Imagine it. You’re reversing your jetski into the water at the boat ramp, getting excited for a day of on-water escapades. Like so many before you, you mess up, your car loses traction, and slides into the drink. Only, in this tale, it doesn’t just get wet. It catches fire and burns to a cinder all while fully submerged. Let’s dig into what we think happened, and explore why the abundant seawater failed to put the fire out.
[Ed Note: Before we get into this, we should admit that the full context of this fire is still unknown (for example, we don’t know if the vehicle had been damaged in some way prior to submersion). We’ve seen a few videos floating around, some posts by organizations that appear to have expertise on these things, and that’s more or less it. Also, it’s worth mentioning that we are not trying to scare people into thinking EVs are dangerous; gasoline catches fire pretty damn quickly, as well. Still, it’s a car on fire underwater — it’s worth sharing these fascinating clips and talking about them a bit. -DT]
We’re talking about the owner of a Tesla Model X at the Polk Street Boat Ramp in Hollywood, Florida. According to Hollywood Professional Firefighters, who attended the scene, the electric vehicle slid into the salty inter-coastal waters, with the conductive water apparently causing a short circuit. The battery proceeded to catch fire, with gases bubbling up through the water and flames visible at the surface, as the pack entered thermal runaway. Thankfully, the occupants of the vehicle were able to flee the vehicle before it sank beneath the waves and caught fire.
Despite being fully submerged, the car continued to burn for an extended period of time. The fire crews attending elected to allow the car to burn itself out while still underwater, rather than attempting recovery. Once the fire ceased, the car was pulled from the water and loaded onto a carrier. A fire engine was assigned to follow the car to the impound lot out of an abundance of caution, as EV batteries have been known to spontaneously reignite after being extinguished.
Here, we’ll just re-quote the post above from Hollywood Professional Firefighters, which describes itself as “a non-profit organization that represents the City of Hollywood’s Firefighters” and whose main objectives are “monitoring and improving Firefighting and Public Safety, and maintaining a cooperative labor management relationship with Hollywood’s Fire and City Administrators, Elected Officials and the City’s residents.”:
WATER RESISTANT FIRE??
On Sunday Oct 1st, a Tesla Model S was attempting to back a jet ski into the water at the Polk Street boat ramp, when it lost traction and slid into the inter-coastal. The salt water reacted with the the vehicle’s electronics causing them to short, sparking a fire that burned underwater for an extended period of time.
The fire was allowed to burn underwater until it extinguished itself. And even then, it had to be loaded carefully onto a special carrier, and followed by the Fire Engine to the impound lot, where they’ll keep the vehicle isolated for a few days in the very real possibility of re-ignition. EVs have been known to reignite even after the initial fire has been extinguished.
This is an issue with all Electric Vehicles, not just Tesla. And their prevalence is adding a whole new level of hazard to the Fire Service, causing Fire Departments worldwide to rethink how they mitigate electric vehicle emergencies.
NOTE: There’s a second bystander-submitted video in the comments section of the original post.
Nobody was harmed in the incident.
A video in the comments of that post has been reposted to popular YouTuber Rich Rebuild’s channel:
It’s worth noting that Tesla CEO Elon Musk is famously on record as saying that a Tesla “works as a boat for short periods of time,” by virtue of having no air intake or exhaust for the propulsion system, and sealed batteries, motors, and electronics. “Submarines are just underwater EVs,” he writes in that tweet:
A Tesla works as a boat for short periods of time, as an electric car has no air intake or exhaust to block & battery/motor/electronics are water-sealed. Submarines are just underwater EVs. https://t.co/1U63ZoVj3q https://t.co/KKfcUQGYnL
— Elon Musk (@elonmusk) January 25, 2020
Seeing is believing, however, and this Model X very obviously caught fire. According to a recounting from those on the scene in this YouTube video (the one above that Rich Rebuild reposted), the car apparently showed a warning to the female occupant to exit the car immediately, and she was rescued by her husband before the car sank fully beneath the water, battery aflame.
The fact that it did would be of no surprise to any experienced fire crew, as it has become well-known that EV batteries can fail in this manner when inundated with flood water or salt water. NHTSA, in its write-up “Responding to Electric Vehicle Fires Caused by Salt Water Flooding,” advises first responders that “residual salt within the battery or battery components can form conductive ‘bridges’ that can lead to short circuit and self-heating of the battery, resulting in fires.”
In some cases, EVs caught in floodwaters from hurricanes or storm surges have caught fire days later, with the vehicles often burning to the ground. It also bears noting that other Teslas have been spotted suffering similar failures in the wild. It’s possible that some other damage was involved, but it’s not a certainty by any means.
A short-circuited battery gets hot very quickly. This is because instead of the electrical power being turned into mechanical power via the car’s motors, instead, it’s being dumped directly back into the battery and turned into heat. Once hot, lithium-ion batteries often tend to go into a state called thermal runaway. It’s so-called because when in an overheated condition, further reactions occur that generate yet more heat, causing the cell’s temperature to runaway with fire the typical end result.
Exact reactions involved in thermal runaway are dependent on a given battery’s exact chemistry, but as a guide, most tend to go down a similar path. Per the book “Lithium Ion Batteries: Advances and Applications,” once temperatures inside a cell push past 175 F or so, the anode material begins to break down in a reaction that is exothermic—which means it releases yet more heat. As temperatures push up to 210 F, the electrolyte itself begins to break down, usually releasing gases like hydrogen, carbon dioxide, carbon monoxide, and methane as it does so. This is often visible as lithium batteries fail, with jets of gas bursting out from within the pack. Around 250 F, the separator materials tend to melt, causing a direct internal short circuit between the anode and cathode, releasing energy even faster. Cathode failure then typically occurs around 260 – 300 F in a chemical reaction that releases oxygen as one of its byproducts.
At this point, the batteries are incredibly hot, spewing out flammable gases and oxygen, while surrounding surviving cells are full of flammable electrolyte. Fire is the usual result. As a bonus, the heat from one failed cell in thermal runaway is usually enough to push neighboring cells to the same point in an ongoing chain reaction. Modern EV batteries are designed to limit this spread as much as possible, but engineering can only do so much.
In the case of this Model X, the thermal runaway reaction apparently continued while the car was submerged because the water couldn’t wick away enough heat versus the amount being generated by the short-circuiting cells. The degrading cell products continued to generate more and more heat, releasing flammable byproducts that then combusted with air at the surface. While some oxygen was likely released from the batteries themselves, we can see most of the combustion occurred at the surface where it is most abundant.
It is possible to stop a thermal runaway reaction, but it’s incredibly difficult in practice. The entire battery pack needs to be cooled enough to below the point where the cells are degrading and releasing further energy. This has to go on until the battery is finished dumping energy through any short circuits that might have occurred internally or externally. In reality, it’s difficult to flow water into the overheating parts of a battery to actually achieve this, and thus many EV fires burn on for extended periods of time, or reignite after being put out.
Ultimately, if an EV battery was perfectly sealed and resistant to corrosion, fires like this wouldn’t happen in salt water. Unfortunately, seals are rarely perfect. An EV battery may have great seals that keep out rain and snow on the road and even splashes from deep puddles. Those same seals won’t necessarily work so well when the battery is fully immersed in water, particularly for minutes or longer at a time. Often, breathers are required on battery packs which further complicate the issue of sealing against full immersion.
Fundamentally, you’d want to do your research before trusting your own EV to survive a full dip in salt water. A great example is Rivian, which has notably demonstrated its vehicles fording up to 3 feet of water. We’d trust an R1T for launching a jetski more than we’d trust a Tesla right now, whatever Elon Musk might have said online. In any case, be careful out there!