NFPA Journal - Winter 2024 - 28

An EV bus charging
terminal in
California. Fleet
vehicles including
buses and trucks
are increasingly
powered by
batteries many
times larger than
those used to power
electric cars.
transition their municipal bus fleets to lithium-ion
power. The problem for safety managers is that most
bus terminals and depots are old and aren't designed
to mitigate the significant new hazards that lithium-ion-battery
buses pose compared to traditional
gas-powered buses.
Generally, the severity of a battery incident correlates
with the amount of energy in the battery.
The size of a typical electric car lithium-ion battery
is about 40 kilowatt-hours, whereas some larger
municipal electric buses can have batteries in the
range of 750 kilowatt-hours. These batteries are so
big that researchers haven't yet been able to even
quantify the hazard, much less provide meaningful
guidance for how to build safer depots.
" The scale of that hazard is monumental and
beyond the capacity of the largest lab to test it, "
Hutchison said. " But this transition is happening
very quickly, and facility operators are trying to
understand what this means for their facilities. Unfortunately,
there isn't any guidance out there yet. "
The design of the typical city bus depot only exacerbates
the problems. Buses tend to be parked very
close together to maximize limited space, which magnifies
the risk of fire spread. What's more, some bus
depots are underground, which increases the risk of
an explosion. Almost all of these depots must also
undergo significant retrofits to accommodate massive
charging stations, adding to the complexities.
28 | NFPA JOURNAL * WINTER 2024
There are similar challenges for parking garages,
which tend to be older, are frequently underground,
and weren't built with electric vehicles in mind.
Many are also being retrofitted to add powerful
charging stations. The Foundation is now working
on research projects on both parking structures and
bus depots to shed light on the hazards and possible
design solutions. Both are expected to be published
in the coming year. A separate project involving
full-scale fire tests of electric vehicles in parking
facilities is slated to begin soon, with completion
expected by the end of 2025. The information will
help engineers and code developers better understand
the changing protection needs of parking
garages as more cars become electric.
This overall trend of putting more and larger lithium-ion
batteries in facilities and structures that
were not designed to protect against the hazards they
pose is a concern that fire protection engineers share
across a spectrum of occupancies. Warehouses, for
instance, can now store millions of devices powered
by cheaply made lithium-ion batteries that have a
much higher failure rate. Warehouses, factories, and
industrial sites are also increasingly home to mobile
lithium-ion robots, which retrieve merchandise for
distribution, move pallets for storage or shipment,
and manufacture products. The same is true at construction
sites, where batteries now power numerous
tools and where fuel loads tend to be high.
PAUL BERSEBACH/MEDIANEWS GROUP/ORANGE COUNTY REGISTER VIA GETTY IMAGES
NFPA Journal - Winter 2024

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