Hey dude, your battery is burning

Timing is everything, so last week when a Tesla Model S was filmed in flames on a motorway off-ramp in Washington State, the timing couldn’t have been worse.

The footage was aired on several national news programs after first appearing on YouTube, which is ironic since Tesla has leveraged the benefits of social media as an incredibly effective tool in building its brand image and product reputation, yet social media was now broadcasting a worst-case scenario globally.

On Friday, several days after the fire, Tesla CEO Elon Musk issued an explanation via a blog post.

The incident follows months of on-going battles between Tesla Motors and several dealer associations in several states. But the real public-opinion pain came with questions about the safety of Tesla’s lithium-ion batteries. These same safety questions forced Boeing in January to ground its fleet of 787 Dreamliners.

GM’s Volt plug-in hybrid also suffered embarrassment when its lithium-ion battery combusted more than three weeks after the National Highway Traffic Safety Administration crashed the car in a controlled side impact test. Fisker and Mitsubishi have also suffered bad publicity from lithium-ion battery fires.

Lithium is lightweight and highly reactive which makes it a desirable ingredient in potent batteries. However, lithium’s reactivity also causes problems in that as an alkali metal it is highly combustible. Damage the battery pack, as happened to the Tesla Model S, and the lithium can create a situation referred to as ‘thermal runaway’ with extremely high temperatures that can result in fire.

According to Tesla after an inspection of the Model S battery pack, a metal object with a force of more than 23 tonnes punctured the battery pack’s 6.35mm thick protective case, causing the fire.

In his blog statement, Musk claims the vehicle’s onboard alert system instructed the driver to exit the highway.

“At no point did fire enter the passenger compartment,” said Musk, who claims the design of the battery pack with internal firewalls contained the fire in a small area at the front of the battery pack before the fire brigade extinguished it using water and dry chemical.

Tesla licenses its lithium-ion battery technology to Mercedes-Benz and Toyota, so Musk is strongly defensive of Tesla’s technology, its pack design and safety.

The battery pack comprises several thousand cylindrical cells (pictured) wired together. Tesla also developed a liquid cooling system that keeps the cells cool and greatly reduces the threat of thermal runaway if a cell is damaged.

Plus, the smaller cylindrical cells resist damage during a crash better than larger flat cells used by other EV and hybrid car-makers and Boeing, according to experts.

Still fire happened, and the fire brigade struggled to extinguish a lithium-ion battery pack suffering from massive thermal runaway. So how do you quell a fire like this one?

“For the Model S lithium-ion battery, it was correct to apply water (versus a dry chemical extinguisher), but not to puncture the metal firewall,” explained Musk, “as the newly created holes allowed the flames to then vent upwards into the front trunk section of the Model S.”

Sure, this may have been a freak incident, but freak happens. The Model S inferno is an untimely lesson for Musk and company, but it is also a priceless lesson for fire brigades around the world that already face the hazard of solid-fuel explosives used to inflate airbags.

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