According to the NTSB, 50,000 gallons of water were needed to fight a Tesla semi-trailer fire in Northern California

WASHINGTON– California firefighters had to use about 50,000 gallons of water to extinguish a burning battery in a Tesla semi-trailer after an accident, the National Transportation Safety Board said Thursday.

In addition to the enormous amounts of water, firefighters also used an aircraft as a precautionary measure to drop fire retardant in the “immediate vicinity” of the electric truck, the agency said in a preliminary report.

Firefighters had previously stated that the battery had reached a temperature of over 500 degrees Celsius during the flames.

The NTSB sent investigators to the Aug. 19 crash on Interstate 80 near Emigrant Gap, about 70 miles northeast of Sacramento. The agency said it would investigate the fire hazard posed by the truck's large lithium-ion battery.

The agency also found that the truck was not running any of Tesla's partially automated driving systems at the time of the crash, the report said. The systems were not operational and “could not be activated,” the agency said.

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The crash occurred at about 3:13 a.m. as the semi was being driven by a Tesla employee from Livermore, California, to a Tesla factory in Sparks, Nevada. The semi left the road on a right-hand curve and struck a tree, the report said. It plunged down a slope and became stuck on several trees. The driver was not injured.

After the accident, the semi-truck's lithium-ion battery caught fire. Firefighters extinguished the flames with water and kept the batteries cool. The highway was closed for about 15 hours while firefighters made sure the batteries were cool enough to recover the truck.

Authorities moved the truck to an open area and monitored it for 24 hours. The battery did not reignite.

The NTSB said it was investigating all aspects of the crash to determine the cause. The agency said it intends to issue safety recommendations to prevent similar incidents.

A message seeking comment was left Thursday from Tesla, based in Austin, Texas.

After an investigation that ended in 2021, the NTSB found that high-voltage battery fires in electric vehicles pose risks to first responders and that manufacturers' guidelines for dealing with them are inadequate.

The agency, which has no enforcement powers and can only make recommendations, asked manufacturers to develop vehicle-specific guidelines to combat battery fires and limit chemical thermal runaway and reignition. The guidelines should also include information on how to safely store vehicles with damaged lithium-ion batteries, the agency said.

Tesla began delivering the electric Semis in December 2022, more than three years after CEO Elon Musk announced his company would begin producing the trucks. Musk said the Semi will have a range of 500 miles per charge when pulling an 82,000-pound load.