Electrical Area Classification of burner gas racks. 1

HiLevel · Aug 22, 2013

I posted this in the codes and standards forum and I'm "reposting" it here. I apologize if this is bad practice; however, it seemed that most discussions around electrical area classification are in this forum.
I have a gas rack located a distance away from an enclosed duct burner. It's a typical gas rack with <5 psig natural gas. Another design engineer has classified the area around the burner as Class I Group D Division 2. And, the result is a big change order and delay from the gas rack manufacturer. There are no other sources of flammable gas in the area, only the natural gas in the pipe. The design engineer is looking at codes like NFPA 497 and API 500 figure 104 to justify the classification. Their position (and these standards) is that the gas rack contains numerous threaded connections and devices such as SSOVs, and instruments that make it a high risk area. So, a Class I Div 2 classification is assigned. However, if this is the case, why don't the burner manufacturers design their equipment to meet this classification? I've never seen a gas rack with Div 2 equipment and wiring, and manufacturers of things like SSOVs (Honeywell, ASCO) don't even make Div 2 certified models. (I see that Maxon now makes a Div 2 valve) I know that NFPA and API both say you don't have to classify an area around a flame; duuuh. But, I don't have this typical condition to fall back on this time. I also know that the codes API 500 5.4.2 and others allude to lighter than air gases (natural gas) being less likely to accumulate; however, they don't go to the point of recommending classifications.
Why don't the burner and gas rack manufacturers build their systems to meet this classification if these standards are truly applicable.
Does anyone know of a reference? I see AGA XF 0277 for electrical classification of gas systems; however, I'm seeing a lot of focus on gas compressors and none on your basic low pressure burner gas rack. So, my guess is that like API their tables, charts, etc. will apply to systems from 0 to 250psig. That's quite a spread. Anyone have experience with this standard? EN 60079-10 appears to be the British equivalent.
Thanks ahead of time!
Bill

HiLevel · Aug 22, 2013

Well, I hate to follow up on my own post; however, I just blew $400 on AGA XF0277 "publication".
Based upon this publication it looks to me like we need to shut down every gas fired steam heating system in the country without explosionproof equipment and wiring. How can companies like Honeywell and ASCO sell their SSOVs when they're not listed for Class I Div 2 areas? "'
I see that Maxon now makes an optional Div 2 labeled valve. I looked into this several years ago and they did not at that time.
What am I missing here?
If the connections to the valve create the hazardous classification, how can the valve not comply?
Thanks for listening, any insights would be welcome.

DRWeig · Aug 23, 2013

Can you post a picture or drawing of the gas rack?

Best to you,

Goober Dave

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DRWeig · Aug 23, 2013

Oh, by the way, a few points from my experience and opinion pile. I pray I don't put too much of a wet blanket on your hopes:

1) 5 psi, 250 psi, 5" WG = all the same. Gas is gas, no point looking any more for an exception based on pressure. I can't think of any reason there would be, until you get into very high pressures that require special treatment of joints.

2) Once an engineer has classified an area, it's done. No way can he waffle on it without embarrassment and all sorts of talk about liability. He may or may not know his way around, but he has erred on the safe side and can claim the high ground. However, you never know...

3) As far as boilers and furnaces go, it's not the open flame that makes them non-hazardous on the outside. Remember, the flame isn't always burning. It's simply that there are no sources of gas in normal operation, and the chances of an upset or failure of a gas containing item at the same time as an upset or failure of an electrical thing (valve, pressure switch, etc...) is so remote that it's not to be considered. UL approves the assembly that way, and they're the same folks who approve explosionproof and intrinsically safe stuff. Factory Mutual approves boilers too. Same deal. Is the power supply to that stuff intrinsically safe? Is it power-limited to the point that it would qualify as intrinsically safe? I don't know, haven't looked in many years. In the old days, it was just a transformer.

In my (UL Listed, brand spanking new) home furnace, the gas valve and pressure switch are within inches of the fan relay, which is a regular source of arcs and sparks as it switches the 230V motor on and off. Two threaded joints into the valve, plus three elbows at two threaded joints each in that little compartment. BOOM! Not.

Notice that I haven't said that I'm on your side yet, HiLevel. I haven't seen your gas rack.

Anyway, good luck with it and do post us a pic or a diagram if you can.

Best to you,

Goober Dave

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wroggent · Aug 23, 2013

Manufactures don't need to develop their products in accordance with NFPA standards. However, it is in their interest to ensure that the end users can apply them properly, otherwise sales might not be as strong. They are able to sell products in this situation because people buy them...

It's unrelated to your question, but see jbartos first response in this thread,

http://www.eng-tips.com/viewthread.cfm?qid=70464,

if you disagree with the above.

danw2 · Aug 23, 2013

I'm not sure what 'gas rack' is, either. But oven or furnace gas trains and associated piping does not normally constitute a hazardous area per NFPA 86, 4.1.3.2 and 4.1.3.3. The preceding paragraphs are included for context:

NFPA 86, Standard for Ovens and Furnaces, 2007 Edition

4.1.3 Electrical.

4.1.3.1* All wiring shall be in accordance with NFPA 70, National Electrical Code, NFPA 79, Electrical Standard for Industrial Machinery, and as described hereafter.

4.1.3.2 Wiring and equipment installed in hazardous (classified) locations shall comply with the applicable requirements of NFPA 70, National Electrical Code.

4.1.3.3* The installation of an oven in accordance with the requirements of this standard shall not in and of itself require a change to the classification of the oven location.

NOTICE: An asterisk (*) following the number or letter designating a paragraph indicates that explanatory material on the paragraph can be found in Annex A.

A.4.1.3.3 Unless otherwise required by the local environment, ovens and furnaces and the surrounding area are not classified as a hazardous (classified) location. The primary source of ignition associated with an oven installation is the oven heating system or equipment or materials heated. The presence of these ignition sources precludes the need for imposing requirements for wiring methods appropriate for a hazardous (classified) location. Refer to Section 3.3 of NFPA497, Recommended Practice for the Classification of Flammable Liquids, Gases, or Vapors and of Hazardous (Classified) Locations for Electrical Installations in Chemical Process Areas, and Section 3.3

HiLevel · Aug 26, 2013

Furnace manufacturers will typically assemble their safety shut off valves, pressure switches, and all the manual components required by FM or whoever is dectating the burner safety system requirements into a "gas rack" that is mounted near or on the furnace. It can be a complicated maze of piping and instruments and will usually have a dedicated control panel mounted on it as well.

So, far the only thing solid that I'm seeing from the NFPA, API, or AGA codes is that they all agree that if there is an open flame or hot surface electrical area classification is not required.
So, it looks like I simply need to stick a perpetual flame in the middle of the gas rack and I'm good!

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