When Does a Non Classified Bldg Become Classified

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DM2-Inc

DM2-Inc

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Houston, Texas
I had a meeting with an engineering firm today and was advised that when a building, which by itself has no commodities that would make it a Class I, Div 1, or 2 location, is located in a Class 1, Div 2 location, the building would be classified by NEC 500, as Class I, Div 1.

Their argument is that because gases could migrate into the building, the area becomes more hazardous due to the walls confining the space, making the ignition of the vapors more dangerous, which I understand, but...

Now I'm aware that if I have a door in a non-classified building, there is an area of the door opening extending into the building, that would be classified.

Am I missing something, or is the Engineering Firm missing something?
 
This is in a refinery.

They want to locate a batteries in a conditioned cabinet. The area that they would put the cabinet may be classed as Class I, Div 2. The UPS is Class I, Div 2, but they're thinking that since the cabinet is enclosed, the UPS would need to be Class I, Div I.
 
DM2-Inc said:
This is in a refinery.

They want to locate a batteries in a conditioned cabinet. The area that they would put the cabinet may be classed as Class I, Div 2. The UPS is Class I, Div 2, but they're thinking that since the cabinet is enclosed, the UPS would need to be Class I, Div I.
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A Class 1 Div 2 atmosphere could become hazardous in the event of equipment failure. Any structure in a larger C1D2 area that has limited ventilation openings is Class 1 Div 1 because when a piece of equipment does fail and the C1D2 area becomes hazardous, those vapors are likely to enter a pumphouse, compressor shelter, or UPS cabinet. Once inside one of those minimally vented locations, the vapors will hang around a lot longer than in an outdoor location where the vapors are free to dissipate or blow away. The difference between Div 1 and Div 2 is the probability that vapors will be present, in other words, how many minutes per year vapors will be present. By confining the vapors and not letting them dissipate as fast, you increase the average number of minutes per year of vapors present, which pushes you from Div 2 into Div 1.

Practical answer:
A large cabinet or small building/prefab shelter with a UPS will need to be climate controlled anyway, so specify an HVAC system with an NFPA 496 Type Z purge & pressurized system. This allows the inside of the building to be general purpose when the outside is Class 1 Div 2. We have a number of such installations at the refinery where I work. One thing to be aware of is you need a hardwired failsafe alarm contact from the 496Z system back to a manned control house to alarm in the event of loss-of-pressurization. This is a Process Safety Management requirement, not an NEC requirement, but when you work in a refinery as an electrical person the line is blurred and since it has to do with wires, the sparkies are still responsible.

Edit: You mentioned using NEC Article 500 to determine the classification of an area in a refinery. An appropriate industry standard to use instead would be API RP 500, "Recommended Practice for Classification of Locations for Electrical Installations at
Petroleum Facilities Classified as Class I, Division 1 and Division 2". This standard has a lot of examples and is much easier to use in a refinery because that's the context that is was written for. It worries me a bit if the engineering firm is actually using the NEC and not API RP 500 for area classification in a refinery.
 
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Actually the issue is whether or not NEC Chapter 5, would require the inside of the building to be classified as Class I, Div 1.

I have yet to see where it would. I'm wondering if I've missed something.
 
DM2-Inc said:
Actually the issue is whether or not NEC Chapter 5, would require the inside of the building to be classified as Class I, Div 1.

I have yet to see where it would. I'm wondering if I've missed something.
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Unless the installation is covered by Articles 511 to 516, Chapter 5 doesn't speak to classifying a location.

Jdsmith is correct that API RP 500 is the appropriate document to consult. See Section NEC 500.4(B) FPN 1 & 2. I'd be VERY concerned the consultant wasn't citing it in the first place.

Without knowing considerably more about the installation, I seriously doubt a Division 1 location would be created by what you have described so far, enclosed or not.
 
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JdSmith and Robert...I'd love to here your feed back on my logic here...

I've had a read through API 500. Figure 3 in chapter 6 describes the issue. This depicts a source where the Class I, Div 1 area extends 5' from the source and the Class I, Div 2 area extends 10' from the source.

An enclosure with vapor tight barriers on that portion of the enclosure that extends within the classified area (Div 1, or 2), is not considered classified.

At issue...
The enclosure that is being considered is a NEMA 4X enclosure, with Class I, Division 2 equipment installed within the enclosure, and where the cooling is provided by either a vortex cooler or other means that would not otherwise compromise the NEMA rating of the enclosure. Further the enclosure will not be installed in a Class I, Div 1 location, but may be installed in a Class I, Div 2 locations.

Section 6.4.2 and 6.4.3 state:
6.4.2 An enclosed area that is adjacent to a classified area, and that is separated from the classified area by a vaportight barrier, is unclassified, considering only the external source. Reference Figure 3

6.4.3 An enclosed area that is adjacent to a classified area, and that is not separated from the classified area by a vaportight barrier. should be classified the same as the highest classification included. Reference Figures 4 and 5.​

6.4.3 implies that the inside of the enclosure (without a vapor seal) would not be classified higher than the are it's installed in (i.e. Class I, Div 2)

Section 8.2.6 addresses Batteries in "Non-Classified" areas and says:
8.2.6.6.2.1 The interior of battery boxes should be unclassified provided: (a) the battery boxes have vent(s) with across sectional area of not less than 6.45 square centimeters (1 square inch) for every 0.14 cubic meters (5 cubic feet) of battery box volume, (b) the vent(s) is not more than 45 degrees from vertical for any point except wall penetrations, and (c) the vent(s) extends from the highest point of the battery box.​

Since the battery box may be located in a Class I, Div 2 area, I can't take credit for the section 8.2.6.6.2.1, on top of which my enclosure is no longer NEMA 4X rated with the vents. However The interior of the enclosure still doesn't seem to me to be classed higher than Class I, Div 2.
 
I agree with your analysis. At this point, "vaportight" usually becomes the sticking point with the inexperienced and timid; but if isn't essentially porous or with actual holes, it's vaportight. At worst, a good coat of paint will do.
 
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