Airbags
File:Kontrollleuchte Airbag black.svg
File:Kontrollleuchte Airbag black.svg

Main

Timeline:



  • 1970s - Ford and General motors started to test air bags
  • 1977- The Carter Administration mandated that all cars must be manufactured with either automatic seat belts or air bags by model year 1984
  • 1980s - "Commercial" Air Bags introduced
  • 1981 - Mercedes-Benz "S-class" is the first production car with driver side air bags
  • 1988 - Chrysler was the first company to make drivers side air bags standard
  • 1989 - Ford installed air bags in 9 models
  • 1991 - President George H.W. Bush mandated that all cars must have airbags by 1998 and trucks must have airbags by 1999.
  • 1999 - All cars/ trucks sold in US must have driver and passenger air bag. (1999 for light weight trucks)



General Information:


Airbags are designed to reduce head injuries. They are not a substitute for seat belts but are designed to work with them. They have the potential to reduce the risk of injury and death in automobile accidents by 83% when used with a seat belt.



Legislation:


In 1996, the government started placing and enforcing regulations on cars relating to airbags. In 1996, the Federal Government required car manufacturers to start to phase in cars with air bags, and by 1998 all new vehicles sold in the United States must have air bags.

Questions of the safety of air bags, especially regarding children in rear facing car seats, soon became prevalent. There were questions about cars with only front seats and with cars with rear seats that were too small to accommodate a car seat. Therefore, the Federal Government allowed these cars to have a switch to turn the front right passenger's air bag on and off.

In 1997, the Federal Government required that manufacturers place warning labels in cars to warn of the dangers of air bags.



Resistance to Legislation:


People understand that airbags can cause injury, so they would like the option to choose whether or not they want to have an airbag turned on in their vehicles. These people feel that the risk of injury from the airbag in a crash is too high, so they don't want to use them at all. For instance, in 1990, a 64 year old woman was killed by a phase one airbag, and in 1993 a 6 year old boy was killed by the same type of airbag. But these deaths have sparked the development of new, safer air bags. It is estimated that 231 people in the United States have been killed by airbags, from 1987 to 2003, but it is also estimated that 13,967 lives have been saved by airbags in the same time period.



The Physics of Air Bags:

Reduction of Force: The purpose of an air bag is, in the event of a collision, to reduce the applied force on the automobile’s occupants while still delivering the same impulse (J) as the collision. From a physics standpoint air bags are very similar to seat belts, the difference is: seat belts are used to keep occupants inside of the car, air bags are used to keep the inside of the car safe. Without air bags head and neck injuries would be much more prevalent in even minor collisions. When a collision occurs, air bags are responsible of applying an impulse to the passengers equal to the impulse of the collision. Since the air bags take time to deploy, they can apply the same impulse while using a much smaller force. This is possible because J = ∫F*dt. So the higher the time the lower the force.
Pressure Reduction: When it comes down to it, most injuries are caused by an applied pressure. Pressure is directly proportional to force, so the lower the force the lower the pressure. However, pressure is also inversely proportional to the area of the applied force. Air bags use this physics concept advantageously. Air bags apply their already reduced force over a maximized area, this reduces the applied pressure on the occupants.
How Air Bags Deploy: Air bags actually use a lot of physics in simply deploying. In every new car there are several force sensors placed throughout the vehicle that feed via electric current directly to an onboard computer. When a force is applied to one of these sensors it creates a potential difference in the sensor, the sensor then sends a current to the onboard computer that is directly proportional to the voltage and therefore the applied force. The computer interprets this current as a force and is programed to deploy the air bags if the force exceeds a certain value.


Important Equations for Air Bags:
Air bags must match the impulse delivered by a collision. They maximize time to minimize applied force.
Impulse.png
The applied pressure on the occupants is what actually causes injury. The area is maximized so that the pressure is minimized.
Air_Bag_Pressure.png
The outside force of a collision, picked up by various force sensors placed throughout the vehicle is directly proportional to the change in voltage in that sensor which is directly proportional to the current the sensor sends to the on board computer.
Car_force_sensor.png



Connection:

Air bags again are designed to keep travelers safe while in a vehicle. They prevent head injuries, which also helps save lives. Since people were very weary about using them, the government stepped in, mandating their use.


Sources:


http://consumerguideauto.howstuffworks.com/the-evolution-of-the-airbag-cga.htm
http://newman.richmond.edu:2370/eb/article-259056
http://www.driverstechnology.co.uk/car-safety-timeline.htm
http://www.nhtsa.gov/cars/rules/import/fmvss/index.html#SN208
http://www.nae.edu/nae/techlithome.nsf/weblinks/KGRG-57XNSR?OpenDocument