The NTSB announced over social media Tuesday morning, March 27, that the agency is investigating the fatal crash and the emergency response from the Mountain View Fire Department.
The crash occurred around 9:30 a.m. March 23, when the Tesla Model X struck the barrier separating the Highway 85 carpool flyover lane from southbound Highway 101, according to California Highway Patrol officials. The Tesla careened into two lanes of Highway 101, where it was struck by a Mazda and then an Audi. Huang was transported to Stanford Hospital, where he died of his injuries later that day.
Emergency fire crews arrived at the crash shortly after 9:30 a.m. and found that the front end of the Tesla had "substantial damage," exposing the vehicle's lithium ion battery and causing it to catch fire, according to Mountain View Fire Chief Juan Diaz.
In a blog post Tuesday, Tesla officials stated that the company is "deeply saddened" by the fatal accident, and is assisting in the investigation. The vehicle's logs, which could provide a window into what happened leading up to the crash, have not been retrieved yet due to the "extensive damage" of the collision, according to the statement.
The blog claims that the damage to the Model X was so severe because the attenuator barrier — a safety barrier that divides the highway from the carpool flyover — had "either been removed or crushed" in a prior collision and had never been fully replaced, leaving little cushion between the tip of the barrier and the cement median.
"We have never seen this level of damage to a Model X in any other crash," according to the company statement.
Tesla vehicle batteries are designed to prevent fires from occurring rapidly, giving occupants time to get out safely, and witnesses at the scene of the crash reported that the driver was not in the Model X when it caught fire, according to the post.
Electric vehicle fires are typically put out by blasting a large quantity of water — 3,000 gallons — directly on the battery to bring down the temperature of the cells, which can overheat and reach temperatures of up to 900 degrees, said fire Chief Diaz.
Diaz said the department was put in a difficult situation. Fire crews had 500 gallons of water at the scene, but getting any more would have required running 2,000 feet of thick fire hose across Highway 101, which would have been catastrophic for traffic in both directions, Diaz told the Voice. But letting the car continue to burn on a busy highway, destroying the battery, would have been a bad choice as well, he said.
"In the middle of the Highway 101 freeway, that's not something we want to do," he said. "And it's not good for the environment with the byproducts of combustion."
Fire crews used the available supply of water and contacted the manufacturer of the vehicle, Palo Alto-based Tesla, to assist in getting the battery's temperature under control. Diaz said the engineers essentially disassembled a portion of the car battery on the spot, and that subsequent thermal imaging showed that the battery was no longer unstable.
Fire engines escorted the tow truck that removed the Tesla all the way to the impound yard out of an abundance of caution, Diaz said. Car batteries are capable of reigniting for 24 hours after cooling.
The challenging situation was made worse by the significant damage caused by collision itself. Diaz said that Tesla vehicles are built to be very safe, with features to help first responders deal with lithium ion batteries that ignite, but in this case emergency crews had no access to the battery's disconnect wires because they were destroyed on impact. This is the first time the department has dealt with this kind of problem, Diaz said, and he commended his department's response to the dangerous situation.
"I'm frankly very proud of how the Mountain View firefighters handled the event," he said.
NTSB spokesman Christopher O'Neil told the Voice that the two investigators assigned to the incident came to Mountain View on Tuesday to conduct what the agency calls a "field investigation" of the crash, which is narrow in scope and examines specific safety issues rather than an all-encompassing accident investigation.
"It's going to focus on the post-crash fire that resulted in this accident, and steps that were taken and necessary to make the vehicle safe for removal from the scene," O'Neil said.
It's unclear whether the automated control system aboard the vehicle was active at the time of the crash. According to Tesla's blog post, its "Autopilot" system has been engaged roughly 85,000 times on the same stretch of road since 2015, and company representatives aren't aware of any accidents. "There are over 200 successful Autopilot trips per day on this exact stretch of road," the post said.
NTSB investigative teams typically spend about five to 10 days working at the scene of the crash, depending on the complexity of the incident, before starting work on publishing the results. O'Neil said the investigation may or may not lead to a preliminary report a few weeks after reviewing the accident, and it's possible the accident report will be rolled into a larger investigative review of similar accidents.
O'Neil said reports on car batteries and the appropriate response to incidents like the accident on Friday are important, given that electric cars are increasingly common on roadways and emergency responders need a good strategy to render the vehicles safe. He said the report is not aimed at affixing blame or liability on the fire department or any of the involved parties, instead taking a close look at what could be done to help save lives and mitigate the effects of the accident.
"The report looks at whether there's something that could be done or should be done," he said. "It's not that we think there's a problem, it's that we want to explore that issue."
Tesla representatives did not respond to requests for comment.
—Bay City News Service contributed to this report
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