Proposed Damage (Deafness) Risk Criteria for Exposure to Steady-State Broadband Noise: An Empirical Study

A-weighted equivalent continuous noise levels of nine companies/industries in Jos-Bukuru metropolis were determined by using Impulse Precision Sound Level Meter Type 2209 in conjunction with -Octave Filter set Type 1616 and an audiometric test of five hundred and twenty four workers out of a total of seven hundred and ninety one volunteers interviewed were carried out. The physical measurements showed that in most of the workplaces e noise was predominantly broad-band, continuous and steady-state and the equivalent continuous noise levels in most of the workplaces were above the 85dBA TWA. The audiometric test results showed that noise-induced hearing loss were prevalent within the exposed workers. Regression analysis showed that the hearing loss which exhibited a variation with the octave-band frequency was directly depended on the exposure level, thereby supporting the equal energy hypothesis (EEH). The damage risk criteria for octave band frequencies between 250Hz and 8000Hz for male and female were computed from the empirically derived expression, as the sound pressure levels at and/or below which there would be no noise-induced hearing loss. An expression for age (presbycusic/sociocusic) hearing loss was also empirically derived which makes it possible to calculate the median threshold shift at various audiometric frequencies for a population exposed to a specified noise level for a specified time, including allowance for presbycusic/sociocusic loss.