If I hit the bottom of the car off a speed bump or a rock, is that likely to damage the battery pack?
There is some potential for this, although it is something that car makers design for and battery packs are protected with high-strength aluminium and steel panels to prevent precisely this kind of damage.
However, concerns remain and insurance company Axa recently attracted some attention over how it raised those concerns.
What kind of attention?
Well, under controlled conditions in a test conducted in Switzerland, Axa rolled and flipped a brightly-painted Tesla Model S. The idea was to simulate a relatively common accident – ploughing straight on at speed over the hump of a large roundabout, flipping the car on to its roof. The idea was that Axa would show that, in just that sort of accident, an electric car’s battery pack could be pierced, leading to damage, to ‘thermal runaway’ – where the battery can no longer regulate its internal temperature – and a fire.
Axa showed a video of the test online, but came under immediate fire (no pun intended) from social media critics who pointed out that the test was faked, and the fire was artificially started.
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Axa’s response? Well of course it was faked. A company official told The Irish Times that: “It was demonstrated at the event that damage to the underside could potentially also damage the battery and cause a fire. This is a rare but very realistic scenario. However, due to the guests present, a demonstration of a battery fire would have been too dangerous. The battery cells of the electric car were therefore removed before the test. As in the Axa Crash Tests in previous decades, the vehicles were propelled by a pulley system using a tow vehicle.”
The test was part of a regular series of crash experiments carried out by Axa to help it better understand how and why cars crash, and therefore how much it can then charge us all for our insurance premiums.
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“The risk of fires is fortunately low for cars, irrespective of whether they are powered by petrol or electricity. Statistics show that only 5 out of 10,000 cars fall victim to fire. Vehicle fires in electric vehicles can, however, be extremely tricky for the emergency services due to “thermal runaways”, ie the battery cells burning.
“The accident researchers wanted to draw attention to this, so a fire was simulated on site. This was all communicated transparently at the event and discussed with experts during a podium discussion” said the official.
“Tesla was chosen for this accident simulation because the make is popular and representative of high-performance electric cars. Later at the event, it was also emphasised that current Tesla models are equipped with additional reinforcement of the underside, which our accident researchers welcomed from a safety perspective.”
However, according to Michael Pfäffli, Axa’s head of accident research, not all EVs are equal in this regard and the underside of the battery pack is a potential Achilles’ heel for many. “Investigations by Axa accident researchers have shown that underbody damage can occur when crossing street islands, stones or even spinning tops. Although the drive battery is very well protected by additional stiffeners of the body front, rear and side, it has a weak point” said Pfäffli. “The underbody seems to be the Achilles heel of electric cars because the battery is not additionally protected there. Motorists should be aware of this.”
Axa is calling for new legislation, or an extra element to the independent Euro NCAP crash tests, to highlight this potential battery vulnerability, and has even recommended that car makers should fit additional underbody armour: “for example by providing the underbody with a titanium plate or similar materials with high resistance.”
“If damage to the battery occurs, immense fires can quickly occur. If there is only a risk that the battery could ignite, the vehicle will be stored in the extinguishing container for days. The fact that we all still have a way to go can be seen, for example, in the fact that there are not yet many firefighting containers and these cars sometimes have to be stored in closed parking lots,” said Nils Reichweiter, Axa’s head of property insurance.
How big a risk is this?
For all this, Axa then went on to say that the risk of fire in a car is actually very low, whether it’s petrol or electric. Only five out of 10,000 cars are statistically victims of a fire. Mind you, the company has also warned about the rising popularity of e-scooters and e-bikes, saying that the lithium-ion batteries in those also present a serious fire risk, and that you should never leave batteries charging in a building that is unattended or overnight when you are sleeping in the property.
Axa says that one recent large claim was the result of a faulty e-scooter battery which was being charged in the kitchen of a ground floor terrace flat. An explosion occurred and fire spread through the home, reaching two storeys above. The second occurred in a block of flats where an e-bike battery was being charged. The fire destroyed the flat and caused smoke damage to the flats on either side. Thankfully, nobody was injured in either incident.
There’s also a difference in the type of battery used. Conventional lithium-ion batteries are indeed vulnerable to damage if the battery casing is pierced, and that can lead to disastrous ‘thermal runaway’ battery fires. However, lithium-iron phosphate batteries – used by the likes of BYD, Volvo, Smart and increasingly others – don’t seem to suffer that kind of problem, or at least not as much as a lithium-ion battery. At a demonstration at BYD’s factory in Shenzhen, The Irish Times was shown, under lab conditions, a lithium-ion battery cell being pieced by a steel spike. The battery promptly exploded (that’s the only word for it) jetting a sheet of flame across the closed-off test cell.
Immediately after, we watched one of BYD’s lithium-iron phosphate batteries undergoing the same spike piercing test, and it might has well have been a plank of wood for all the reaction it caused. No smoke, no flames, no nothing. Of course, this was a BYD test, and not conducted ‘under oath’ so to speak, so we cannot absolutely confirm that the battery contained any active chemicals at all, but it’s food for thought.
Even with a lithium-iron phosphate battery of course, there is the potential for underbody damage from poorly maintained roads, road furniture, or other foreign objects, and such physical damage could be expensive to repair, although that’s equally a problem for petrol and diesel cars.
