CL1 DIV2 Enclosure purge gas?

[derjr]

I currently have fourteen (14) enclosures with Z purge systems on them and 9 are in CL1 DIV2 areas with a N2 purge on them, while the remaining are not purged at all. This CL1 DIV2 area is a warehouse type of building with four (4) large overhead doors, two (2) on opposing ends, and large ventilation fans on one end. That being said my feelings are that any fumes are minimized but the area is still classified as such.

My problem is that the non-purged enclosures are experiencing moisture build up and I want to use instrument air on them. While we are using N2 on the others, N2 is very expensive and I was wondering if I could switch these over to instrument air as well without violating any codes?

I have looked at NEC 500.2 Definition of "Purged & Pressurized" which only states that protective gas be used. Also NEC 505.8(B) "Purged & Pressurized", which of course does not state what is approved and ANSI/FPS 496.2003 does not state what is approved either.

I have seen from the purge panel manufacturer that instrument air is the most widely used, because N2 is so expensive.

Does anyone know if this has been done or is suitable?

 

[don_resqcapt19]

Instrument air is fine for the purge, just make sure it has a low enough dew point to prevent condensation. Most instrument air will have air dryers to bring the dew point well below the expected minimum temperature where the instrument air is being used.

 

[derjr]

Thanks! Confirmation of my thoughts is great to hear.

Yes, we do have instrument air dryers on our system. Each enclosure has a small heater to keep down unwanted moisture build up, but evidently the ones with moisture build up happened when we had the power off during a six-month outage.

I just wanted to eliminate a huge N2 waster while correcting the moisture problem.

Thanks for the advice and confirmation.

 

[petersonra]

Instrument air is fine for the purge, just make sure it has a low enough dew point to prevent condensation. Most instrument air will have air dryers to bring the dew point well below the expected minimum temperature where the instrument air is being used.

I agree.

The main reason I have seen for using n2 is because there is no instrument air available in the area of the enclosure. A big bottle of n2 will last quite a while if the box is sealed well.

If you have air available, get a good coalescing style filter with automatic drain on it to take out most of the liquid.