OK, a class I group D area is defined as an area where a flammable vapor/air mixture can exist under normal operations. If this mixture is contained within a vessel, is the area around the vessel classified, or only if a flammable vapor/air mixture exists under normal operations in the atmosphere outside the vessel?
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Classified Location Question 1
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It will not be necessary to classify it Division 1 around the vessel; in fact, if it weren't for avoiding "boundary seals" most of the Division 2 would disappear too.
In general, “closed” systems do not need classification except in the immediate vicinity of “… valves, fittings, flanges, and similar accessories…”
Even in those cases it is usually easy to justify very limited hazard radii. The problem is that it leaves you with a bunch of Division 2 “bubbles” that used to create a “boundary seal” nightmare. It was easier to just connect all the “bubbles” into one big one to avoid those seals. Over the last 15 years or so the NEC Code Panel in charge of Hazardous (Classified) Locations has begun to recognize more and more justifications to eliminate Division 2/Unclassified boundary seals - almost (but not quite) to the point you could eliminate them altogether.
Bottom line - unless you have reason to believe the vessel will “leak” under normal operation, no Division 1 is necessary.
BTW; per the NEC, “Classes” are designated by “Roman” numerals and “Divisions” are by “Arabic.” The significance can be significant legally, since specifying equipment by “Division II” is technically meaningless.
In general, “closed” systems do not need classification except in the immediate vicinity of “… valves, fittings, flanges, and similar accessories…”
Even in those cases it is usually easy to justify very limited hazard radii. The problem is that it leaves you with a bunch of Division 2 “bubbles” that used to create a “boundary seal” nightmare. It was easier to just connect all the “bubbles” into one big one to avoid those seals. Over the last 15 years or so the NEC Code Panel in charge of Hazardous (Classified) Locations has begun to recognize more and more justifications to eliminate Division 2/Unclassified boundary seals - almost (but not quite) to the point you could eliminate them altogether.
Bottom line - unless you have reason to believe the vessel will “leak” under normal operation, no Division 1 is necessary.
BTW; per the NEC, “Classes” are designated by “Roman” numerals and “Divisions” are by “Arabic.” The significance can be significant legally, since specifying equipment by “Division II” is technically meaningless.
Good stuff there rbalex!
Hey what specifically/physically do you mean by a "boundary seal"?
And I'm not clear on your answer "Bottom line" [unless you have reason to believe the vessel will “leak” under normal operation, no Division 1 is necessary.]
Are you saying the adjacent area doesn't necessarily need to be classified at all or just not Division 1?
Hey what specifically/physically do you mean by a "boundary seal"?
And I'm not clear on your answer "Bottom line" [unless you have reason to believe the vessel will “leak” under normal operation, no Division 1 is necessary.]
Are you saying the adjacent area doesn't necessarily need to be classified at all or just not Division 1?
"Boundary Seals" are those installed under [2005] Section 501.15(B)(2) or, in the case of Division 1, 501.15(A)(4).
If you read the Division 2 requirements carefully you will find enough exceptions to the general rule that most boundary seals aren't necessary. This is NOT to say all are unnecessary. Most of the exceptions were developed over the 10-15 years; but historically, it was easier to just create one large Div 2 area to avoid a seal at each boundary.
The NEC is an installation standard. Except for the few specific applications in Arts 511 to 516, it does not actually tell you HOW to classify an area. You have to go to another document such as NFPA 497 or API RP500 for general applications. If you use those documents as the basis of electrical area classification, you would find many currently classified locations that are actually over classified. But, as I said, to avoid Div 2/unclassified boundary seals it used to be simpler to just lump the locations together in one “mega Division 2.”
Personally, I believe the time is ripe to eliminate them as the general rule and specify the few limited places where they are necessary. I am in the process of submitting a formal Proposal to do just that this coming November.
If you read the Division 2 requirements carefully you will find enough exceptions to the general rule that most boundary seals aren't necessary. This is NOT to say all are unnecessary. Most of the exceptions were developed over the 10-15 years; but historically, it was easier to just create one large Div 2 area to avoid a seal at each boundary.
The NEC is an installation standard. Except for the few specific applications in Arts 511 to 516, it does not actually tell you HOW to classify an area. You have to go to another document such as NFPA 497 or API RP500 for general applications. If you use those documents as the basis of electrical area classification, you would find many currently classified locations that are actually over classified. But, as I said, to avoid Div 2/unclassified boundary seals it used to be simpler to just lump the locations together in one “mega Division 2.”
Personally, I believe the time is ripe to eliminate them as the general rule and specify the few limited places where they are necessary. I am in the process of submitting a formal Proposal to do just that this coming November.
![[nosmiley]](/data/assets/smilies/nosmiley.gif "[nosmiley] [nosmiley]")
I think I did answer what a boundary seal is. But specifically, it is a seal mandated by Section 501.15(B)(2) at the boundary of a Division 2/unclassified location.
With regard to your second question: it definitely doesn’t need to be Division 1 for any distance around the vessel there is a pressure relief device mounted on the vessel. In that case, there would both be a small Division 1 location centered on the relief port and a slightly larger Division 2 location also centered on the port. It’s unlikely that the maximum hazard radius would exceed 5’ inclusive of both unless the pressures involved were exceptionally high.
Otherwise, there probably doesn’t need to be Division 2 either. It may. It depends on several operating parameters, such as pressure, volume and flow rate. None of them were specified, so it’s difficult to make any but the most general statement and refer to NFPA 497 for more specific guidance.
With regard to your second question: it definitely doesn’t need to be Division 1 for any distance around the vessel there is a pressure relief device mounted on the vessel. In that case, there would both be a small Division 1 location centered on the relief port and a slightly larger Division 2 location also centered on the port. It’s unlikely that the maximum hazard radius would exceed 5’ inclusive of both unless the pressures involved were exceptionally high.
Otherwise, there probably doesn’t need to be Division 2 either. It may. It depends on several operating parameters, such as pressure, volume and flow rate. None of them were specified, so it’s difficult to make any but the most general statement and refer to NFPA 497 for more specific guidance.
Thanks for the reattempt rbalex and your patience.![[snail]](/data/assets/smilies/snail.gif "[snail] [snail]")
Still I'm not getting the... place hand on, real..um thing. Is the seal a rubber gasket or a wall or calculated region? What physically con-notates these types of seals.
I understand #2 now. Thanks!![[flowerface]](/data/assets/smilies/flowerface.gif "[flowerface] [flowerface]")
Still I'm not getting the... place hand on, real..um thing. Is the seal a rubber gasket or a wall or calculated region? What physically con-notates these types of seals.I understand #2 now. Thanks!
Ah...now I think I understand your question. The "seals" I refer to are conduit seals. They serve two purposes as described in the Fine Print Note No.1 of Section 501.15:
The “basic” physical characteristics of these seals are described in Section 501.15(C). It’s a relatively long Section with six (6) Subsections. Conceptually, the ones I think you may be most interested in are:
Most of the “listed” sealing compounds are literally a cement-like material.
Note they “prevent the passage of flames” but only “minimize the passage of gases and vapors.”
The “basic” physical characteristics of these seals are described in Section 501.15(C). It’s a relatively long Section with six (6) Subsections. Conceptually, the ones I think you may be most interested in are:
Most of the “listed” sealing compounds are literally a cement-like material.
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