Experts question pre-fire change to key Moss Landing safety system

A modification made before the recent Moss Landing battery storage plant fire may have compromised the effectiveness of the plant’s fire safety system, experts say.

The plant burned for two days in January, ravaging a showpiece of the state’s green energy future. When it opened in 2021, Texas-based Vistra boasted in news releases that the world’s largest plant was a “keystone” to the state’s clean energy efforts.

The maker of the thousands of batteries housed at the plant said its system met “the industry’s strictest fire safety standards.”

The system employed water sprinklers to protect thousands of LG Energy Solution batteries against the rapid overheating phenomenon known as “thermal runaway.”

“Thermal runaway is basically a chain reaction that happens because the chemical reactions inside the batteries speed up with more heat,” says Bernard Cuzzillo, a mechanical engineer and veteran fire investigator. “The heat builds up to damaging temperatures and to ignition temperatures … out of control.”

Cuzzillo, who has studied the phenomenon, says the key to combatting thermal runaway is having cooling water at the ready when an alarm sounds. The original system kicked in the so-called very early smoke detection apparatus, or VESDA, sensed smoke. Batteries were deactivated and water was immediately pumped into pipes equipped with heat- activated sprinkler nozzles.

“Its design intent is to enable faster water delivery,” said Adam Barowy, a lead battery safety expert with Underwriters Laboratories’ Fire Safety Research Institute. “

It's actually considered to be higher performance in terms of suppression when you take that approach.’’

But after two prior incidents that Vistra’s own analysis blamed on false alarms and damaging leaks, the company adopted what it called “corrective actions” to its early warning system in 2022.

“They essentially disabled the system,” Cuzzillo said.

The company billed the modification at the time as preventing false alarms and leaks. Under the new configuration, company officials said, the cooling water would not flow immediately, as soon as a smoke alarm sounded.

Instead, they said, water would only start to flow after battery temperatures reached 135 degrees. Hot enough to set off heat-activated sprinklers.

Only loss of air pressure tied to sprinkler activation – not after the initial smoke alarm – would cooling water start to flow.

But experts said that could introduce delay in getting water to sprinklers. Any delay, they said, could be disastrous.

“If it's a fast-growing fire and you delay water getting on it -- the fire can get bigger before the water gets on,” Barowy said.

“You've lost the time advantage of the early reaction system,” said Cuzzillo.

While it is not clear whether, in fact, a delay in the sprinkler system’s function played a role in January’s fire, Barowy says the modification should have been pre-tested to verify prompt water delivery.

North Monterey County fire officials said, however, that their technical consultant on the battery project okayed the change, without a test, because Vistra characterized the modification as an upgrade. But Cuzzillo said that was the wrong call.

“It's reckless,” he said, “to disable it or degrade a safety system instead of addressing the underlying situation.”

The battery system maker, LG Energy Solution, referred questions to Vistra, which told us in a statement that it has enlisted experts to investigate the fire.

For now, it said, “any suggestion as to the fire’s cause or contributing factors would be pure speculation.”

Vistra officials told us separately that they did test the revised system for leaks and stressed the modified heat suppression system would still activate when batteries reached temperatures of 135 degrees, far lower than the triggering threshold for thermal runaway.

UL’s Barowy says he understands the dilemma Vistra faced – weighing the need to prevent leaks from false alarms versus the potential for introducing some delay in getting water to overheating batteries.

“I don't envy the decision that had to be made.”