered to be exposed live parts? Why would they have a flash protection boundary if not?

 

[rbalex]

Start by reviewing the definition of "Electrical Hazard." It states that there are four recognized classes: Shock, Flash Burns, Thermal Burns and Blasts.

Then read 130.1 "Justification." While insulation and or enclosing may protect from Shock,[the context of 130.6(F)]other hazards may exist and must be addressed as part of the scope of the justification.

Both Flash and Blast are still potential hazards in enclosed spaces and must be addressed. Section 130.7 addresses the full scope of PPE regardless of the identified hazard. See Sections 130.2&3 "Blast" is generally assumed to be a corollary to Arc-Flash with respect to incident energy. It isn't the whole story and needs further development. The 70E TC is working on it.

 

[dpc]

jtinge,

I believe you're right. There are no clear guidelines on determining when a hazard exists or when it doesn't. This is left to the employer to determine, based on the general guidelines in NFPA-70E.

Someone standing underneath a cable tray carrying 15 kV cable is almost certainly within the flash hazard boundary if one of those cables were to fail. However, I have never heard anyone suggest that PPE should be required to stand under a cable tray.

The confined space of a manhole is a different situation, but still requires judgement.

There are a lot of ambiguities and a general lack of consistency in NFPA-70E. But it's the best starting point we have at this time.

 

[rbalex]

It may be well to review the distinctions between NFPA's definitions of Codes, Standards, Recommended Practices, andGuides at this site:

http://www.nfpa.org/categoryList.as...evelopment process/How the code process works

The NEC is a Code, 70E is a Standard. There is a link to the Regulations Governing Committee Projects on that page that covers the other two document types.