501.15(B)(2) Exception No. 4

[Natfuelbilll]

501.15(B)(2) Exception No. 4
Exception No. 4: Segments of aboveground conduit systems shall
not be required to be sealed where passing from a Division 2
location into an unclassified location if all of the following conditions
are met:
(1) No part of the conduit system segment passes through a
Division 1 location where the conduit segment contains unions,
couplings, boxes, or fittings that are located within 300 mm (12
in.) of the Division 1 location.
(2) The conduit system segment is located entirely in outdoor
locations.
(3) The conduit system segment is not directly connected to canned
pumps, process or service connections for flow, pressure, or
analysis measurement, and so forth, that depend on a single
compression seal, diaphragm, or tube to prevent flammable or
combustible fluids from entering the conduit system.
(4) The conduit system segment contains only threaded metal
conduit, unions, couplings, conduit bodies, and fittings in the
unclassified location.
(5) The conduit system segment is sealed at its entry to each
enclosure or fitting located in the Division 2 location that
contains terminals, splices, or taps.

Soooo....

1. An aboveground conduit leaving an C1D2 location and ran underground (an unclassified location) will not need a boundary seal if (1) through (5) are satisfied?

2. An aboveground conduit leaving an C1D2 location and ran aboveground (to an unclassified location) will not need a boundary seal if (1) through (5) are satisfied?

3. What exactly is the difference between a conduit run and a conduit system segment?

4. How does not installing a seal, as allowed per this exception, fulfill the purpose minimizing the passage of gases being accomplished with a boundary seal?

Thank you in advance for your responses.

 

[rbalex]

A bit out of your order:

3. With respect to this Exception, a "segment" is that part of a "run" that meets all of the sub-conditions of the Exception 501.15(B)(2)(1) through (5).
1. No, a boundary seal is required at grade. (The run is no longer aboveground)
2. Yes, this is the basic intent of the Exception.
4. What gases are you worried about in Division 2 - there aren't supposed to be any in normal operations? If there were any they would bypass the seal in the open-air anyway.

CMP14 has been trying to eliminate Division 2/unclassified seals for ages. Personally, with rare exception, I don't believe need you need any unless the boundary is a physical barrier and there is a substantial positive pressure from the Division 2 side of the seal OR at grade where heavier than air gasses may collect in underground raceways.

 

[Natfuelbilll]

1. No, a boundary seal is required at grade. (The run is no longer aboveground)

The underground conduit can re-emerge in a unclassified area or a C1D2 area. A boundary seal is still required for either emergence?

4. What gases are you worried about in Division 2 - there aren't supposed to be any in normal operations?

No worries. Just trying to make sure the Code is followed. This job is LNG/natural gas and the C1D2 are those locations adjacent to a C1D1 LNG spillway.

 

[rbalex]

The underground conduit can re-emerge in a unclassified area or a C1D2 area. A boundary seal is still required for either emergence?

Once a run goes underground, that part no longer has the benefit of the Exception. When it emerges, whatever applies is what applies.