NFPA 409 and Fire Suppression in 2023

Feb. 9, 2023
Last year, a new edition of NFPA 409 was published, and with it a revision to foam fire suppression systems for aircraft hangars. AMT asks the experts what this revision means for hangar operators and gets the latest on hangar fire safety.
Megan Eisenstein Headshot

Hangar fires are an all too real concern and having the right suppression systems in place should one occur is critical. The National Fire Protection Association (NFPA) standard on aircraft hangars (NFPA 409) gives guidance to what suppression systems a hangar needs.

Last year, the 2022 edition of NFPA 409 was published and with it revisions to the guidelines around hangar suppression systems – namely foam fire suppression.

To get the latest on aircraft fire suppression needs and what the change to NFPA 409 means, AMT spoke with Megan Eisenstein, managing director, industry affairs & innovation, NATA, and Doug Fisher, principal fire protection engineer, Fisher Engineering, Inc. Eisenstein sits on NFPA’s Technical Committee on Airport Facilities, with Fisher as the NATA’s designated alternate.

AMT: To lay the foundation, what are some of the leading causes of hangar fires?

According to a 2019 University of Maryland report on the review of foam fire suppression system discharges in aircraft hangars, there were 174 incident reports of foam system discharges between 2004 and 2019. The 174 incidents include 37 incidents where the foam systems discharged in response to a fire and 137 incidents where there was an accidental foam discharge, i.e., no fire was present. None of the 37 incidents involved a fuel spill from an aircraft. The leading causes of incidents with foam discharge in response to fire were:

  • Fuel spill
  • Electrical
  • Started in office or living quarters
  • Boiler
  • Compressor
  • GPU short
  • Hot glue gun left plugged in
  • Jet crashed into hangar
  • Paint fumes on roof
  • Scrubber
  • Welding set off fire in MRO
  • Unknown

As noted above, none of the incidents were related to a fuel spill from an aircraft. Fires do occur in hangars, like other buildings, however, foam is only required due to the potential for a fire from an aircraft fuel spill.

AMT: What are some of the fire suppression systems (or technologies) hangars should be equipped with? How does hangar size and type affect fire suppression options?

NFPA 409 categorizes aircraft hangars into four groups based on the floor area and the door height. Within each of these groups, NFPA 409 provides options for different fire protection measures. At least three research reports have been completed in the last few years documenting the minimal risk of a fire in an aircraft hangar due to a fuel spill from an aircraft. This has led to changes in NFPA 409 related to when foam is required. If foam is still required, NFPA also recognizes the use of an Ignitable Liquids Drainage Floor Assembly (ILDFA) as an option in lieu of foam. There has also been some investigation related to the use of a clean agent fire suppression system or a water mist fire suppression system in a hangar in lieu of foam.

AMT: What training, if any, do workers need for these suppression systems and how often should they be maintained?

NFPA 409, and other NFPA standards, provide specific requirements for inspection, testing and maintenance (ITM) of foam fire suppression systems and their associated releasing system. For example, the foam concentrate is required to be tested annually while the foam proportioning system is required to be tested every five years. ITM, however, should only be performed by properly trained personnel to ensure proper testing and maintenance and reduce the risk of an inadvertent discharge.

Facility personnel should understand how the system operates and how to shut it down in the case of an inadvertent discharge. Check with your local fire marshal to ensure you are permitted to shut the system down in the case of an inadvertent discharge prior to fire department arrival.

AMT: Broadly, what is National Fire Protection Association (NFPA) 409, what is its history and what are the latest changes to it?

The National Fire Protection Association (NFPA) 409: Standard on Aircraft Hangars is the primary standard for hangar fire protection and is referenced by the international building code (IBC), the international fire code (IFC), and state and local statutes, ordinances, and regulations. Historically, NFPA 409 has required most modern general aviation hangars to have automatic foam fire suppression systems installed.

The 2022 NFPA 409: Standard on Aircraft Hangars incorporates changes proposed and supported by NATA, providing aviation businesses significant tools to protect against fire without the use of foam fire suppression systems. The 2022 edition contains provisions that:

Create an alternative Performance-Based Design process allowing modification of any part of the NFPA 409 standard

Create a Risk-Assessment process that allows businesses to propose alternative fire protection schemes with or without foam

Exempt Group II hangars that prohibit hazardous activities from foam requirements

Approve the use of ignitable liquid floor drainage systems in lieu of foam systems

AMT: Why were the changes made to NFPA 409?

NATA and its members have long advocated that aircraft hangar foam fire suppression requirements within the previous versions of the standard do not reflect the reality of the current risk of fuel fires, nor do they consider the public and private liability and expense of environmentally hazardous cleanup after accidental system discharges.

The 2022 standard better reflects the current operating environment, which has evolved significantly since its original writing in 1966.

AMT: Given the changes, what should our audiences’ main takeaways be for their own hangar fire suppression systems?

Determine if hazardous operations, as defined in NFPA 409, are being performed in the hangar. If not, look at possibly removing foam from the hangar as permitted by NFPA 409, 2022 edition. The NATA Aircraft Hangar Fire Protection Guidance provides additional information and resources to assist with this review. Most importantly, engage the services of a qualified professional fire protection engineer or architect, with experience in working with the AHJ [Authority Having Jurisdictions] to permit the removal of foam from the hangar.

AMT: Should people be thinking of upgrading or replacing their fire suppression systems in light of the updates to NFPA 409?

There are a variety of design options, already permitted by the codes, and equivalency approaches that may allow for the removal of a foam fire suppression system. It is strongly recommended to utilize the services of a licensed design professional, typically a fire protection engineer or architect, to assist you in working with your local code authorities when discussing the need for a foam fire suppression system in your hangar. Experienced design professionals can help bridge the knowledge gap between the operations being performed in the hangar and the requirements for a foam fire suppression system.

AMT: When evaluating their current fire suppression system, what should a hangar operator be aware of and what are the key points they should have in mind?

Determine if the operations being performed in the hangar meet the definition of hazardous or not, per NFPA 409. From there, determine if your hangar requires foam or an equivalent protection method (i.e., the ILDFA) or if foam is not required per NFPA 409, 2022 edition. If foam is required, have a qualified professional review the system installation and current inspection, testing and maintenance practices to determine if there are options to reduce the potential for an inadvertent discharge. For example, a typical foam system will discharge from activation of a single sprinkler water flow switch. However, the use of optical flame detectors in lieu of a sprinkler water flow switch can reduce the potential for an inadvertent discharge. Further, the system can be sequenced to require two flame detectors to go into alarm rather than one. Finally, the flame detector can be multi-spectrum (vs. UV), which will further reduce the potential for false activation.

AMT: Are there any other changes to NFPA 409 on the horizon and/or new fire suppression technology/methods our audience should keep an eye out for?

For background, NFPA 409 and the model building codes define fire protection criteria for aircraft hangars based on “Groups.” One of the determinations for a Group II hangar is a door height of 28 feet or less. This height limit was put into the codes/standards a long time ago to limit the quantity of fuel that might be in an aircraft hangar by limiting the size of the aircraft that could fit into a hangar. The thought process was that an aircraft with a tail height less than 28 feet holds significantly less fuel than an aircraft with a tail height greater than 28 feet. Over the past 40 or so years, changes in aircraft design, aerodynamics, fuel efficiency and fuel tank size have possibly made this distinction, based on tail height, obsolete.

For the next edition of NFPA 409, NATA will advocate to change the door height maximum for Group II hangars. Increasing the door height poses no additional risk, as it does not allow a greater volume of fuel to be present, but does provide additional flexibility to aircraft manufacturers, FBOs and hangar operators.

AMT: What final advice do you have for our readers when it comes to their hangar’s fire safety and suppression?

  • Ensure proper and complete ITM is being performed on your system.
  • Understand how your system operates and how to properly shut it down in the case of an inadvertent discharge, including how employees will safely evacuate the building and how accountability of employees will occur.
  • Retain the services of a qualified design professional to evaluate if foam is required for your facility based on the current requirements in NFPA 409, 2022 edition and industry guidance. If it’s not, have the design professional engage in discussions with the AHJ to determine if the foam can be removed.
  • Retain the services of a qualified professional engineer to evaluate your current system installation and make recommendations to increase reliability of the system and reduce the potential for an inadvertent discharge.