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PubMed1987

The efficiency of earmuffs against impulse noise from firearms.

Young men conscripted into the armed forces still run a risk of suffering hearing damage during their military service. This risk could be reduced by effective personal hearing protectors. The standard tests to determine the attenuation values of hearing protectors cannot be applied to high-intensity impulse noise from firearms, but the protectors should be evaluated under actual firing conditions. The attenuation values of the hearing protectors (earmuffs) most commonly used in the Finnish Army were tested for impulse noise from different weapons. The attenuation was found to be good for pistol shots, moderate for rifle shots and very poor for cannonfire. The tested earmuffs gave only minimal protection against low-frequency impulse energy.

Ear Protective Devices↗
PubMed1990

Recognition of low-pass filtered words in a noisy and reverberant environment with and without earmuffs.

The effect of earmuffs on the recognition of low-pass filtered Finnish speech test material was investigated by presenting both the unfiltered and filtered words at two speech levels, 60 dB(A) and 85 dB(A) to a group of students with normal hearing. The background noise level (quiet, S/N +10, +5, 0 dB) and reverberation time (2.1 s and 1.6 s) were altered in a multi-purpose hall. Unfiltered words were recognized better without earmuffs in quiet conditions and at S/N +10 and +5 dB. At S/N 0 dB, however, better scores were obtained when earmuffs were used. Filtered words were recognized significantly better without earmuffs at both reverberation times and at all S/N conditions tested. The decrease in the reverberation time improved all the recognition scores essentially.

Adolescent↗
PubMed1992

Models for studying the progression of hearing loss caused by noise.

A computer-controlled fixed-frequency Békésy audiometer has been used together with simplified mathematical models for hearing threshold measurements and analysis in 1,796 subjects from seven different noise environments with exposures varying from less than 80 dB(A) to greater than 95 dB(A). The methods of measurement and analysis have been used to determine hearing loss caused by noise for various age groups for men and women. It has also been possible to estimate the equivalent noise level to which workers are nowadays subjected under hearing protectors and the reduction in exposure level over the past 40 years. The results illustrate the effects of noise-reduction measures and the use of hearing protectors on the development of hearing loss suffered by workers in the actual Swedish industries.

Adult↗
PubMed1992

Speech recognition in noise when wearing amplitude-sensitive ear-muffs.

Speech recognition in background noise when wearing amplitude sensitive (non-linear) ear muffs was studied in the laboratory in 15 young normal-hearing test subjects. Low-redundancy sentences were presented from a loudspeaker in a background noise level of 70 dB (A) and the speech-to-noise (S/N) ratio yielding 50% correctly recognized words was determined. Three background noise spectra were tested: white noise, low-pass filtered noise (-12 dB/octave) and high-pass filtered noise (12 dB/octave). Five listening conditions were used: no protectors, a pair of normal ear-muffs, a passive amplitude-sensitive ear-muff and two types of electronic amplitude-sensitive ear-muffs. An ANOVA shows that speech recognition is significantly influenced by type of hearing protector and by noise spectrum. The interaction between these factors was not statistically significant. In general, the test subjects obtained somewhat better speech recognition thresholds in noise when wearing electronic amplitude-sensitive ear muffs than without muffs, whereas the opposite was true for the passive amplitude-sensitive and the normal ear muffs.

Acoustic Stimulation↗
PubMed1993

An audiological survey of officers at an infantry regiment.

We carried out an audiological survey of 204 officers at an infantry regiment in southern Sweden. The officers were exposed to impulse noise from firearms with peak levels up to 185 dB (SPL). The audiological measurement results were summarized in four age-groups, all of which showed significant hearing loss compared to ISO 1999 (1990) database A of a non-noise-exposed male population. Even officers who claimed regular use of hearing protectors during their entire military career showed these significant hearing losses. In the survey we also studied the association of the hearing thresholds with subjective exposure to heavy detonations and the annoyance of tinnitus. We found a significant relation between exposure to heavy detonations and tinnitus.

Adult↗
PubMed1994

Progression of hearing loss caused by occupational noise.

This review is a compilation of 11 investigations by different authors regarding the progression of hearing deterioration during severe long-term exposure to noise in mines, shipyards, forges, weaving mills, other factories and industries and from field artillery and hunting. With one exception, the reports concern conditions at times when ear protection was virtually unknown or only seldom used. The different investigations are described in a broad outline with their essential measurement and background data. For the first eight studies the results of the hearing deterioration with increasing exposure time are illustrated in figures showing, on the one hand, the original data and, on the other, the progression of hearing loss with increasing age, though reduced by the ISO 1999 (1990) values from database A for the normal threshold of hearing as a function of age. This is followed by a discussion of the results and a compilation of the data from the 11 investigations for, particularly, a noise exposure time of about 5 to 10 years, corresponding to an age of around 30 years, in comparison with an exposure time of 30 to 40 years, i.e. at an age range of about 50 to 60 years. Despite the great diversity in the character and level of the noise, the compilation shows for the higher ages in the range of 3 to 8 kHz a similar median hearing loss from nearly all investigations; however, at 1 kHz and, particularly, at 2 kHz the differences in the character of the noise are apparent in a wide spread of the median hearing loss between the different studies. In addition, it was found that at higher ages and hearing loss levels of more than 45 to 50 dB it is not possible to distinguish between the effect of the noise, on the one hand, and that of ageing, on the other; the ad hoc assumption of their additivity is no longer valid and thus the term "age correction" inadequate. A series of further figures illustrates the progression of the hearing loss with exposure time in the different investigations at particularly 1 kHz, 2 kHz and 4 kHz.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗
PubMed1994

Noise-induced hearing loss in an automobile sheet-metal pressing plant. A retrospective investigation covering 25 years.

Hearing damage suffered by male workers in an automobile sheet-metal pressing plant has been studied on five occasions during the period 1964-89. The hearing threshold data have been analysed in order to determine hearing loss due to noise in various age groups. The hearing thresholds were better on later occasions. In the youngest group of workers only 45% exhibited normal hearing in 1964, while in 1989 the corresponding figure was 88%. The same tendency towards improved hearing could also be seen in the age groups 30-39 and 40-49 years. In the oldest age group, 50-59 years, hearing handicap decreased from 58% in 1964 to 11% in 1989. With the aid of the average hearing loss, it has also been possible to estimate the equivalent noise level to which present-day workers have been exposed, as well as the reduction in level of exposure during the past 25 years. The effects of a long-term technical and medical occupational health care programme including noise-reduction measures and improved use of hearing protectors are discussed.

Adult↗
PubMed1994

Noise-exposed male sheet-metal workers using hearing protectors. A longitudinal study of hearing threshold shifts covering fifteen years.

The hearing thresholds of male sheet-metal workers have been studied in a longitudinal investigation with pure tone audiometry during three periods covering 1972-1987. Using these data, the hearing threshold shifts were calculated in various age groups. When the annual rate of mean hearing threshold shift over the frequency range 2-8 kHz was considered, it was not possible to establish a difference in the threshold shift between noise-exposed groups and an otologically normal 'highly screened' male population from ISO 7029, database A. The correction for ageing in the noise-exposed group according to the empirical formula in ISO 1999 (1990) is discussed. The results show that a hearing conservation programme including effective use of hearing protectors and reduction of noise emission levels can eliminate noise-induced hearing threshold shifts and progressive hearing loss.

Adult↗
PubMed1995

Physical characteristics of gunfire impulse noise and its attenuation by hearing protectors.

The peak sound pressure level (SPL), spreading of pressure wave and other physical characteristics of the impulse noise from weapons were studied in actual shooting conditions for assessment of gunfire noise exposure. Additionally, the attenuation of SPL by hearing protectors was measured with miniature microphones to evaluate protection efficiency in real shooting conditions. The peak SPLs at the shooter's ear ranged from 132 dB (miniature rifle) to 183 dB (howitzer). The spectral content of the main part of the acoustic energy was less than 400 Hz (peak 16-100 Hz) for large-caliber weapons and 150-2,500 Hz (peak 900-1,500 Hz) for small-caliber weapons (rifles). The safe distances from the noise source (less than 140 dB peak SPL) were 50-200 m for large-caliber weapons. Rifle impulses (assault rifle, caliber 7.62) had a peak SPL of 154 dB at a distance of 4 m from the muzzle. The peak SPLs of different explosives ranged from 125 to 185 dB at distances of 10 to 300 m. In rifle shooting, the attenuation efficiency of earplugs (16dB) or small-volume (thin) earmuffs (17 dB) was not sufficient and their use as sole protectors cannot be recommended. Instead, large-volume earmuffs should be used. Impulses from pistol and shotgun were fairly effectively attenuated both by small-volume and large-volume earmuffs. All kinds of earmuffs appeared to be ineffective (attenuation less than 15 dB) against impulses from large-caliber weapons with energy content at very low frequencies. Therefore, the combined use of earmuffs and earplugs is recommended for the most noisy operations. On the basis of the present data, wider safety zones were adopted in the Finish Defence Forces at shooting with different weapons.

Ear Protective Devices↗
PubMed1995

Temporary threshold shift and otoacoustic emissions after industrial noise exposure.

The objective of the present study was to investigate whether employees in a noise-exposed environment developed changes in cochlear function as manifested by elevation of pure-tone threshold and/or reduction in transient evoked otoacoustic emission (TEOAE) amplitude. Pure-tone air-conduction audiometry, otoacoustic emissions (OAEs) and tympanometry were recorded in 13 healthy employees on three consecutive days both before and after 7 h of noise exposure. Employees exposed to an industrial noise level of 85-90 dBA developed significant pure-tone air-conduction threshold elevation at 4 and 6 kHz. A significant reduction of the TEOAE amplitude was found. There was no correlation between temporary threshold shift (TTS) and TEOAE reduction.

Acoustic Impedance Tests↗
PubMed1996

Sound localization. The interaction of aging, hearing loss and hearing protection.

The effect of conventional ear plugs and ear muffs, and muffs with limited dichotic amplification on the ability to localize one-third octave noise bands was investigated under semi-reverberant listening conditions. Forty-eight normal-hearing subjects, half over 40 years of age, and 23 subjects with bilateral sensorineural hearing loss participated. Sound localization was assessed using an array of six loudspeakers surrounding the subject at azimuth angles 60 degrees apart. One block of 120 forced-choice speaker identification trials was presented for each of 16 listening conditions defined by ear condition (unoccluded, E-A-R plug, E-A-R muff, and Bilsom 2392 muff), stimulus frequency (500 Hz and 4000 Hz), and background (quiet and continuous 65 dB SPL-white noise). Plugs and muffs, particularly active muffs, resulted in decrements in right/left judgments based on interaural intensity but not time-of-arrival differences. High-frequency front/back discrimination was affected more by muffs than by plugs. Error patterns for the conventional and active muffs were dissimilar. Aging resulted in a decrement in unoccluded front/back discrimination. Trends for the impaired subjects were the same as those for normal subjects at 500 Hz. Many could not hear 4000 Hz with conventional protectors. Their performance was no different from normal with the active muffs.

Adolescent↗
PubMed1996

Hearing protection in acute acoustic trauma in Finnish conscripts.

A prospective study was performed in all Finnish conscripts who were referred to the Central Military Hospital for acute acoustic trauma (AAT) in 1989-93. The study was designed to provide information on hearing protection at the time of AAT and also on the general habits of using hearing protection at shooting drills and combat training in the field. Altogether 449 conscripts with verified AAT were included. According to their statements, all conscripts always used hearing protectors at shooting drills on the range and 97% always or nearly always during combat training in the field. At the moment when AAT occurred, hearing protectors were not used in 83% of cases. Accidental shots or explosions (25.6%), unforeseen exposure to impulse noise, e.g. during combat training (17.5%), and loss of applied protectors (14.9%) were the most common reasons for absence of hearing protection. AATs can be avoided by improving instruction in handling firearms, planning combat training more carefully and making sure that application of earplugs is properly taught and mastered.

Adolescent↗
PubMed1997

Impulse noise and acute acoustic trauma in Finnish conscripts. Number of shots fired and safe distances.

This prospective study of acute acoustic trauma (AAT) from exposure to impulse noise during compulsory military service focused on three issues the number of shot or explosion impulses that the conscript was exposed to at the time of AAT, distance of injured ear from causal firearm, and the circumstances under which AAT occurred protected ears. The series includes 449 consecutive, verified cases of AAT seen at the Central Military Hospital in Helsinki, Finland, in the period 1989-1993. AAT usually occurred during combat training (87%) as a result of exposure to impulses from small arms (83%). In 41%. AAT was caused by a single shot or detonation impulse. As many as 92% of all AATs occurred within 2 m of the causal firearm. Fourteen percent were wearing hearing protectors when the accident took place, but every third had badly fitting protectors or had neglected safety regulations and used insufficient protection. Of all AATs caused by one noise impulse in protected ears. 83% were attributable to heavy arms and only 14% to small arms. The results of the study suggest that combined use of earmuffs and earplugs in association with a safe distance of over 5 m from the noise source gives adequate protection against AAT. However, for conscripts using certain heavy arms e.g. hazooka. more effective hearing protection should be developed.

Acute Disease↗
PubMed1993

Hearing loss risk from exposure to shooting impulses in workers exposed to occupational noise.

The effect of shooting impulses on hearing was analysed in 150 professional forest workers exposed to noise from chain saws. The exposure to shooting impulses (Lesi) was designed to take into account the peak levels of shooting impulses, their number and use of hearing protectors. Hearing loss was dependent on Lesi even after allowing for the age of subjects and their exposure to chain saw noise. Hearing threshold levels were compared between pairwise matched groups with high and low Lesi. Proper matching was achieved for age, chain saw noise, salicylate consumption, blood pressure, cholesterol, smoking and vibration-induced white finger symptoms. The workers with high Lesi had 9 dB greater hearing loss at 4 kHz and 10 dB greater hearing loss at 8 kHz than those with low Lesi, the difference being significant at P < 0.05 level. In evaluation of noise-induced hearing loss the exposure to shooting impulses from different calibre weapons should be determined since they increase the extent of hearing loss. The present study describes the Lesi method which more accurately evaluates the harmful effects of shooting noise impulses on hearing.

Adult↗
PubMed1993

Cochlear damage in guinea pigs following contralateral sound stimulation with and without gentamicin.

The effect of a minimally damaging sound exposure and a sub-ototoxic dose of gentamicin on cochlear hair cells contralateral to the sound exposure was evaluated. The cochleae of pigmented guinea pigs exposed to an 8 kHz pure tone at 116 dB SPL for 1 h and/or 50 mg/kg/day of gentamicin for 10 consecutive days and repeated after an interval of 3 weeks, were used for this purpose. Hair cell loss was found to have occurred in the contralateral cochleae following the sound exposure alone. The occurrence of potentiation, synergism and differential synergism between the agents in the contralateral ears was also seen. Possible explanations for these phenomena are proposed.

Acoustic Stimulation↗
PubMed1993

Warning signal detection and the acoustic environment of the motorcyclist.

A two-part study was undertaken to investigate warning signal detection by motorcyclists. First the acoustic environment was established for both the helmeted and bareheaded rider between speeds of 0 and 100 mph. For the helmeted rider it was found that below 20 mph vehicle noise was dominant and between 20 and 40 mph there was a variable contribution from both vehicle and wind noise. At 40 mph wind noise became the dominant sound source and increased linearly with the log10 of speed from 90 dB(A) to reach 112 dB(A) at 100 mph. Sound levels were consistently 18 dB(A) greater for the bareheaded rider once above 10 mph, and followed a similar pattern. Recordings of these sounds were sampled into an Amiga computer. Suitable sound combinations were played back at levels appropriate to speed to recreate the rider's acoustic environment at differing speeds. The minimum detection level (MDL) of four traffic warning signals was then measured in 19 normal hearing subjects for three test conditions: no helmet, helmet and helmet with earplugs. The MDL for all warning signals was lowest with a crash helmet in place for sound levels equivalent to speeds of 30 mph or less. The addition of earplugs led to significant reductions in MDLs at sound levels equivalent to speeds of 40 mph, or greater. Signal detection was poorest at all speeds greater than 0 mph, when bareheaded. We would conclude that earplugs are not required for motorcyclists in the urban environment.(ABSTRACT TRUNCATED AT 250 WORDS)

Accident Prevention↗
PubMed2003

Effects of a hearing protection campaign on the discotheque attendance habits of high-school students.

This study investigated whether a hearing education campaign would prompt adolescents to display hearing-protective behaviour when attending a discotheque. A sample of 169 high-school students participated in the campaign. A questionnaire was administered to them before and 1 year after the campaign, asking for the frequency of discotheque attendance within the past 6 months, and whether they used earplugs in the discotheque. The percentage of subjects who went to discotheques more than 10 times within 6 months decreased from 34% to 24% after the campaign. The overall difference between pre- and post-campaign frequencies of discotheque attendance, however, was not significant. The percentage of subjects using earplugs in the discotheque rose from 0% before to 3.7% after the campaign. In essence, the campaign had little effect in inducing hearing-protective behaviour in adolescents when attending discotheques. The need for sound level limitations in discotheques is highlighted.

Adolescent↗