Fueling the Fire

Stuart White 18-10-2019 9:00 AM
Categories: HRMC Articles written by Managing Director, Stuart White

A chance call on a phone-in radio show this week highlighted a problem I didn’t even know existed, and I suspect many of you are also unaware of.  The discussion topic was on the inherent dangers of the recently-introduced ‘smart motorways’ in the UK with no hard-shoulder for breakdowns and other emergency situations. One tow-truck driver called in to point out the high rate of fatalities from members of his profession attending to incidents on such roads after dark.  He then went on to point out a very modern danger to which he and his colleagues are exposed – the potential of electrocution or conflagration from the lithium ion batteries in electric cars involved in accidents.


The incidence of post-crash fires has already been highlighted as an increasing problem in such cars.  In May 2018, a German driver died after a Tesla car he was driving crashed into a guardrail in Switzerland and burst into flames. Following the accident, the local  fire brigade posted a Facebook comment suggesting the vehicle's lithium ion batteries could have triggered a phenomenon involving a "rapid and unstoppable increase in temperature" causing the accident, though the comment was later retracted.


The U.S. National Transportation Safety Board is also investigating a further two fires involving Tesla vehicles, a Model S that caught fire after crashing into a wall in Florida, trapping two 18-year-olds who died in the flames and the company's semi-autonomous Model X SUV which crashed into a barrier on a California highway. The driver in that incident also died, but Tesla said he was pulled from the vehicle before it caught fire.  


According to industry safety group the Society of Automotive Engineers (SAE), fuel-saving petrol-electric hybrid and all-electric cars and trucks powered by sizable battery packs and high voltage motors could present a new kind of danger at serious accident scenes.  The report highlighted risks to first responders and tow operators from potential electric shock from damaged systems not disengaged during or immediately after a crash.

"As electric vehicles enter the marketplace in greater numbers, it's an appropriate time to recognize best practices that facilitate a safe response when these vehicles are in an accident," said Todd Mackintosh, chairman of the SAE technical committee.  The group recommended automakers install switches that would kill battery power in the event of an accident. The location of those switches should be standardized for safety.  Another recommendation would create a guide for emergency workers, to quickly identify the location of high-voltage components allowing them to be disabled.Tow truck drivers also need better information and training on how to handle hybrids and electric vehicles without receiving an unexpected jolt, the report said.  

More than one million battery powered electric and hybrid electric vehicles were sold in the United States last year, raising the chances of such vehicles being involved in road traffic accidents.  In May, auto industry officials and the National Highway Traffic Safety Administration (NHTSA) and the Energy Department discussed potential dangers faced by first responders from electrical charges produced by hybrid and electric cars.
NHTSA later issued interim guidance for consumers, emergency responders and tow truck operators to increase awareness about specific dangers.  Dangers can be reduced if responders have easy access to battery packs and if auto manufacturers create common disconnect locations in all hybrid and electric vehicles, NHTSA said.

The potential problems of such vehicles are not, of course, confined to Tesla and car manufacturers are getting the message out to drivers and responders. Nissan places the battery pack of its LEAF all-electric car in a steel case. The Japanese automaker also designed the battery pack to sense a crash and disable its electrical charge when involved in an accident.  Ford has published a guide for first responders encountering its Focus EV involved in accidents. The Focus EV includes what Ford calls "Electric Badges," which are clearly marked logos on the doors and trunk lid to warn responders of possible electric shock. Cables wrapped in orange high-voltage warning sleeves are located under the hood of the Focus EV.  General Motors, maker of the Chevy Volt, is also helping to prepare fire service and other first responders. Moreover, GM took steps to better protect the Volt battery pack following a fire that flared after a crash test in 2011. NHTSA found no defect with the lithium-ion battery system nor were any real world crash-fires ever reported. But the case highlighted potential safety concerns for first responders.

For those of a technical bent this is the science behind the danger.  What happens with a lithium ion battery fire is typically a short circuit within one or more of the battery's cells, which generates heat. The heat can then ignite the chemicals within the battery. That can cause problems in the adjoining cells and lead to the condition known as "thermal runaway" in which the fire spreads and builds. That's apparently what happened in a fatal Tesla crash in Switzerland.  The big difference between a lithium ion battery and petroleum fire is the time it takes to ignite. Petrol fires start almost immediately when the fuel comes in contact with a spark or flame, and spreads rapidly. Battery fires typically take some time to achieve the heat necessary to start the fire.  In some instances, that delay is good because it means the occupants of a car involved in a crash can exit the vehicle before the fire starts. But it can pose its own problems. Sometimes a battery can be damaged, perhaps by the car running over some debris, and the driver might not be aware of the damage. And then a fire can start well after the initial incident. That could theoretically cause a fire after the car is parked in a garage. And even when the battery fire is obvious, Tesla warns first responders that it can take 24 hours for a it to be fully extinguished.

The fire risk for electric cars will undoubtedly be reduced in the years to come.  Research is taking place for new materials that might not only make batteries lighter and more efficient but could possibly make them safer. Steven Risser, senior research leader at Battelle, a non-profit research and development firm, and one of the leading experts on the risk of fires in electric vehicles makes a valid point.  "Gasoline is a very risky material. We have had 130 years of designs and experience to make a gasoline powered vehicle as safe as possible. We're still at early stages of understanding how to make lithium ion batteries safe.”

To paraphrase Aldous Huxley, it’s a brave new world we’re entering into and clearly with new technologies come new dangers.  Let the buyer (of an electric car) beware.
 

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