NFPA Journal

On a clear morning in June, what appeared to be a large remote-controlled drone floated gracefully over Le Bourget airport, a civilian airstrip just north of Paris. It wasn’t a drone, though—it was an electric vertical takeoff and landing, or eVTOL, aircraft made by the 10-year-old German aviation company Volocopter, designed to carry two people in its application as a flying taxi.

As part of the 2021 Paris Air Show, Volocopter hoped to use the three-minute demonstration flight to showcase the technology it claims will reshape the future of ride-sharing. By the time of the 2024 Summer Olympic Games in Paris, Volocopter says it will have its eVTOL aircraft up and running for people to travel around the city, unencumbered by traffic in the streets below. 

Volocopter is hardly alone in its aspirations to do to air travel what Uber and Lyft have done to terrestrial travel. All around the world, there are companies touting eVTOL—and to a lesser degree gas-powered and hybrid gas-and-electric VTOL—aircraft designs aimed at revolutionizing the way people get around, especially in dense urban areas where vehicle traffic has become increasingly congested. “It’s a faster, cleaner, and smarter way to carry people through their lives,” California-based Joby Aviation, which in 2020 bought the division of Uber that had been working to develop a flying taxi business, states on its website. “Flying with us might feel more like getting into an SUV than boarding a plane.”

Companies like Joby Aviation and Volocopter operate in what’s known as the urban air mobility, or UAM, market, one that’s expected to become a $15 billion industry over the next decade, according to an August 2020 article published in Inside Unmanned Systems magazine. A Morgan Stanley Research report released the same year estimates that the UAM market could become a $1.5 trillion industry by 2040.

But the UAM market also has a problem: a lack of fire safety guidance when it comes to building the infrastructure needed for VTOL aircraft to operate. This includes facilities known as vertiports, where VTOL aircraft will take off and land. As with helicopters, the vertical take off and landing capabilities of VTOL aircraft mean vertiports can fit into relatively small urban spaces. They could be standalone facilities, like an airport, mainly serving passengers who want to fly from one city to another, or single VTOL landing pads incorporated into or onto existing structures, which could be more useful to passengers flying from one spot to another within a city.

“The rules applicable to UAM ground infrastructure are literally all over the map and are not forward-thinking,” the Inside Unmanned Systems article says. The Federal Aviation Administration (FAA) is working on writing standards related to vertiports, but like existing FAA regulations, those likely won’t discuss the fire safety considerations for such facilities in detail.

That’s why current efforts by the technical committee to add more information about vertiports to the 2024 edition of NFPA 418, Standard for Heliports, are critical to filling this gap in the UAM space. Experts say that guidance can’t come soon enough, as a number of vertiports are already being planned for cities worldwide.

“Right now there’s no standardized fire safety guidance that speaks to vertiports,” said Rex Alexander, a veteran helicopter pilot and president of Five-Alpha, an Indiana-based consulting agency specializing in aviation infrastructure. “We really need to put something in writing so that a municipality that wants to embrace this new technology has somewhere to look when determining what standard they’re going to build to. If we don’t have that, it makes it really rough. The way things are moving, we need to have that in place in the next three to five years.”

A DECADES-OLD CONCEPT TAKES SHAPE

The idea of flying in a VTOL aircraft from one end of a city to the other in the same way you’d hop in a cab is not new. In fact, it’s several decades old.

In 1968, the Institute for Defense Analyses, a private nonprofit research group, published a report titled “The Demand for Intercity Passenger Transportation by VTOL Aircraft.” The report envisioned a theoretical future of intercity VTOL transport beginning in 1975 and thriving by 1985. It did, however, recognize it was making some pretty big leaps in order to arrive at this imagined future. “In this study we have assumed the VTOL [aircraft] have overcome some very real problems involved in operating … in densely populated city centers—noise, air pollution, safety, and the availability of city-center vertiports,” the report says.

Fifty years later, those limiting factors are just being overcome, said Alexander, who is leading a task group for the NFPA 418 technical committee to explore the fire safety challenges at vertiports and to incorporate solutions into the standard. Mostly, he said, it’s due to improvements in battery technology. While industry statistics are hard to come by, the vast majority of emerging VTOL aircraft designs seem to use battery-powered electric motors, which offer a quieter, cleaner alternative to traditional fuel–powered aircraft.

“We’re seeing huge advancements in battery technology,” Alexander said. “Batteries are getting smaller and lighter, and they’re storing more energy.”

It wasn’t long ago that batteries suitable for the UAM industry seemed out of reach. But now those batteries are here, Alexander said, and the industry is poised to take off in the same way the electric vehicle market has in recent years. For air travel, the challenges to getting to where we are now have been more nuanced than in the world of electric vehicles, however, and they provide hints as to what the fire protection challenges will be for this technology.

“In the helicopter world, for instance, if I’m flying from point A to point B, the regulations state that when I arrive at point B, I should still have 20 minutes of fuel on board,” Alexander said. For eVTOL aircraft, that translates to the need for very energy-dense batteries—something with the energy density of 325 to 400 watt-hours per kilogram, according to industry experts. The batteries in most Tesla cars, for comparison, deliver about 250 watt-hours per kilogram.



As recently as 2018, engineering such energy-dense batteries seemed like an impossible feat, with headlines from that year reading, “Why Tesla batteries won’t work for air taxis” and “The battery to power Uber’s flying car dreams doesn’t exist (yet).” Fast-forward to 2021, however, and we see headlines like “Innovative batteries put flying cars on the horizon” and “Air taxis will utilize next-generation batteries and motors.”

What that means for experts like Alexander is there’s no time to spare in addressing the fire safety challenges of vertiports.

From Asia to the United States to Europe, plans are already underway to construct vertiports. Many renderings of these planned facilities look similar to airports but built to a much smaller scale, although others are more distinctive. One concept being developed in Italy, for example, is inspired by the African baobab tree—a natural wood–forward design featuring VTOL landing pads stationed 100 feet in the air.


FROM ORDINARY TO EXTRAORDINARY Vertiport designs run the gamut of aesthetics, from designs that look similar to traditional airports (top) to out-of-this world designs (below).  TOP: VOLOCOPTER; BOTTOM: GIANCARLO ZEMA DESIGN GROUP

There are also plans to add VTOL landing pads to existing structures—configurations sometimes referred to as vertistops. In June, Joby Aviation announced a partnership with Miami-based parking garage operator REEF Technology to add vertistops to parking garage rooftops in several metropolitan areas. “Parking structures are ideal locations for us as they allow us to deliver our customers as close to their destination as possible while minimizing any local impact and reducing the need for building new infrastructure,” the company said in a press release.

LIKE EVs BUT MORE COMPLICATED

For any vertiport configuration, fire safety experts agree there is one concern that tops all others: the energy-dense eVTOL aircraft batteries and the infrastructure needed to charge those batteries.

“These eVTOL aircraft would have to charge at astronomically large voltages,” said Michael Gorin, an emerging issues program manager at NFPA. “We’re talking about 800 to 1,000 volts of direct current charging, which is more than twice what a Tesla Supercharger provides.”

A study published by the National Institute of Aerospace and NASA in 2020 found that for a proposed vertiport in Houston, eight eVTOL aircraft charging stations would use about 50 megawatt hours of energy per day. The average American household uses roughly 11 megawatt hours of energy in an entire year.

All of this electricity use at vertiports introduces the potential for fires. It’s an issue the fire service has experienced with the proliferation of electric vehicles in recent years. When batteries are damaged, such as in a crash or through an internal battery cell defect, energy can remain trapped in the battery. This stranded energy can trigger a process known as thermal runaway, where the battery essentially continuously overheats and over-pressurizes and is prone to fires, arc-flashing, off-gassing, and sometimes explosions.

Currently, the only way the fire service is able to get a reaction like that under control is to put copious amounts of water on it. In April, when a Tesla Model S crashed and caught fire in Texas, firefighters had to use about 30,000 gallons of water before the blaze was finally extinguished. Most car fires involving traditional fuel vehicles require a few hundred gallons of water to put out.

With eVTOL aircraft and vertiports, the issue could be even more complex.

“Say you have a worst-case scenario, a lithium-ion battery thermal runaway and fire. If it’s at a ground-based vertiport, that’s one thing, but what do you do if it’s on a roof?” Alexander said. “How do you control it? How do you deal with it? Once you get the fire under control doesn’t mean it’s out for good. So you can’t put the aircraft in an elevator and take it down because closed spaces can accumulate explosive gases.”

RELATED: A Tesla crash in Texas in April required nearly 30,000 gallons of water to put out

“This will be similar to EV hazards, but I think more significant,” said Gorin. “If you have multiple eVTOL aircraft sitting on a flight deck at the same time, that’s thousands of batteries sitting there. They could be 20 stories up on top of a building. What type of suppression system are you going to have? What type of firefighter access and egress are you going to have?”

These are the kinds of questions the NFPA 418 technical committee will be grappling with in the months to come. Already, what’s known as a reserved chapter exists in the 2021 edition of the standard, meaning there is a general outline of the topics the future chapter on vertiports will cover. Many of them center on the batteries and charging stations.

It appears that even industry insiders are not entirely sure what the future of vertiport fire protection will look like, but they’re aware of the challenges. That includes Simon Whalley, head of regulation for United Kingdom–based vertiport design firm Skyports, which in 2019 unveiled the world’s first vertiport prototype in partnership with Volocopter in Singapore.

“Unlike a traditional airport, Skyports’ vertiports are being designed and equipped to fight and mitigate against risks from alternative aircraft fuel systems, like lithium-ion batteries,” said Whalley. “We are working with VTOL [manufacturers] to understand the characteristics of their aircraft and power systems to develop the necessary systems and procedures to either fight an onboard fire or safely isolate the vehicle or component at a vertiport.” What exactly that looks like, though, is not clear.

In an interview with Urban Air Mobility News in 2020, Whalley speculated what to do with a burning eVTOL aircraft. “It’s hotly debated,” he told the website. “You might have to leave the vehicle to burn out or put it in a bath or something.” Firefighters in the Netherlands made headlines in 2019 when they dropped a smoldering EV made by BMW into a giant tank of water to cool its batteries.


DUNK TANK In 2019, firefighters in the Netherlands extinguished a BMW electric vehicle fire by dunking the car in a large tank of water.  CENTRAL AND WEST BRABANT FIRE BRIGADE

In emails to NFPA Journal, two other companies currently working on vertiport design declined to comment on the fire safety considerations for their facilities, citing proprietary concerns and saying that, currently, “standards are somewhat unknown.”

The massive amount of electricity vertiports will need to supply aircraft also introduces the potential for energy storage systems (ESS) to be located at those facilities. (Learn more about how NFPA is addressing the ESS hazards faced by the fire service in our feature story “Learning from Surprise.”)

Alexander realized that a few years ago when he was helping Uber plan to enter the UAM market in Los Angeles. Scorching heat at the time led to rolling blackouts from the city’s power grid. “If it’s 3, 4 in the afternoon and you have a brownout, you’re going to have to have something to augment your electrical provider, which is then a storage system,” he said. “It’s going to have to be a pretty good size, too. If you have a rooftop facility, you can’t put it on the ground and run cables up there because the farther away it is, the bigger the voltage drop, the bigger the cables. You have to have it as close [to the vertiport or vertistop] as possible. Well, the average fire inspector is not really keen on having an electrical storage supply system on his roof, especially on an occupied structure.”

This is also a challenge the UAM industry recognizes. “Apart from fighting aircraft fires, vertiports will also have suppression systems for terminal facilities as well as on-site, high-wattage hookups and stationary energy storage infrastructure,” Whalley said. “These are primarily based off industry standards including NFPA 855, Standard for the Installation of Stationary Energy Storage Systems.”

‘A CODE ABYSS’

According to some experts, the resistance of authorities having jurisdiction (AHJs) to vertiports will be enough to slow the growth of the UAM market.

“It’s not like seeking to use a new building material,” said David Phelan, who works for South Carolina–based Davidson Code Concepts, a company that offers code compliance consulting for designers, manufacturers, and others. “This is a ground shift and evolutionary moment in technology and transportation. Do we somehow think the code officials will embrace the unknown, which isn’t addressed in the codes they may be using every day?”

Phelan described the current lack of information on vertiports in codes and standards not as a gap, but as “an abyss.” And until language on vertiports is introduced to model building codes such as the International Building Code and NFPA 5000®, Building Construction and Safety Code®, Phelan doesn’t think the UAM industry will be embraced by code officials. Even then, he cautioned, it may not be until jurisdictions adopt the latest versions of these codes and standards, which often doesn’t occur until years after they’re published.


LIFE-SIZED PROTOTYPE The world's first vertiport—the Voloport by Volocopter and Skyports—opened in 2019 in Singapore.  VOLOCOPTER

One idea that could make things easier for VTOL companies, Phelan said, is to utilize existing airports and heliports as opposed to building new vertiports. It’s a concept that hasn’t been lost on VTOL manufacturers. A white paper published by Volocopter in March said as much. “Of course, existing aviation infrastructures, such as airports or heliports, can also be used,” the company wrote.

But while there may be less red tape to deal with by running UAM operations out of existing aviation infrastructure, current fire protection systems, which are designed for traditional fuel–powered aircraft, won’t work for eVTOL aircraft, so there would still be a need for new infrastructure. “For current heliports we use a foam fire suppression system,” Alexander said. “Foam doesn’t really do a whole lot of good with an electrical fire.”

Furthermore, existing helipads don’t usually include facilities like terminals, where passengers would line up for a ride, and Phelan understands this is another limitation on using existing aviation infrastructure. “These will be publicly accessible aircraft, which will have waiting areas, business offices for staff and operators, possibly some type of control station or flight operations center,” he said. “Those types of use and spaces would fall to the model building codes and fire codes,” which lack information about this industry.

Beyond the gap in code language, there is also a gap in guidance for how the fire service and other first responders would answer future calls involving VTOL aircraft and vertiports.

“As soon as technology creates something, the emergency service world has a whole new set of problems, and solutions to develop,” Phelan said. “Without question there’s going to be a huge need for emergency response training and tactic development.”

A white paper published in 2019 by the National Air Transportation Association also recognized this gap. “First responders may have limited options in terms of stand-off distances in the initial response stages, and it is unclear whether existing personal protective equipment is suited for first response to an eVTOL fire at a vertiport,” the paper reads.

This is another area where NFPA could help, similar to how it has developed first responder training related to electric vehicles. “There certainly will be a need for safety training for first responders if this technology comes to fruition,” Gorin said.

Alexander said he also sees the need for first responder guidance coming from manufacturers. “There are over 400 VTOL aircraft designs out there right now, so the question when you respond to an incident is going to be, well, which one is it?” he said. “The automotive industry has really stepped up and come up with a lot of great documentation for first responders on electric vehicles. We’re going to have to do the exact same thing with this industry.”

The good news, Gorin said, is that we’re still at least a few years away from commercial VTOL aircraft flight, and NFPA is in a position to be ready when that day comes—at least from a codes and standards perspective. “We’re very much ahead of the game,” he said.

That’s in large part due to the decision by the NFPA Standards Council last year to move NFPA 418 from a five-year cycle to a three-year cycle, paving the way for the new vertiport chapter to be completed by 2023. “NFPA 418 has gone from being one of NFPA’s smaller documents to now writing some of these requirements for an emerging industry,” said Kevin Carr, the NFPA staff liaison to NFPA 418. “This stuff isn’t just science fiction anymore.”

Watch a related video from NFPA Journal about fire safety and flying taxis 

The task force Alexander is leading will meet once every two weeks through the fall, with plans to produce an internal draft of the vertiport chapter by the winter. He urged anybody with a hand in the UAM market to get involved now by submitting a public comment. The public comment period ends in January 2022.

“I would encourage anybody in this urban air mobility space to get involved,” Alexander said. “Now is the time to go online, go to nfpa.org/418, and provide your input because that’s going to drive what we come up with.”

ANGELO VERZONI is associate editor of NFPA Journal. Follow him on Twitter @angelo_verzoni. Top photograph: Volocopter