NFPA 409 - Aircraft Hangar Fire Protection System Design

Discussion created by suhaskurikkal on Nov 12, 2020
Latest reply on Nov 12, 2020 by bigraymasoom3

Dear Team,

We have an Aircraft Hangar of size 90*81 M in our project and I am designing the fire protection system for this Hangar as per NFPA 409-2011, section 6.1.1 (3) – overhead automatic sprinkler system with low level high expansion foam system. Kindly review my below queries and give your valuable feedback.

  1.       Total Area

The total hangar area is 78,440 sq.ft. As per NFPA 409-2011, section, the maximum system size shall not exceed 52,000 sq.ft. The whole area is a single fire zone, kindly advice whether I need to split the sprinkler system in to two risers to meet this requirement.


  1.       Design area for overhead sprinkler system

In this case can I design the sprinkler system only for the hydraulically most demanding area of 15,000 sq.ft with application rate 0.17 gpm/ft2 as mentioned in section or consider the minimum area of 2500 ft2 with application rate 0.3 gpm/ft2 as per NFPA 13-2019 figure for the extra hazard group 1.


  1.       Low level High Expansion Foam system

For the foam depth & discharge time, I followed the NFPA 409-2011, section – 3ft within 1 minute. But this contradicts with NFPA 11-20110, section, where the minimum depth to be 1.1 times the height of the highest hazard. The total height of aircraft is 4.37 M. Kindly advice which clause to be followed.


  1.       Safety factor

Do we need to consider any additional safety factor in the water demand calculations other than the CN & CL values considered in the Rate of Discharge calculations? In addition to this, 2X 60 GPM foam hose stations & 500 GPM external hose allowances considered in the pump calculation as per NFPA 409-2011 sections &


Thank you for your time & consideration.