The following is an excerpt from Musk's post:
Earlier this week, a Model S travelling [sic] 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.
You can read the full statement here.
Musk claims that the fire department's standard procedure of puncturing holes in the battery's firewall to gain access to the source of the blaze allowed the flames to travel into the vehicle's front trunk, suggesting that simply dousing the fire with water would have been preferable. The fire was eventually extinguished through a combination of water and dry chemical extinguisher.
According to Musk, the fire never entered the passenger compartment. He speculates that a gas-powered car would have performed much worse under the same circumstances.
"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," said Musk. "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."
To back up his claims, Musk points to the data, as he's done in the past when defending the performance of his Model S. "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," said Musk. "That equates to 1 vehicle fire for every 20 million miles driven, compared to 1 fire in over 100 million miles for Tesla."
While Musk has demonstrated a preference for supporting his arguments with numbers, he also recently gained notoriety for distorting NHTSA's Model S safety rating. In this instance he draws the conclusion that "you are 5 times more likely to experience a fire in a conventional gasoline car than a Tesla," but we wonder if this statement glosses over a host of important considerations, such as sample size and the driving habits of Model S owners--not that 100 million miles is an insignificant data set.
That said, Musk's point is well-taken. For all the concern over electric vehicle fires, most drivers seem oddly comfortable with the safety of a combustion engine running on flammable gasoline traveling at highway speeds. Even so, that does not mean we should be dismissive of this or any incident that relates to vehicle safety, electric or otherwise.