• Hybrid cars like the Prius have a number of significant advantages over gas-powered vehicles, but their battery packs make them no safer. This is especially true because those responding to an accident involving a Prius or any other hybrid may not be trained (or equipped) to deal with the specific dangers they pose.
  
  

Electrocution

• The Prius' nickel-metal hybrid (NiMH) battery is a well-designed unit, but poses a serious danger to mechanics and first-responders if it is not disconnected. All Priuses have a battery-disconnect switch located in the car's trunk, and can be accessed by removing the left-front corner liner.
  
  This removes the ground from the battery, rendering the car's electrical system dead and the battery inert unless the contacts are bridged. High voltage cables and components can be recognized by their bright orange coatings.
  
  

Overcharging

• Although it is theoretically possible to cause a fire by overcharging the Prius' battery pack, it is extremely unlikely. The car's electronic control unit is programmed to avoid just such a condition by siphoning off unwanted power and using it to run the internal combustion engine. Still, any failure of this system will rapidly cause an overheat condition, resulting in a breach of the battery's housing and potential fire.
  
  

Fire

• Crashes, overheating and short circuiting can cause a battery fire. Of the toxins produced by a burning Prius battery (including oxides of cobalt, cerium, neodymium and praseodymium), the most dangerous of them are probably nickel oxide and potassium oxide, which pose an immediate respiratory hazard to anyone present. Nickel and cobalt gases are serious carcinogens, so inhaling them will drastically increase the risk of cancer.
  
  Additionally, NiMH batteries are almost impossible to extinguish with water and attempting to do so might create explosive hydrogen gas. Water will cool the surrounding areas and prevent spreading of the inferno, but the batteries themselves must be smothered with ash or foam.
  
  

Acid Burns

• The NiMH batteries used in the Prius contain sulfuric acid, which can cause caustic burns to anyone or anything it comes in contact with. Ask any experienced mechanic, and you'll be regaled with stories of acid burns caused by a leaking battery.
  
  The good news here is that the Prius uses a great number of small batteries, all of which are surrounded by a thick, thermally and chemically resistant housing. This means that the release of sulfuric acid will be limited only to those cells that are severely affected.