NEC 513.3 B- Areas Not Cut Off or Ventilated.

[faresos]

Hello everyone:

I'm not sure if I'm quite sure I do understand this article (513.3 B):

(B) Areas Not Cut Off or Ventilated. The entire area of
the hangar, including any adjacent and communicating areas
not suitably cut off from the hangar, shall be classified as a
Class I, Division 2 or Zone 2 location up to a level 450 mm
(18 in.) above the floor.


If I have an adjacent area to the hangar and separated by a door. The hangar space is ventilated (exhaust ducts located at 1'-0" above finished floor) . Does the areas adjacent to the hangar (example: Corridor or any rooms) with direct doors to the hangar space consider to be unclassified areas?

Thanks,

 

[rbalex]

... Does the areas adjacent to the hangar (example: Corridor or any rooms) with direct doors to the hangar space consider to be unclassified areas?

Assuming there is adequate ventilation - yes. However, establishing that ventilation is adequate may be an issue. Exhaust ducts located a foot above the floor alone may not be enough. [It's unlikely actually with non-forced air flow indoors.] See NFPA 30, referenced in Section 513.1 IN No 2, to determine if the ventilation is adequate.

 

[faresos]

Assuming there is adequate ventilation - yes. However, establishing that ventilation is adequate may be an issue. Exhaust ducts located a foot above the floor alone may not be enough. [It's unlikely actually with non-forced air flow indoors.] See NFPA 30, referenced in Section 513.1 IN No 2, to determine if the ventilation is adequate.

Thanks Robert

I looked at NFPA 30 but there is no Chapter 5 (2015), has it been renumbered?

 

[rbalex]

My post was a bit misleading; there is no Chapter 5 in NFPA 30, but my stated cross-reference was to NEC Section 513.1 IN No 2.

Technically, adequate ventilation is the ventilation rate required to limit incidental releases to 25% LFL. Probably the best practical definition is in NFPA 496. Part 3.3.1:

Adequate Ventilation. A ventilation rate that affords either 6 air changes per hour, or 1 cfm per square foot of floor area (0.3 m³ / min / m²), or other similar criteria that prevent the accumulation of significant quantities of vapor–air concentrations from exceeding 25 percent of the lower flammable limit (LFL).

This usually takes an HVAC engineer to determine AND to verify there are no "dead-air flow" (usually in corners) locations in the enclosed space.