NFPA Journal - Fall 2021 - 31

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. "
" 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
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NFPA Journal - Fall 2021

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