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Clarification required in water supply calculation in Aircraft hangar fire protection as per NFPA 409

Question asked by shivaji.santhanakrishnan on Jun 7, 2019

Details of the Aircraft Hangar:

We need to protect an Aircraft Hangar - Group 1 as per NFPA 409. Our protection scheme is Option 1. Foam water deluge system shall be installed under roof ceiling as primary protection & Low expansion foam monitors as secondary protection. 


Hangar Classification -       Group 1

Protection Scheme -          Option 1

Primary Protection -           Foam Water Deluge Systems

Secondary Protection -      Low expansion foam monitors


NFPA 409 - Question about fire water supply calculation:

Section -     the concentrate for the foam expansion deluge system shall be sufficient for 10 minutes                                foam discharge.

Section -   the total water supply duration shall be minimum for a duration of 45 minutes when supplementary                                systems are installed.

Please confirm, the water quantity for the protection is,

      a) design density in LPM x Operational Area x 45 Minutes (sufficient for compliance to and


      b) design density in LPM x Operational Area x 10 Minutes (sufficient only for compliance to


Thanks in advance,