Objectives—To investigate the relation between diVerent types of exposure to noise and a classic sign of noise induced hearing loss (NIHL), the audiometric notch. Methods—The study sample had exposure to both continuous and impulse noise and was drawn from a population of electrical transmission workers. Audiograms, taken as part of a hearing conservation programme, were read by three clinicians experienced in the assessment of NIHL. Working independently and using their clinical judgment, they were asked to identify localised increases in the threshold of hearing (audiometric notches) which they would attribute to noise, had a suitable history of exposure been elicited. Prevalent cases of NIHL were identified by the presence of a notch in either ear. Risk factors for NIHL were assessed by a questionnaire which sought information about exposure to air blast circuit breaker noise; firearms; explosions, and continuous noise. The odds of exposure to these factors in those with and without hearing loss were calculated, and odds ratios (ORs) and 95% confidence intervals (95% CIs) were estimated by logistic regression. Results—Of the 648 questionnaires sent out 357 were returned, a response rate of 55%. Of these, at least two out of the three assessors identified 175 (49%) people with a notch at any audiometric frequency. There was no association between these cases and the NIHL risk factors identified by the questionnaire, but a further frequency specific analysis showed a small proportion of people (15 (4%)) with notches at 4 kHz who had the expected associations with exposure to noise and a significant OR for firearms of 4.25 (95% CI 1.28 to 14.1). The much larger proportion of people with 6 kHz notches (110 (31%)) did not show these associations. Conclusions—To diagnose NIHL it is important to elicit a detailed and accurate history of exposure to noise: although the notch at 4 kHz is a well established clinical sign and may be valuable in confirming the diagnosis, the 6 kHz notch is variable and of limited importance. (Occup Environ Med 2001;58:46‐51)

https://oem.bmj.com/content/oemed/58/1/46.full.pdf

Audiometric notch as a sign of noise induced hearing loss.

Current mitigation levels for noise transients impinging on marine mammals are specified by rms pressures. The rms measure critically relies upon choosing the size of averaging window for the squared pressures. Derivation of this window is not standardized, which can lead to 2-12 dB differences in rms sound pressure for the same wave forms. rms pressure does not represent the energy of the noise pulse and it does not prevent exposure to high peak pressures. Safety levels for transients should therefore be given by received peak-peak sound pressure and energy flux density instead of rms sound pressure levels.

/pdf/marine-mammals-and-noise-problems-with-root-mean-square-3pivb323nb.pdf

Marine mammals and noise: Problems with root mean square sound pressure levels for transients

Technology needed to predict damage and hazards from explosions of propellant tanks and bursts of pressure vessels, both near and far from these explosions is introduced. Data are summarized in graphs, tables, and nomographs.

Workbook for predicting pressure wave and fragment effects of exploding propellant tanks and gas storage vessels

On the basis of the impulse diagrams of various weapons and many audiometric tests, the CHABA impulse‐noise damage‐risk criteria (DRC) are compared with those of the Federal Republic of Germany. Both DRC indicate maximum permissible exposures in terms of peak‐pressure level and of effective duration. Both DRC aim to protect 95% of the exposed population from permanent auditory damage. The computation of the effective duration differs between the CHABA DRC and the German DRC, and it generally results in a longer effective duration for CHABA. The current study is based on the results for more than 10 000 soldiers, who were audiometrically tested in a mobile monitoring station before firing practice and beginning 2 min after exposure until complete recovery. In a special study, it was possible to compare the results for 478 German soldiers and to evaluate the relative value of the CHABA DRC and the German DRC. This comparison showed that the CHABA DRC are too restrictive, permitting unnecessary ’’less maximum permissible load’’ than the German DRC. Moreover, owing to the large variability in TTS2, measurement of the whole recovery time beginning 2 min after exposure has a greater predictive value. Therefore, recovery time should be used in the evaluation of the DRC.

Danger of auditory impairment from impulse noise: A comparative study of the CHABA damage-risk criteria and those of the Federal Republic of Germany.

The purpose of this study was to conduct an acoustic analysis of incubator noise under two conditions: when the incubator was associated with different types of life-support equipment; and when impulse noise was created by striking the side of the incubator or by opening and closing the doors of the storage unit. It was found that the life-support equipment increased the overall noise levels of incubators by as much as 15 to 20 dB. Much of this increased energy was in the high frequency region. Impulse signals created by striking the side of the incubator ranged from 130 to 140 dB. A representative impulse for opening the incubator was 92.8 dB, whereas closing the door produced a peak amplitude of 114 dB.

Further observations on noise levels in infant incubators.

This paper presents impulse‐noise damage‐risk criteria based on conclusions of independent British and American studies and on the work of other research workers in this field. Most of the studies that led to this criterion were performed with noise from small arms, but the criterion is general enough to permit assessment of most other types of impulse noise. The variables that must be considered in determining the potential hearing hazard and in the practical application of the criteria are presented, and the parameters that must be measured are defined. The measurement technique and type of transducers to be used are discussed.

Hazardous Exposure to Impulse Noise

: Criteria are presented for assessing damage risk from impulse-noise exposure. The criteria are based on conclusions of independent British and American studies and on the work of other research workers in this field. Most of the studies which led to these criteria were performed with noise from small arms, but the criteria are general enough to permit assessment of most other types of impulse noise. The variables which must be considered in determining the potential hearing hazard and in making practical application of the criteria are presented, and the parameters which must be measured are defined. The measurement technique and type of transducers to be used are discussed.

/pdf/criteria-for-assessing-hearing-damage-risk-from-impulse-2p41gcsjsw.pdf

Christopher G. Rice

Papers

Hazardous Exposure to Impulse Noise

Criteria for Assessing Hearing Damage Risk from Impulse‐Noise Exposure