Gas Vent Classification

[justahand]

I have a natural gas vent which is a emergency vent that is 30ft above grade and the pressure of the gas is 200psi,I am trying to determine the area classification and radius around the vent for the classification. Any Ideas?

 

[rbalex]

Re: Gas Vent Classification

Unfortunately you can't go directly to a figure in NFPA 497. I would prefer using "Appendix D" of API RP500. Its a straight-forward analytical approach.

The only real problem in the analysis is determining whether a Division 1 location is created or not.

From 500.5(B)(1)(1):

Class I, Division 1. A Class I, Division 1 location is a location
(1) In which ignitible concentrations of flammable gases or vapors can exist under normal operating conditions, or ...

Except for motors in 500.8(A)(5), the NEC doesn't define "normal" with regard to installations in Classified locations. Since most folks would say the relief vent was "doing its job" they would also reasonably consider it "normal" if not "common."

What you have is a lighter-than-air gas at an elevated vent. Methane disperses very quickly and the 200 PSI expulsion pressure actually works in you favor.

Assuming 3 mph or greater prevailing winds, I would recommend a 3' Division 1 radius and a additional 2' (5' total) radius for Division 2.

Hope this helps.

 

[justahand]

Re: Gas Vent Classification

Thanks Bob you are a great help, Have a great day!