Aircraft Hangars - NFPA 409

[skdesigner]

My question will probably betray my lack of experience with aircraft hangar fire suppression systems, so let me preface this post by saying that I am not attempting to design something outside my abilities, not trying to engineer a solution when I am not a licensed engineer - heck, I haven't even priced the job yet. I am looking at a set of floor plans, reading NFPA 409 and just want to clarify the following:

NFPA 409-2004 defines a group I hangar as having an aircraft access door over 28'-0 in height. A group II aircraft hangar is defined as having an access door 28'-0 or less, and a maximum fire area not exceeding a certain square footage (40,000 sq.ft in this instance).

The building I am looking at has two separate hangar bays, each with an area of 21,600 sq. ft. The catch is that the demising wall separating the hangars is unrated. NFPA 409-04 5.2.1 requires that when walls separate hangar fire areas, they must have a minimum 3 hr fire resistance rating. Am I correct in stating that this unrated wall automatically kicks the hangar classification up to group I as one would have to look at the two hangars as a single fire area exceeding 40,000 sq. ft?

Thanks in advance.

 

[cdafd]

Reduce it to 40000 sq ft


Do not have access to 409 but does group II require fire protection?

 

[stookeyfpe]

SD2:

Correct. However, this gets even more interesting if your jurisdiction has adopted the 2009 IBC. If you are under the 2006 IBC, no separation is required. Under the 2009 IBC, a 2-hour fire wall is required (see IBC Section 412.4.6.2, 2009 edition). Because specific requirements in the IBC supercede a requirement in a NFPA standard, the wall only requires a 2-hour fire resistance rating.

One option is that if the hanger has some accessory office spaces not associated with storage or repair, you could separate those with 2-hour construction, and possibly reduce your fire area to < 40K square feet, which would return you to Group II.

If the hangers are being constructed in a a jurisdiction under the 2009 IBC, you have some other options assuming no hazardous operations are occurring. I suggest you review 2009 IBC Section 412.4.6 as well as the rest of Section 412 becuase it's pretty darn apparent that Bubba (or Bubbette) The Architect didn't crack open the code book. Most likely the person was busy permitting a dentist office when this jewel of a project landed in the office.

 

[skdesigner]

Hi Stookeyfpe,

I am in Canada, so not under the IBC. I have suggested the same - reduce hangar area to 40,000 sq. ft or less (not a large concession given that it would only mean dropping ~3,200 sq. ft from the hangar area) in order to be classified as a group II hangar. Either that, or build a 3-hr fire wall. Or a group I hangar suppression system c/w Hi-ex generators and a preaction system with a 15,000 sq. ft design area.

Your arch. comment is right on point. "NFPA four-oh-what?" was how the conversation started...

Thanks again.