/ Motoring

How safe are electric cars in a crash?

Crash test dummy

You may not have thought about this before, but is there a difference between a crash involving a conventional car and a crash with an electric car? There’s more to it than you might think.

After recently attending a Technical Working Group meeting at Euro NCAP, the discussion turned to the ins and outs of crash testing electric vehicles. If you didn’t know, Which? was a founding member of Euro NCAP, an independent crash test body established in 1997 – its aim is to make cars safer for all of us.

With more and more manufacturers wanting a slice of the electric pie, Euro NCAP has to consider how well electric cars will protect in a crash.

When I saw the agenda, my first thought was that an electric car’s weight distribution is likely to differ greatly from a conventional car, with concentrations around the engine and battery pack possibly also affecting ride and handling.

But there are far more significant hazards to consider, that most of us wouldn’t have thought of.

The potential dangers of an electric car

In a conventional car there’s a need to make sure that the un-fused electrical circuit (the main cable from the battery to the starter motor) doesn’t short out, as otherwise it could potentially create a fire hazard. And there’s a need to contain fuel for the same reason.

In an electrical car the short circuit problem could be much exaggerated. The Nissan Leaf, for example, runs at 400V instead of the 12V used by conventional cars. So if that shorts, it won’t just be sparks that fly – if you become part of the circuit, you’ll certainly know about it!

But that isn’t the end of it. Those lithium-iron batteries offer a good deal of power when they’re neatly tucked under the floor. But in a crash, if the batteries are damaged, any fluid spilled is highly flammable. And, according to the labs that run the Euro NCAP tests, a fire in these circumstances is pretty much unstoppable.

So it would seem an on-site fire tender and a well thought through evacuation plan might be the order of the day when we start testing electric cars.

Our faith is with the crash testers

I’ve no doubt the manufacturers have thought this through – after all, Nissan is controlled by car safety champions Renault. Plus, all the labs assured us at the meeting that all their staff have been appropriately trained, and that they’ve installed appropriate equipment for crash testing electric cars.

But it does make me wonder if the public (and the emergency services) are quite prepared for what happens if one is involved in a pile-up.

Comments
Member

Actually this raises the question of road safety of Hydrogen Cars – somehow the mix of hydrogen gas and Oxygen fills me with dread.

But have to wonder what happens at other times with 400 v batteries – I used to use these in electronic research (anti submarine devices) and the “belt” was horrendous – One incident causing the victim to retire permanently – the users were all experts in 400v supplies. And these were much lower power devices. I have to wonder how long it will be before a user dies of an electric shock.
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Member

I think many people’s views of electric cars are blurred by the CO2 figures and potential savings when owning them. How safe they are doesn’t seem to be at the forefront of people’s minds when they’re considering them right now. When Dave explained about this to me this week there were so many things I just hadn’t thought about – especially the weight distribution issue and protection benefits of conventionally powered cars.
I think manufacturers need to be more open with consumers about the safety aspects of their electric cars.

Member

400 volts dc is scary, its a much more dangerous voltage to have around than the 415 volts 3 phase supply feeding commercial machinary in factories. unlike ac current if you make contact with a high dc voltage it is likely to make all your muscles contract and you wont be able to let go so resulting in a much much higher chance of death, my personal opinion is that the maximum voltage available from the batterys should not exceed 60 volts since its a well known fact that high dc voltages are much more dangerous than ac voltages, I can from an accountants point of view understand why Nissan have gone for 400 vdc, it will save Nissan a lot of expense on the battery charger as well as being able to wire all the batterys and motors up in much thinner cable!
Its time europe legislated and set a low maximum voltage for car battery packs

Member

The 400 v dc from the battery supply is considerably less of a hazard than the 240v mains supply in the house because it is not referenced to earth. i.e. You only have to come into contact with the Live wire on your house supply to get a shock, with the battery supply you have to come into contact with both the supply leads . Also with fuses and cutouts near the battery itself the battery is likely ( by design) to get fully isolated in any “incident”.
Compared with a tankful of petrol and a fuel pump trying to empty it at high pressure I would say the risk is lower.

I think you will find that using 400v rather than say 60v isnt about saving the cost of a bit of copper but in the high costs of making high current control circuits and motors rather than lower current ones which also have lower power losses.

Member

Err

I was an electronic research scientist working on military detection systems – One device was activated by a sea water 415 v battery – Due to my carelessness (used uninsulated cutters) – I received the full charge – This threw me about 15 feet causing me to hit a bench – I was almost unconscious with shock with many bruises and chipped bones.

By contrast a 250 v ac shock (I’ve had several) only made me jerk my hand away without after affects. (I had to operate on live mains.)

Have also received a 440 v ac shock ( directly from local area supplier ) this was not much worse than the 250 v ac – though the overall effect was to put a section of East Acton (London) electrical supply out of commission.

It may seem I was accident prone – but really they were years apart 🙂

Member

@rarrar – comparing the 400v of a car to the 240v of a house is a very misleading comparison because houses aren’t usually involved in collisions, and certainly not in places where assistance may not be close at hand.
Also, in a house, especially if its electricity supply has been uprated to modern standards, with a circuit breaker system in place of a fuseboard, exposure to the current would be of the order of milliseconds before the trip trips and cuts off the supply.
But has anyone taken into account the sheer mass of the batteries, and their kinetic energy, in the event of a crash? An engine is heavy, but is usually at the front of a car. The batteries in an electric car seem to be much more likely to be distributed through, or under, the car. In the event of an accident involving a head on crash, whether into another car or, for instance, a tree, what are those batteries going to do with regard to the passenger cabin? Would the passengers be protected from the weight of batteries?

Member

One problem I see is fire – The enormous current produced if a battery of this power shorted out will melt cables – a lot of electrical cable in cars are pvc which can easily catch fire and release noxious gases – causing possible death by burns or suffocation.

Member
Gordon Foat says:
31 July 2011

Some interesting points. Our engineers have worked out that optimum safety can be achieved with low voltage systems to avoid any chance of harm to the drivers if a breach in the insulation occurred, especially if there was an accident in wet conditions. Green MotorSport already has lightweight vehicle bodywork and the additional weight and battery capacity to make up for losses is offset by the reduced cost of our low voltage control systems and motor drives. Safety is paramount. Although high voltage control systems are in carefully sealed and tested containers, when there are hundreds of thousands of electric vehicles on the road, there will be accidents. It will also be much easier for local garages to maintain low voltage systems and for the electric vehicles to be recycled. Young student engineers are safer with low voltage battery voltages. More at greenmotorsport.com

Member
Arnie L. says:
13 September 2011

There is a lot of energy in a fully charged battery pack. What happens if the battery pack itself is damaged or distorted in a crash? Where is the energy going to go? What is it going to do? What will the electrodes and electrolytes do if the case of the battery is damaged or if the electrodes are smashed together? Are damaged batteries toxic or otherwise hazardous? I have seen numerous essays on the external protections of electric vehicle batteries but so far none on the internal hazards. The external protections are fine, [but some idiot(s) will still manage to do something stupid.] Are there any protections against internal battery hazards? BTW, I have seen people injured on 55 volts AC.

Retired EE who worked on high energy electronics.