NFPA Journal - January/February 2020 - 30

SSTTRRAANN
COVER STORY

THE NUMBER OF ELECTRIC VEHICLES ON THE ROAD IS GROWING RAPIDLY.
EVEN SO, CRITICAL QUESTIONS REMAIN ABOUT STRANDED ENERGY AND HOW
TO RESPOND EFFECTIVELY TO THE MOST SEVERE EV CRASHES.
J E S S E

AT 9:27 A.M. ON MARCH 23, 2018, just as the morning
rush hour was starting to ease in Mountain View, California, a
violent collision threw a ho-hum Friday commute into chaos.
For reasons still unexplained, a Tesla Model X SUV, traveling at 70 mph down a flat, straight stretch of the 101 freeway,
abruptly drifted left and slammed into a concrete median that
divided the freeway from an offramp. Bystanders risked their
lives to pull the 38-year-old driver from the wreck before it
burst into flames. He later died at the hospital from his injuries.
The crash resulted in a complex and dangerous accident
scene. The impact tore the front end off the vehicle's frame,
ripping open the Tesla's 1,200-pound, 400-volt lithium ion
battery and scattering energized cells across the road. By the
time units of the Mountain View Fire Department arrived,
just after 9:30 a.m., the badly damaged battery was shooting
flames five feet into the air. Firefighting crews readied their
gear and got to work.
If there was a fire department anywhere in the world
equipped, trained, and prepared to handle the situation on
the 101 that morning, it was the Mountain View Fire Department. The Bay-area city of 80,000 is in the heart of Silicon
Valley and home to a who's who of technology behemoths,
including Tesla itself. Tesla vehicles are assembled nearby,
and the company routinely hosts emergency responders
from Mountain View and elsewhere to teach them about
its EV batteries, high-voltage wires, and emergency cut
loops, straight from the engineers who designed them. Tesla
has donated hundreds of vehicles to local departments to
practice emergency extractions and other procedures, and
Mountain View's firefighters have had plenty of live training.
Nearly 10 percent of passenger vehicles in Silicon Valley are
either hybrid or fully electric, double the national average,
according to a recent study. "We've been through a lot of
Tesla and other EV crashes," Juan Diaz, chief of the Mountain

30 | NFPA JOURNAL * J A N U A R Y / F E B R U A R Y 2 0 2 0

R O M A N

View Fire Department, said in a recent interview. "I hear
reports come in every day."
As they'd been trained, firefighters shot copious amounts
of water directly at the flaming battery, and extinguished the
fire in a couple of minutes. After eight more minutes with no
reoccurrence of fire, they turned off their hoses. But the severed battery continued to hiss and pop, sounds Diaz likened
to "slamming a hand on a kitchen table."
NFPA.ORG/
Firefighters feared the vehicle's frame
STRANDED
could be energized, but they lacked tools
Watch an
to test it. They also lacked the proper proNFPA Journal
tective equipment to handle or remove the
video about EV
crashes and the
battery's energized lithium ion cells, and
stranded energy
there was no way for responders to drain
conundrum.
the massive amount of energy still clearly
trapped in the unstable battery. The tow company refused to
load the hissing car onto a flatbed for fear of electrocution.
Firefighters found themselves in the middle of a busy freeway
with a battered EV and few options for what to do next.
As in all Tesla models, the battery in the Model X is comprised of more than a dozen separate modules, each made
up of hundreds of individual cells. All of these components
are neatly packaged in a rectangular metallic case that runs
the length of the chassis beneath the passenger cabin. Fully
charged, the battery has a capacity of 75 kWh-roughly
enough energy to power the average US home for more than
two-and-a-half days, and more than enough to instantly kill
anyone exposed to it. If punctured, breached, or otherwise
damaged, heat can build rapidly inside the compromised
battery cells and spread to surrounding cells in a cascade-like
process called thermal runaway, which can lead to fire, arc
flashing, off gassing, and sometimes explosions. Faced with
these hazards, the Mountain View firefighters resorted to one
of their few remaining options: call Tesla.

MOUNTAIN VIEW (CA) FIRE DEPARTMENT

B Y

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NFPA Journal - January/February 2020

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