Document ZBKkoaDYx3Yo60xdeKxrqakyV

Industrial Noise dBA FlC 45-6 --Permissible (low nsk) noise exposures for one exposure per day components of noise-exposure in producing hearing loss? Limitations of a practical hearing conservation program The aim of hearing conservation is to pre vent loss of heanng for all persons exposed to noise, but unfortunately, complete pro tection cannot always be realized Sometimes practical programs can achieve only a limited goal For example * If prevention of heanng loss at all audible frequencies does not prove possible, par ticular efforts should then be made to protect heanng at the frequencies most important to communication by speech (500, 1000, and 2000 Hz) Prevention of heanng loss in every person who is exposed to noise may not be possible, as some few persons' ears may be highly sus ceptible to noise-induced heanng loss As yet, there is no predictive test that will en able us to identify these persons To com plicate matters, no practical general rule of protection has been found to be equally effective for all persons exposed to noise, the protective measures that prevent loss of hear ing m ears that are normally-susceptible may not be effective for highly susceptible ears Noise-exposure and hearing loss Noise-induced heanng loss depends upon noise levels and exposure time Any attempt to assess the need for heanng conservation must take account of both The effects of continuous exposure to steady noise may depend on the way the sound energy is distnbuted in the noise Early noise-induced heanng losses are usually confined to the frequencies around 4000 Hz As the exposure lengthens, losses spread to lower frequencies whose audibility is more directly involved in the understanding of speech Studies of noise-induced heanng losses indicate that losses occur at frequen cies above those that eharactenze the ex posure sounds Since the most important frequencies to be protected are in the speech range (500 to 2000 Hz inclusive), it follows that the 300-600, 600-1200, and 1200-2400 Hz bands deserve the major attention Our knowledge of the relations of hearing loss to steady noise-exposure permits us to propose these general guidelines for establish ing standards for preventing significant noisemduced heanng loss in the majority of ex posed persons When the exposure to broad band noise is habitual and the noise is continuous dunng the working day (8 hour day) the A-scale level should not exceed 90 dB If the A-scale level exceeds 90 dB, hearing conservation measures should be initiated When the exposure to broad band noise is habitual and the noise is continuous for less than 5 hours per day, Fig 45-6 should be consulted for recommended allowable ex posure levels and times When the exposure to broad band noise 1528