The HANS (Head And Neck Support) device was created to prevent head injuries caused by the sudden deceleration that often accompanies in impact at racing speeds. It consists of a collar that is strapped to the torso of the driver, that also supports the head, and two tethers which are attached to the driver's helmet. The collar and yoke are made of carbon fiber and kevlar.
When a racing car impacts an immovable object such as a wall, the vehicle impact decelerates the car abruptly. Inertia dictates that if the car is travelling at 170 MPH at the moment of impact, so is the driver. The driver will be wearing a five or six point harness, which is sort of an uber seat belt so it will decelerate along with the car. But the driver's head is not similarly restrained, so it continues forward at 170 MPH until its own neck and muscle structures stops it. This can cause two types of damage. First of all, the skull structure may prove inadequate to handle G-loads Mother Nature never designed us for. For example, the skull can handle a load of about 740 pounds without damage. A sixty mile per hour impact can generate that. But I have lapped at an average speed of eighty MPH in my four-cylinder bottom feeder race car. At a g-loading of 80, an average 15 pound skull has a weight of 1200 pounds. Champ car impacts of 100 G's have been recorded.
One result of such crushing impacts can be basal skull fracture, or a breakage of the skull bones where the skull is attached to the neck. This breaks the neck right where it is loaded with autonomic nerves, and can lead to instantaneous death. This is what killed Dale Earnhardt.
Another problem is that the brain itself also falls prey to inertia. The brain is essentially suspended in fluids inside the skull. Many concussions are caused by the brain slamming into the side of the skill. The device also makes extractions of injured driver easier. One problem a corner worker faces with a driver who has a potential spinal injury is the need tp maintain proper alignment of head and spine during the extraction. The device itself will hold the head in proper position, so the worker does not have to do this.
The HANS device was designed by Robert Hubbard who is a Professor of Engineering at Michigan State University. His inspiration and partner is Jim Downing a veteran endurance racer from IMSA and the American LeMans racing series who just happen's to be Hubbard's brother-in-law. Wearing the device has been made mandatory in Formula 1, CART and NASCAR . Where it is not mandated, it is recommended. The device should be matched to the type of car driven, as the driving position in an Indy Car is much different than in a stock car. Different sizes of the device are available, including a children's size for kart racers.