haz location

[paul renshaw]

What would you consider an outdoor area that recieves natural gas at high pressure and regulates it down for low pressure distribution. This is outdoors,and has a fence around it. Would this fall under Class I Div II? There is normally not gas present in the air.

[ February 01, 2005, 11:34 AM: Message edited by: paul renshaw ]

[charlie tuna]

paul,
article 500.5 b (1) 3 considers this a class one-division one area. not normally present is one thing --- but if it "could be" present is mentioned. and i'm assuming every once in a while it is present....

[petersonra]

Originally posted by charlie tuna:
paul,
article 500.5 b (1) 3 considers this a class one-division one area. not normally present is one thing --- but if it "could be" present is mentioned. and i'm assuming every once in a while it is present.... Just out of curiousity - the section you cite would seem to imply the area around any gas meter should be classified. there are a lot of gas meters out there, including at my house. i don't recall my side yard is classified.

[steve66]

Sorry Charlie, but I also think this is a non-classified area. If it were classified, we would have to classify the area around every natural gas pipe. That would include my entire house.

Also, I don't see how a leak would also cause a simultaneous electrical source of ignition that 500.5 b talks about. :)

By the way, something that:

recieves natural gas at high pressure and regulates it down for low pressure distribution. probably includes every residential gas meter.

Steve

[ February 01, 2005, 12:19 PM: Message edited by: steve66 ]

[charlie b]

I'm moving this to the new "Hazardous (Classified) Locations" topic area.

[paul renshaw]

"Paul:
It is a gas regulator station containing valves, regulators and reliefs. Escaping gas would occur under abnormal conditions (relief valve popping) or a blow down of the line during maintenance."

This was sent to me from the gas Dept.

[rbalex]

Originally posted by paul renshaw:
"Paul:
It is a gas regulator station containing valves, regulators and reliefs. Escaping gas would occur under abnormal conditions (relief valve popping) or a blow down of the line during maintenance."

This was sent to me from the gas Dept. This installation would normally fall under NFPA 54, The National Fuel Gas Code . Unfortunately, NFPA 54 gives very little direction for Electrical Area Classification.

The Gas Dept has given some hints though. The most important being that they do, in fact, anticipate releases of gas. The problem is that they have confused “abnormal” with “infrequent” or “uncommon.” A relief valve release may be infrequent or uncommon but, if it is doing what it was designed to do, it is not abnormal. And a scheduled maintenance blow down is definitely “normal.”

From the description, you definitely have a Division 2, Group D location and probably a Division 1 location, albeit small.

The critical issues are the pressure and flow rates of the gas and you haven’t mentioned them.

Edit added "relief"

[ February 01, 2005, 02:48 PM: Message edited by: rbalex ]

[nhee]

If this is a gas utility regulating station, the American Gas Association (AGA) XF0277 makes recommendations for classification of these types of facilities. Classification is based on a number of factors, including equipment installed, operating pressures, ventilation, etc. At utility regulating stations, it is typical to consider areas within 5' of relief stacks to be Cl 1 Div 1, and within 15' of relief stacks, process valves, and flanged connections to be Div 2, assuming outdoor, adequately ventilated area.

[rbalex]

I'm not familiar with that publication, but the distances (and sources) sound about right for pressures up to 500psi. Although I probably wouldn't include flanges.

[ February 01, 2005, 03:03 PM: Message edited by: rbalex ]

[paul renshaw]

It arrives at 60 psi and leaves at 15 psi, 10 psi and 7 "wc.

[rbalex]

Below 100psi I would probably limit the Division 1 location to 3' around the relief vent and the Divison 2 to 10' around the relief vent. I'd ignore the valves and flanges as sources.

Having said that, it may still be prudent to use the AGA recommendations unless they also recognize low pressure designs. Industry standards are usually easy to defend as a basis for electrical area classification.

[paul renshaw]

I found out today exacly what they want. A pedestal type service consisting of a meter and RT panel will be installed outside the fence, I should be able to keep it plenty far away from the relief. Then they want a 120 volt circuit run inside to power a transducer and an outlet for a cable modem. If I leave the service with a seal off and pipe it in rigid, then put another at the other end, will that satisfy my needs?

[ February 02, 2005, 12:57 PM: Message edited by: paul renshaw ]

[paul renshaw]

The modem,transducer,and assosciated power is all contained in one Hoffman type box, 6 feet from the relief horizontally, and about 5 feet lower vertically.

[paul renshaw]

I have now convinced them to move all the wiring to outside the fence,12' from the relief. That should eliminate a lot of the wiring issues.

[rbalex]

Paul,

First, I apologize that I missed your post yesterday.

Second, it is critical that someone qualified to do so creates "proper documentation" (http://www.mikeholt.com/codeforum/ultimatebb.php?ubb=get_topic;f=22;t=000007;p=2#000 018) per 500.4(A). Once that is done, the rest of the design and installation falls into place.

Part of the documentation is a reference to the Standard used to determine the electrical area classification. Personally, the AGA document nhee referred to sounded appropriate; however, unless the "someone qualified" had access to it, it is fraudulent and unprofessional to refer to it.

My estimates were just that; i.e., they are what I think I would arrive at if I were the Engineer of Record. I’m not – I don’t know the details of the installation; so these are just “educated guesses.” At this point, until someone qualified to do so creates the “proper documentation,” there is little else we can do to help.

[nhee]

I just looked again, and AGA really doesn't distinguish between low and high pressure sources for area classification. Another document, API RP-500 (American Petroleum Institute) distinguishes between sources that are above/below 275 psig. Recommended distances can vary depending on the piping valves/components used. Many control valves will use natural gas as their pneumatic source and could be constant-bleed, creating a constant source of flammable gas. Most times, the relief/vents are piped up and away, automatically moving the Div 1 area away from the electrical installation. Also, many of the transducers and modems used in these facilities are listed for Div 2 usage, yours might be as well.

As rbalex has pointed out, a control drawing identifying area classifications, references used should be created to clearly identify the area boundaries.

[paul renshaw]

I will see if the gas department manager has these documents, then talk to our engineers and try and come up with a solution. Thank you guys for your inputs,and anything else you may come up with. Once we determine the boundaries, the NEC should be able to govern what we install.

[ February 03, 2005, 01:13 PM: Message edited by: paul renshaw ]

[paul renshaw]

14.3.2 of API RP 500 seems to apply to this installation, figure 96 gives a good reference point for distances. Also, 8.2.3.4.1 refers to figure 18 as a minimum for relief valves and rupture discs. Does this sound feasible to you guys for the installation I mentioned?

[rbalex]

The problem with Fig 96 is it is dealing with heavier than air gases and you are dealing with methane. Fig 104 may be more appropriate.

Since you now appear to have RP 500 available, I suggest you digest all Chapters up to 8 and become familiar with Appendix D. I like D; it gives a very analytical approach to electrical area classification.

[paul renshaw]

Yeah, 104 does seem more appropriate for this. I am in the process of absorbing the info today. What I think we will do is put the service outside the classified area, and use the appropriate wiring once I get inside. I am going to try and obtain a drawing of the station with all of the equipment inside and confer with our EE and the gas department to get a set of drawings made up and approved to show the classified area. I will probably be the one to do most of the legwork, and then the EE will approve the drawings after we go over everything. This will be a good learning experience, if my head does not explode first.

[ February 14, 2005, 06:09 PM: Message edited by: paul renshaw ]