The 2016 Edition of NFPA 409 Standard on Aircraft Hangars was issued by the Standards Council at their April 2015 meeting. This new edition incorporates several significant changes that impact the design of fire protection systems in new Group I and Group II aircraft hangars.
#1 - Foam System Zoning. Low-level foam systems in Group I hangars can now be divided into zones that are independently activated, based on activation of an associated sprinkler zone or automatic detection zone. Manual activation is still required to cause all zones to discharge simultaneously and to provide coverage over the entire storage and servicing area. However, automatic activation of smaller zones may limit the affected area and the consumed quantity of foam solution in the event of an isolated fire or accidental discharge.
#2 - Water Reservoirs. The standard has long required water reservoirs to be divided into equal parts, in order to ensure that at least half of the required supply is always maintained in service. This has been changed to a recommendation, because the water reservoirs for hangars are dedicated supplies that do not require redundancy in all cases.
#3 - Redundant Fire Pumps. Historically, NFPA 409 has attempted to ensure the reliability of hangar protection systems by requiring the installation of a redundant fire pump, such that the minimum water demand can be met with the largest pump out of service. This has been relaxed in recognition of the reliability of modern fire pumps that are maintained in accordance with industry standards. The 2016 edition requires a minimum of two pumps, but a redundant pump will not be required for systems that use two or more pumps to meet the minimum demand. All pumps must be of equal capacity.
#4 - Reserve Supplies of Foam Concentrate. Previous editions have required the installation of a connected reserve supply of foam concentrate with a manual means of switching between the main and reserve supplies. The reserve supply is now permitted to meet the requirements of the 2016 edition of NFPA 11 Standard for Low-, Medium-, and High-Expansion Foam. This edition of NFPA 11 does not require a connected reserve (though it is obviously permissible to provide one). Instead, the reserve supply must be either stored on-site or available within 24 hours in order to put the system back into service after operation.
To review all of the changes in the new edition of NFPA 409, see the Second Draft Report.