Musk described the cause of the incident, writing, "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 Tesla CEO says the car alerted Carlson, as it should, and the fire was contained within the battery pack. He then issued a strong defense for the safety of electric cars and downplayed the potential threat of EV battery packs catching fire.
"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," he wrote.
Tesla shares rebound
The Model S fire and the online video fueled a selloff of Tesla shares Wednesday afternoon and all day Thursday. During those two days, the stock fell 11% and posted its biggest two-day decline since July. That happened despite some analysts coming to Tesla's defense and saying the Model S fire was likely an isolated one-time event. On Friday, shares of TSLA rebounded 4.4 percent, clawing back some of the losses, but still ended the week down 5.2 percent at $180.98.
—By CNBC's Phil LeBeau. Follow him on Twitter @LeBeauCarNews.
Questions? Comments? BehindTheWheel@cnbc.com.