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Two case reports of possible noise trauma after inflation of air bags in low speed car crashes

Graham Buckley, consultant otolaryngologist, ^a Nicholas Setchfield, chief audiologist, ^b Richard Frampton, principal consultant. ^c

^a Department of Otolaryngology (Head and Neck Surgery), St James's University Hospital, Leeds LS9 7TF, ^b Department of Audiology, St James's University Hospital, ^c Vehicle Safety Research Centre, Loughborough, Leicestershire LE11 3UZ

Correspondence to: Mr Buckley jgrahambuckley{at}compuserve.com

Air bags have contributed substantially to the safety of car occupants in road accidents, but concern exists that they may inflate unnecessarily in low speed crashes.¹ Previous articles have reported eye, face, upper limb, and chest injuries caused by air bag inflation.² Despite the high noise level generated by the bags on inflation, we are aware of only one paper reporting that air bag inflation might induce hearing loss.³ We describe two cases of hearing loss and persistent tinnitus that may have resulted from air bag inflation in low speed collisions. Neither subject sustained other injuries. Audiometry results are shown in the figure.

View larger version (43K): [in this window] [in a new window]   Audiograms for subjects in both cases (pre-exposure thresholds are shown in dotted line for case 2)

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Case 1

Case 2

	Comment

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The pre-injury hearing level in case 1 is unknown, but the pattern of the hearing loss, its severity in a woman of this age, and her apparently previously normal hearing strongly suggest a causal link. In case 2, the subject had a pre-existing hearing loss, but his hearing deteriorated substantially in the right earat 1 kHz and in the higher frequencies. Alteration of hearing at 1 kHz is unusual but recognised after noise trauma. Both subjects perceived an immediate threshold shift, which decreased in severity with time and so was not as great by the time audiometry was performed.

The inflation of an air bag is triggered by vehicle deceleration and can generate a sound pressure level of 150-170 dB in <100 ms.⁴ The level depends on the size of car, number of occupants, ventilation, size and number of air bags, and inflation rate. In a study of the effect of air bag "slap" on the ears of squirrel monkeys, the researchers found no permanent hearing damage, ear drum perforation, or disruption of ossicles in air bag velocities of up to 100 mph with a sound pressure level on inflation of 150 dB.⁵ None the less, this level might cause acoustic trauma in some humans. Cochlear damage may arise from the effects of noise or blast injury. The likelihood of damage depends on the noise level, the exposure time, and individual sensitivity.

Injury from air bags may be more likely in the future. Current safety design is moving towards vehicles with air bags that inflate in frontal and side crashes for both front seat positions. Lack of space means that side air bags inflate very quickly and are closer to the ear.

It is surprising that hearing loss is not reported more frequently after air bag inflation. Any loss identified is perhaps ascribed to other factors associated with a car accident. Also, in an accident the victim is unlikely to register and remember the noise of the air bag. It is therefore unclear whether these cases are isolated or represent a more widespread occurrence.

	Acknowledgments

   Contributors: GB had the original idea, NS advised on and carried out the audiometric testing, and RF provided information on air bag construction and literature on testing. The paper was jointly written by all three authors. GB will act as guarantor.

Funding: None.

Competing interests: None declared.

	References

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1. Third report to Congress. Effectiveness of occupant protection systems and their use (http://www.nhtsa.dot.gov:80/cars/rules/rulings/208con2e.html).
2. Antosia RE, Partridge RA, Virk AS. Air bag safety. Ann Emerg Med 1995; 25: 794-798[Medline].
3. Saunders JE, Slattery III WH, Luxford WM. Automobile airbag impulse noise: otologic symptoms in six patients. Otolaryngol Head Neck Surg 1998; 118: 228-234[Medline].
4. Rouhana SW, Webb SR, Wooley RG, McCleary JD, Wood FD, Salva DB. Investigation into the noise associated with air bag deployment. Part 1. Measurement technique and parameter study. Warrendale, PA: Society of Automotive Engineers , 1994(Report 942218.)
5. Richter HJ II, Stalnaker RL, Pugh JE Jr. Otologic hazards of airbag restraint system. Society for Automotive Engineers, 1974. (Paper No 741185; can be ordered through the SAE at www.sae.org.)

(Accepted 23 October 1998)