NFPA Journal

BY ANGELO VERZONI

When a battery-powered electric vehicle catches fire, it can be a difficult beast for the fire service to control. Even so, the instructions remain fairly simple: put water—lots of it—on the batteries. The same principles will apply to fires involving the batteries of electric vertical takeoff and landing (eVTOL) aircraft, which are poised to become a reality in the next three to five years.

But what happens when those aircraft use a hydrogen fuel cell, instead of batteries, to generate electricity? The approach first responders take, and the fire protection systems that are needed, to control such a blaze will be markedly different. And what about when the aircraft is powered mainly by batteries but also has a gas tank on board?

These questions are currently being weighed by the technical committee for NFPA 418, Standard for Heliports, as it works to draft a new chapter in the standard addressing the emerging urban air mobility (UAM) industry. Specifically, the group is determining what fire safety measures will be needed at vertiports, the facilities where these aircraft will operate from. While batteries seem to be the most popular type of power source envisioned by VTOL aircraft manufacturers, some companies have also introduced hydrogen-powered and hybrid gas-and-electric designs—propulsion types that will present different challenges requiring different solutions.

“Whether you have a hydrogen leak or a gas spill or a battery fire, you’re going to need to have specific requirements for mitigating the hazards in those situations,” said Kevin Carr, the NFPA staff liaison to NFPA 418.

According to Rex Alexander, current aviation infrastructure around the world is mainly designed to protect against gas fires and spills, with foam fire suppression systems and systems designed to contain leaked gasoline. In addition to being a member of the NFPA 418 committee, Alexander is a veteran helicopter pilot and founder and president of Five-Alpha, an Indiana-based consulting agency specializing in aviation infrastructure. Alexander said vertiports may need to include those same systems, plus systems designed to handle incidents involving batteries and hydrogen.

Some experts see hydrogen, in particular, becoming a prominent part of the UAM industry in the future. According to an article published in January by eVTOL.com, a UAM industry news website, the use of hydrogen as a power source “could significantly expand the possibilities of air taxis beyond the limitations posed by battery-electric powertrains, according to proponents of the fuel.” Those proponents say hydrogen “has a higher energy density than lithium batteries, meaning it can increase operational range and flight time. Additionally, hydrogen systems can be refueled fairly quickly, increasing the utilization rate of those platforms.” But, the article concedes, hydrogen is also highly flammable—it holds the highest flammability rating on the scale described in NFPA 704, System for the Identification of the Hazards of Materials for Emergency Response—and “creates significant challenges for use in rooftop-based vertiports.”

As a result, the committee is making it a point to include hydrogen and hydrogen fuel cells in its scope of work for the vertiport chapter, Alexander said. “The application of hydrogen will no doubt bring with it some unique challenges," he added, "but NFPA 2, Hydrogen Technologies Code, first published in 2011, has a significant amount of great language that can be directly referenced by NFPA 418.”

NFPA 2 includes fire safety guidance for both liquid hydrogen and gaseous hydrogen applications, both of which could be utilized in VTOL designs. In general, its requirements focus heavily on hydrogen storage quantity and distancing requirements, pressure valves, and leak detection.