APS Details Cause of Battery Fire and Explosion, Proposes Safety Fixes

Utility Arizona Public Service has�completed its exhaustive
study of the most high-profile U.S. grid battery fire.

The company filed its
Monday with the Arizona Corporation Commission, which
regulates the utility. The report, produced in collaboration with
DNV GL, lays out new safety requirements to prevent dangerous
failures at current and future battery installations.

APS planned to massively increase its battery fleet to store
solar power for use in the evenings, but put the buildout on hold
after the setback last spring. A lithium-ion battery container near
Phoenix caught fire in April 2019, and after first responders
opened the door, it exploded, sending several of them to the

The fire ignited in just one of the 27 racks of batteries in the
McMicken facility, and did not spread, GTM previously
. That suggests the layout of the racks effectively
isolated them from each other. But the aerosol fire suppressant was
powerless to stop a buildup of explosive gas, which combusted when
the first responders opened the door and let oxygen into the

The explosion revealed that lithium-ion batteries can be
dangerous, even in the hands of experienced professionals like
APS, storage vendor Fluence, and battery manufacturer LG Chem. The
new report offers a chance to identify what went wrong and ensure
that future constructions eliminate the failure pathways, said
Scott Bordenkircher, director of technology integration and
innovation at APS.

“Conversations and learnings around an event like this are
hypercritical, because that’s how you get the information out
that needs to be considered in the next generation,†he said in a
Monday interview.

Immediate changes

The findings include two major categories of recommendation:
physical changes to battery system design to eliminate the gaseous
buildup scenario, and changes to how utilities train first
responders to deal with emergencies at battery plants.

The report breaks down the event into five crucial steps:

  1. It appears that a single lithium-ion cell developed dendrites,
    or accretions of material that grew from one electrode to the
    other, which caused a short circuit. This caused the cell to heat
    up and catch fire.
  2. As that fire spread to neighboring cells, the aerosol fire
    suppressant proved incapable of stopping such a powerful
  3. The placement of pouch batteries in close proximity within
    modules meant that the fire spread quickly from cell to cell. There
    was no physical barrier to prevent that spread, although the layout
    of the facility prevented spread beyond the vertical rack that
    caught fire.
  4. As hundreds of cells burned up, they released explosive gas,
    which built up in the container without a means of escape. The
    container lacked sensors to count this gaseous accumulation.
  5. The lack of sensors or remote viewing limited operational
    awareness for the first responders, who also had limited training
    on this type of scenario.

Dendrites are a well-known failure mode for batteries, but it
was unexpected that they would appear on a battery that had only
operated for about two years.

“Over a long period of time it may be kind of expected, but
nowhere near the severity we saw in this short period of time at
this system,†Bordenkircher said.

As this event makes clear, even top tier integrators buying
batteries from top tier suppliers can end up with flawed cells.

“Our focus is on when it fails, how do you mitigate it,â€
Bordenkircher said.

To do so, APS will require remote sensing and ventilation, so
that if a malfunction ever leads to releasing dangerous gases, the
operators can identify them and flush them from an enclosure
without exposing any people to risk. This has not been standard
practice in the storage industry, although New York City
authorities required it for systems installed there.

Other upgrades include cooling systems or barriers between cells
to prevent fires from spreading, and inclusion of more intensive
fire suppression in case a gaseous clean agent fails to stop a

These steps add materials and labor to a battery project, so
they will likely increase costs. But there’s no way around that,
Bordenkircher said.

“You’re not going to sell it, regardless of cost, unless
it’s safe,†he noted. “The communities and the regulators are
going to mandate it, and it’s the right thing to do.â€

On the training side, APS will conduct broader regional
education around fire response at its battery sites. It had trained
local responders in the city where a battery was located, but the
hazardous materials team that arrived at McMicken drew personnel
from the surrounding area. Battery response training needs to cover
anyone who could arrive at a battery fire, and the trainings should
be followed with regular refresher briefings, Bordenkircher

But the earlier emergency response plans did not contemplate an
explosive scenario, which left the responders unprepared for what
happened when they decided to open the door.

Actions to restart battery construction

APS shut down its other battery facilities from Fluence—one at
Festival Ranch, which is a twin of the McMicken system, and a
larger one at the desert community of Punkin Center. Before those
reopen, they will need to be retrofitted with ventilation

Going forward, new battery plants will have to meet these
requirements as well. When McMicken happened, APS was about to
finalize the first contracts in a planned
850 megawatt battery buildout
to pair the utility’s
large-scale solar fleet with batteries.

Those plans have been on hold since then, but APS maintained
that it remains committed to battery technology. The utility is
already working with the contract winners to see if they can update
their projects to meet the new safety standards emerging from the
investigation. Those standards will be baked into new requests for
proposals going forward. 

APS only has the power to enforce these standards in its own
territory, but Bordenkircher implored people elsewhere to consider
how the McMicken failure scenario would play out in their own
battery plants.

“There are many other containerized batteries installed across
the world,†he said. “I would sure hope that everyone will take
a look at the system they own and operate and do a risk assessment
based on these findings.â€

The report is accessible on
APS’ website
, and the company has planned outreach to several
industry groups in the next few days.

In January, the company committed to
eliminating carbon emissions
from power production. The ability
to store power in batteries will play a crucial role in delivering
evening peak power as decarbonization proceeds.

“You can’t get there with intermittent reources that only
generate during daylight,†Bordenkircher said. “We know
[storage] is the answer to how you get to a clean energy commitment
like that.â€

In other words, the rollout of the battery fleet has been
delayed by the fire and its aftermath, but the endpoint has not

Source: FS – GreenTech Media
APS Details Cause of Battery Fire and Explosion, Proposes
Safety Fixes