Elon Musk talks sense on Tesla Model S Fire

Fri, 22 Nov 2013

We’ve never pretended we’re fans of the electric car as a replacement for mainstream ICE cars; the technology is just too expensive to be viable. But we do see a good case for electric city cars, electric delivery vehicles that work in a confined area and electric taxis in cities.

But you can add to that list luxury cars fitted with an electric powertrain where the cost of the technology can be absorbed more easily by a much higher list price. Step forward the very impressive Tesla Model S.

Despite our cynicism, Tesla seems to have delivered an astonishingly capable EV in the Model S, with high degrees of luxury, comfort and performance, and even a range you can live with.

So when reports started to come in about fires in the Tesla Model S, we looked at the reports and decided the fires were just a case of ‘Shit happens’ and had nothing to do with the Model S’s electric powertrain per se.

But it seems many are looking for a stick to beat Tesla with, and much of the media has sensationalised the Model S fires and implied the Model S is a fire hazard. Which seems an odd interpretation of the facts.

Now Elon Musk has weighed in to the discussion – as you would expect – with a perfectly reasoned argument that should put to bed the idea of the Model S as a fire hazard.

We received an email from Elon Musk recently and, although we wouldn’t normally publish it in full, we decided it was worth the read to put the argument to bed, especially as the sensationalising of the Model S fires seems to be on-going

Elon Musk said:

Earlier this week, a Model S traveling at highway speed struck a large metal object, causing significant damage to the vehicle. A curved section that fell off a semi-trailer was recovered from the roadway near where the accident occurred and, according to the road crew that was on the scene, appears to be the culprit. The geometry of the object caused a powerful lever action as it went under the car, punching upward and impaling the Model S with a peak force on the order of 25 tons. Only a force of this magnitude would be strong enough to punch a 3 inch diameter hole through the quarter inch armor plate protecting the base of the vehicle.

The Model S owner was nonetheless able to exit the highway as instructed by the onboard alert system, bring the car to a stop and depart the vehicle without injury. A fire caused by the impact began in the front battery module – the battery pack has a total of 16 modules – but was contained to the front section of the car by internal firewalls within the pack. Vents built into the battery pack directed the flames down towards the road and away from the vehicle.

When the fire department arrived, they observed standard procedure, which was to gain access to the source of the fire by puncturing holes in the top of the battery’s protective metal plate and applying water. For the Model S lithium-ion battery, it was correct to apply water (vs. dry chemical extinguisher), but not to puncture the metal firewall, as the newly created holes allowed the flames to then vent upwards into the front trunk section of the Model S. Nonetheless, a combination of water followed by dry chemical extinguisher quickly brought the fire to an end.

It is important to note that the fire in the battery was contained to a small section near the front by the internal firewalls built into the pack structure. At no point did fire enter the passenger compartment.

Had a conventional gasoline car encountered the same object on the highway, the result could have been far worse. A typical gasoline car only has a thin metal sheet protecting the underbody, leaving it vulnerable to destruction of the fuel supply lines or fuel tank, which causes a pool of gasoline to form and often burn the entire car to the ground. In contrast, the combustion energy of our battery pack is only about 10% of the energy contained in a gasoline tank and is divided into 16 modules with firewalls in between. As a consequence, the effective combustion potential is only about 1% that of the fuel in a comparable gasoline sedan.

The nationwide driving statistics make this very clear: there are 150,000 car fires per year according to the National Fire Protection Association, and Americans drive about 3 trillion miles per year according to the Department of Transportation. That equates to 1 vehicle fire for every 20 million miles driven, compared to 1 fire in over 100 million miles for Tesla. This means you are 5 times more likely to experience a fire in a conventional gasoline car than a Tesla!

For consumers concerned about fire risk, there should be absolutely zero doubt that it is safer to power a car with a battery than a large tank of highly flammable liquid.

There have now been three fires involving the Tesla Model S, but they all appear to be just a case of bad luck and not any fault in the Model S or its electric drivetrain components.

So unless we suddenly find Models S EVs all over the world, we really should put these incidents in to context and not seek to find a fault that isn’t there.

By Cars UK