Cross contamination from classified area to unclassified area? 1

[sabotage]

I have a small wastewater facility which consists of two rooms, a main area which houses the pumps and wet well and a bathroom. The bathroom is partitioned off from the rest of the facility with the entrance on the exterior of the building. Any personnel wishing to use the bathroom has to leave the main area and walk around the building. The main area is classified Class 1 Div 1 while the bathroom is unclassified. If I have a ducted roof mounted exhaust fan exhausting the main area while a branch duct also exhausts the bathroom, does this now classify the bathroom as a Class 1 Div 1 area? Meaning, if the same exhaust fan exhausts from both a classified and unclassified area, am I linking both areas together via the fan system?

I've tried looking in NFPA 70 Article 500, NFPA 497 and local building codes, but I only find requirements about sealed cable/conduits penetrating Class 1 Div 1 areas and not this particular situation. Any help provided on this is much appreciated.

 

[DRWeig]

The answer is "maybe."

If you've been trained well or certified to deal with classification of areas, get hold of a copy of ANSI/ISA 12.24 and 12.27. The whole ANSI/ISA 12 series is a good thing to have.

If you haven't been trained or certified, which seems to be so if you don't know about the standards and recommended practices, you'll need an engineer on site to make that determination. That can't be done from afar. Start with the engineer who classified the areas to begin with.

Best to you,

Goober Dave

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[sabotage]

Do you mind explaining a bit more on why this would be a maybe? I'd like to be as knowledgeable as possible when I approach others for help.

As for the engineer who classified the area to begin with, because hes electrical he knows what to do with his own equipment but he was unsure as to how the ducts within both spaces fit in. He said it COULD be an issue based upon his experience but couldn't bring up any sources to back it up, which is what I was hoping for.

 

[DRWeig]

Depending on how well the partitions seal, the restroom may be Div 2, or it may be non-hazardous. Certainly the exhaust flow will be balanced to keep the restroom at a positive pressure relative to the hazardous space, or you'd have a health hazard as well as a flammable hazard. That may require a makeup air fan in the restroom. Nobody will want to visit a Tom Crapper full of explosive gases. I personally like to light up a fine cigar if I'm going to be in there for a while. Thus, it's probably not Div 1.

We don't know the composition of the hazardous gases. In my wastewater treatment work at two municipal plants, we were advised that the densities of the flammables might cover the spectrum of lighter-than-air, heavier-than-air, and mixes-well-with-air. Heavier gases won't rise up the exhaust, and light ones won't fall back down. It's the ones that mix well that will have a path through your joined-up exhaust duct in the event of fan failure.

We also don't know your local codes or local AHJ. Probably the mechanical, electrical, and fire inspectors will all have opinions that are the law.

But it's mainly a maybe because I can't see it before deciding...


Best to you,

Goober Dave

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[ProcessHVAC]

Have you checked what NFPA 820 says about this? I might be wrong but I think you would need separate exhaust system.

 

[sabotage]

Ah, thats what I was looking for, thanks!. I hadn't thought to look in NFPA 820. NFPA 820 9.2.9 says "Ventilation systems shall not transfer air between unclassified interior spaces and classified interior spaces." So it looks like I've provided a transfer path between the classified and unclassified areas.

A followup question, if I isolated the two spaces with a motor operated damper interlocked with the fan, would this be sufficient to meet code requirements? Assuming the actuator is out of the airstream of explosion proof. I'm specifically thinking about sealing requirements, as there are pretty stringent requirements for electrical equipment.

 

[chicopee]

Sabotage it would not be the case when the transfer of air between the two rooms is ducted. So in order to insure the integrity of the wall between the two rooms 1) you will need a duct that can withstand a fire rating equivalent to the wall 2) install an an approved fire damper within the duct that can seal the opening in the event of a fire 3) maintain, I believe, a 5' distance between duct opening and electrical equipemnt within the bathroom 4)and last install an exhaust system rated for classified areas.
I personally would install a separate approved exhaust system for the pump and wet well room which is a classified area, and a small wall mounted exhaust fan (non rated for classified areas) for the bath room.

 

[sabotage]

chicopee,

When you say a duct that can withstand a fire rating equivalent to the wall, are you saying that if the wall is 2 hr rated, the duct needs to be 2 hr rated also? With either some fire rated insulation or a fire rated enclosure? We already have an approved fire damper in the wall, so why would the entire duct run need to match the wall rating?

Also, do you know what reference the 5' distance between wall opening and electrical equipment comes from?