Running an air line from safe area into classified area.

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when

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I have a question that has stumped an examiner.

If one has an air line that goes from an enclosed compressor in a safe area and goes to a classified area, but the compressor runs only rarely, is the interior of the compressor enclosure subject to gas buildup and possibly considered a classified area? Why or why not? (the compressor intake is also in the safe area.)

I know that we use poured seals in conduit to prevent gas from migrating through them, is this the same kind of situation?

In reading about spray booths the booth itself may be C1D1 but what about the compressor supplying it?

TIA
 
It would seem to me that there are two means by which gas could migrate from the classified area into the safe area.
One would be via the hole or opening in the building fabric through which the airline pases, this may be prevented by applying a suitable seal.

The other way would be via the air line itself when the compressor is shut down, probably more theoretical than actual, but a non return valve would be sensible just in case.
 
when said:
I have a question that has stumped an examiner.

If one has an air line that goes from an enclosed compressor in a safe area and goes to a classified area, but the compressor runs only rarely, is the interior of the compressor enclosure subject to gas buildup and possibly considered a classified area? Why or why not? (the compressor intake is also in the safe area.)

I know that we use poured seals in conduit to prevent gas from migrating through them, is this the same kind of situation?

In reading about spray booths the booth itself may be C1D1 but what about the compressor supplying it?

TIA
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Electrical Area Classification in NEC Article 500 only addresses electrical equipment installation and use in areas where flammable mixtures may be present. It has no authority or interest in addressing mechanical equipment, or other sources of ignition.

In other words:http://www.moviesoundclips.net/download.php?id=3549&ft=wav
 
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when said:
I have a question that has stumped an examiner.

If one has an air line that goes from an enclosed compressor in a safe area and goes to a classified area, but the compressor runs only rarely, is the interior of the compressor enclosure subject to gas buildup and possibly considered a classified area? Why or why not? (the compressor intake is also in the safe area.)

I know that we use poured seals in conduit to prevent gas from migrating through them, is this the same kind of situation?

In reading about spray booths the booth itself may be C1D1 but what about the compressor supplying it?

TIA
Click to expand...

I can't really see an issue here. What could happen? The compressor conks out, now the airline is full of compressed air, how does an explosive mixture migrate back to the compressor? If there's a leak, the gross momentum of the gas in the pipeline tends to keep any explosive mixture from entering the pipe. Usually the compressor has an air receiver, especially for industrial occupancies. Besides storing a minute or three worth of air usage, it's usually festooned with check valve assemblies. Not much is getting past. If you're really worried, put a normally closed valve in the air line at the classified boundary. Use a relay powered across the compressor power feed to keep the valve open. If power fails, the valve closes.
 
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