<prompt> Upper limit of exposure to noise up to which there is no damage to hearing?160 dB70 dB85 dB100 dB  <response>: Ans. c 85 dB Ref. Park, PSM, 22ndpg. 688NOISE A daily exposure up to 85dB is about the limit people can tolerate without substantial damage to their hearing. An acceptable noise level in classroom is 30-40 dB and in wards 20-35 dB. The human ear can hear frequencies from about 20 to 20,000 Hz. The ranges of vibrations below 20 Hz are infra audible and those above 20,000 Hz ultra-sonic. Effects of noise exposure auditory effects:EffectLevel of noiseAuditory fatigueDeafnessIt appears in the 90 dB region and greatest at 4000-6,000 Hz.Most temporary hearing loss occurs in frequency range of 4000 -6000 Hz.Permanent hearing lossRepeated or continuous exposure to noise around 100 db.Rupture the tympanic membrane and cause permanent loss of hearing.Exposure to noise above 160 dB. Also remember:Corrected effective temperature deg C1. Pleasant and cool...202. Comfortable and cool...20-253. Comfortable...25-274. Hot and uncomfortable...27-295. Extremely hot...28 6. Intolerably hot...30 Predicted four-hour sweat rate P4 SR1. Comfort zone...1-3 litres2. Just tolerable...3-4.5 litres3. Intolerable...4.5 litres 