Damage Risk Criteria Research Articles

Objective measurements of the singer's voice as a “damage risk” indication

Professional singers, particularly beginning performers, seldom have any objective means to determine safe performance limits of their voices, and so must rely on trial and error experience to know what singing ranges are feasible for the individual. This almost invariably leads to vocal difficulty, ranging from simple laryngitis to chronic, profession threatening vocal pathology. This presentation will discuss normative data on the singer's voice, particularly with respect to the physiological and acoustic limits of the instrument measured in a “F0-SPL Profile.” Examples of professional performers' voice profiles will be used to illustrate the usefulness of the technique in estimating a type of damage risk criteria for voices.

Loss of auditory sensitivity following exposure to spectrally narrow impulses.

Damage-risk criteria (DRC) for impulse noise do not presently take the spectrum of an impulse into direct account; yet it is clear that the ear is spectrally tuned. In order to establish the sensitivity of various sections of the cochlear duct to trauma from impulses, ears were exposed to 100 spectrally narrow impulses (1.0, 5.0, or 10.0 kHz) delivered in 10 min. Changes in auditory sensitivity were measured by an electrocochleographic technique in 43 cat ears and a threshold of loss established for each type of impulse. Expressed in SPL at the ear drum, the loss threshold rose at 3.2 dB/octave between 1.0 and 10.0 kHz. Expressed in stapes displacements, the loss threshold fell at 5.4 dB/octave in the same region. This curve was used to establish a tentative shape for a DRC for the human ear for impulse noise. The patterns of loss, rates of loss, lack of recovery, and loss thresholds are discussed with respect to their probable physiological basis with conclusion that mechanical displacement rather than metabolic exhaustion is the most reasonable causative factor.

Spectrum as a factor in rating the hazard from intense acoustic transients

It is generally agreed that the ear is spectrally tuned; yet neither of the two damage‐risk criteria (DRC) for impulse noise in use in the world today specifically takes spectrum into account. At a recent meeting of the Acoustical Society an analysis was presented, based on the combined responses of the inner, middle, and external ears, which produced a curve showing the relative hazard from impulses with spectral peaks in various locations [G. R. Price, J. Acoust. Soc. Am. 62, S95(A) (1977)]. This approach has been carried further, and when coupled with the concept of a critical level for intense stimulation, has led to a new form for a DRC for impulse noise. This formulation rates the hazard differently than the previous DRCs and appears to be in consonance with the available data on hearing changes from impulsive stimulation. It is formulated so that the risk to varying proportions of the population for varying numbers of impulses can be rated, as well as the effectiveness of various hearing protectors. This analysis also generates a rationale for rating the hazard from stimulation below 130 to 140 dB SPL according to a different rule.

Growth of TTS as a function of the duration of impact noises

The effect of the duration of impact noises was investigated to assess the importance of this variable in establishing hearing damage risk criteria. Fifteen normal listeners were exposed to repeated series of 60 impacts presented once every 2 s at increasing peak levels from 107 dB SPL up to an individual critical level (CL). The CL was defined as the peak level producing a TTS3 of 15 dB at one frequency. Six different impact noises were studied. In each case, their average spectrum showed a maximum amount of energy in the third-octave band centered at 3.15 kHz. The e duration (the time for the pressure envelope to decay to 8.7 dB of its initial peak level) ranged from 20 to 210 ms. Results indicated that amounts of TTS3 at 4, 6, or 8 kHz are not a linear function of the impact energy but rather an exponential one. Moreover, data analysis confirmed, for each impact duration, that the TTS grows exponentially with the peak-pressure level of the noise. It also showed that the rise time may not be a highly relevant variable for predicting TTS from impact noise.

Hazard from gunfire impulses with peak energy at low frequencies

A tentative damage-risk criterion (DRC) for impulse noise was derived from theoretical and empirical considerations [G. R. Price, J. Acoust. Soc. Am. 62, S95(A) (1977)]. It predicted that gunfiretype impulses with their energy peaks at low frequencies would be less hazardous than impulses with peak energies in the midrange, which is contrary to the prediction from the currently accepted DRC [CHABA. Rep. WG-57 (1968)]. As a first step toward determining the validity of this position, 13 restrained, unanesthetized, cats were exposed to 60 impulses at 15 per min from a 105MM Howitzer at peak pressures from 158 to 165 dB. Auditory sensitivity was estimated by evoked response audiometry at 2, 4, 8, and 16 kHz. Pre-exposure measures were compared with measures made immediately after exposure, 1 day, and 10 days later. Shifts in sensitivity were small at 158 dB and much larger at the higher intensities. Higher intensities were accompanied by blood spots on the tympanic membrane, although without visible perforations. Later measures showed some recovery of sensitivity, although large initial losses are associated with long lasting shifts. The loss for this particular exposure begins, by extrapolation, at just under 158 dB and grows very rapidly with increases in intensity.

Threshold shifts in chinchillas exposed to octave bands of noise centered at 63 and 1000 Hz for three days(a).

Audiograms were obtained on eight binaural chinchillas trained on a shuttlebox avoidance procedure. Four of the animals were exposed to three successive levels of an octave band of noise centered at 63 Hz: 100 dB SPL (74 dBA), 110 dB SPL (84 dBA), and 120 dB SPL (94 dBA). The other four animals were also exposed to three successive levels of an octave band of noise centered at 1000 Hz: 75 dB SPL (75 dBA), 85 dB SPL (85 dBA), and 95 dB SPL (95 dBA). All exposure durations were 75 h. Little threshold shift (TS) resulted from the lower two exposure levels of the 63-Hz noise band. At the 120-dB exposure level, maximum TS of 43 dB occurred at 2000 Hz. Permanent threshold shifts (PTSs) of 16 dB at 2000 Hz and 11 dB at 1400 Hz were found. Exposure to the three levels of the 1000-Hz noise band produced TSs of 20, 45, and 61 dB at 1400 Hz. The 95-dB exposure level resulted in PTSs of 6 dB at 1400 Hz and 9 dB AT 2000 Hz. The major results were (1) high-frequency hearing loss to a low-frequency noise and (2) that noise bands matched within 1 dBA were not equally hazardous as dictated by damage-risk criteria. The 63-Hz noise band produced nearly twice as much PTS as the 1000-Hz noise band.

Importance of the waveform of the impulse in formulating an Impulse Noise Damage Risk Criteria

Two experiments show the importance of the microstructure of the impulse in producing cochlear lesions and hearing loss. One group of chinchillas was exposed to 50,155 dB, 1-msec A-duration waves and another group was exposed to nominally the same impulse except that the rarefaction phase of the impulse was increased from 2.5 to 4 msec. The animals exposed to the larger duration waves developed 45 dB TTS (X̄,1,2,2.8 kHz) while the animals exposed to the shorter duration impulses developed less than 20 dB TTS. In a second experiment, two groups of five chinchillas were exposed to 50,158 dB, 40-msec A-duration impulses or the same wave with two low level reflected components. The animals exposed to the “clean” impulses had no PTS and only slight hair cell loss, while the animals exposed to the impulse with reflections developed 20–30 dB PTS (X̄2,4,8 kHz) and corresponding lesions in the base of the cochlea. These results point out the pitfalls of establishing a Damage Risk Criteria for Impulse Noise on the basis of only the amplitude and duration of the impulse. [Work partially supported by National Institute for Occupational Safety and Health, Public Health Services, Department of Health, Education and Welfare, Grant No. 1-R01-OH-00364.]

The Effects of Noise on Hearing

This 579-page volume represents the proceedings of a symposium on the effects of noise on hearing sponsored by the National Institute for Occupational Safety and Health. The contributors include 40 experts from the fields of acoustics, anatomy, physiology, audiology, epidemiology, otolaryngology, and biochemistry who were invited to write critical essays on this issue. The book is divided into six sections. The first of these puts the problem of noise pollution into perspective. The second and third sections outline the current understanding of the anatomical, biochemical, and physiological changes underlying noise-induced hearing loss. The fourth section reviews the contributions of animal research. The fifth section integrates information from demographic studies, and the final section deals with scientific medical and legal considerations for establishing a damage-risk criteria. There are numerous black-and-white illustrations and charts. The references are excellent and the post-chapter discussions taken from the symposium make the presentation especially valuable. This

Threshold shifts in chinchillas exposed to low-frequency noise

Audiograms were obtained on eight binaural chinchillas trained on a shuttlebox avoidance procedure. Four chinchillas were exposed to three successive levels of an octave band of noise centered at 0.063 kHz: 100 dB SPL (74 dBA), 110 dB SPL (84 dBA), and 120 dB SPL (94 dBA). The other four chinchillas were exposed to these successive levels of an octave band of noise centered at 1.0 kHz: 75 dB SPL (75 dBA), 85 dB SPL (85 dBA), and 95 dB SPL (95 dBA). All exposures lasted 72 h. Maximum amounts of threshold shift (TS) of 20, 40, and 60 dB were found for the 1.0-kHz exposures at 1.4 or 2.0 kHz. At the highest level a 10-dB shift was present 30 days postexposure. Little TS was found for the 0. 063 kHz exposure at 100 and 110 dB. At the 120-dB exposure a TS of about 40 dB was found at 2.0 and 4.0 kHz and 10 dB remained at 2.0 kHz 30 days postexposure. Implication for human damage risk criteria will be discussed.

Diving Injuries to the Inner Ear

Most of the previous literature concerning otologic problems in compressed gas environments has emphasized middle ear barotrauma. With recent increases in commercial, military, and sport diving to deeper depths, inner ear disturbances during these exposures have been noted more frequently. Studies of inner ear physiology and pathology during diving indicate that the causes and treatment of these problems differ depending upon the phase and type of diving. Humans exposed to simulated depths of up to 305 meters without barotrauma or decompression sickness develop transient, conductive hearing losses with no audiometric evidence of cochlear dysfunction. Transient vertigo and nystagmus during diving have been noted with caloric stimulation, resulting from the unequal entry of cold water into the external auditory canals, and with asymmetric middle ear pressure equilibration during ascent and descent (alternobaric vertigo). Equilibrium disturbances noted with nitrogen narcosis, oxygen toxicity, hypercarbia, or hypoxia appear primarily related to the effects of these conditions upon the central nervous system and not to specific vestibular end-organ dysfunction. Compression of humans in helium-oxygen at depths greater than 152.4 meters results in transient symptoms of tremor, dizziness, and nausea plus decrements in postural equilibrium and psychomotor performance, the high pressure nervous syndrome. Vestibular function studies during these conditions indicate that these problems are due to central dysfunction and not to vestibular end-organ dysfunction. Persistent inner ear injuries have been noted during several phases of diving: 1) Such injuries during compression (inner ear barotrauma) have been related to round window ruptures occurring with straining, or a Valsalva's maneuver during inadequate middle ear pressure equilibration. Divers who develop cochlear and/or vestibular symptoms during shallow diving in which decompression sickness is unlikely or during compression in deeper diving, should be placed on bed rest with head elevation and avoidance of maneuvers which result in increased cerebrospinal fluid and intralabyrinthine pressure. With no improvement in symptoms after 48 hours, exploratory tympanotomy and repair of a possible labyrinthine window fistula should be considered. Recompression therapy is contraindicated in these cases...

B-duration impulse definition: Some interesting results

Impulse noise is arbitrarily described as either an A or B duration impulse: (1) an “A” type is a free-field impulse where there is no reverberation component and the “A” refers to the duration of the maximum overpressure. (2) A “B”-type impulse is either an inherently reverberant impulse or an A-type impulse in an acoustically hard environment. The B-duration is, by definition, the impulse duration to a point on the total wave envelope 10 or 20 dB down from the peak. Two groups of chinchilla were exposed to 40-μsec A-duration impulses with a peak PLS of 158 dB. The first group of animals suffered minor TTSmax of about 20 dB at 4 kHz and virtually no PTS or hair cell loss. The second group of animals had large values of TTS (65–70 dB TTSmax at 4 kHz) that resolved to a 25 dB PTS at 4 kHz with concommitant severe cochlear lesions. The increased trauma suffered by the second group is apparently the result of the accidental addition of a reflected wave component that trailed the A-duration impulse. The reflected wave was 10–20 dB down from the initial peak and, therefore, might be discounted by the existing damage risk criteria or by using the B-duration measurement scheme. However, the data do suggest a temporal interaction between these two relatively innocuous impulses that is not accounted for within the present framework of the A- and B-duration concepts. Ultimately, these fortuitous results can be important in showing the necessity of specifying the total waveform when describing an impulse noise.

Toward damage risk and habitability criteria for pure-tone pulse trains.

Reports from this and other laboratories are summarized to the effect that pulse trains in the 3–4-kHz region, with pulse duration ?1 sec and with on fractions up to 0.05, are habitable when presented a round the clock for weeks, and yield no TTS greater than can be borne, when the level does not exceed 85 dB SPL. For more onerous acoustic loads, a damage risk criterion of 80 dB should be set for long-lasting continuous exposures. The ear is more susceptible to this sort of acoustic load than is any other system of the body, and can serve as an early warning device for potential damage to those systems. Subject Classification:[43]65.50,[43]65.64, [43]65.66.

Damage risk criteria for hand-transmitted vibration : D.E. O'Connor and T.I. Hempstock 1975. United Kingdon Informal Group Meeting on Human Response to Vibration, University of Southampton, 1–4. (4 pages, 3 tables, 3 references)

Damage risk criteria for hand-transmitted vibration : D.E. O'Connor and T.I. Hempstock 1975. United Kingdon Informal Group Meeting on Human Response to Vibration, University of Southampton, 1–4. (4 pages, 3 tables, 3 references)

Evaluation of human exposure to hand-transmitted vibration

The relative importance of some of the parameters instrumental in the production of Vibration Induced White Finger have been identified. Difficulties encountered in the measurement of the vibration signal are mentioned, and possible means of overcoming them discussed. The problems of setting up a damage risk criteria are looked at and reference is made to a number of proposed criteria. Particular reference has been paid to the relevance of a new draft British Standard and the way in which it deals with a number of spectra relating to different processes known to cause Vibration Induced White Finger.

Symposium: new data for noise standards. I. New data for noise standards.

AbstractContinuous and impulse noises, considered “safe” by existing damage risk criteria were combined to model more realistic noise environments. Monaural chinchilla were exposed to one of the following conditions: a. 50 impulses with a 40 m̈, sec A‐duration at 158 db SPL peak pressure, 1/ minute; b. 95 db SPL continuous noise at 2–4 kHz for one hour; and c. superimposed combination of the continuous and impulse noise. Quiet thresholds were measured before and after exposure using the auditory evoked response, and histology was obtained, using the surface preparation technique. The audiometric and histological findings agree in showing that the superimposed combination of two “safe” noises produces traumatic effects that more than exceed the additive effects of either component. The existing damage risk criteria do not provide guidelines for such noise combinations.

Audiometric and histological effects of exposure to three levels of reverberant impulse noise

Monaural chinchillas were exposed to 140, 150, or 155 dB peak SPL impulses with 200-msec B-duration. Each animal received 50 impulses, 1/min. Thresholds were estimated by the auditory evoked response technique at 0.5, 1, 2, 4, and 8 kHz before and after exposure. Animals were sacrificed at 30 days postexposure for surface preparation. The 140-dB group sustained no permanent hearing losses and had normal cochleas. The cochleas of the 150-dB group ranged from normal to severe losses of both OHC and IHC. The 155-dB group had consistently large cochlear lesions. The magnitude of cochlear lesions is not always completely reflected in the audiograms. The cocklear lesions induced by the reverberant impulse are compared to the lesions caused by 1-msec and 40-μsec A-duration impulses. Finally, the data are discussed in terms of the present impulse noise damage risk criteria. [Study supported by Grant No. 1RO1 OH 00364-01, National Institute for Occupational Safety and Health, Public Health Service, Department of Health, Education and Welfare.]

On the Trading Relation between Time and Intensity for Intermittent Noise Exposures

Present damage-risk criteria (DRC) are based almost exclusively on studies of the effects of continuous 8-h/day noise exposures. However, most actual daily exposures are intermittent in nature. Therefore a series of 8-h exposures to intermittent noise was undertaken in order to determine whether the trading relation between level and time should be 3 dB per doubling time, as advocated by ISO, or 5 dB, as incorporated into present American DRC. The results of studies with on-fractions of 1, 12, 14, and 18 periods of 90 sec, 9 min, and 40 min indicate that a trading relation of 5 dB per doubling time will keep constant a 6- to 20-dB TTS2 produced by a 4000- or a 1000-Hz octave band of noise. In the case of a 250-Hz octave band, a TTS2 of 10 dB (the criterion for this octave band, one produced by continuous exposure at about 98 dB SPL) could not be reached even with a level of 115 dB as long as the on-fraction was 12 or less. It is clear that a trading relation of 5 dB per doubling time is more appropriate than 3 dB for intermittent exposures. [Research supported by the National Institute for Occupational Safety and Health, Public Health Service.]

Interaction of continuous and impulse noise: audiometric and histological effects.

Continuous and impulse noises were combined to model more realistic noise environments. Monaural chinchillas were exposed to one of the following conditions: (a) 50 impulses with 40-μsec. A duration at 158-dB-SPL peak pressure, 1/min; (b) 95-dB-SPL continuous noise at 2–4 kHz for one hour; (c) superimposed combination of the continuous and impulse noise; (d) 50 impulses with a 40-μsec. A duration at 175-dB-SPL peak pressure, 1/min; (e) interrupted combination of the continuous and impulse noise with the continuous noise off for 2 sec during the impulse delivery. Quiet thresholds were measured before and after exposure using the auditory evoked response and histology was obtained using the surface preparation technique. The audiometric and histological findings agree in showing that the superimposed combination of two noise exposures, shown to be safe for the chinchilla, produces traumatic effects that more than exceed the additive effects of either component. The existing damage risk criteria do not provide guidelines for such noise combinations.

Letter: Susceptibility to damage from impulse noise: chinchilla versus man or monkey.

Behavioral audiograms were taken on five surgically monaural chinchillas at 0.75, 1.5, 4.0, 6.0, 7.9, 11.0, 14.5, and 16.5 kHz. After exposure to 1 to 4 impulses of 168-dB peak SPL and 60-μsec A-wave duration, temporary threshold shift was monitored at 1.5, 6.0, and 14.5 kHz for 32 days and complete audiograms taken at 64 days post-exposure. Shifts were similar to those found by other researchers who have exposed the chinchilla to similar impulses, but were larger than those seen in monkeys and men exposed to the same impulse noise source. Cochlear hair cell losses for the five subjects exposed to one to four impulses were small and not significantly different from those of five others exposed to 10 to 40 impulses (but not tested behaviorally). The conclusions paralleled those of Hunter-Duvar and Elliott [J. Acoust. Soc. Am. 52, 1181–1192 (1972)] in that stimulation “sufficient to produce permanent threshold shifts of 10–20 dB may not produce anatomical injuries to the organ of Corti that are detectable by phase microscopy.” Caution was urged in generalizing the results of impulse noise studies in chinchilla to human damage risk criteria. The use of pre-exposure impedance measures to rull out middle ear conductive losses was also suggested for future studies.

Impulse noise damage risk criteria

New possibilities for unification of impulse noise damage risk criteria with the “immision” principle of equivalent A-weighted sound energy for continuous noise exposure are presented and discussed.