Effect of periodic rest on hearing loss and cochlear damage following exposure to noise

Changes in hearing sensitivity and cochlear damage were determined in two groups of chinchillas exposed to an octave band of noise (OBN) centered at 0.5 kHz, 95 dB SPL on two different schedules: 6 h per day for 36 days, or 15 min/h for 144 days. Hearing sensitivity was measured behaviorally at 1/4-oct frequency intervals from 0.125 to 16.0 kHz before, during, and for a period of 1 to 2 months after the exposure, at which time the animals' cochleas were fixed and prepared for microscopic examination. Cochlear damage was determined by counts of missing sensory cells. Both exposures produced an initial shift of thresholds of 35-45 dB; however, after a few days of exposure, thresholds began to decline and eventually recovered to within 10-15 dB of original baseline values even though the exposure continued. Measures of recovery made after completion of the exposures indicated minimal permanent threshold shifts in all animals. The behavioral and anatomical data indicated that these intermittent exposures produced less temporary and permanent hearing loss and less cochlear damage than continuous exposures of equal energy.     

Auditory hazard from airbag noise exposure

Airbag deployment includes very intense acoustic stimulation, yet almost no tests of auditory hazard have been done with real ears. Therefore 32 anesthetized cats, positioned at the driver and passenger locations in a pickup truck, were exposed in pairs to one airbag deployment (electrically initiated). Hearing was tested at 1, 2, 4, 8, and 16 kHz by evoked-response audiometry just before exposure, immediately after and at 1 month and 6 months. Exposure conditions included doors open, compartment closed, and closed compartment sealed with tape: seven exposures to passenger bag only and nine to driver and passenger bags. Peak pressures ranged from 167 to 173 dB with unweighted energies as high as 4000 J/m2 (or 8 hr LEQA = 95.5 dB). The immediate threshold shift averaged 60 dB at 4.0 kHz that resolved to an average permanent shift of 37 dB. By extrapolation, these data from cats may indicate that susceptible human ears risk permanent hearing loss from airbag noise.     

Hearing loss from simulated work-week exposure to impulse noise.

Six monaural chinchillas were exposed to a repetitive, reverberant, impulse noise for a total of five days, 8 h per day. The average peak overpressure within the holding cage was 113 dB. The reverberation time (pressure fluctuation envelope within 20 dB of peak) was 160 ms. Auditory thresholds were measured at 0.25, 0.5, 1, 2, 4, and 8 kHz before and after each day's exposure using either the average-evoked response technique or shock avoidance conditioning. After the last exposure, recovery was monitored for five successive days. Final thresholds were obtained starting at 30 days postexposure after which the animals were sacrificed for cochlear histology. The high frequencies (4, 8 kHz) showed a daily median shift of 40 dB and a 27 dB recovery before the following day's exposure. The low frequencies (0.25, 0.5 kHz) were shifted 35 dB after each day's exposure with a 15 dB recovery overnight. Final median audiograms showed little permanent threshold shift. The cochleagrams for two test animals were found to be normal while the remaining four displayed 10%--40% losses in hair cells at specific cochlear sites.     

Relationship between exposure to multiple noise sources and noise annoyance

Relationships between exposure to noise [metric: day-night level (DNL) or day-evening-night level (DENL)] from a single source (aircraft, road traffic, or railways) and annoyance based on a large international dataset have been published earlier. Also for stationary sources relationships have been assessed. Here the annoyance equivalents model concerning noise annoyance from combined sources and the underlying assumptions are presented. The model first translates the noise from the individual sources into the equally annoying sound levels of a reference source, road traffic, and then sums these levels giving total level L. The annoyance from the combined sources is found by substituting exposure L in the road traffic exposure-annoyance relationship. The most important assumption, independence of the contributions of the sources, is discussed. It appears that independence will be violated substantially only due to the effect of the presence or absence of a quiet side of building which is not incorporated in the model. For use in practice the application of the model is broken down in five steps. The step by step procedure can be used for the assessment of the total noise level and the associated total annoyance on the basis of the DNL or DENL values of the individual sources.     

Assessment of community noise exposure from rifle shooting

A study of noise conditions around a suburban rifle range was carried out in conjunction with a social survey of nearby residents. These studies were aimed at providing some information on the relationship between noise levels from rifle shooting and human reaction to the noise. The exposure at each surveyed residence was calculated in terms of eight exposure measures. All units gave similar low correlations with residents' reactions, but from other points of view the energy-mean value of the Sound Exposure Level (possibly A-weighted) seems the most useful unit. Units relying on the peak overpressure would not be generalizable to other impulsive noise sources. Even in the case of Sound Exposure Level, the relationship between exposure and reaction is not generalizable to non-impulsive noises, such as aircraft overflights, without some “correction”. This indicates that units such as L_dn in which noise exposures from different sources are added on an energy basis are inappropriate for measurement of rifle noise. Noise from the range was found to be very directional, and variable between days. It therefore appears that accurate characterization of such noise requires comparatively extensive measurements on a number of days.     

Noise dosimeter for monitoring exposure to impulse noise

Commercially available noise dosimeters do not perform properly in impulsive noise environments because they suffer from instrumentation limitations and lack metrics that characterize impulse noise. In this paper, a design concept is proposed for an impulse noise monitoring dosimeter that addresses the current dosimeter’s limited capabilities and describes the various parameters that can appropriately be used to measure and evaluate exposure to impulse noise. The design concept is based on the accurate acquisition and storage of the original impulse waveform. For data analysis (using MATLAB) and calculation of “impulse noise metrics,” National Institute for Occupational Safety and Health (NIOSH) used a prototype impulse noise dosimeter system that consisted of a Bruel&Kjaer 4136 microphone and a Panasonic Digital Audio Tape Recorder. The proposed instrument would enable collection of data for validation of presently defined and yet to be defined metrics quantifying noise-induced permanent threshold shifts (NIPTS) resulting from impulse/impact exposures. It will also enable occupational safety and health professionals to make accurate measurements of ultimately approved metrics.     

General transformations from multiplicative noise to additive noise

General transformations from multiplicative noise to additive noise are obtained for systems whose dynamical evolution is given by multidimensional Langevin equations.     

The UK noise climate 1990-2001: population exposure and attitudes to environmental noise

During 1999-2001 the building research establishment (BRE) undertook a measurement based survey of environmental noise levels and a social survey of population attitudes to environmental noise in the UK. The surveys involved a total of 1160 24-h noise measurements at a sample of dwellings in the UK, and over 5500 in-depth interviews with a sample of the UK adult population. Both samples were of a clustered random design, and were representative of the UK population. The results of the surveys have been compared with those from similar surveys undertaken by BRE in 1990/1991 and are currently being used to help formulate a more strategic approach to the control of environmental noise both nationally and in London.     

Industrial noise and its effects on human hearing

The effects of industrial noise on hearing loss of workers in Cyprus was studied over the period from 1996 to 1999. Measurements of the noise exposure doses of more than 200 workers from 90 Cypriot industries, ranging from timber to food and beverage were evaluated. Audiometric examinations of the studied workers showed that 27.8% suffered some hearing damage while 7.7% suffered serious hearing loss.     

Response to changes in noise exposure: testing a model

Data gathered in the course of a large-scale study of the subjective effects of change in household exposure to traffic noise have been used to test a model of response which is specifically intended to apply to noise control measures. Analysis shows that the model is no more and no less successful in predicting response to change than empirical dose-response relationships. This implies that the discrepancy between steady-state response and response after change in exposure is not explicable in terms of changes in either traffic composition or the difference between annoyance threshold and actual exposure.