by Julian Spector
April 30, 2019

It’s time to have a serious conversation about safety.

The U.S. energy storage industry made it this far with only a handful of fires, and most of them were seven years ago, ancient history in grid storage terms.

That success has made it possible to treat battery safety as a rather distant concern. It merits some boilerplate generalities — number-one priority, of the utmost importance, etc. — but robust, uncomfortable conversations have been hard to find, at least out in the open.

The frankest warnings about lithium-ion come most frequently from the flow battery makers and other unconventional long-duration storage companies that have taken it upon themselves to challenge the undisputed market leader. However legitimate these concerns may be, those messengers aren't spending the time to make lithium-ion safer; that would eliminate the selling point of the alternatives.

So, as deployments skyrocket, the conversation about battery safety has largely kept out of the spotlight. That applies to these pages as well: Storage Plus has spent a lot more time unpacking market growth and parsing various technologies than investigating the fundamentals of safe system operation.

That’s going to have to change.

The plume of smoke followed by an explosion at an Arizona Public Service battery facility earlier this month altered the conversational landscape. Really, the 21+ battery fires among South Korea’s deployment boom should have sufficed, but that market’s geographical distance and breakneck speed of growth allowed U.S. installers to point to more differences than similarities between them.

We don’t know what caused the fire in Arizona, and we may not know for some time. What we do know is that a fire at a battery facility sent four emergency responders to the hospital with chemical burns, and that the storage industry had better provide a clear accounting of how it's minimizing the odds that something like that happens again.

First step is acknowledging the risks

That accounting requires a dispassionate assessment of the risks inherent in this technology.

Lithium-ion cells are useful because they pack a lot of energy into a small amount of material. That also makes them dangerous. And while the industry talks a lot about how to suppress thermal runaway, I was startled to learn there is a whole other type of physical danger that gets hardly any airplay: When heated, lithium-ion cells can release flammable gases that conventional fire suppression fails to adequately protect against.

It’s also worth noting that the U.S. lacks a cohesive national standard for battery facility design. That policy — NFPA 855 — is still being assembled. “Because that doesn’t exist, everything goes based on what the local rule is,” said one storage integration expert I spoke with.

It’s hard to argue that this is ideal for ensuring a standard of quality throughout the nation.

Whether or not the battery technology itself is to blame for the Arizona fire, now is the time for the industry to show it’s not afraid to confront this issue head on.

To its credit, the Energy Storage Association had already moved ahead with an industrywide safety initiative, launched at its conference in Phoenix, which, somewhat eerily, concluded just one day before the conflagration down the road (the conference also featured a visit to a storage system identical to the one that burned).

Operational hazards and incident response are at the top of the priority list, said ESA CEO Kelly Speakes-Backman. The 30+ companies participating will start by taking inventory of current best practices and identifying any gaps. Then the group can develop an industrywide set of safety standards to inform its own operations and help jurisdictions as they craft their local codes for storage permitting.

"There are risks to operation, and we have to recognize that as an industry and figure out how to minimize that," Speakes-Backman said in an interview Monday. "We want steady and strong growth of our industry, but we want it done in a safe manner."

We need to talk about the explosive gas problem

Seeking clarity on the topic of battery safety, I turned my investigation to the locale with the strictest approach to the matter: New York City.

Despite its insatiable electricity demand and intractable transmission constraints, New York City has only installed a handful of batteries, in large part because the city’s Fire Department and Department of Buildings take a diligent interest in minimizing the threat a battery fire might pose to them or its surroundings.

In the course of developing its understanding of this technology, New York stakeholders commissioned extensive fire testing of battery cells and published the results. By intricately tracking the materials that emerge when the cells heat up, researchers from DNV GL found that cell fires are not the only danger.

“You’ve got a fire that is also emitting more flammable gases as it burns,” said Davion Hill, DNV GL’s global energy storage leader. “The gas explosion is more dangerous than heat from the fire.”

Hill breaks down battery fire risks into three separate categories. There’s the fire itself; the risk of cascading, whereby one cell heats up and sets off nearby cells; and the possibility of dangerous gases emanating from the cells and filling an enclosure.

The same solutions don’t work for all three. Chemical fire suppressants work by releasing aerosols into the room that suppress combustion, either by lowering the oxygen concentration in the air or absorbing heat. This should interrupt conditions for a fire, but it doesn’t get rid of flammable gases.

The best way to prevent cascading is to separate cells so that if one heats and swells, it can’t heat up its neighbors. Cooling systems that reach each cell directly help keep temperatures in the safe zone.

The best way to deal with flammable gases is to vent them out, so they don’t ignite when responders enter to inspect the room. Ventilation adds its own complications, though: It works against aerosol fire suppressants by venting them out of the room, and could potentially allow a fire to escape the enclosure (as opposed to a closed-loop system).

This flammable gas scenario doesn’t garner much attention, perhaps because it has not been documented at an operating grid battery in the U.S. Again, there had only been two fires at U.S. grid batteries before this month; good battery management systems should spot signs of trouble and shut them down before a fire erupts, and the record suggests they rarely fail to do so.

But that’s no reason to dismiss the risk of gas explosion, because Hill and his team observed it “routinely” in controlled laboratory burns.

“That’s frankly our biggest concern from a safety standpoint when we do any kind of testing,” he said. “We have to design our tests to protect our [staff] from that scenario.”

He recommends including ventilation systems that can whisk away such gases, so they don’t build up and combust. This approach would also involve off-the-shelf sensors that detect the concentration of these gases and trigger the ventilation.

But ventilation is not a common practice in grid battery design.

Asking around, I couldn't find anybody who knew of places other than New York City demanding ventilation for flammable gas as a standard safety precaution. I had never heard anyone talk about it before I went down this rabbit hole, and the discrepancy between a publicly documented explosive scenario and the muted reaction the findings received struck me as unnerving. 

Insights from New York City

I did find a proof of concept for these and other safety precautions working in an operating battery system.

Demand Energy navigated the labyrinth of New York City battery siting requirements and lived to tell the tale. More than that, it helped the New York stakeholders develop their understanding of the new technology, and even got acquired by Enel and rolled into the energy storage practice at its Enel X subsidiary.

The lithium-ion system Demand Energy installed at the Marcus Garvey housing complex in Brooklyn in 2017 showcases the discipline required to operate in that market. 

It contains not one but three layers of defense against fire: a dry chemical suppressant in the box, a remotely controlled ventilation system and a “dry pipe,” where emergency responders can hook up a fire hose to pump water directly into the storage enclosure.

The site features an emergency station designed to make things easy for responders. It contains controls for remote shutoff and ventilation, plus the dry-pipe hookup. It also lists contact information for the company’s network operations center.

If first responders want to enter, they can ensure that the system is shut down and that any gases that may have been released are flushed out.

“The ventilation piece is key before you open and enter,” said Doug Staker, head of utility business development at Enel X. “As far as I know, we’ve only seen that requirement in New York.”

If the situation inside appears too dangerous to inspect by hand, the dry pipe connects to sprinklers in the enclosure that will only release if the temperature reaches a threshold that melts the fusing attached to the nozzles.

All else held constant, tougher permitting requirements make it harder to develop storage. To earn one "Letter of No Objection" from the Fire Department, Staker’s team had to respond to 39 specific safety inquiries.

“It’s added cost, it’s added complexity, but it helps build something from a first responder’s perspective that we think mitigates risk,” Staker said. 

As the requirements complete their evolution from a project-by-project basis to standardized rule, the cost of compliance will come down, he added.

Storage has to get this right

The latest fire came at a sensitive moment for the storage industry.

Utilities had finally started to take this technology seriously and buy it in large amounts. Two days before the incident, I sat down with Arizona Public Service at the ESA show in Phoenix to hear about how excited the company is to pair all its utility-scale solar plants with batteries as part of an 850-megawatt building spree.

The fire distracts from all that good news. It dominated the headlines in the same week that utility Southern California Edison picked 195 megawatts of storage in place of the proposed Puente gas plant in Oxnard — a major victory for the industry.

The fire shouldn’t stop that momentum.

I mean that descriptively, in that history shows us that the Flagstaff and Oahu fires of 2012 failed to halt the growth of battery deployments in the early days. These days, many more people have a stake in the growth of energy storage, and it has a vital role to play in several states’ commitments to zero-carbon electricity.

I also mean that prescriptively: The arguments for building energy storage to shift cheap solar power into the night make just as much sense for Arizona now as they did a month ago. Vessels for immense power occasionally blow up. Gas mains do it, transformers do it, and yes, very rarely, batteries do it. A non-zero risk of danger is a necessary tradeoff for the vast potential of ubiquitous and affordable electricity.

If the batteries caused the problem, the industry needs to own that. If something else sparked the fire, but the fire’s interaction with the batteries gave those firefighters chemical burns, the industry needs to own that too.

Storage has been implicated in real human harm. The best thing that can come out of this is a reckoning with any blind spots that persisted in the years when storage never hurt anybody.