Commissioning in a Classified Area

[WastefulMiser]

I've never been in the process of commissiong (start up) of control / power room that is located in a classified area (Class 1 Div 1/2) where they used NFPA 496 to purge the air inside the facility in order to declassify the interior to unclassified.

I was wondering what is the best way to provide power to the purge equipment? I believe ideally it should be from a separate source (not within the enclosure) routed in a NEMA 7 disconnect, etc. How would you account for redudancy of power if you wanted to tie the purge into a power source that would be located inside the area you are purging. I'm assuming a NEMA 7 ATS would work, but would there be other options? What is the standard practice?

I've also heard of people during commissioning to get around having to provide a separate source using an apparatus to "sniff" the area inside the room to detect the presence of gas, thus being able to use a source inside the area they are declassifing to operate the purge equipment. Is this a common practice?

I'd appreciate any education given on the subject. There may be several threads already on this subject, if so, could someone point me in the direction if they know of one?

 

[rbalex]

NFPA 496 gives some pretty comprehensive requirements for control rooms in Chapter 7.

 

[jdsmith]

...I've also heard of people during commissioning to get around having to provide a separate source using an apparatus to "sniff" the area inside the room to detect the presence of gas, thus being able to use a source inside the area they are declassifing to operate the purge equipment. Is this a common practice?

Are you in a refinery or chemical plant where hazardous locations are common, or are you in a location where the owner and operations staff are unfamiliar with the safe operating procedures related to Class 1 Div 2 areas?

I started up two blast resistant operator's shelters with NFPA 496 type Z systems last year in a refinery. The power feed for the HVAC system was from external NEMA 7 sources, but the HVAC control panel was a NEMA 12 enclosure inside the purged and pressurized area. We used our normal hot work and gas testing procedure for startup - a gas test was taken inside and around the shelter to check for flammable or hazardous gasses. Given a safe atmosphere, a hot work permit was written for 8 hours which allowed us to use general purpose rated electrical equipment inside and around the shelter. Normally a hot work permit is for drills, saws, welders, lifts, trucks, and other tools, but it can also be applied to the HVAC control panel in this case. We used the exterior NEMA 7 power source to energize the HVAC units and HVAC control panel, then commissioned the 496Z system. Once the system was commissioned it ensured a safe atmosphere inside and daily gas tests were not longer necessary.

The above procedure should work for you if you are at a location where other folks are familiar with hazardous location work procedures. If not you'll have to educate the facility owners first.