A few years ago at Hearing International we did a post regarding air bags and their effect on hearing.  That report was primarily about how these miracle devices work and save lives with a comment about the impulse noise issues surrounding the their deployment. 

Among people in accidents with airbags deploying, Price (2007) suggests that 17 percent suffer permanent hearing loss.  Additionally, his research also suggests that the injury is greater with the windows rolled up as having car windows rolled up, whereas deployed airbags are actually less hazardous to the ear than rolled-down windows. Price feels that the higher pressure generated in the closed cabin actually prevents greater damage to the ear. The pressure causes a displacement in the middle ear that stiffens the stapes, a small bone outside the inner ear. This stiffening limits the transmission of energy to the inner ear, where hearing damage takes place. In airbag experiments where the cabin is completely sealed and pressure is even higher, hearing damage is reduced even further.  This interesting concept is similar to the stimulation of the acoustic reflex prior to a crash deployed in some Mercedes Benz vehicles.  Price’s study only included cars sold in the United States with front and side airbags. Under U.S. regulations, American cars must have larger, more powerful airbags than cars sold in places like Europe. “Cars with smaller airbags sold in other parts of the world would likely pose less auditory danger when tested under identical circumstances, Price said.”

The Takata Recall

Recently vehicles made by 19 different automakers have been recalled to replace frontal airbags on the driver’s side or passenger’s side, or both in what National Highway Transportation Safety Administration (NHTSA)  has called “the largest and most complex safety recall in U.S. history.” The problem is that airbags are made by major parts supplier Takata, which started out as a Japanese textile manufacturer more than 80 years ago and later came to specialize in seat belts and other auto safety equipment.  These defective Takata air bags mostly installed between 2002 and 2015 could explode, injuring or even killing the occupants of the vehicle.  The company’s faulty airbag inflators affected by heat wings and moisture can blast shrapnel into drivers and passengers, have resulted in the recall of tens of millions of vehicles and been linked to 11 deaths in the U.S. and several others elsewhere.  While audiologists are concerned about the 150-170 dB noise exposure from air bag deployment, the real concern lies in how the airbags are meant to inflate when they are activated. The defective ones use a compound called ammonium nitrate to assist the bag to go from its very compact form inside your steering wheel or door panel to something big enough to protect your head or body in a collision. The compound, however, can break down and become unstable when your car is exposed to moisture or temperature swings over time, leading to a risk of explosion.  This has caused the largest automotive recall in US history and the June 25, 2017 filing of bankruptcy by Takata.  Hopefully, this tragedy will lead to better designs that do not employ rocket fuel and shrapnel for deployment.  You can click here to see of your vehicle is due for replacement air bags.

The Future of Air Bag Future & New Designs

In the immediate future, it appears that there will be significant developments in “active safety,” such as pre-collision systems and lane departure warnings, to prevent accidents, rather than “passive safety,” such as airbags and car crumple zones, that minimize injuries during an accident.  The sensor, processing and “by-wire” technologies have advanced very quickly over the last few years, says John Hanson, national manager of advanced technology business communications for Toyota. This lets manufacturers develop a wide variety of high-level driver assistance features to improve crash avoidance or crash mitigation, Hanson says.  Looking further out, it is predicted that automakers will begin to fit forward-looking sensors that work in concert with airbags, such as those now incorporated in the new Mercedes Benz vehicles that stimulate the Acoustic Reflex prior to the air bag.  Montoya (2015) indicates that in the near future their may be airbags that deploy just before the crash, with even less energy than they do now,” he says. This will help reduce injuries from airbag deployment even further.  There may even be air bag type seat belts as well.

 Another innovative research concept is the Aeromorph that takes origami structures made with inflatables from various materials. They introduce a universal bending mechanism that creates programmable shape-changing behaviors with paper, plastics and fabrics.  Researchers have developed a software tool that generates this bending mechanism for a given geometry, simulates its transformation, and exports the compound geometry as digital fabrication files. A custom heat-sealing head that can be mounted in a useable “air bag” format precisely designed fabricate a transforming material according to the needs.  Still research to be conducted on this one…..

Whichever concept is designed it will not use rocket fuel inflators and expose the occupants to shrapnel.  Additionally, the new concepts are much quieter and will not expose the occupants to 150- to 170 dB of impulse noise.

 

References:

Montoya, R. (2015).  The Future of Car Airbags.  Retrieved September 5, 2017.

Newswise (2007). Car Airbags Will Cause Permanent Hearing Loss in 17 Percent. Retrieved September 5, 2017. 

Phen, R., Dowdy, M., Ebbeler, D., Kim, E-H., Moore, N., & Van Zandt, Y., (1998). Advanced Air Bag Technology Assessment, Final Report.  National Highway Traffic Safety Administration and
     National Aeronautics and Space Administration prepared by the Jet Propulsion Laboratory California Institute of Technology, Pasadena, California.  Retrieved September 4, 2017.

Price, R. (2007).  Impulse Noise-Hearing Conservation’s Poison Gas?  National Hearing Conservation Association’s 32nd annual hearing conference, Savanah, Ga. Retrieved September 5, 2017.  

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