Agreement between hearing thresholds measured in non-soundproof work environments and a soundproof booth

Abstract

Aims: To study the agreement between audiometric test results measured in non-soundproof environments at the worksite, and in a soundproof booth. Methods: In a cross sectional prevalence study on noise induced hearing loss, 885 transport workers whose hearing thresholds were measured by a standard audiometric test method in non-soundproof environments at the worksite were identified to have some hearing loss (>25 dB), and were retested in a soundproof booth. Results: At 4-8 KHz, the mean of the absolute differences in hearing threshold obtained by these two methods was 2 dB or less. When the proportions of hearing loss ( >30 dB for any frequencies at 3-8 KHz, or >90 dB for three low frequencies at 0.5-2 KHz, or >90 dB for three high frequencies at 3-6 KHz) were compared, considerable differences existed. A much better agreement was obtained when the criteria for hearing loss as measured in the field test under non-soundproof conditions were relaxed by 5 dB. At 4 KHz, the difference between the proportion of subjects with hearing loss as measured in the field and that as measured in the booth was the smallest. The kappa statistic was highest at 3 and 4 KHz. Conclusions: Audiometric test results conducted in non-soundproof environments in the field are comparable to those obtained in a soundproof environment among transport workers with a hearing loss of >25 dB. The hearing threshold at 4 KHz appears suitable for the estimation of the prevalence of hearing loss when appropriate adjustments are made in the diagnostic criteria. Sound is a form of energy generated by vibration. It can be characterised by its frequency, measured in Hertz (Hz), which represents the number of vibration cycles per second, and its intensity, a measure of energy level, expressed in watts per square metre (W/m 2 ). Sound intensity level is measured by a logarithmic scale, in decibels (dB), because the human ear can detect a wide range of intensities. A reference intensity of 10 −12 W/m 2 , corresponding to the human hearing threshold, is arbitrarily set as 0 dB. Noise, defined as unwanted sound, is one of the most common occupational and environmental hazards. Prolonged exposure to excessive noise causes a sensorineural hearing deficit that begins at the higher frequencies (3-6 KHz). This deficit is commonly described as "noise induced hearing loss" (NIHL).It has been shown that once exposure to damaging noise levels is discontinued, further significant progression of hearing loss will stop.1 This implies that the early detection of NIHL through audiometry among high risk workers is useful in the prevention of further hearing losses. Periodic screening for hearing impairment among the workers exposed to excessive sound levels is therefore an important component of hearing conservation. Ideally, audiometric measurements are made in a soundproof environment at different frequencies and intensities to detect the hearing threshold of the subject at the respective frequencies. However, this environment is not always available in field surveys, e...

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“…Research carried out by Wong et al (25) highlighted that low frequency ambient noise levels result in the increased variance of hearing thresholds for the lower frequencies with higher frequencies being less affected, findings consistent with current findings. Research carried out by Wong et al (25) highlighted that low frequency ambient noise levels result in the increased variance of hearing thresholds for the lower frequencies with higher frequencies being less affected, findings consistent with current findings.…”

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