Isobutane-Class I Div 2 location below grade

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Omega142

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Manchester, TN, USA
I have an Isobutane pipe system, mostly welded but it does have several non welded fittings and valves. One valve in particular is above a forced air ventilated pit and the pit has an adjacent raised floor area seperated by a poured concrete wall that is not isolated from the pit due to conduit entries and past access holes for old equipment. I understand from NFPA 58 that there is a 15 ft radial and cylindrical boundary down to grade from a potential leak source but it also includes the below grade pit and any adjacent, non-isolated below grade areas. So I under stand this to include the raised floor area. My problem is that there are quite a few I&C cabinets and conduits sitting on and exiting the perimeter on the raised floor areas, my understanding is that all the conduit and cabinets should be sealed off at the boundary. So how to best seal an open bottom I&C cabinet? Do they make any seal offs for existing conduit systems? Or do I even really have to seal these at the top boundary since Isobutane is heavier than air and won't travel up the conduit or into the cabinets?

This area was never considered by past engineering, so we are trying to go back to correct issues.

Typing this on my phone, so apologies if any of this is unclear, I may have missed some needed edits.
 
Omega142 said:
I have an Isobutane pipe system, mostly welded but it does have several non welded fittings and valves. One valve in particular is above a forced air ventilated pit and the pit has an adjacent raised floor area seperated by a poured concrete wall that is not isolated from the pit due to conduit entries and past access holes for old equipment. I understand from NFPA 58 that there is a 15 ft radial and cylindrical boundary down to grade from a potential leak source but it also includes the below grade pit and any adjacent, non-isolated below grade areas. So I under stand this to include the raised floor area. My problem is that there are quite a few I&C cabinets and conduits sitting on and exiting the perimeter on the raised floor areas, my understanding is that all the conduit and cabinets should be sealed off at the boundary. So how to best seal an open bottom I&C cabinet? Do they make any seal offs for existing conduit systems? Or do I even really have to seal these at the top boundary since Isobutane is heavier than air and won't travel up the conduit or into the cabinets?

This area was never considered by past engineering, so we are trying to go back to correct issues.

Typing this on my phone, so apologies if any of this is unclear, I may have missed some needed edits.
Click to expand...

You did better than I could or would have done on a phone!

A gas will spread out in the space available. Just because it has a greater density does not mean it won't diffuse in the entire space it can get to.
With no air movement and different densities of gasses you will theoretically have greater concentration of the heavier density at the lower elevation but I don't think you can hang your hat on that from a safety perspective because we all know air currents exist almost everywhere.
 
Ok, understand the air current concern, but from what i'm gathering from your post then how do I determine the boundary as the top of the pit if currents can cause the gas to spill, or travel outside the pit....the pit is open on top minus some grating around the edges, and the raised floor is comprised of removable tiles and supports, and the cabinets have hundreds of wires transitioning above "grade" from under the floor through pulled or cut tiles. So is the top of pit which is also even with the raised floor truly my boundary? Oh, the pit is bigger than the 15 ft radius as well, should have included that too
 
Omega142 said:
I have an Isobutane pipe system, mostly welded but it does have several non welded fittings and valves. One valve in particular is above a forced air ventilated pit and the pit has an adjacent raised floor area seperated by a poured concrete wall that is not isolated from the pit due to conduit entries and past access holes for old equipment. I understand from NFPA 58 that there is a 15 ft radial and cylindrical boundary down to grade from a potential leak source but it also includes the below grade pit and any adjacent, non-isolated below grade areas. So I under stand this to include the raised floor area. My problem is that there are quite a few I&C cabinets and conduits sitting on and exiting the perimeter on the raised floor areas, my understanding is that all the conduit and cabinets should be sealed off at the boundary. So how to best seal an open bottom I&C cabinet? Do they make any seal offs for existing conduit systems? [1. below] Or do I even really have to seal these at the top boundary since Isobutane is heavier than air and won't travel up the conduit or into the cabinets?

This area was never considered by past engineering, so we are trying to go back to correct issues.

Typing this on my phone, so apologies if any of this is unclear, I may have missed some needed edits.
Click to expand...
Omega142 said:
Ok, understand the air current concern, but from what i'm gathering from your post then how do I determine the boundary as the top of the pit if currents can cause the gas to spill, or travel outside the pit....the pit is open on top minus some grating around the edges, and the raised floor is comprised of removable tiles and supports, and the cabinets have hundreds of wires transitioning above "grade" from under the floor through pulled or cut tiles. So is the top of pit which is also even with the raised floor truly my boundary? Oh, the pit is bigger than the 15 ft radius as well, should have included that too[2. below]
Click to expand...
1. There are no listed "post-installation" seals for conduit systems.
2. Since isobutane is significantly heaver than air, the pit is a potential collection point and is considered a source as well the valve. The new 15’ envelope includes measurements taken from the pit’s edge. If it weren’t forced air ventilated, the pit would be Division 1 as well. [See NFPA 58, Table 6.23.2.2 Part H]

Now the possibly good news: as long as there are no ignition sources inside the "new" overall Division 2 envelope, any boundary seals that may be necessary don’t need to be explosionproof. See NEC Section 501.15(B)(2).
 
rbalex said:
1. There are no listed "post-installation" seals for conduit systems.
2. Since isobutane is significantly heaver than air, the pit is a potential collection point and is considered a source as well the valve. The new 15’ envelope includes measurements taken from the pit’s edge. If it weren’t forced air ventilated, the pit would be Division 1 as well. [See NFPA 58, Table 6.23.2.2 Part H]

Now the possibly good news: as long as there are no ignition sources inside the "new" overall Division 2 envelope, any boundary seals that may be necessary don’t need to be explosionproof. See NEC Section 501.15(B)(2).
Click to expand...

Whoa, hang on, you just blew my mind with the underlined part. I didnt state this above but the valve is above the pit is about 20' up (indoors), welded pipe up to it and flanged fittings at the valve that we consider as possible leak points if the gasket fails, and some other non welded fittings (not sure of the type) for instrumentation. The pipe system is normally nitrogen purged, even though we understand that butane will still be present in the pipe, even under purge, and is only pressurized and flowing at certain times. So what pops it my mind by your statement is that if we have a failure, the pit also becomes a source and we have to update the boundary as not just 15' around and down from the valve/fittings and the entirety of the pit and raised floor area, but also 15' out from the pits/floor edge? And if so, how many feet up? I'm starting to think Id better run some more Calc's to see how much volume of butane we actually have to see if we can even fill up the pit if it all leaked out.

On the non-explosion proof boundary seals, I'm use to Chico, but a what types of sealING material can be used (spray foam, beeswax, duct seal, etc?) and what listing is required? Sorry, don't have my code book with me right now, but I'll look myself some tomorrow, just not something I've looked for yet.


Sorry for the long posts, just trying to learn, better understand, and take the safest corrective actions we can.
 
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I cited the basis for my comments; i.e., NFPA 58, Table 6.23.2.2, Part H and NEC Section 501.15 (B)(2). Review them and, if you believe I've misinterpreted them, feel free to express your interpretation. BTW, the Division 2 envelope extends 15' above the pit and 15' horizontally from it outdoors or in a well ventilated area.

The classified envelopes described in NFPA 58, Table 6.23.2.2 are fairly consistent with those of NFPA 497, which is a bit easier to understand as it has several diagrams as well. NFPA 497 is the most general NFPA electrical classification document and discusses the "philosophy" of classification as well. You might want to check NFPA 497, Part 5.5.4 for some potential relief. Of course, I have no "experience" with your particular installation but it may apply. The problem is NFPA 58 is a full-blown code and NFPA 497 is only a recommended practice. However, both are recognized documents in Section 500.4(B) Informational Notes (IN)

As far as acceptable alternate sealing materials, as far as I can tell, Code Making Panel 14 (CMP14) still hasn't seen fit to declare specifically what they believe is suitable although there may be a hint in the Section 502.15, Informational Note. Personally, I believe duct-seal is fine since I believe most Division 2/Unclassified boundary seals are unnecessary in the first place - but that is ​only my opinion.
 
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