The Physics
An encyclopedia of scientific essays

Acceleration That Would Deploy Car Airbags

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Bibliographic Entry Result
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Federal Motor Vehicle Safety Standards. National Highway Traffic Safety Administration. September 1998. "Standard No. 208 currently specifies five injury criteria for the … adult male dummy in barrier crash tests … chest acceleration must not exceed 60 g's, (4) chest deflection must not exceed 76 mm (3 inches), and (5) upper leg forces must not exceed 10 kN." 60 g
Romeo, David J. Front Passenger Aspirator Air Bag System for Small Cars Phase II Evaluation: Final Report. New York, March 1978: Page 20 "These restraint systems offer the occupants passive protection in large size production automobiles at frontal barrier impact into the 30 to 40 mph crash speed range. A value of 36 g's peak acceleration was believed to be best representative of this crash condition." 36 g
Barnes J. S., Morris A. P. Airbag Effectiveness in Real World Crashes [pdf]. The Road Safety Research, policing and Education Conference, 2001
  Performance Criteria
Head HIC shall not exceed 1000 over 36 ms
Sternum Compression not to exceed 76.2 mm
Thorax Chest deceleration not to exceed 60 g
Femur Axial force not to exceed 10 kN
Barrier To conform to SAE document J850
Speed 48.3 km/h (30 mph)
60 g

Technology in automobiles has long surpassed the invention of the airbag, which was first implemented in 1970 by General Motors. And in spite of the fact that the use of airbags remains a controversy, they are nonetheless built in every car manufactured in the US.

An airbag system consists of two or three sensors that detect and/or decide whether a collision occurred. The most essential detection of a collision is in measuring the deceleration of the car. If a car collides with a barrier, there would naturally, be rapid deceleration since the car's speed changed so suddenly. Depending on the value of the deceleration, and/or the other sensors' readings, a decision is made whether or not to inflate the airbag.

The National Highway Traffic Safety Administration upgraded the air bag requirements of all cars in 1998; one of these revisions was that acceleration could not exceed 60 g's. In the event of this rate of acceleration, deployment must occur. Comparing this value with the 36 g's needed for deployment to occur in 1974, we see that safety measures have increasingly demanded that only under severe impact should the air bag inflate.

In contrast to the requirements mandated by the NHTSA, in 1995 in Australia, the Australian Design Rule 69 was implemented. It stated the exact same regulations as the NHTSA, which is that chest deceleration must not exceed 60 g's. This brings us to the conclusion that 60 g's must be a value that has proved to be efficient in crash-laboratories in at least two countries located on opposite sides of the globe.

Michelle Yee -- 2003