would a hangar consturcted out of PEMB with a SF area of 16,250 SF, an office space within the hangar of 1,800 SF and an eave height of 35ft...be considered a Group 2 or Group 3 hangar?
Group II aircraft hangars shall have both of the following features:
Group III aircraft hangars may be either a row hangar with multiple units or an open bay hanger capable of housing multiple aircraft or a freestanding unit for a single aircraft. Group III hangars shall have both of the following features:
The PEMB building should be Type II construction in accordance with NFPA 220, Standard on Types of Building Construction. When the fire area of the hanger has 16,250 sf, the Group II Aircraft Hangers can be used for Type II (000), Type II (111), or Type II (222) Type of Construction.
In accordance with Table 4.1.3 of the 2016 NFPA 409 when the fire area of the hanger has 16,250 sf, the Group III Aircraft Hangers can be used for Type II (222) Type of Construction.
NFPA 409 does allow separation of a hanger into smaller single fire areas in accordance with Section 5.2 and 8.2 of NFPA 409 to take advantage of a Type II (000) and Group III construction.
The design would have to consider the size of the fire area, the fire resistance of the structure, and compare the construction criteria of Group II against Group III.
Group II (only somewhat less severe, still lots of requirements, including foam and sprinklers)
Group III. (Few requirements: no sprinklers or foam, no fixed fire suppression systems at all, as long as there are no hazardous activities such as welding, painting, etc.)
When the IBC is the governing code consult with Section 412. Table 412.4.6 simply determines which hanger classification to which the fire suppression must be designed in accordance with NFPA 409 using the IBC designations for Type of Construction. IBC Type IB is equivalent to NFPA Type II(222). Remembering that in general Group III in NFPA 409 are exempt from providing fire suppression unless hazardous operations in accordance with Section 4184.108.40.206 occur within the hanger. So the Group classification for a 16,250 sf hanger can be II or III was dependent on the Type of Construction of the structure.
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