First published in Fire & Safety Journal Americas
When an electric vehicle hit road debris on a dark country highway and caught fire, we expected it to be just another entry on our database.
What our highly qualified team actually got was incredibly detailed experience that provides vital information for emergency responders and fire investigators working in a world of EVs.
This is the story of ‘Testla’ and how one EV battery fire enabled EV FireSafe to develop a complete timeline of events for fire and investigation knowledge.
The Testla EV Battery Fire Investigation is the first of several timelines the EV FireSafe team are developing to enhance safety for everyone around electric vehicles.
A ‘slightly’ singed gift
In September 2023 the EV FireSafe team was gifted a Tesla Model 3 electric vehicle, one of only 6 EVs ever to go into thermal runaway – the technical term for lithium-ion battery fire – here in Australia.
Our generous benefactor was the Aussie arm of Tesla Motors, who we’ve built a collaborative working relationship with. While there’s some (plenty!) of anti-EV sentiment out there, our experience is that Tesla has constantly set a very high bar for emergency response research and knowledge that no other EV manufacturer has yet been able to match.
We dubbed the vehicle ‘Testla’, as in our ‘test’ vehicle; but immediately regretted it when well-meaning emails starting coming through saying ‘did you know you’ve spelt ‘Tesla’ wrong?’
Four of our team – which included a qualified risk assessor, trained EV technician and an experienced fire investigator, who are all also operational firefighters – worked on the Testla teardown and fire investigation.
I want to be clear that this article, and the complete timeline we’ve developed into an online course, are not a ‘how-to’ guide; this is highly dangerous work posing new hazards and risks to everyone working in investigation and forensics.
What happened to Testla?
While travelling at 111.98 kph on the Hume Highway near Goulburn, New South Wales, Testla hit an 18 kg chunk of steel lying in the road. The ‘chunk’ was a heavy vehicle tailshaft that was being carried as scrap metal by a truck that had lost its load.
The size and weight, combined with the speed of Testla, resulted in impact at 0.5 G on the leading front edge of the high voltage battery pack. The tailshaft was then dragged down almost the entire length of pack module 2, tearing it open and exposing several hundred of the 4416 cylindrical NMC 2170 lithium-ion battery cells.
Airbags did not deploy. Upon coming to a stop on the highway shoulder, the front passenger exited the vehicle within 4 seconds using the electric door handle button; the driver was out within 10 seconds.
Impressed by the level of data yet?
There’s more, much more. Tesla-supplied data also indicates the passenger opened the rear door and closed it, then the boot, presumably to remove personal belongings. The boot was closed, again using the electric close button, approximately 3 minutes later.
In a short phone interview, the driver told me there were ‘popping’ noises and smoke slowly building as they were exiting the vehicle and, once they were safely away, flames from beneath the vehicle where the battery pack sits.
He estimated it was 12 minutes from impact to when the vehicle was clearly on fire.
Learning No 1: Teslas are more like computers on wheels than traditional cars
This data isn’t just available to EV FireSafe because we took the Tesla guys out for beer and dumplings.
Any agency can request incident data from Tesla Motors online at tesla.com/legal bearing in mind that in some scenarios it may not be available, such as areas with limited internet access.
Some other EV manufacturers can also provide data, so it’s always worth asking.
Teardown, seven hours and six people
With head to toe protection and a detailed risk assessment, we tore down Testla’s battery pack in November, almost two months to the day after the fire.
Tesla again supported us, by offering to bring the vehicle to their Melbourne workshop so we could work on it together.
This was greatly appreciated, because even though we had the technical knowledge, a full-scale professional workshop with hoists, disposal skips and a top line industrial floor cleaner, it still took six of us a whopping seven hours to tear down Testla.
Of course, it was dirty and smelly, and even with personal protective clothing, ventilation and regular cleaning, quite a challenge.
A large number of battery cells had been scooped up from the roadside and dumped into the back seat of Testla, so our first job was to sift through those to check for any live cells that pose a secondary ignition risk to our teardown team.
In total, we estimate over 4300 of the 4416 cells were present, either inside the cabin or the pack itself.
And every single one had to be checked and sorted into ‘burnt’ and ‘live’, and then disposed of responsibly.
In addition to the ‘normal’ products of combustion, we were dealing with an unknown amount of vapourised electrolyte and remnant heavy metals from the battery cell cathode, both new hazards for fire investigators.
Learning No 2. A burnt, impacted or submerged battery pack poses a delayed or secondary ignition risk
Our research indicates delayed ignition – where a pack is damaged but does not go into thermal runaway at the time of the incident - is extremely rare.
In fact, we only have two incidents to point to, both of which occurred in salvage yards where we suspect, but can’t prove, misplaced forklift tines may be the cause (regardless, this is important knowledge for salvage companies!)
Secondary ignition – where a pack has been in thermal runaway but not all cells have burnt out, leading to the remaining damaged and heat impacted ones catching fire at a later time - in electric vehicles is rare, showing up in around 5-10% of incidents on our database.
While it’s rare in electric vehicles, there has been at least one serious injury during fire investigation of smaller lithium-ion battery packs, particularly ebikes and escooters.
A US-based investigator was hospitalised when a seemingly burnt out cell went into thermal runaway 24 hours after the initial fire, causing it to become projectile and hit him in the face. He was thankfully OK.
While we didn’t experience a secondary ignition, the hazard was very much front of mind.
The ’smoking gun’ and a clear cause
As our team fire investigator put it, we had the ‘smoking gun’; the truck tailshaft that had been placed in the back of Testla at the scene.
With that we were able to identify point of impact and the path of travel of the tailshaft along module 2 of the pack, which was torn open, causing massive impact damage to multiple battery cells.
Testla was also at a high state of charge, meaning there was more energy to be released, which manifests as more violent fire behaviour and a longer duration incident.
There were a lot of interesting ‘aha’ moments through the process, such as identifying a ‘cap’ of molten aluminium on the top of the tailshaft where the battery pack base had heated and dropped away.
However, with regards to other incidents on our global database, a high number have an ‘Unknown’ cause; currently sitting at 51%.
Learning No 3. There’s a world of information yet to learn about investigating EV battery fires
Of the incidents making up that 51%, most were not investigated, perhaps because there were no injuries, fatalities or property losses.
But it’s very clear we’re just starting the journey of EV fire investigation, particularly in real-world incidents where cause is unknown, as opposed to a test burn that can’t mimic the exact point of failure and pattern of propagation through the pack.
Comprehensive timelines such as Testla’s provide vital information along the whole emergency and secondary response chain; for incident managers it provides data on expected burn time, response and resources required; for investigators, an awareness of cell failure causes and safety risks.
However, all responders will need an increased and constantly informed knowledge of lithium-ion battery types, chemistries, use cases and thermal runaway as the world continues to electrify.
About EV FireSafe:
EV FireSafe is a company funded by the Australian Department of Defence to research EV battery fires and emergency response, however as our work on Testla sits outside that funding and contains significant intellectual property, there is a fee to access the timeline, which we’ve tried to keep as cost-effective as possible. All purchases support our work in delivering free emergency responder data and knowledge via our research website evfiresafe.com
The full investigation timeline is at ‘Testla’ EV Battery Fire Investigation