Safety and Reliability: Gasoline or Batteries?
We have always had a lead acid battery in our gasoline vehicles and never worried about its safety, but with the advent of lithium ion batteries in the new plug in cars there is increasing concern about fires from consumers and firefighters themselves. Let’s look at the facts:
We all know that gasoline is highly flammable, therefore let’s not kid ourselves that a gas car is so safe, even after being around for 100 years. The National Fire Protection Agency reported that there were 219,000 gasoline vehicle fires in the United States in 2009. That is one gas vehicle fire every 146 seconds!1 11% of all fire deaths in 2008 were caused by these vehicle fires.2
In the lithium ion battery packs, found in the plug in cars coming out now, the worst-case scenario is thermal runaway. Thermal runaway is when a short circuit inside a battery sparks a chain reaction and causes overheating or a fire. It can occur in 1 of every 5 million to 10 million cells in laptops, cell phones and other handheld gizmos.3 
A laptop battery, for example, has about six cells, but electric cars contain about 75 or 80 cells, meaning the likelihood of thermal runway could increase. Batterymakers, however, are very cognizant of the potential problems and have worked very hard to mitigate overheating and produce extremely reliable batteries. Nissan, to name one, puts its all electric Leaf battery through stringent stress tests. The pack is exposed to extreme temperatures, and charged and depleted continuously. Devastating crashes are simulated by crushing cells with huge force and piercing cells with nails. EVs, like Mitsubishi’s i-MiEV, have a steel cage around the car and a second impact cage around the pack.4 Tesla Motors and other car companies have installed electronically controlled liquid cooling systems. Tesla’s decision to install 7,000 small batteries in its Roadster was in part for safety: each battery in the pack is encased in steel to isolate it from its neighbor. Overcharging protection and sensors to trigger the batteries to disconnect in the case of high-temperatures or a road accident are also installed in many electric vehicles.5 Onboard computers monitors battery pack health to troubleshoot.
Automakers are taking the concerns of fire very seriously. As Peter Roth, lead researcher for Sandia National Laboratories’ FreedomCAR program, says, “The energies that can be released [from a battery pack] are certainly less of a concern than driving with 20…gallons of gasoline. Are there scenarios in which the battery may get into an accident or an environment that causes it to burn? Yes, it can burn, but you're not driving around in a [gasoline] bomb.”6
