NFPA 409, Standard on Aircraft Hangars, contains the minimum requirements for the proper construction of aircraft hangars and protection of aircraft hangars from fire. Intended to provide protection to both life and property from fire, this standard applies to buildings or structures used for aircraft storage, maintenance, or related activities. Other uses within an aircraft hangar, such as offices or tool storage, should be protected in accordance with applicable NFPA Standards. Protection systems include overhead deluge foam water sprinklers, or overhead closed head water sprinklers combined with supplementary low-level, low or high expansion foam systems. Under certain conditions, overhead closed head foam systems are also permitted.
NFPA 409 has specific requirements for acceptance testing of individual systems, since hangars usually have multiple, large flow foam conditions. Full flow water testing of each deluge system must be performed as a means to check sprinkler distribution and to ensure against pipe clogging by foreign matter. The smallest single foam system must be discharged using foam concentrate. The maximum number of systems expected to operate must be simultaneously discharged with foam. All proportioners must be tested using foam. Supplementary and low level foam systems must also be tested to assure accurate proportioning. Special provisions are provided for flowing overhead and supplementary low-level systems simultaneously.
Additionally, NFPA 409 requires testing of fire protection systems in aircraft hangars to be performed in accordance NFPA 25 Standard for the Inspection, Test and Maintenance of Water-Based Fire Protection Systems. The NFPA 25 requirements include monthly inspections and annual testing of proportioning and other equipment. Alternate methods to match full flow conditions are allowed where there are conflicts with local regulations. Discharge time and patterns are to be noted, along with key pressure readings and the foam concentration.