NFPA Journal - September/October 2020 - 22

UNWELCOME SURPRISE
The damaged energy storage system in
Surprise, Arizona, following an explosion
that injured four responding firefighters.

E M E R G I N G T E C H N O L O GY

IMPROVEMENTS
WELCOME

NEW REPORTS HIGHLIGHT WHAT WENT
WRONG IN AN ENERGY STORAGE SYSTEM
EXPLOSION IN ARIZONA-AND WHAT WE
CAN LEARN FROM THE EVENT
By Angelo Verzoni
ust over a year after an explosion at an

J

energy storage system (ESS) injured four
firefighters in Surprise, Arizona, two new
reports shed light on what happened as well
as on some of the shortcomings of the safety
systems, guidelines, and procedures in place to deal with
ESS incidents.
"Both documents are examples of how we can learn from
past incidents to improve our codes and standards, increase
the safety of our first responders, and build a safer environment," Brian O'Connor, an engineering technical services lead
at NFPA, wrote in a blog about the two reports. "It's encouraging to see that such a collaborative approach was taken in
response to this incident to determine what happened and

what can be done to prevent
this type of equipment failure
in the future."
The first, released on
July 18, came from Arizona
Public Service, the utility
company that maintained the
ESS that exploded. The APS
report focuses on the battery technology in question,
concluding that the incident
most likely resulted from the
internal failure of a single
battery cell caused by a defect
in the cell. When heat built
up in the one defective cell,
it spread to others-a process
known as thermal runaway-
and the fire suppression
system installed in the ESS
couldn't stop that process,
the report said. As this
thermal runaway occurred,
flammable gases built up
inside the structure housing
the batteries and eventually
triggered the explosion.
The second report, released by UL on July 23, focuses on
the emergency response aspects of the incident. The UL
report "does a great job at addressing some of the contributing factors that led to...firefighter injuries," O'Connor
said. It points to deficiencies in responding firefighters'
preparation for the incident, which included hazardous
materials training that did not cover ESS hazards, and their
ability to monitor the conditions of the ESS container from
a safe distance.
NFPA's standard related to ESS-NFPA 855, Standard for
the Installation of Stationary Energy Storage Systems-was
first published five months after the Arizona incident, and
the APS report includes recommendations for strengthening that document. For example, the standard doesn't
include requirements for preventing thermal runaway at
the battery cell level, but instead mentions it in an annex
section. That should change in the future, according to the
report's authors.
O'Connor hopes concerns like this will be considered as
part of the standards writing process. "NFPA codes and
standards are living documents that are constantly looking
for ways to improve and keep up with new technology," he
said. "Recommended improvements are always welcome in
the form of Public Inputs or Public Comments." The next edition of the standard is set for release in 2023. To learn more
about the schedule and process of updating the standard,
visit nfpa.org/855next.
Find the APS and UL reports online by visiting nfpa.org/
dispatches and selecting "ESS Explosion Reports."

ARIZONA PUBLIC SERVICE

Dispatches

22 | NFPA JOURNAL * S E P T E M B E R / O C T O B E R 2 0 2 0

Dispatches_09.20 V3 DCS.indd 22

8/27/20 12:25 PM
http://www.nfpa.org/855next http://www.nfpa.org/dispatches http://www.nfpa.org/dispatches
NFPA Journal - September/October 2020

Table of Contents for the Digital Edition of NFPA Journal - September/October 2020
