AREA CLASSIFICATION FOR LNG GENERATION

[Engels]

I need put a liquid natural gas gen-set inside a generator room. The question is: I need consider this area, a hazardous area, according NEC or IEC rules or not?
I think that if a put an air removing system, like a exhaust fan, I can consider a non-hazardous area; naturally, I need stop the generator systems if ventilation fails.

Thanks

 

[DRWeig]

Hi there!

This is a question that you really need to pose to your local electrical authority, or else get a local engineer to look it over and issue an opinion based on your local community standards for safety -- now, having disclaimed my own liability, here are some things to consider:

1. Is there any portion of the LNG piping, controls, etc... that vents gas during normal operation? If not, you should be able to classify the area as Div 2 (Zone 2).

2. Can you set the actual LNG bulk storage tank outside? If so, and if it's equipped with appropriate valving, you may be able to consider the entire room non-hazardous. Your room will have to be ventilated anyway in order to make up combustion air to the generator, so if you add an exhauster you will have to take control action to maintain air pressure in the room when the engine runs.

3. I would be inclined to classify the room non-hazardous, add a combustible gas sensor that is wired to a shunt-trip breaker (killing all electricity to the room that is not rated for hazardous atmosphere) and an external alarm. An LNG generator is not that much more hazardous than a simple pipeline-fed natural gas generator or even a gasoline or diesel unit (unless your storage volume is over the limits specified in the NFPA codes). Even so, you might want to put in a single explosion-proof light and switch so you can see if you need to service a leak.

Let us know how it works out, friend!

Old Dave

 

[peebee]

I'd recommend talking to your insurance company, too. They may well have the last word on this. US codes typically do not specify how to classify an area, only how it should be built once classified. That classification is often specified by a safety engineer or the insurance company.

 

[geo57]

Hi,

You may want to take a look at API RP 500. It states it is not necessary to classify the following "1. Adequately ventilated areas where flammable substances are contained in well maintained, closed piping systems which include only the pipe, valves, fittings, flanges, and meters." It goes on to state that "An enclosed or partly enclosed space may be considered as adequately ventilated if it is provided with artifical ventilation in an amount equivalent to natural ventilation under low wind velocity conditions, and there are adequate safeguards against the failure of the ventilation equipment." I also would agree with both of the above comments you have already received. This is usually a judgement call.

George Griggs
Sr Process Controls Engineer