GROUND SUPPORT… Risk Based Support

Hangar Fire Protection: Is it time for a new approach?

A fleet of five Navy attack F/A-18s are undergoing maintenance and modifications in a hangar in north Florida. Without warning, the airplane hangar fire suppression system is activated and discharges its high-expansion fire-retardant foam onto the aircraft below. At a cost that was initially estimated at more than $1 million, this will be classified as a “Class A” mishap by the Navy. The cause of activation remains undetermined.

Further south, a deluge system is activated inside of an aircraft manufacturing hangar. This activation is due to an electrical short in a pull station that has gotten wet from high winds and rains. It causes damage to the fire protection and pump system and results in more than $500,000 worth of repairs and lost work time.

These are not isolated incidents. As we will see, inadvertent foam system activations are much more probable than an actual activation due to fire. Is it time for a new approach to hangar fire protection?

NFPA 409, Standard on Aircraft Hangars, requires the primary fire suppression agent for aircraft hangars 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 40,000 sq.ft. 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 30,000 sq.ft. 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. In the event of a fuel fire, water alone would not be sufficient for extinguishment. There is a growing majority of fire protection engineers, fire code officials, fixed base operators (FBO) managers, airport owners, pilots, and aviation associations that are vocalizing the fact that “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.[1] Rather, the data shows that the more probable, and costly risk is that of an unnecessary or inadvertent system discharge.

Though not impossible, the data shows that the frequency of hangar fires caused by a fuel spill is very low. Insurers are having a hard time finding, gathering, and analyzing any data that shows a hangar foam fire suppression system being activated by an ignited fuel spill. Insurance companies that insure these aviation facilities are starting to mine their data for hangar fires to support the use of foam, however, what they are discovering is that there are a disproportionate amount of claims involving uncommanded activations, unintentional dispersion of foam, erroneous operation to fire suppression system, inadvertent discharge, and virtually no claims related to a system discharge in response to fuel spill fire.

The average claim for a foam discharge exceeds $1 million and includes damages associated with physical damage to the aircraft, lost time and business opportunities, environmental damage and clean-up, and fire suppression system repair and restoration.  What has been suggested by the aviation industry is a shift in the standard from a prescriptive-based approach to a performance-based, or risk-based, fire protection design approach.

NFPA 409 currently takes a prescriptive based approach to the fire protection of hangars. The standard clearly outlines, prescribes, the required fire protection and construction features. For example, if the hangar is x size or type of hangar then y fire protection and construction requirements must be met. A performance-based option would allow a registered design professional, engineer, or other entity approved by the authority having jurisdiction, to assess the hangar and its use, and design a fire suppression system based on the hazard presented and risk of fire or life loss. A commonly drawn comparison to this approach, is to that of the mass notification requirements of NFPA 72, National Fire Alarm and Signaling Code.  Several years ago, when mass notification systems were added to the code Chapter 24, of NFPA 72, outlined a “Risk Analysis for Mass Notification Systems”. This permitted only those buildings and properties where the analysis indicated to require the installation of mass notification systems. The standard clearly outlines what items must be assessed and indicators for a system requirement.

Similarly, a risk-based assessment could be applied to the aviation hangar environment. Applicable codes and standards would provide precise guidance on items to be assessed, with clear indicators of types of fire protection systems to be installed. Such a risk-based approach to hangar fire protection may include an analysis of such items as:

  • 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

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.

About the Author: Aaron Johnson serves as Fire Marshal for Rural/Metro Fire Dept. in West Palm Beach, FL. He holds multiple fire service certifications, and has over a decade of fire protection/ life safety experience. He regularly writes on fire protection, and can be contacted at his website, www.TheCodeCoach.com.