NFPA 409: The Evolving Landscape of Aircraft Hangar Fire Protection

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Pierce Lushinsky, P.E.


December 15, 2023

NFPA 409 is a standard to determine construction and fire protection requirements for aircraft hangars. Traditionally, larger aircraft hangars were required to use foam-based suppression systems to mitigate potential fuel fires. However, this approach ended up causing more harm than good. The industry is shifting its strategy, with NFPA 409 playing a significant role. In this blog, we look at what NFPA 409 is and how it’s evolving.

What Is NFPA 409?

NFPA 409 is the Standard on Aircraft Hangars developed by the National Fire Protection Association (NFPA). It provides guidance for the design, construction, maintenance and fire protection of aircraft hangars. The primary goal is to enhance the safety of these facilities and reduce the risk of fire-related incidents.

What Types of Aircraft Hangars Does NFPA 409 Apply To?

NFPA 409 categorizes aircraft hangars into specific groups based on their design, size and purpose:

  • Group I
  • Group II
  • Group III
  • Group IV

Group I

Group I aircraft hangars must possess at least one of the specified features or operational conditions:

  • An aircraft access door height exceeding 28 feet (8.5 meters).
  • A single fire area larger than 40,000 square feet (3,716 square meters).
  • Accommodation capability for an aircraft with a tail height greater than 28 feet (8.5 meters).

Group II

Group II aircraft hangars are required to have both of the following features:

  • An aircraft access door height equal to or less than 28 feet (8.5 meters).
  • A single fire area not exceeding 40,000 square feet (3,716 square meters) and in compliance with Table 4.1.2 in NFPA 409 based on the type of construction and the size of the single fire area.

Group III

Group III aircraft hangars can be either a row hangar with multiple units, an open bay hangar accommodating multiple aircraft or a freestanding unit designed for a single aircraft. Group III hangars are required to incorporate both of these features:

  • An aircraft access door height not exceeding 28 feet (8.5 meters).
  • A single fire area not surpassing 30,000 square feet (3,716 square meters), in accordance with the maximum single fire areas specified for each construction type outlined in NFPA 409, Table 4.1.3.

Group IV

Group IV aircraft hangars must be constructed as a membrane-covered rigid steel frame structure.

What Type of Fire Suppression Systems Should Aircraft Hangars Use?

Before 2022, NFPA 409 offered a more “one-size-fits-all” approach to aircraft hangar fire protection. For example, many aircraft hangars were required to provide foam suppression systems to combat fuel fires, which presented multiple concerns.

For decades, aircraft hangars used foam containing PFAS and PFOA to suffocate the fire efficiently. However, it is now known that these chemicals are forever chemicals. These substances pose a significant risk of contaminating groundwater and leading to chronic health issues, so there is a strong aversion to using these foams, resulting in stringent regulations.

The alternative high-expansion foams are free from PFAS and PFOA. However, these detergent-based foams are corrosive to aircraft, which can cause extensive damage and costs. Insurance industry statistics indicate that the minimum claim value for a foam system discharge is approximately $1,000,000. 

In 2022, an update to NFPA 409 provided alternatives to the requirement for foam fire suppression systems in all groups of aircraft hangars. Included in the 2022 Edition is the option of an ignitable liquid floor drainage assembly, as well as a risk-based and performance-based design approach.  

What Were the Changes Made to NFPA 409 in 2022?

As previously mentioned, NFPA 409 implemented major changes in 2022. Providing alternatives to the foam fire suppression system requirement, NFPA 409 created provisions that allowed for more tailored fire suppression approaches. Three types of approaches include:

  • Prescriptive: A set of specific, predetermined requirements or guidelines based on the classification of the hangar.
  • Risk-based: A customized and effective approach that assesses and manages the specific risks associated with a particular aircraft hangar.
  • Performance-based: An approach centered around setting specific performance goals and criteria for an aircraft hangar’s fire safety rather than adhering strictly to prescriptive standards.

Another impactful change was the introduction of the ignitable liquid floor drainage assembly, which functions like a perforated platform for aircraft. During a fuel leak, any liquids filter through the perforations into floor trenches, preventing the formation of pools that could pose a fire hazard. This system effectively mitigates fuel fire risks but comes with a high cost. An ignitable liquid floor drainage assembly is a prescriptive alternative to foam-based fire suppression.

A comprehensive fire risk assessment offers an alternative. By stepping away from the “one-size-fits-all” approach, this assessment examines the unique characteristics of the aircraft, building and local operations. It considers factors such as the type of aircraft, the type of operations occurring within the hangar, the size and quantity of aircraft within the hangar, fire department operations and jurisdictional regulations, as well as other factors, to tailor a fire protection solution that aligns with the specific needs of the facility and balances the risk with the protection strategy. This holistic approach is particularly appealing to hangar owners, offering a more customized and potentially more cost-effective solution that better addresses the actual risks associated with the facility.

How Can a Fire Protection Engineer Help Protect an Aircraft Hangar?

A fire protection engineer specializes in evaluating hazards and designing, implementing and maintaining systems and strategies to prevent and mitigate the impact of fires in buildings and other structures.

Regarding aircraft hangars, experienced fire protection engineers have the knowledge and skillset necessary to keep your valuables safe. They can help you with a prescriptive, risk-based or performance-based approach depending on the needs of your hangar and operation.

Let’s say you want to incorporate a risk-based approach because you don’t want to spend money on prescriptive requirements that may not make sense for your hangar. Since jurisdictions haven’t widely adopted the 2022 changes to NFPA 409, the fire risk assessment is still considered an alternative means. Therefore, you would need a fire protection engineer to work with the jurisdiction and go through the process of getting the approach approved for your particular hangar.

Fire protection engineers utilize alternative means to keep up with the latest codes and standards as they develop based on new research and testing. The adoption cycle of the building codes typically falls behind. Utilizing the 2022 Edition of NFPA 409 allows your facility to be designed with the latest industry approaches based on the latest research and data. 


The transformative changes to NFPA 409 in 2022 signify a pivotal shift in aircraft hangar fire protection strategies. The new alternatives to the long-standing foam fire suppression system requirement in aircraft hangars open the door to more custom and flexible approaches that reduce costs, improve overall safety, and lower overall risk from a non-fire related foam system discharge.

To keep up with these changes, consider partnering with a fire protection engineer who understands your aircraft hangar’s needs. With their help, you can develop a fire protection solution that protects your property while adhering to NFPA 409’s standards.

When you need to protect valuable assets, turn to the experts at Performance Based Fire Protection Engineering. We have extensive experience in providing fire risk assessments for all types of aircraft hangars. Contact us to learn more about how we can protect your hangar.