Author(s): Angelo Verzoni. Published on January 5, 2022.

Beyond Foam 

The latest edition of NFPA 409, Standard on Aircraft Hangars, allows users to consider alternatives to foam suppression systems for aircraft hangars


In 2020, a foam fire suppression system went off in a Delta Air Lines aircraft hangar at Los Angeles International Airport. Within minutes, the cavernous space was packed from floor to ceiling with thick white foam. When employees opened the hangar bay door, foam poured out onto the nearby tarmac. 

Watch security camera footage of an aircraft hangar in Charlotte, North Carolina, filling with foam in 2017 (What You Haven't Seen/YouTube)

In a tweet, one aviation blogger called it “a very big and expensive mess.” A Delta spokesperson told the aviation news website that an unspecified fire suppression system malfunction caused the discharge of foam. 

According to a 2021 study published by researchers at the University of Maryland, about a dozen incidents like this occur in the United States each year—and that figure is slowly increasing. On average, each incident results in about $100,000 of property damage, the study found. 

But changes to the 2022 edition of NFPA 409, Standard on Aircraft Hangars, released in the fall, allow for alternative methods of hangar fire protection and may help limit those losses. “In the past, for large hangars, foam was the only fire protection method prescribed by NFPA 409,” said Matthew Daelhousen, an operations chief engineer at FM Global and chair of the NFPA 409 technical committee. “Now there are other options available.”
Not just accidental discharge

While incidents like the one in Los Angeles and those reported in the University of Maryland study served in part to influence NFPA 409 committee members to write the recent change, Daelhousen said another key reason the document was updated related to environmental concerns over foam. Research has shown that some firefighting foams used to combat fuel fires contain chemicals that can be harmful to human health and the environment. 

“I think there are some misconceptions about different types of foam, and which ones contain which chemicals and which don’t,” Daelhousen said. “But the push against foam in general in recent years, combined with the fact that alternative protection methods have emerged for hangars, created the perfect storm of factors to put this change into the 2022 edition.” 

Instead of only requiring foam protection in hangars, the 2022 edition of NFPA 409 now lets users decide what system would work best after a professional approved by the authority having jurisdiction conducts a risk assessment for the space. “It allows people to use some judgement,” said Daelhousen.  

One prescriptive method of protection committee members specifically referenced in the new edition of the standard is known as an ignitable liquid drainage floor assembly, which combines a water-based fire suppression system like fire sprinklers with a fuel-drainage system on the floor. “It achieves the same performance goal as a foam system in getting rid of the fire hazard, which in an aircraft hangar would be a leak of fuel and burning pool of fuel on the ground,” Daelhousen said.

Building on the University of Maryland research from last year, the Fire Protection Research Foundation, the research affiliate of NFPA, will soon release a study that further examines non-foam protection methods for aircraft hangars, including drains, sprinklers, water-mist systems, and more. 

“Similar to the previous research, we also looked at fire incident and accidental discharge data—finding, for instance, that accidental foam discharge was about four times more likely than discharge because of a fire—but our primary focus was looking at alternative methods of hangar protection,” said Victoria Hutchison, a project manager at the foundation.

ANGELO VERZONI is associate editor of NFPA Journal. Follow him on Twitter @angelo_verzoni. TOP PHOTOGRAPH: GETTY IMAGES