T Vaillant | PubMed Health

PubMed1992

Effectiveness of earplugs in high-intensity impulse noise.

The efficiency of different types of earplugs was assessed by means of Békésy audiometry following the exposure of 42 human subjects to weapon impulses. The peak pressure of the impulses ranged from 2.3-27.8 kPa (from 161 to 183-dB peak SPL) and the A-weighted equivalent level (over 8 h) of each exposure ranged from 100-114 dB. All subjects wore earplugs fitted by an experienced individual. The devices tested included one brand of conventional foam earplugs and a number of different models of perforated earplugs, one type of which had been previously shown to provide nonlinear attenuation. Perforated earplugs were tested because they provide better speech communication than conventional passive earplugs, and in the nonlinear case also afford attenuation that increases with the peak pressure of the impulses. The temporary threshold shifts (TTSs) observed in these experiments were very small and indicated no significant hazard for hearing. Well-fitted perforated earplugs seem to be able to protect the ear from infrequent exposures to the high-level impulses produced by small and large weapons while allowing good speech communication, and without impairing the operational capacity of soldiers who must remain aware of their acoustic environment.

Adult↗

PubMed1991

Delayed temporary threshold shift induced by impulse noises (weapon noises) in men.

Most of the available information on the effects of impulse noise on hearing is derived from temporary threshold shift (TTS2) measurements performed 2 min after a single exposure to small-weapon noises. TTS is known to recover as a linear function of the logarithm of time when it is induced by a continuous noise of moderate intensity. Following the exposure to impulse noise, several investigators have reported individual exceptions to the log-time relation, e.g. increases in TTS during the first hour of recovery. These authors observed a 'rebound recovery function' for most of the exposed men, and they conclude that this phenomenon '... has implications for the use of TTS in the construction of damage risk criteria for hazardous noise exposure ..., a single measure, such as the widely used TTS2 may not be an adequate index of the magnitude of the TTS'. In order to thoroughly investigate in man the existence of 'delayed' TTS following the exposure to actual weapon noises, the 'French Committee on Weapon Noises' carried out the following study. Three groups of soldiers (28 subjects) wearing no hearing protection were exposed in the free field over 2 days to impulse noises produced by a rifle. Békésy audiograms were obtained from each subject just before the exposure, and at 5 min, 1 h and 4 h after exposure. All audiometric tests were carried out even when no TTS was observable in the first postexposure audiogram. A significant number of subjects showed a 'delayed TTS' and/or 'rebound recovery'. The maximum TTS was observed at 1 h after exposure, but the observation of a delayed recovery and a rebound recovery indicate that audiometric tests should be performed in all cases at least up to 4 h after the exposure. More detailed work is necessary to establish what changes may be necessary in the present damage risk criteria for impulse noises of a very high level.

Adult↗