Hybrid and all-electric vehicles are increasingly commonplace in Santa Clara County, with a Tesla car, a Nissan Leaf or a Toyota Prius around every corner. And with the pervasiveness, emergency responders now have to size up a new possibility: what if one of them catches fire?

Last Friday, Mountain View fire crews had to tackle the problem directly, when an electric car battery overheated to temperatures of about 500 degrees and emitted a dangerous plume of smoke. The car, parked in the first block of E. Evelyn Avenue, had been converted for an internal combustion engine to all-electric, said Mountain View Fire Department spokesman Lynn Brown. The overheating likely resulted from thermal runaway, which can happen in a lithium ion battery for a range of reasons, including defects or improper use.

Brown said this is the first time he could remember local firefighters responding to an emergency related to an electric vehicle battery. Firefighters blasted the battery with carbon dioxide extinguishers, which Brown said served a dual purpose of both cooling down the battery as well as reducing oxygen that might fuel a fire in the battery. After emptying "several" extinguishers, fire crews were able to get the battery down to a still-piping hot 250 degrees.

After the battery stopped giving off smoke, Brown said the car was cordoned off in a safe location and the owner stayed overnight with the vehicle in case the battery began overheating again. Mountain View police officers frequently returned to the site that night to ensure that the vehicle was in a stable condition.

During the incident, fire crews were told not to use water to cool down the battery, based on information from the department's materials safety data sheet, and were told to exercise caution to avoid getting shocked, Brown said.

"The lesson here is really to be careful with batteries," Brown said. "They are a little different than your standard internal combustion engine."

There's been steady interest over the last seven years by first- and second-responders for training to deal with electric vehicles in case of a fire, according to Andrew Klock, senior project manager at the National Fire Protection Association (NFPA). The association offers training programs, mostly online, on how to deal with various car batteries if they catch fire or overheat, and has since trained over 200,000 emergency personnel throughout the country.

Although the carbon dioxide extinguishers worked on the car battery in Mountain View, Klock said the association advises using water to put out vehicle fires, regardless of whether it's an internal combustion, hybrid or all-electric car.

"Water is the standard agent for vehicle fires, we don't recommend anything else," he said.

In one training exercise, the NFPA set seven high-voltage batteries on fire, including lithium ion and nickle-metal-hydride batteries, in mock cars and had fire fighters put them out with water. In all instances, it was totally acceptable and safe. The only caveat to that, Klock said, is that it can take thousands of gallons of water over a long period of time to bring the battery down to a safe temperature, meaning fire crews will need a sustained water supply from either a hydrant or two trucks full of water.

"If you can't establish a sustained water supply, there's a high likelihood the battery will reignite," Klock said. "You won't be doing any good if you don't have enough water to cool down the battery and extinguish it."

The threat of re-ignition goes well beyond when fire crews leave the scene. Similar to trick birthday candles, a lithium ion battery can catch fire hours, days or even weeks after it has been brought down to a normal temperature.

Alternative fuel vehicles have become ubiquitous over the last decade, with an estimated 3.2 million hybrid and electric vehicles on U.S. roads in 2014, according to the NFPA website. Data on vehicle fires shows that these high-tech vehicles are no more dangerous to emergency responders or the public than a normal internal combustion engine, but training and experience handling electric vehicle fires has lagged behind the surge in popularity.

"There's a car fire in the United States every two minutes, but if a Tesla or a Nissan Leaf catches fire, you're going to see it on tonight's news," Klock said. "This is new technology, not more dangerous technology. We just need to train or first- and second-responders how to deal with these new vehicles."