It stands for Head and Neck Support, and the HANS device is a vital piece of safety gear every race car driver should be using. The Motorsport Safety Foundation has put together a video showing exactly why you need to be wearing a HANS device when you're out on the racetrack.
A fire suit-wearing crash test dummy is belted into a seat with a proper helmet fitted over its head. For some, this appears to be enough "safety." It's not though, as the forces presented in even a low-speed collision can wreak havoc on your head and neck. The average human head weighs between 10 and 11 pounds, and then you add another three to four pounds due to the weight of the helmet. While the safety belts keep your body in check, your neck is working tremendously hard to stop the forward movement of your head during an accident.
With a HANS device in place, your helmet is tethered in place. This allows for some movement, such as is necessary to drive the vehicle. But it prevents your head from whipping forward during a collision. Such restraint is imperative for reducing the potential for serious head and neck injuries.
There's a deadly injury known as a basilar skull fracture, and the HANS device greatly reduces the likelihood of such an injury occurring. Formula 1 driver Roland Ratzenberger died from such an injury during the 1994 San Marino Grand Prix. This is also the type of injury that claimed the life of NASCAR legend Dale Earnhardt. There are many more names on this injury list.
In the video posted above, you can see just how much movement occurs when a HANS device is not in place. With the HANS employed though, the crash test dummy retains a proper head position throughout the incident. They can now live to crash test another day. And you could live to turn more laps on the racetrack.