An evolution in aircraft hangar fire protection

An evolution in aircraft hangar fire protection

Within 10 years of the first recognised manned flight in 1902, the Wrights’ Vin Fiz hd crossed the United States in 84 days, with 70 stops including innumerable crash landings. Inventors continued to improve airplanes and within 8 years the Atlantic was conquered by flight and by the 1930s the jet engine had entered the arena.  One hundred years later, innovations in flight continue apace and as Aaron Johnson, a leading authority on fire protection, life safety, and code compliance for aviation facilities writes, we must communicate and share the new technology which is emerging to protect the lives and property in that sector.

NFPA 409, standard on Aircraft Hangars, requires the primary fire suppression agent for aircraft hangars to be foam. Specific fire protection requirements are based on the hangar group as defined in NFPA 409. Group I aircraft hangars are those that have a hangar access door height of 28 feet or greater or a single fire area in excess of 40,0002ft. Group II hangars have a hangar door height less than 28 feet and a single fire area of less than 40,000 sq. ft., based on construction type. Group III hangars are those with a door height of less than 28 feet and a single fire area of 30,0002ft. or less, based on the construction type. Group IV hangars are those constructed of a membrane-covered rigid steel frame. 

For the two largest hangar types, Group I and Group II, foam systems are the required fire suppression medium. Fire protection options consist of the following types:

  • Foam-water deluge system
  • A combination of automatic fire sprinkler system and low-level low-expansion foam
  • A combination of automatic fire sprinkler system and low-level high-expansion foam
  • A closed head foam-water sprinkler system (for Group II only)

The scope of NFPA 409 is to “provide a reasonable degree of protection from fire for life and property in aircraft hangars, based on sound engineering principles, test data, and field experience.” The original intent for the foam requirement of NFPA 409 was to protect the structure against the risk of fuel spills and fuel fire. There is a growing majority of fire protection and aviation professionals that are vocalising the fact that the “test data, and field experience” stated in the purpose statement of this standard no longer support the need or requirement for foam fire protection systems. Rather, the data shows that the more probable, and costly risk is that of an unnecessary or inadvertent system discharge.

The data shows that the frequency of hangar fires caused by a fuel spill is very low. While the average claim for a foam discharge exceeds $1 million dollars in damages to the aircraft, lost time, clean-up costs, and system repair. Insurers are discovering that there are a disproportionate amount of claims involving uncommanded activations; unintentional dispersion of foam; erroneous operation to fire suppression systems; inadvertent discharge, and virtually no claims related to a system discharge in response to an ignited fuel spill fire. 

NFPA 409, Standard on Aircraft Hangars, combined with NFPA 415, Standard on Airport Terminal Buildings, Fueling Ramp Drainage, and Loading Walkways, and NFPA 423, Standard for Construction and Protection of Aircraft Test Facilities, are under the purview of the technical committee on airport facilities. However, the biggest developments in moving toward the future of fire protection for aviation facilities is found in the proposed changes, and product developments, related to NFPA 409 and aircraft hangars. 

It has long been a requirement for the largest aircraft hangar groups, Group I and II, to provide some level of foam based fire protection systems. Historically, the foam was required to combat the potential fire risk of a pooled fuel spill fire. Insurance company data, and research, by organisations such as National Air Transportation Association and University of Maryland, have shown that these incidents do not occur. Far more costly, is the incident of an inadvertent foam system activation or foam dump. 

The development of new technologies for providing power to aircraft such as electric, hydrogen, or hybrid based technologies would potentially eliminate the “fuel” based fire hazards, or even create situations in which water-based fire protection would only contribute to the hazard and/or fire growth. Taking all this into consideration, a risk based approach has been proposed. This risk based approach will require a registered design professional to evaluate the hangar, the aircraft, and its intended functions and activities, and then develop a more performance-based design that will address any potential hazards.

Some items to be considered in this risk based approach may include: 

  • Services provided
  • Risk exposure to surrounding properties, the general public, or first responders
  • Importance or impact of business continuity
  • Fuel types and quantities, or products used or stored
  • Potential economic loss
  • Total occupants and life safety
  • Local fire department capabilities, resources, and response times
  • Construction, compartmentation, infrastructure
  • Size and value of the aircraft or the structure

Moving Forward

The invention of flight made our world smaller, our neighborhoods bigger, and allowed for the integration of nations and peoples. Innovations in flight are continuing this tradition. As we step into this new future of aviation, we must always remain vigilant as to what is going on in our world. We must stay observant to the changes that are happening around us and within our response areas. We must communicate and share the new technology that we see. 

As the aviation industry continues to evolve, this approach may not just be a “convenience”, but may be the only option. Considering new types of “fuel”, advances in unmanned aerial vehicles, innovative aircraft shapes, sizes, and configurations, a required foam system may become impractical, counter-productive, or even dangerous. As fire protection experts, and advocates for the best interests of our community, it is important that we work with our industry partners to address these concerns. These types of system innovations will be just one of the alternative, performance-based, fire protection methods that may be employed in the future of aircraft hangars.