Boundary seal

[Natfuelbilll]

Lighter than air gas c1d2 location (source is a flange) located 5 feet above ground.

Is below grade classified ?

Situation is conduit runs from within haz location, underground and emerges in non classified location.

If yes, then I need a seal at the non-hazardous end.

If below grade is non classified, then I need a seal in classified location where conduit enters ground.

Hmmm......

 

[Smart $]

My guess, with strong emphasis, is that below grade is unclassified.

 

[rbalex]

Two things to consider:

• The area around the flange is not necessarily classified at all if it is the only "source." It is still generally considered to be “closed piping.” See API RP500, Annex D, Section D.5.4 for an explanation

The problem here is, while various electrical area classification documents clearly indicate piping "...without valves, flanges and similar devices..." is unclassified, it leaves the incorrect impression that locations around valves, flanges, etc, must be - which just ain't so. They may be, of course, but they don't have to be.

​

• As S$ indicates, the underground isn't in any case; in fact, except in certain very limited conditions, the underground is never classified - even with heavier than air volatiles.

 

[Natfuelbilll]

Another case of AGA XFO277 not equal API 500......

The AGA shows flange as center of 15' C1D2 radius.

So, considering this document, and your (gratefully accepted)! comments then I have a boundary, and a requirement for a boundary seal. Right?

If, on some other project, the engineer calls below grade classified, then no boundary seal required at grade, but yes where seal emerges from below grade.

 

[Smart $]

Another case of AGA XFO277 not equal API 500......

The AGA shows flange as center of 15' C1D2 radius.

So, considering this document, and your (gratefully accepted)! comments then I have a boundary, and a requirement for a boundary seal. Right?

I'm not familiar with either of the referenced documents, but my guess would be that your 30' sphere can be influenced by physical structures cutting through the sphere, e.g. a wall within but extending in all directions beyond the outer edges of the "bubble". The ground (i.e. below grade) may have a similar effect on the effectual classified area. For example, you noted the flange was 5' AFG. The bottom 10' of the classified sphere may be in essence chopped of by the ground.

If, on some other project, the engineer calls below grade classified, then no boundary seal required at grade, but yes where seal emerges from below grade.

If the latter (raceway, not seal) emerges in an unclassified area, that's what I'd do (install a seal). Of course that is assuming there is more raceway buried inside the classified boundary than the maximum permitted distance for the seal to be on the classified side of the boundary.

 

[rbalex]

I'm not nearly as familiar with XFO277. All I have is an old 1992 copy for reference. It's an old "hard-copy" with a terrible (that is, NO) index, and is extremenly hard to navigate), but I still believe it is the "latest" edition. It is extremely outdated, citing documents that no longer exist or have been revised themselves 4-5 times. For what it's worth, it appears to be largely drawn from an old API RP 500C (pre-1991).

In any case, it appears to recognize that filled, below grade locations are not classified. See the last sentence of Section 6.1.2 and all of the Appendix C diagrams truncate the classified envelope at grade. In other words, from your OP, running below grade under a classified location, does not require seals.

Edit add: If your company has any influence with AGA, I'd say it's time for an XFO277 update.

 

[Natfuelbilll]

Edit add: If your company has any influence with AGA, I'd say it's time for an XFO277 update.

Nope nada zilch.


The OP meant to describe a conduit leaving the C1D2 aboveground area into the ground and running underground and emerging from a non-classified area.

So I need a boundary seal where the conduit enters the ground in the hazardous location - right?

 

[rbalex]

Nope nada zilch.


The OP meant to describe a conduit leaving the C1D2 aboveground area into the ground and running underground and emerging from a non-classified area.

So I need a boundary seal where the conduit enters the ground in the hazardous location - right?

Yes; in that case. it is a "classic" example of 501.15(B)(2) with none of the Exceptions applying.

Edit add: After rereading the OP, just to clarify, there is only one (1) boundary seal necessary for the installation - at the Division 2 / "at grade" interface. There is no need for an additional seal where the raceway re-emerges into an unclassified above grade location. Technically no classified location boundary exists at that site.