Is There an Overreaction To EV Safety Concerns?
In October 2013 an electric vehicle (EV) was once again front page news after a Tesla Model S experienced a fire in one of the lithium-ion (Li-ion) battery modules after colliding with a metal object on a Washington State highway
This comes weeks after displaying the Model S at the Frankfurt motor show as part of the launch into the European market; and barely two months after being awarded a NHTSA Five-Star rating. With an overall Vehicle Safety Score of 0.42, for frontal, side, and roll-over crashes the "S" was proclaimed "The safest car in America".
With all these accolades it’s little wonder that this single event saw Tesla Motors’ shares drop ten percent in forty eight hours; shedding $2.4 billion along the way.
Deutsche Bank analyst Dan Galves summed up the prevailing sentiment when he stated: "Investors will be concerned because electric cars represent a new technology with a high sensitivity to safety risks."
In actual fact it’s not surprising that an EV, such as the Tesla, should rate very highly in many of the crash tests:
- The absence of a large and heavy engine in the front compartment (usually) means that the crumple zone can be better utilised to absorb energy from a frontal impact.
- The positioning of the relatively heavy battery pack, which is fixed to the floor in the Model S (And several other EV’s), creates a low Center of Gravity which reduces the Roll Moment making the vehicle less likely to roll over when compared to conventional configurations.
Image credit: www.boronextrication.com
Notwithstanding all these inherent safety features the source of energy for these EV’s remains a concern. In particular, with regard to the fire risk that Li-ion batteries present.
The recent Model S predicament was not the first EV battery fire to attract public attention. At least 8 other brands have reported incidents related to the Li-ion batteries. The Zotye M300 EV, Chevrolet Volt, Fisker Karma, BYD e6, Dodge Ram 1500 Plug-in Hybrid, Toyota Prius Plug-in Hybrid, Mitsubishi i-MiEV and Outlander P-HEV have all experienced problems; mostly related to "thermal runaway" within the battery’s cells.
Although there have been several onboard fires only one incident has resulted in fatalities. In Shenzhen, China, three people died when a BYD e6 taxi caught fire after a high-speed car crashed into them.
The fatalities were not due to the fire
The Chinese authorities concluded that the fire was due to electric arcing caused by a short-circuit in the high voltage lines from the distribution box. This in turn set fire to the interior trim and a section of the power batteries. Despite the damage, the battery pack did not explode and 75% of the single cell batteries never ignited.
The team concluded there were no flaws in the safety design of the vehicle and the occupants died as a result of the collision, not the fire.
Possibly the most publicised fire was that of a Chevrolet Volt which was subjected to a 32 km/h side pole impact crash test, followed by a post-impact rollover, conducted by the National Highway Traffic Safety Administration (NHTSA). The cause of the fire, that occurred three weeks later in the test centre parking lot, was believed to be the battery.
The cause of the Chevrolet Volt fire
Shortly after the incident the NHTSA concluded that the crash test damaged the Volt’s Li-ion batteries resulting in the vehicle fire which occurred several weeks later. Notwithstanding these findings, GM contended the fire was due to the prototype test vehicle’s programming being incomplete.
All (later) production Volts have programming that "depowers" the battery after a crash, dissipating any remaining charge and rendering the battery inert. The test car didn’t have that. To further improve the safety of the Volt, GM introduced battery coolant sensors and structural improvements in 2012.
Although this fire may have been an indirect result of a simulated crash, National Fire Protection Agency in America statistics show that there were an estimated 184,500 conventional highway vehicle fires in 2010. In the extremely rare incidents where a fire involved an EV, no findings of any relationship to the electric drive components were found.
Consumers understand an EV catching fire after an accident; possibly even accept an incident while driving, or even when charging the battery – but when this happens with the vehicle switched off and parked in a garage, concerns are raised.
It doesn’t take an accident to start a fire
This is exactly what happened to a Fisker Karma plug-in hybrid luxury sports sedan, in Texas in 2012.
The vehicle caught fire while parked in the owner’s garage. With the battery intact the cause of the fire is unknown as the car wasn't plugged in, but investigators did establish that the fire originated in the Karma.
Unfortunately for Fisker, the Karma was involved in another incident which highlighted one of the safety risks of EVs: Submersion in water. This was graphically illustrated during Hurricane Sandy when sixteen Karmas and one Toyota Prius plug-in caught fire (separately) while parked in the port terminal in Newark after being completely submerged in saltwater.
With Lithium being a highly reactive, flammable metal alkali, production processes are critical in producing safe high energy batteries. In March 2013 Mitsubishi experienced battery problems with an i-MiEV and Outlander plug-in hybrid crossover after the battery in one car melted and the other caught fire.
An internal investigation found that one battery had been dropped causing parts of the battery to break off and contaminate the cells. In the other case, a screening process applied excessive force to the battery, which also caused internal damage to the cells.
But it’s not only vehicle accidents and onboard fires that have consumers concerned: In June 2013 a charging unit for Hong Kong’s electric taxis, manufactured by BYD Co. nearly caught fire at a taxi parking lot, raising enough product safety concern to pull the company’s stock price down by more than 9 percent in Hong Kong.
Reviewing the available statistics, crash test performance and the fact that Li-ion batteries hold about 10% of the energy contained in gasoline, one can only conclude that EVs are inherently safer than current conventional vehicles.
Of greater concern is the preparedness of bystanders and emergency rescue personnel in dealing with EV emergencies. Dealing with high voltages and very reactive materials in the batteries require a degree of training and understanding.
Notwithstanding all the accolades and laboratory testing, the safety of the vehicle design and construction can receive no better confirmation of its success than, what the driver of the Tesla S described as: "a doomsday event that has now been tested, proving the design and engineering works".
Wall Street Journal - Tesla Model S Is ‘Safer Than Conventional Vehicles’: Analyst.
MIT technology review – GM Announces Retrofit to Address Volt Fires
International business times - Electric Car Charging Station Partially Melts, Freaking Out Investors (Angelo Young)
Bloomberg – Fisker Karma Fire in Texas Garage Being Probed by NHTSA (Angela Greiling Keane)
New York Times – Tesla Says Car Fire Started in Battery (Christopher Jensen)
Tesla Motors forum – Elon Musk comments
Peter Els is a technical writer for Automotive IQ