Gas Meter Area Classification

[nickoliver]

OK, I have exhausted my resources and am looking for opinions. This is the scenario. I am completing a small prime power generating station with natural gas generators. There is a dispute as to the classification around the in coming gas supply metering area. I asked the question weather or not it is class 1 Div 2 or not. The plant is in operation and you can usually smell gas in the area. It is most likely blow off from the pressure regulator. The engineers are saying that the area is unclassified. The CM (who works for the engineering firm) is saying it is. The issue is the cost of adding seals to the conduits where they come out of the ground. Back when the question was first asked, by my predecessor, it would have been easy. When I asked the question the conduit was installed, concrete encased and backfilled. Spacing is not adequate for seals. When I explained the difficulty and cost to add these seals now of course nobody wants to do it. My question is would you consider this a classified area? Here is a link to a picture so you can see what I am talking about. There is a 120V motorized gas valve (the termination box faces away from us in the pic) A flow meter, temperature meter and two pressure meters all of which will operate at 24V 4-20ma. The tall cylinder in the pic is a filter element that must be periodically changed. There is bypass piping so the plant would not have to be shut down. Thanks for any input.
BTW: This is an old picture. Now the area is complete so we would be starting over to add seals at this point.

 

[nickoliver]

http://webpages.charter.net/zigmeister/Web Pics/ECN/DSCF0355.JPG

I guess we can't hot link here.

 

[itsmoked]

I'm not sure, but two questions come to mind.

1) Is this structure inclosed now? (I doubt it)

2) Is Natural Gas and or any of it's constituents
heavier than air?

Last point why not use the (again I mention) the EXP rated goo that you mix with water in the blue can that you then spatula around the wires filling and sealing the conduit at the last access points. The less the clearance the better.

 

[alehman]

I don't think this would be classified unless there is normally a flammable concentration of gas in the area. I doubt the small quantity normally vented from a regulator would fall in that category. The local inspector would have final say.

Interestingly NFPA 37 specifically exempts engine rooms from classification due the presence of fuel systems.

 

[mc5w]

A gas pressure will not bent any natural gas unless the diaphragm is punctured or cracked. The pressure regulators in household furnaces are not a safety hazard.

If you smell gas that means that you have a leak somewhere. You shoud not smell ANY natural gas. If the leak is in a pressure sensor then finding it could be difficult unless the vent hole is small enough for soap bullbe testing.

 

[stevenal]

"Locations shall be classified depending on the properties of the flammable vapors, liquids, or gases, or combustible dusts or fibers that may be present, and the likelihood that a flammable or combustible concentration or quantity is present."

The question is not whether you can smell it, but whether it is ignitable. Natural gas is odorless, so a distinctive odorant is added to alert the presence of leaks. My understanding is that the natural gas is lighter than air, while the additive is heavier, so odor can exist well after the gas is gone. In any case, natural gas in low concentrations in air is not ignitable.

 

[alehman]

Some types of regulators do vent small amounts of gas in normal use. Regulators designed for indoor use must be non-venting type or have their vent piped outdoors.

http://www.ventskirts.com/

http://www.fisherregulators.com/products/literature/289/

 

[mc5w]

aleham,

You are speaking of the pressure relief valves that are attached to commercial natural gas services downstream of the pressure regulator to relieve overpressure if the pressure regulator somehow malfunctions. These are more properly termed pressure relif valves. If a pressure relef valve on a service vents natural gas that is both a safety problem and a revenue loss.

There may also be some combination regulators on the market that have in integrated pressure relief valves, but under no NORMAL circuitstance would a pressure relief valve or regulator vent any gas.

A pressure relief valve fail to fully close which I have seen on domestic water heaters as they typically do not have an expansion tank. Failure of a relief valve to rully close initiated the 3 mile island reactor incident. See another thread title Interview at Nuclear Plant or something like that.

The fuel cutoff solenoid for the generator could also be leaking gas when off.

In other words, there has to be a leak or something malfunctioning somewhere if you are smelling gas.

 

[alehman]

mc: I am speaking is the pressure relief device, commonly integral to the regulator. In my experience it seems there is sometimes a slight odor of gas around these devices (like the one in my back yard).