classified vs non-classified area separation in aircraft hanger

[glim]

513.3.D states "Areas suitably cut off and ventilated adjacent areas in which flammable liquids or vapors are not likely to be released, such as stock rooms, electrical control rooms, and other similar locations, shall not be classified where adequately ventilated and where effectively cut off from the hanger itself by walls or partitions."

The hanger I'm designing for has an electrical room (panels, FA panel and a telephone board) with a door opened to the hanger, does the door constitute as a "partition" that suitably cuts off the electrical room so that it is not classified?

 

[rbalex]

The essential issue is ventilation. Assuming the room is adequately ventilated, the door is a suitable separation.

Unfortunately, adequately ventilated is not directly defined in the NEC. See Section 500.4(B) FPN No 1 as the general reference to look elsewhere. A generally acceptable definition is from NFPA 497, it is compatible with the NFPA 30 which is a central reference standard for Art 513. :​

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, or other similar criteria that prevent the accumulation of significant quantities of vapor–air concentrations from exceeding 25 percent of the lower flammable limit.​

 

[weressl]

513.3.D states "Areas suitably cut off and ventilated adjacent areas in which flammable liquids or vapors are not likely to be released, such as stock rooms, electrical control rooms, and other similar locations, shall not be classified where adequately ventilated and where effectively cut off from the hanger itself by walls or partitions."

The hanger I'm designing for has an electrical room (panels, FA panel and a telephone board) with a door opened to the hanger, does the door constitute as a "partition" that suitably cuts off the electrical room so that it is not classified?

Only a solid wall would constitute adequate separation. If a door opens to an adjacent hazardous area; positive pressure ventilation, without the number of air exchanges mentioned is satisfactory. The most energy efficient way to construct this to have a draft gauge temperature transmitter drive a fresh air supply fan equipped with an ASD(Adjustable Speed Drive). Follow NFPA 496 directives.

 

[rbalex]

A soilid wall is not necessary. In fact, a wall is not necessary at all, if the ventilation is adequate.

 

[weressl]

A soilid wall is not necessary. In fact, a wall is not necessary at all, if the ventilation is adequate.

If the ventillation is adequate AND there is no wall then the office is part of the hangar and the entire area has the SAME classification.

I was responding to the original question, not your response. I responded that the door is not an adequate separator itself. Then went on to suggest that a positive pressure ventilation is a cost effective way to provide the lowering of the classification of that room. 6 air exchange of an airconditioned and heated office is rather costly.

497:
5.2.2.4 In cases in which an unpierced barrier, such as a blank
wall, completely prevents the spread of the combustible material,
the area classification does not extend beyond the barrier.

also figure

FIGURE 5.9.1(e)

 

[rbalex]

Since you have cited 497, come back after you have read Section 5.4. All of it carefully, especially subpart 5.4.2(3). The door alone is suitable for the application.

FIGURE 5.9.1(e) does not apply since the source is already inside the enclosed area. A better Figure which more closely supports your view is API RP500, Section 6.4.3, Figures 4 and 5; however, you also need to consider Section 6.4.4.

You keep trying to apply NFPA 497 as a general Standard - it isn't. It is a good one I grant you; however, it is simply a recommended practice intended for chemical processes. See the Scope statement Section 1.1.3. The applicable standards for this particular application are NFPA 30 and 409. Do not misunderstand me ? I like NFPA 497. I served on its Technical Committee, as well as API RP500?s and NEC CMP14.

 

[weressl]

Since you have cited 497, come back after you have read Section 5.4. All of it carefully, especially subpart 5.4.2(3). The door alone is suitable for the application.

FIGURE 5.9.1(e) does not apply since the source is already inside the enclosed area. A better Figure which more closely supports your view is API RP500, Section 6.4.3, Figures 4 and 5; however, you also need to consider Section 6.4.4.

You keep trying to apply NFPA 497 as a general Standard - it isn't. It is a good one I grant you; however, it is simply a recommended practice intended for chemical processes. See the Scope statement Section 1.1.3. The applicable standards for this particular application are NFPA 30 and 409. Do not misunderstand me ? I like NFPA 497. I served on its Technical Committee, as well as API RP500?s and NEC CMP14.

So is my solution is valid or not?

Is it the more cost effective or not?

Is it legally defendable or not?

 

[rbalex]

Since any valid solution must be legally defensible, the last question is a red herring; however, the other two questions are legitimate.

So is my solution is valid or not? …

It would work.

… Is it the more cost effective or not? …

Not necessarily.

What you overlooked was context – and your original response assumed “facts not in evidence.”

The context of the question is an aircraft hangar. The electrical area classification is determined by Section 513.3 exclusively. I must admit I also assumed the hangar was classified although that is not necessarily true - see Section 513.1. I made the assumption based on the idea the designer would not otherwise be asking the question the way they did.

However, if the electrical room is “off” the hangar area the Division 2 location would only 18” above grade – even with the door to the room wide open. See 513.3(B). There is no need to assume that the room would need an HVAC system that provides 6 air changes. Indeed, 1 cfm/sqft of surface area is quite easy to achieve. A good fan with a clean air source could do it easily. And that is the most the NEC would require. No alarms, pressure switches or other common NFPA 496 issues need to be addressed.

The basic reason for this is Art 513 is based on incidental spills, not pressurized process incidents.

Edit typo correction