Question about 2008 NEC Section 511.3(E)(1) Re: "Walls or Partitions"

[Samuel_Johnston]

Hi everyone,

My question is about 2008 NEC Section 511.3(E)(1) which says:


Areas adjacent to classified location in which flammable vapors are not likely to be released, such as stock rooms, switchboard rooms, and other similar locations, shall be unclassified where mechanically ventilated at a rate of four or more air changes per hour, or designed with positive air pressure, or where effectively cut-off by walls or partitions.


I'm wondering what constitutes a "wall or partition". Specifically can the wall or partition have a man door and still effectively cut-off the space? It seems to me that you would want to maintain positive air pressure in case the seal on the door were to wear out over time.

 

[LEO2854]

Hi everyone,

My question is about 2008 NEC Section 511.3(E)(1) which says:


Areas adjacent to classified location in which flammable vapors are not likely to be released, such as stock rooms, switchboard rooms, and other similar locations, shall be unclassified where mechanically ventilated at a rate of four or more air changes per hour, or designed with positive air pressure, or where effectively cut-off by walls or partitions.


I'm wondering what constitutes a "wall or partition". Specifically can the wall or partition have a man door and still effectively cut-off the space? It seems to me that you would want to maintain positive air pressure in case the seal on the door were to wear out over time.

True but how much time?


Welcome to the forum...

 

[rbalex]

511.3(E) Modifications to Classification. (1) Specific Areas Adjacent to Classified Locations Areas adjacent to classified location in which flammable vapors are not likely to be released, such as stock rooms, switchboard rooms, and other similar locations, shall be unclassified where mechanically ventilated at a rate of four or more air changes per hour, or designed with positive air pressure, or where effectively cut-off by walls or partitions.

Ordinarily, I'd "blame" this on the fact that Article 511 is largely extracted from NFPA 30A-2008, Code for Motor Fuel Dispensing Facilities and Repair Garages and Code Making Panel 14 [CMP14] has little direct input beyond coordinating it the best they can with the rest of Articles 500 through 504. [See Section 510.2 and Article 511 (Title) FPN]. However, in this case, I can't find the original NFPA 30A source/context for Section 511.3(E)(1).

...
I'm wondering what constitutes a "wall or partition". Specifically can the wall or partition have a man door and still effectively cut-off the space? It seems to me that you would want to maintain positive air pressure in case the seal on the door were to wear out over time.

Basically, a wall is fixed, floor to ceiling; a partition is partial or mobile. That said, where more general area classification philosophies prevail, assuming a Division 1 source is very unlikely (unventilated pits only), a 3' radius Division 2 envelope would surround any wall or partition openings. [See the rest of Section 511.3] Also remember, even if the room wasn't ventilated, the Division 2, 3' envelope would still be no more than 18' AFF.

 

[north star]

~ ~ ~ >

Samuel_Johnston,

Welcome to the Mike Holt Forum !

" ...the Division 2, 3' envelope would still be no more than 18' AFF."

I'm sure that Mr. Robert meant to type in 18 inches instead of 18'......Also, ...to be
technically accurate, the definitions of walls, partitions & barriers are defined in
the Int'l. Bldg Code.............Walls, ...see Ch. 2 - Definitions [ `12 IBC ].......For a Bldg.
Code definition of partitions & barriers, see Section 708 for a Fire Partition.
for a Smoke Partition, ...see Section 710, ...for a Fire Barrier, ...see Section
707, and for a Smoke Barrier, ...see Section 709.

Hope this helps !

< ~ ~ ~

 

[rbalex]

It is 18" indeed. (I could have sworn I caught that myself before posting :ashamed1 Thanks for the catch.:thumbsup:

Technically, NFPA Standards don't recognize other building codes unless they are specifically cross-referenced. Even then the cross-reference will be in the form of a nonenforceable FPN/IN or appendix. In fact, NFPA generally discourages external cross references even between NFPA documents. In absence of a Standard's internal definition: The NFPA Manual of Style says:

3.1.2 Where terms are not defined in this chapter or within another chapter, they shall be defined using their ordinarily accepted meanings within the context in which they are used. Webster?s Collegiate Dictionary, 11th edition, shall be the source for the ordinarily accepted meaning.

 

[rbalex]

This is a link to the full NFPA Manual of Style.

 

[Samuel_Johnston]

Thanks everyone. If I am understanding your reponses correctly, having a door in the wall means that there is a 3' zone around the door where we need to maintain the classification 18" from the floor and ceiling unless we provide the air changes or positive pressure. Is this accurate?