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Noise, the Silent Killer
Abstract
Noise, the 'unwanted sound', is now realised as one of the most important environmental hazard in the present day industrial world. Exposure to noise is imminent, spearheaded by man's casual attitude and ignorance of its effects. Thus, the indiscriminate hooting of horns and shrieking of loudspeakers continue unabated and disturb man's peace and tranquility. Noise leads to impaired hearing and causes general stress resulting in rise of blood pressure, enhanced sweating, muscle cramps, changes in cardiac functions and biorhythm, and increase in blood cortisol and cholesterol. Defence Institute of Physiology & Allied Sciences (DIPAS), DRDO, has been working towards combating noise pollution for over the last four decades for both the Defence Forces and for the civilians. In the Armed Forces, personnel are exposed to noise resulting from arms and ammunitions, gun and artillery firings, movement of heavy armoured vehicles, flying of aircraft and helicopters, engine rooms of naval ships and submarines etc. The high level of noise experienced by the personnel in their working environment is responsible for impairment in hearing functions and liable to trigger adverse reactions in extra-auditory systems. The auditory effects of noise directly influence the peripheral auditory system and the hearing function. Noise encountered by man in his occupational environment could be either loud or impulsive, of short intermittent duration or continuous noise of mixed intensities over a prolonged period. It acts as a biological stressor which results in various non-auditory system responses, leading to physiological and psychological stress. Researches on physiological and psychological effects and on performance and comfort have provided an extensive technology pool that serves as the basis of exposure guidelines, criteria and standards. Controlling noise and safeguarding hearing are important environmental issues that need to be addressed with care. The ill effects of noise on the auditory system may be alleviated by adequate hearing protection with the use of appropriate ear defenders, electronic noise reducing head sets, inhalation of carbogen (gas mixture of 5% CO2 and 95% O2), supplementation with antioxidants and restricted working time in noise environment as per the laid down environmental safety guidelines. These and other management techniques including use of musical sounds may also be useful in coping with the extra auditory effects of noise.
... However, ground vehicles, other air-craft, watercraft, communication systems, and industry-type activities also serve as sources of potentially damaging noise. [8] According to Annual Benefits Report 2013, the two most prevalent service connected disabilities for veterans in the United States at the end of fiscal year 2012 remain tinnitus and hearing loss, with tinnitus affecting 115,638 veterans (9.7%) and hearing loss affecting 69,326 veterans (5.8%). In Finland, despite the increasing use of hearing protection devices, a large proportion of professional soldiers experience disabling tinnitus and hearing loss. ...
Objective:
Hearing plays a crucial role in the performance of a soldier and is important for communication and speech processing. Service personnel are constantly exposed to high levels of noise and hence predisposed to occupational health disabilities, principally noise-induced hearing loss (NIHL) and tinnitus. NIHL is a significantly common impairment in the military and can affect the warfare performances. Parochial awareness about the effects of uproarious noise which exacerbates their hearing, acceptance rate of use of hearing protection devices and follow-up audiological tests have become the major drawback for prevention of NIHL and are less pondered upon.
Method:
The present study focuses on the effects of noise on the hearing of service crew operating and maintaining military equipment and explores the efficacy of DPOAE's to substitute pure tone audiometry as a quick, easy to operate and implementable test technique for monitoring of hearing status.
Results:
The results suggest that DPOAE test is important and more coherent than audiometry alone for the early detection of cochlear injury due to noise from military operations and efficacious for detecting NIHL.
... Exposure to intense noise is known to cause damage to the hearing apparatus of man and it also implicates various non-auditory systems of the body through the secondary pathways [1][2][3][4][5][6][7][8][9][10][11] . In the defence and civil sectors, different types of machines, equipment, systems and processes, while in operation give rise to an environment full of noise. ...
p>Seafarers are exposed to intense noise due to running of powerful gas turbines present in the engine room and in other compartments due to the operation of various sub systems that adversely affect their hearing acuity and proficiency. A large body of persons is employed in the Shipping industry and it is of paramount importance to preserve and promote health in the work place. Hence, this particular study was undertaken with a view to precisely quantify the noise levels associated with the operation of turbine engines and examine the impact of exposure on hearing sensitivity of the individuals. The preventive measures that can control the adverse effects like the use of ear defenders, and, supplementation of carbogen, a mixture of 5% CO2 and 95% O2 were examined</p
... One of the most important sources of noise pollution is industrial noise. Meanwhile, 16% of incapacitating and irreversible cases of hearing loss in adults are caused by exposure to occupational noise worldwide (1,2). The effects of noise exposure on the auditory system in working populations have been recognized in several countries (3)(4)(5). ...
The article is an attempt to delve into the complex interplay between physical and psychological wellness, for pre, during and post-pandemic span, concentrating on the influence of noise levels. This conceptual investigation aims to categorise the documented studies into different sections and explicate their comparison pertaining to the dimensions and outcomes of the studies. A conceptual framework that aligns with the dimensions has been structured, in reference to the prior studies, and has been validated in aggregate. The path model substantiates how exposure to noise has positive, as well as, negative impacts on physiological and mental health, further, resulting in affirmative or damaging results on human wellness and productivity. In addition, the paper is a contribution to the theoretical domain which endeavours to identify the research voids and suggests new arenas for future research. The outcomes will facilitate the health care policymakers for formulating policies for promoting health, besides, the academic researchers to investigate, globally.
The relative hazard posed to the peripheral auditory system by impact/impulse and continuous noise of the same power spectrum was determined. Impact noise was generated by striking a nail with a hammer and was digitally recorded. The acoustical power spectrum of the impact was determined and pink noise was filtered to produce a continuous noise stimulus with the same acoustic power spectrum. Pre-exposure auditory evoked response (AER) thresholds were obtained at 1, 2, 4, and 8 kHz on 16 adult chinchillas. The pool of animals was divided into two equal groups based upon pre-exposure AER thresholds. One group was exposed to impact noise and the other group to the filtered pink noise. Exposures were 4 h/day for 5 days. Thirty days following the exposure, auditory evoked response thresholds were remeasured. Changes in auditory sensitivity were determined by subtracting the pre-exposure thresholds from the post-exposure thresholds. Hearing threshold shifts of the impact noise group were significantly greater (p less than 0.0001) than the hearing threshold shifts of the continuous noise group. These data indicate a need to more closely examine the parameters and effects of impact noise. There may be a need to develop expanded damage-risk criteria for occupational exposure to impulse/impact noise.
Although accumulating evidence over the past two decades points towards noise as an ambient stressor for children, all of the data emanate from studies in high-intensity, noise impact zones around airports or major roads. Extremely little is known about the nonauditory consequences of typical, day-to-day noise exposure among young children. The present study examined multimethodological indices of stress among children living under 50 dB or above 60 dB (A-weighted, day-night average sound levels) in small towns and villages in Austria. The major noise sources were local road and rail traffic. The two samples were comparable in parental education, housing characteristics, family size, marital status, and body mass index, and index of body fat. All of the children were prescreened for normal hearing acuity. Children in the noisier areas had elevated resting systolic blood pressure and 8-h, overnight urinary cortisol. The children from noisier neighborhoods also evidenced elevated heart rate reactivity to a discrete stressor (reading test) in the laboratory and rated themselves higher in perceived stress symptoms on a standardized index. Furthermore girls, but not boys, evidenced diminished motivation in a standardized behavioral protocol. All data except for the overnight urinary neuroendocrine indices were collected in the laboratory. The results are discussed in the context of prior airport noise and nonauditory health studies. More behavioral and health research is needed on children with typical, day-to-day noise exposure.
Before the opening of the new Munich International Airport and the termination of the old airport, children near both sites were recruited into aircraft-noise groups (aircraft noise at present or pending) and control groups with no aircraft noise (closely matched for socioeconomic status). A total of 326 children (mean age = 10.4 years) took part in three data-collection waves, one before and two after the switch-over of the airports. After the switch, long-term memory and reading were impaired in the noise group at the new airport. and improved in the formerly noise-exposed group at the old airport. Short-term memory also improved in the latter group after the old airport was closed. At the new airport, speech perception was impaired in the newly noise-exposed group. Mediational analyses suggest that poorer reading was not mediated by speech perception, and that impaired recall was in part mediated by reading.
This is a review of the research into endocrine effects of noise since the early 1980s at the Institute for Water, Soil and Air Hygiene. According to our knowledge, no other group has studied systematically the endocrine effects of acute and chronic noise exposure. Mechanisms of acute noise-induced stress reactions as well as long-term increase of stress hormones in animal and persons under chronic noise exposure were studied. Our theoretical background was Henry's psychophysiological stress model with the two reaction alternatives : (i) The fight-flight reaction, characterised by an increase in adrenalin and noradrenaline (ii) The defeat reaction with increased cortisol. Extremely intense acute noise exposure near the threshold of pain caused an increased release of cortisol from the suprarenal cortex but acute noise exposure with levels between 90 and 100 dB(A) caused an increase of catecholamines. Non-habituated noise increased primarily the release of adrenalin from the suprarenal medulla, whereas habituated noise caused a chronic increase of noradrenaline from the sympathetic synapses under longterm noise exposure at work. Environmental noise exposure (Leq >/= 60 dB(A)) caused catecholamine increase if activities such as conversation, concentration, recreation etc were disturbed through noise. In sleeping persons, traffic noise with only Leq >/= 30 dB (A) and Lmax >/= 55 dB(A) caused significant acute increase of cortisol, which developed into chronic increase if the noise exposure was repeated consistently. Parallel to cortisol, chronic noradrenaline increase was also observed. Based upon the empirical results, a noise stress model was developed which is a first step forward in the theoretical understanding of endocrine noise effects.
Exposure to environmental stressors can impair children's health and their cognitive development. The effects of air pollution, lead, and chemicals have been studied, but there has been less emphasis on the effects of noise. Our aim, therefore, was to assess the effect of exposure to aircraft and road traffic noise on cognitive performance and health in children.
We did a cross-national, cross-sectional study in which we assessed 2844 of 3207 children aged 9-10 years who were attending 89 schools of 77 approached in the Netherlands, 27 in Spain, and 30 in the UK located in local authority areas around three major airports. We selected children by extent of exposure to external aircraft and road traffic noise at school as predicted from noise contour maps, modelling, and on-site measurements, and matched schools within countries for socioeconomic status. We measured cognitive and health outcomes with standardised tests and questionnaires administered in the classroom. We also used a questionnaire to obtain information from parents about socioeconomic status, their education, and ethnic origin.
We identified linear exposure-effect associations between exposure to chronic aircraft noise and impairment of reading comprehension (p=0.0097) and recognition memory (p=0.0141), and a non-linear association with annoyance (p<0.0001) maintained after adjustment for mother's education, socioeconomic status, longstanding illness, and extent of classroom insulation against noise. Exposure to road traffic noise was linearly associated with increases in episodic memory (conceptual recall: p=0.0066; information recall: p=0.0489), but also with annoyance (p=0.0047). Neither aircraft noise nor traffic noise affected sustained attention, self-reported health, or overall mental health.
Our findings indicate that a chronic environmental stressor-aircraft noise-could impair cognitive development in children, specifically reading comprehension. Schools exposed to high levels of aircraft noise are not healthy educational environments.
This paper presents the design and implementation of an adaptive feedback active noise control (ANC) system for headphone applications. The ideal position of the error microphone in the ear-cup was studied and determined experimentally, and music signals were used for adaptive system identification of the secondary path. The designed ANC headphone was implemented using the TMS320C32 digital signal processor for real-time experiments. Performance has been evaluated and compared with a high-end commercial ANC headphone using the same set of primary noises including real-world engine noises. Experiment results show the proposed ANC headphone achieves higher noise cancellation, especially for low-frequency harmonics
Noise induced hearing loss (NIHL) is a common cause of preventable sensorineural loss in the adult population. However with stringent legislation, advent of better technology, effective use of protective devices and implementation of regular audiological screening of workers can reduce this occupational hazard.
This paper presents the peak pressure level, frequency spectrum, rise time (ms), B-duration and exposure conditions of individuals of impulsive noise produced by bursting of crackers on a hard ground in a free field environment. These measurements were made for the assessment of auditory risk to users of the firecrackers in light of the exposure condition and the existing safety norms based on peak pressure level and duration of exposure. Further, the auditory hazards to users have been evaluated directly by exposing two groups of subjects to cracker noise of 135-150 dB pk continuously for 30 minutes at 6 meters from the source. Pre and post audiograms were recorded in both the groups to determine the temporary threshold shift (TTS). The audiometry was repeated 1 hour after exposure in both the groups and also 2 hours after exposure in one group to study the recovery status profile and assess time for complete recovery. The risk of auditory hazard from firecracker noise and safe peak pressure level has been discussed.
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.
This important document replaces the 1980 Environmental Health Criteria No.12 – Noise. It is destined to become widely used and quoted in relation to environmental noise problems. All who have even a passing involvement in this area must become familiar with it and with its recommended levels. The Report considers noise sources and their measurement, adverse effects on health and noise management, whilst introducing a new set of recommendations and guideline values to take account of changes in knowledge and expectations over the past 20 years. Attention is drawn to inadequacies of equivalent level for intermittent noises, to the need to consider effects of low frequency noise and to the rights of vulnerable sub-groups. The Guide can be viewed in full on the World Health Organisation website – www.who.org
Active noise reduction (ANR) in headsets promotes the electro‐acoustic cancellation of sound within the ear cups of a hearing protector. Operating at frequencies below 1000 Hz, ANR augments attenuation where passive protection is minimal. Personal ANR can reduce the potential for hazardous noise exposure and can facilitate auditory communications. ANR system performance has been characterized to assist purchasing departments in making informed decisions about commercial devices suitable for use in high‐noise environments such as helicopters and tracked vehicles. Test methods were developed to assess: (a) active attenuation properties, (b) issues of fitting integrity, (c) speech discrimination performance, (d) saturation or overload threshold limit, and (e) general suitability for long‐term use. When properly designed and applied, personal ANR can enhance the listening environment for the user. Nonetheless, performance limitations have been identified in certain devices. Some tended to overload easily or to cease operating under adverse conditions, and others became unstable when the seal around the ear was broken. Proper fitting is pivotal to satisfactory ANR operation, particularly in units with low overload tolerance. Ultimately, the function of any ANR system must be understood in relation to its intended operating environment.
Book on noise effects on man covering audiometry, aural reflex, hearing damage risk, physiological responses, motor performance and speech communication
Temporary threshold shift (TTS) measurements on 11 subjects, resulting from exposures to steady-state noise, impulse noise, and combinations of both types of noise are reported. Twenty minute exposures to wide-band steady-state noise at levels of 78, 84, 90 and 96 dBA, and impulse noise at levels of 96, 102, 108, 114, 120, 126 and 132 dB(peak), and repetition rate of 3.2 pulses/s, were used. When a hazardous level of steady-state noise was combined with various levels of impulse noise, there was a significant reduction in the measured TTS at 4 and 6 kHz. This reduction was greatest when the peak level of the pulse exceeded the r.m.s. level of the steady-state noise by 6-18 dB. When a hazardous level of the pulse was combined with several levels of steady-state noise, no significant reduction in TTS was observed. These findings are interpreted as a result of acoustic reflex stimulation; the pulses superimposed on a hazardous steady-state noise continually re-activated the reflex and prevented fatigue. The converse did not apply, that is, the non-hazardous (but high-level) steady-state noise did not appear to counteract fatigue resulting from hazardous impulse noise.
The purpose of the study was to survey the incidence of noise-induced hearing loss among United States Army troops. Accurate hearing threshold data were obtained from a heterogenous sample of 2726 men representing different branches and lengths of time of active duty. The study provides evidence suggesting that noise-induced hearing loss is the number one hazard to the health of Army personnel. The report summarizes the magnitude of the problem among career Army personnel with over 10 years on active duty.
Audiometric study has been carried out on 45 naval gunnery crew having different lengths of service. With increasing length
of service, the degree of hearing loss increased and was quite conspicuous in subjects with more than 10 years of service.
The nature of audiogram depicted sensori-neural loss in these subjects. Together with bone conduction, air conduction measurements
showed middle ear involvement as well. The speech frequencies were also affected in subjects with more than 10 years of service.
The study explores the effect of occupational noise on oxidative stress status and prophylactic effect of Vitamin E and carbogen (5% CO 2 +95%O 2 ) breathing in alleviating the oxidative damage and conserving the hearing in human volunteers exposed to intense occupational noise. Plasma total antioxidant status, blood glutathione (GSH), malondialdehyde (MDA), antioxidant enzyme activities of GSH peroxidase (EC 1.11.1.9, GPx), superoxide dismutase (EC 1.15.1.1; SOD) in erythrocytes, nitric oxide and nitric oxide synthase in plasma were assessed before and after 6 days of administration of Vitamin E and Carbogen. Results of the study indicate that the exposure to noise for 6 days increased blood concentration of MDA, decreased concentrations of reduced GSH, antioxidant enzyme activity of SOD and plasma total antioxidant status in control (noise) group. Vitamin E- supplemented group showed decline in oxidative stress reflected by significant decrease in blood concentration of MDA and increase in antioxidant enzyme activity of erythrocyte SOD. Results of audiometric studies revealed that breathing of carbogen prevented the development of temporary threshold shift; thereby reducing the risk of noise induced hearing loss.
The study was carried out in 200 male volunteers. They were divided into two groups. The study group was exposed to noise levels of more than 80 dB(A) for more than 8 hours a day for a period of 6 months, working in the steel and hammer industry, whereas the control group was working under normal conditions. The mean age of subjects was 33.33 + 0.867 years and the mean noise level to which they were exposed was 90.34 + 0.781 dB(A). Various autonomic function tests were carried out in both the groups and results were analyzed using Z test. Heart rate was recorded on cardiofax ECG machine and blood pressure (BP) was recorded using sphygmomanometer. The tests depicted significant increase in the mean resting heart rate and the heart rate response to standing (P=0.000), 30:15 ratio (P=0.002), the valsalva ratio (P=0.017), the % change in diastolic BP response to standing (P=0.000) and valsalva maneuver (P=0.000), the systolic BP and diastolic BP after cold pressor test (P=0.000) in study group as compared to the control group. The significant higher results in study group may be attributed to increased sympathetic activity. Thus, noise presents as a significant health hazard. It is recommended that maximum allowable duration of exposure should be reviewed and strictly followed.
Workers in industries with impact noise, as well as soldiers exposed to supersonic blasts from armament and explosive devices, appear to be more at risk for hearing loss than are their counterparts exposed to continuous noise. Alternative considerations for hearing protection are dictated because of a disproportionately increased biophysical response in comparison to continuous noise. Impulse noise is a significant and distinct problem that requires a new strategy for hearing protection. A review of current clinical and occupational literature suggests that impulse noise may be more damaging than continuous sound. Statistical measurements such as kurtosis hold promise for the quantitative prediction of hearing loss. As sound energy to the cell increases, the mechanism of cochlear damage shifts from biochemical injury to mechanical injury. Outer hair cells appear to be more sensitive than inner hair cells to impulse noise because of their energy requirements, which lead to increased production of reactive oxygen and nitrogen species and self-destruction by apoptosis. Hearing protective devices currently in use for impulse noise include hunters' hearing devices, active noise-reduction headsets, and various in-ear plugs, including nonlinear reacting inserts. Existing equipment is hampered by the materials used and by present-day electronic technology. Antioxidants administered before sound exposure show promise in mitigating hearing loss in industrial and combat situations. New materials with improved damping, reflective, and absorption characteristics are required. Hearing protective devices that allow passage of ambient sound while blocking harmful noise might improve the compliance and safety of those exposed. Sensing devices that instantaneously and selectively hyperpolarize outer hair cells are discussed as alternate protection.
Six groups of chinchillas were used. Each exposure group contained five animals. The animals were made monaural onaural by surgically destroying the left cochlea and the animal was then prepared for auditory evoked response recording by implanting a dural electrode over the tentorium. There is a consistent, orderly relationship between the level of impulse superimposed on the continuous noise and the audiologic and histologic effects. The interaction effects between an impulse and continuous noise which individually are deemed as being safe, adds a further complication to the development of noise standards.
Influence of noise spectra on auditory frequencies of 131 audiometrically normal human volunteers was assessed. Each subject was exposed to four different types of noise on different days for a period of 30 min. Noises utilized in this study were broadband noise (100 dBA), broadband noise (BBN) mixed independently with tones of 0.5, 1.2 and 4 kHz at three intensity levels (85, 95 and 105 dBA) and noises of different bandwidths (100 dBA) around the above tones as centre frequencies. BBN produced maximum TTS2 at 4 kHz (21.42 +/- 0.61 to 26.15 +/- 1.00 dB), while concentration of sound energy around these tones, affected hearing at one-half octave above the point of concentration of sound energy. TTS2 produced by 4 kHz tonal component of 95 and 105 dBA and 2 kHz of 105 dBA were significantly higher than the one produced by BBN at 4 kHz. The single tones of 2 and 4 kHz and noise of 1/3rd octave bandwidth (cf 4 kHz) produced TTS2s which were significantly higher as compared to that of BBN at 4 kHz. At the same centre frequency, noise concentrated in thinner bands was more injurious than that in the thicker bands. Lower frequencies of hearing appears to be more resistant to noise as for the same sound pressure level the TTS2 observed in low frequencies was less as compared to higher frequencies.
The therapeutic role of carbogen was evaluated in subjects with sensorineural hearing loss by administering carbogen, a gas mixture of 95 per cent O2 and 5 per cent CO2, for seven consecutive days (30 min/day) and monitoring puretone audiometry before and after the administration. Significant improvement was observed both in air and bone conduction threshold levels on seventh day, indicating that there was some recoverable portion in the hearing level of these subjects. The improvement in hearing may be due to action of CO2 as an otic vasodilator coupled with supplementation of the O2 requirement of degenerating hair cells. Carbogen thus appears to be useful in persons with impaired hearing, involving the inner ear.
A cross-sectional epidemiological survey was carried out in a car-body workshop involving 234 workers divided into three groups according to age and noise exposure duration. Their hearing levels, determined by using a standardized audiometric testing procedure, were compared to those of a reference population not exposed to noise, to those of a population exposed to quasisteady noises at 95 dB(A), and also to ISO 1999-1987. Results reveal significant hearing loss after 9 years of exposure, greater than that from quasisteady noise exposure with the same equivalent continuous A-weighted sound-pressure level.
An analysis is made of data from a number of field investigations concerning the influence of steady‐state broad‐band noise on the hearing of workers, exposed to it continuously for eight hours a day. The results relate to exposure times ranging from 10 to 40 years and to noise with noise‐rating numbers for 500 to 2000 Hz (NR) ranging from 75 to 98 or sound levels from 80 to 103 dBA. Noise‐induced shifts of the median hearing levels as well as shifts indicated at the 90th, 75th, 25th, and 10th percentiles, were determined for seven frequencies between 500 and 8000 Hz as a function of exposure years and sound level. The variability in hearing levels associated with noise exposure was shown to be constant after ten exposure years and an increasing function of sound level at each frequency except 4000 Hz. At this frequency, the variance in hearing levels decreased with increasing sound level. The limit of permissible noise exposure, defined as the maximal level which did not cause measurable noise‐induced shift in hearing levels of workers exposed to it irrespective of exposure years, was shown to be NR 75 or 80 dBA. An acknowledgment is made of the need for hearing‐conservation measures given exposure conditions which exceed 80 dBA.
8 Males (in their twenties) with normal ears were exposed to steady state noise, (broad band noise, 90 dB), impact noise with a frequency of once per 2 sec (peak value 105 dB, with about 25 msec B duration and peak value 120 dB with 25 msec and about 100 msec B duration), and a combination of steady state noise and impact noises. Impact noise alone, with peak value 105 dB, produced no significant temporary threshold shift (TTS) due to steady state noise or combined noise above both. TTS due to combined noise with impact noise (peak value 120 dB, B duration about 25 msec) and steady state noise were larger than that due to steady state noise alone, and the difference was statistically significant. In the case of third impact noise (peak value 120 dB, B duration 100 msec), the effect on hearing loss was as follows: impact noise alone > combined both > steady state noise.
Continuous and impulse noises were combined to model more realistic noise environments. Monaural chinchillas were exposed to one of the following conditions: 50 impulses with 40 μsec A duration at 158 dB SPL peak pressure, 1/min; 95 dB SPL continuous noise at 2-4 kHz for 1 hr; superimposed combination of the continuous and impulse noise; 50 impulses with a 40 μsec A duration at 175 dB SPL peak pressure, 1/min; and 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 which more than exceed the additive effects of either component. The existing damage risk criteria do not provide guidelines for such noise combinations.
Summary 7 audiometrically normal, male students were exposed to a steady state noise S of 98 dBA and 2 steady state-impulse combined noises A and B (steady state component of 97 dBA, hammer noise 102 dBA and air exhaustion noise of 118 or 110 dBA) for 40–60 min. The regression line of temporary threshold shift (TTS) growth due to noise A on exposure duration was significantly steeper than that due to noise B. Both the lines were steeper than that due to noise S. The reason of the relatively larger effects of the noises A and B as compared with noise S could be explained by the fact that the noise S did not contain impulse components, because the octave band level at center frequency of 3 kHz of the noise S was roughly equal to that of the steady state noise component of noise A or B. The relatively larger effect of the noise A than B might be attributed mainly to the air exhaustion noise. It was suggested that the effect of a steady state noise on hearing might be additive to that of an impulse noise. The trend relationship between TTS during recovery and recovery time was nearly the same with the 3 noises.
Temporary threshold shifts (ITS) in pure tone hearingacuity are reported for 15 subjects exposed in separate 15‐min periods to taped impact sounds [played back at 124‐ to 127 dB peak sound‐pressure level (SPL)], to three levels of filtered (75‐ tn 1200 cps) steady‐state noise (90, 100, 110 dB SPL), and to combinations of the recorded impact sounds with each level of the steady‐state noise.TTS's from all such exposures were typically small, with the largest shifts occurring in the 1000‐ to 3000 cps frequency range. When combined with 90‐ and 100 dB steady‐state noise, the impacts caused less threshold shift than when presented alone. Such TTS reductions were believed due to the relatively greater ability of the steady‐state noise to arouse and sustain the acoustic reflex with its consequent sound‐attenuationeffect. The addition of the 110 dB steady‐state noise did not induce a similar result quite possibly because this exposure, by itself, caused threshold shifts equal to or exceeding those of the impact sounds. More‐effective stimulation of the acoustic reflex was believed responsible for findings showing less TTS for combined impact/steady state noise than from exposure to just the steady‐state component of the combination. Indirect measures of acoustic‐reflex response [contralateral remote masking (CRM)] generally indicated that those ears with a strong reflex response show less noise‐induced shift. Correlations between TTS from impact and from steady‐state noise for the subject group indicated some degree of positive correspondence limited to frequencies of of 2000 cps and below and strongest for those subjects with a poor reflex response as shown by their CRM data.
A-weighted equivalent continuous noise levels for hammer and press operations in a drop-forging industry were determined using both tape recordings of the noise and personal noise dosimeters. The results indicated average A-weighted Leq values of 108 dB for hammer operators and 99 dB for press operators. Comparison of hearing level statistics for 716 hammer and press operators and 293 control subjects indicated the severe hazard to hearing of impact noise exposures. For mean exposure times of less than 10 years, hearing levels for the press (99 dB) and hammer (108 dB) operator age groups are nearly identical, and in the latter case are less than those predicted for exposure to equivalent continuous noise. For long-term exposures of 10 years or more, the results of this study indicate that hearing losses resulting from impact noise in the drop-forging industry are as great or greater than those resulting from continuous noise.
This work was an attempt to characterize the various types of noise impulses in terms of their excitation mechanisms. It also studied how impulse noise affects the Leq, on the basis of measurements made at a number of workplaces. The paper concludes with a review of the incidence of hearing damage among groups of personnel exposed to different types of noise in the building industry.
Audiometry was carried out in 130 weavers exposed to a continuous noise level of 102 dBA to 104 dBA. While audiograms were obtained for all the weavers at the pre-exposure level, 70 of them had undergone audiometric testing after 4 and 8 hr of exposure, for assessment of threshold shifts. Almost all the weavers, irrespective of age and length of exposure to occupational noise, suffered hearing loss at frequencies from 3000 Hz through other frequencies up to 8000 Hz, with a remarkable loss at 4000 Hz. Threshold shifts were only marginal. Control measures for noise reduction have been suggested.
Certain individuals, such as police officers, are exposed to traumatic events as part of their occupational roles. In an effort to prevent psychological illnesses, notably the post-traumatic stress disorder, from arising out of work-related traumatic incidents, psychological interventions have been developed such as Critical Incident Stress Debriefing (Mitchell, 1983; Mitchell & Everly, 1996). The present study tests the hypothesis that debriefing reduces the psychological morbidity caused by work-related incidents. Because debriefing techniques were not designed for application on a 'one-off' basis (Robinson & Mitchell, 1993), the procedure studied here consisted of three successive debriefing sessions (at 24 hours, 1 month and 3 months post-trauma), which included traumatic stress education. In a sample of 243 traumatized police officers, a subgroup of debriefed officers (N = 86) was compared with non-debriefed internal (N = 82) and external (N = 75) control groups. No differences in psychological morbidity were found between the groups at pre-test, at 24 hours or at 6 months post-trauma. One week post-trauma, debriefed subjects exhibited significantly more post-traumatic stress disorder symptomatology than non-debriefed subjects. High levels of satisfaction with debriefing were not reflected in positive outcomes. The findings are translated into recommendations for the future use of debriefing in police practice.
Some children with learning problems (LP) experience speech-sound perception deficits that worsen in background noise. The first goal was to determine whether these impairments are associated with abnormal neurophysiologic representation of speech features in noise reflected at brain-stem and cortical levels. The second goal was to examine the perceptual and neurophysiological benefits provided to an impaired system by acoustic cue enhancements.
Behavioral speech perception measures (just noticeable difference scores), auditory brain-stem responses, frequency-following responses and cortical-evoked potentials (P1, N1, P1', N1') were studied in a group of LP children and compared to responses in normal children.
We report abnormalities in the fundamental sensory representation of sound at brain-stem and cortical levels in the LP children when speech sounds were presented in noise, but not in quiet. Specifically, the neurophysiologic responses from these LP children displayed a different spectral pattern and lacked precision in the neural representation of key stimulus features. Cue enhancement benefited both behavioral and neurophysiological responses.
Overall, these findings contribute to our understanding of the preconscious biological processes underlying perception deficits and may assist in the design of effective intervention strategies.
The auditory system is permanently open - even during sleep. Its quick and overshooting excitations caused by noise signals are subcortically connected via the amygdala to the hypothalamic-pituitary-adrenal-axis (HPA-axis). Thus noise causes the release of different stress hormones (e.g. corticotropin releasing hormone: CRH; adrenocorticotropic hormone: ACTH) especially in sleeping persons during the vagotropic night/early morning phase. These effects occur below the waking threshold of noise and are mainly without mental control. Animal experiments show noise-induced changes in sensitivity of cellular cortisol receptors by increase of heat-shock proteins, and ultrastructural changes in the tissue of the heart and the adrenal gland. Increased cortisol levels have been found in humans when exposed to aircraft noise or road traffic noise during sleep. The effects of longer-lasting activation of the HPA-axis, especially long term increase of cortisol, are manifold: immuno suppression (e.g. eosinopenia), insulin resistance (e.g. diabetes), cardiovascular diseases (e.g. hypertension and arteriosclerosis), catabolism (e.g. ostoeporosis), intestinal problems (e.g. stress ulcer) etc. Even worse may be the widespread extrahypothalamical effects of CRH/and/or ACTH which have the potential to influence nearly all regulatory systems, causing for example stress-dysmenorrhea etc. as signs of disturbed hormonal balance.
Noise is one of the commonest physical stressors to which industrial workers are exposed. Many workers complain of symptoms associated with a non-specific generalized stress response, including disturbed sleep. However, industrial workers may be exposed to more than one source of stress and it is not possible to completely attribute the disturbed nocturnal sleep and changes in heart rate to the effects of loud noise alone. This study was done to find out whether acute exposure of healthy individuals to loud occupational noise during the daytime would cause changes in their nocturnal sleep architecture, heart rate during sleep and serum cortisol levels.
Baseline polysomnography was done on ten subjects who were exposed for eight hours either to continuous occupational background noise levels of >75dB(A), or a quiet environment. Sleep polysomnography was done on the night prior to and after exposure. Blood was collected for serum cortisol estimation at night prior to sleep and in the morning after waking up. Statistical analysis was done by repeated measures ANOVA with Tukey's post test.
The sleep efficiency was less than 80% and the total time spent in Rapid Eye Movement (REM) sleep, Slow Wave Sleep (SWS) and the REM onset latency were significantly decreased on the night after exposure to noise. There was a significant increase in stage shifts. The percentage fall in heart rate during sleep was decreased compared to the baseline values. The serum cortisol levels in the morning after exposure to noise was significantly increased.
Workers exposed to loud background occupational noise react to the stress and show changes in nocturnal sleep architecture and heart rate which may be contributed to the exposure to noise.
The association of aircraft noise exposure with cognitive performance was examined by means of a cross-sectional field survey. Two hundred thirty six children attending 10 primary schools around Heathrow Airport in west London were tested on reading comprehension, immediate/delayed recall and sustained attention. In order to obtain the information about their background, a questionnaire was delivered to the parents and 163 answers were collected. Logistic regression models were used to assess performance on the cognitive tests in relation to aircraft noise exposure at home and possible individual and school level confounding factors. A significant dose-response relationship was found between aircraft noise exposure at home and performance on memory tests of immediate/delayed recall. However there was no strong association with the other cognitive outcomes. These results suggest that aircraft noise exposure at home may affect children's memory.
Noise: a health problem. United States Environmental Protection Agency – Office of Noise Abatement and Control
- Epa
The Okinawa study: effect of chronic aircraft noise exposure on memory of school children
- K Hiramatsu
- T Tokuyama
- T Matsui
- T Miyakita
- Y Osada
- T Yamamoto
Occupational noise induced oxidative stress and remedial measures
- N Kapoor