Are lithium-ion batteries a big fire risk? Depends what you compare them to

The fire started on May 15th in a lithium-ion battery storage facility in Otay Mesa. The large number of batteries in the huge warehouse raised the possibility of a devastating, facility-wide explosion.

“They sent robots into space to try to measure the atmosphere. Is there hydrogen present? How much hydrogen is there? Is there an explosive atmosphere?” said Robert Rezende, a battalion chief for the San Diego Fire-Rescue Department. “And they confirmed yes, there was hydrogen present. Yes, there was the potential for an explosive atmosphere.”

But that warehouse fire ended with a whimper, not a bang. Rezende, an expert on lithium battery fires, said the control of that fire came down to many things. They included good firefighting and the size of the warehouse.

“Now we did have battery explosions inside. I was at the incident. We heard the batteries exploding. But again, it's a massive space,” Rezende said. “So the sheer fact that it was a really large space meant that it was less likely to have a catastrophic event.”

Many fires have shown the volatility of lithium-ion batteries, and their use is increasing exponentially.

It began a debate over how dangerous they really are, especially when compared to other sources of energy.

Lithium batteries: The dangers we know

Lithium-ion batteries release very flammable gases — notably hydrogen — when they burn. But even in a normal state they can become combustible.

In his lab at UC San Diego, chemistry professor Kent Griffith uses a special chamber to make lithium metal batteries. He uses equipment to help control the atmosphere in it, reaching in through glove holes to reduce the risk of fire.

“It's what we call a glove box,” Griffith said. “It's basically a low-oxygen chamber. It has extremely low oxygen content and extremely low moisture content.”

He said most rechargeable consumer batteries don't use highly combustible lithium metal. However, even lithium-ion batteries, which use graphite to hold and release ionized particles, are at risk of fire.

“Anything you do to create that short circuit that causes all that heat to be released, means you're heating up a lot in a very small volume. So that has the possibility to turn into a fire if there's a source of fuel around,” he said.

One source of fuel that is immediately available in a lithium-ion battery is the flammable electrolyte that physically separates the batteries' positive and negative electrodes.

Chief Rezende said the buildup of heat in these batteries that leads to fire is called a thermal runaway. It can also lead to powerful explosions.

Videos show what these explosions look like when, for example, a battery on an electrical bike gets exposed to heat in an apartment fire.

“More often than not, we arrive at the incident to find the windows were blown out. The doors are off the hinges. And of course for us in the fire service that makes it a more complicated incident, because now we have a ventilated fire, a fire that has all the air it wants and needs to go very fast and very hot and very quick,” Rezende said .

Pondering the future, he said the billions of lithium-ion battery cells being created can only mean more flawed batteries, more short circuits and many more fires, which cannot be smothered with a blanket or extinguished with water.

But how common are these battery fires, really, when compared to other technology?

“What's actually amazing is, in some sense, how safe lithium-ion batteries actually are. Right?” Griffith said. “We produce billions of these every year and every car has, you know, something on the order of several thousand batteries in it. And yet still, we have very very few fires in the context of all of that.”

He said we should compare the risk of fire in a battery-powered car to one that runs on an internal combustion engine. One estimate showed old-fashioned combustion engines were more than 10 times more likely to catch fire than EVs with lithium-ion batteries.

Chief Rezende agrees. Car fires are much more common per vehicle when they use an internal combustion engine. But remember, he said, lithium-ion battery fires are very tough to put out.

“From a fire department's perspective, an electric vehicle fire is much more difficult to manage. It's going to take a lot longer. An internal combustion engine fire we can handle in five to ten minutes, max. An electric vehicle fires, you're lucky if you get out of there in two hours,” he said.

A threat to homes and hospitals?

There are other issues. Some hydrogen gases emitted by lithium battery fires are considered toxic. This has been used as an argument against locating a battery storage facility in Eden Valley, near homes and hospitals.

The proposed Seguro Battery Storage Project would be located less than a mile from North County's Palomar Hospital. Project opponent Joe Rowley, a former vice president of project development at Sempra US Gas and Power, told KPBS it is also surrounded by nearby homes.

“It should not be near residences. “It should not be near a hospital or schools,” Rowley said. “When batteries burn they emit hydrogen fluoride, hydrogen chloride, hydrogen cyanide.”

Chief Rezende said a lithium-ion battery fire releases toxic gases, adding that any large structure fire will produce hydrogen cyanide, as plastics and synthetic fabrics catch on fire.

He said many gases that are released by burning batteries are present at the site but quickly dissipate as they move through the air and they tend to have a small footprint. This is true of some of the so-called “acid gases” that are released from burning lithium ion batteries.

“They don't have a long persistence in the atmosphere,” he said. “They break down pretty readily within a short distance.”

One fact remains. Griffith said no other technology we know stores energy as well as a lithium ion battery. So as our power supply moves from fossil fuels to electric battery power, don't expect those batteries, or their fire risk, to go away.