The battery of a Tesla Model S that was involved in a road accident in the US state of Florida in early May caught fire again twice after being extinguished. It is not the first time such a battery has unexpectedly caught fire again. What exactly is the situation?
A Tesla Model S was involved in a road accident in Florida on 8 May, in which the vehicle collided with a metal street lamp at a speed of 186 kilometres per hour (converted). The vehicle subsequently caught fire and was extinguished by the Fort Lauderdale Fire Department using a combination of water and foam.
Battery catches fire again
A report by the US National Transportation Safety Board (NTSB) now shows that the vehicle's battery caught fire twice after being extinguished. This happened once during the towing of the vehicle away from the scene of the accident and once in the car park of the body shop to which the vehicle was towed.
This is not the first time an incident has been reported in which the battery of a crashed Tesla vehicle caught fire again after being extinguished. Such was the case after a fatal accident involving a Tesla Model X that occurred in March in US Mountain View, California. California's San Jose Fire Department reported that the battery of this vehicle caught fire again six days after the accident. Speaking to KTVU, part of Fox, the fire service indicates that the battery even caught fire again three to four times.
Opinion from Tesla
That Tesla batteries can reignite is something Tesla itself acknowledges, by the way, in a safety manual for emergency responders. The company recommends extinguishing burning batteries with large amounts of water or using dry chemicals, CO2, foam or another fire extinguishing agent. It can take 24 hours to completely extinguish a battery fire. If possible, Tesla recommends letting the battery burn out in a controlled manner.
"When fire and smoke are no longer visible, a thermal imaging camera can be used to actively measure the temperature of the high-voltage battery and monitor the heating or cooling trend. No fire, smoke or heat should be present in the high-voltage battery for at least one hour before the car can be released to Second Responders (such as the police, towing service, etc.). The battery must have cooled down completely before the car can be released to Second Responders or leave the scene of the incident. Always warn Second Responders of the risk that the battery may re-ignite," the company writes in the manual.
Storing on an open site
"Because of the danger of possible reignition, a Model S that has been submerged in water, involved in a fire or in a collision that has damaged the high-voltage battery should always be stored in open terrain at least 50 ft (15 m) from any exposure."
Other car manufacturers also recognise this danger, Nissan being one example. In its 'Roadside Assistants Guide' for the Nissan Leaf, the carmaker recommends never storing a Nissan Leaf whose battery is damaged near other vehicles or in a building. This as the damaged battery could catch fire.
Afraid of being electrocuted
Besides the risk of battery ignition, electric vehicles also pose other risks for emergency responders. In the Netherlands, for instance, confusion arose earlier about how firefighters should handle the battery in a Tesla. A driver of a Tesla was killed in an accident in Baarn, Utrecht, in September 2016, in which the vehicle caught fire. RTL News points out that firefighters were quick to arrive but for a long time did not dare to enter the vehicle for fear that the vehicle was under high voltage. Firefighters were afraid of being electrocuted as a result. In its manual for emergency workers, Tesla gives advice on how to work safely on the company's vehicles.
Electric vehicles are generally equipped with a safety measure called 'cut loop', which basically functions as a killswitch for the battery in an electric vehicle. For instance, in the Tesla Model S, this cut loop - called the 'First Responder circuit' by Tesla - is located in the luggage compartment at the front of the vehicle. Cutting this cut loop disables the high-voltage circuit, SRS components and airbag components.
Cut loop is not always usable
In practice, however, this killswitch does not always prove useful. For example, in the Californian accident involving the Tesla Model X in March, the cut loop had become inoperable, according to the NTSB, preventing firefighters from safely removing power from the vehicle. This while this step is necessary to ensure that when cutting loose a trapped victim, for example, no live cables are touched.
Author: Wouter Hoeffnagel
Source: Tesla
Source: National Transportation Safety Board
Source: KTVU
Source: RTL News
Source: National Fire Protection Association
