The influence of the acoustical environment on audiometric test results

Abstract

South African legislation requires that screening audiometry be conducted in an environment that complies with the requirements specified by the South African Bureau of Standards (SABS). The SABS Code of Practice 0182: 1998 specifies the maximum permissible ambient sound pressure levels in an acoustic enclosure used for screening audiometry. Since many industries use audiometry for screening purposes only, audiometric testing tends to be conducted in the absence of an acoustic enclosure. The rationale is that the screening process of hearing-impaired people will not be influenced by environmental sound pressure levels. A study was conducted with students of the Technikon Free State (men and women) between the ages of 18 to 34 years as test subjects to determine whether the test environment would have a significant influence on screening audiometry results. Audiometric testing was conducted according to OSHA 29 CFR 1910.95, with calibrated Tremetrics RA 400 audiometers in two different audiometric test environments with known sound pressure levels. An approved acoustic environment that complies with the specifications of the SABS Code of Practice 0182: 1998 was used as one environment A non-approved acoustic environment was simulated by operating a GilAir™ personal air-sampling pump in an approved acoustic environment. Octave band analysis was conducted in both test localities to determine and compare the sound pressure level at the different frequencies of the two test environments. The results indicate that hearing threshold levels in the approved acoustic environment differed from hearing threshold levels in the simulated non-approved acoustic environment. Statistically significant differences existed between the approved and simulated non-approved acoustic environments at frequencies of 500 Hz and 1000 Hz (Student's t-test, p = 0.05, n = 1000) for all the age groups and both genders.subjects tested in the approved acoustic environment revealed a lower hearing threshold than in the simulated non-approved acoustic environment. The difference could possibly be explained by the presence of higher sound pressure levels in the simulated non-approved acoustic environment that interfere at these frequencies during simulation. No statistically significant differences were found between the hearing thresholds in the approved and simulated non-approved acoustic environments at frequencies 2000, 3000, 4000, 6000 and 8000 Hz (Student's t-test, p = 0.05, n = 1000). The identification of high-frequency noise induced hearing loss would still be possible using tests conducted in the non-approved acoustic environment because the frequencies around 4000 Hz did not show a statistically significantly difference when compared to the results obtained in the approved acoustic environment. The results coincide with previously conducted research, which indicated that the high ambient sound pressure levels would mask the test signal. The threshold of hearing at 500 and 1000 Hz could not accurately be determined in the simulated non-approved acoustic environment. However, unnecessary referrals result from using a non-approved acoustic environment. This will have a financial impact on industries because they are responsible for the cost of medical examinations. The results show that the legislated environment is appropriate for the accurate determination of hearing thresholds to categorise a person's hearing status and calculate the percentage binaural hearing loss. Screening audiometric tests should always be done in an approved acoustic environment that complies with the specification of the SASS Code of Practice 0182: 1998. Further research is necessary to confirm the conclusion with employees working in a noise zone. Additional research using different types of earphones is necessary because this could also have an influence on the accurate determination of the threshold of hearing. The research should also include different test environments including the mobile audiometric test facility placed in different locations on site as well as the use of different types of earphones with each environment and each location.