Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Hearing loss wikipedia , lookup
Auditory system wikipedia , lookup
Sound localization wikipedia , lookup
Audiology and hearing health professionals in developed and developing countries wikipedia , lookup
Sound from ultrasound wikipedia , lookup
Sensorineural hearing loss wikipedia , lookup
Noise-induced hearing loss wikipedia , lookup
Chapter 24: Hearing and Noise Defining and understanding noise & its effects complex problem not always intuitive critical for occupational health Level of noise affects comfort, performance, and long-term hearing – 80 dBA annoyance > 90 dbA risk of hearing loss 55 ISE 311 - Ch. 24 1 Anatomy of the Ear ISE 311 - Ch. 24 2 The Organ of Corti ISE 311 - Ch. 24 3 Hearing Measurement Audiograms test the air pathway and give total loss. Normal Hearing Losses can be temporary or permanent. Temporary threshold shift, TTS Conduction Hearing Loss Recovery after 14 hrs of exposure < 80dBA Permanent threshold shift, PTS (or NIPTS) TTS PTS Audiograms should be performed annually. ISE 311 - Ch. 24 4 Sound Definitions Wavelength: length of sound wave = speed of sound / frequency Frequency: rate of oscillation of the sound Pure tone: one-frequency sound White noise: distribution of sound through the audible range Impulse sound: duration of <1 s Decibels measure level of sound pressure. ISE 311 - Ch. 24 5 Decibels Sound pressure and sound power are analogous to temperature and heat. Sound pressure level: SPL = 20 log10 (P / P0) Power watt level: PWL = 10 log10 (W / W0) When combining or subtracting noises, use the power formula. Doubling of power results in 3 dB increase in noise level. Mean minimum level of hearing for the unimpaired-hearing population is 4 dB. ISE 311 - Ch. 24 6 Calculating dB ISE 311 - Ch. 24 7 Noise Measurement Noise at different frequencies have different perceived loudnesses for the same pressure level. Phon is the unit of loudness (see fig. 24.6, pg.465.) Sone is the unit of loudness for pure tones. Sound-level meters provide one number, combining various frequencies. Octave band analyzers provide detailed information. ISE 311 - Ch. 24 8 Determining Machine Noise Measure noise level with machine running. Measure noise level with machine off. Calculate the difference. If <3 dB, the background noise is too high for accurate measurement. Recall: when combining or subtracting noises, use the power formula. ISE 311 - Ch. 24 9 Example (Refer to table 24.1, pg. 464) Assume the vacuum cleaner and the disposal are being operated at the same time in a kitchen. What is the total sound level in dBA? PWL = 10 log W + 120 PWLA = _________ WA = _________________ PWLB = _________ WB = _________________ PWLcombined = _________________________ ISE 311 - Ch. 24 10 Effects of Noise Comfort and Annoyance Workers must increase concentration. Noise reduction may be required even if costs are high and benefits are small. Community reaction to industrial noise is variable. Performance Productivity is probably unaffected by noise except for high mental tasks. Speech interference is measured by words missed. To reduce speech interference, reduce noise or improve the message, the speaker, the transmission system, or the listener. ISE 311 - Ch. 24 11 Speech Interference Figure 24.11, pg. 469 Note: in loud environments (>85 dB), earplugs improve speech transmission. ISE 311 - Ch. 24 12 Hearing Hearing loss is a type of repetitive trauma (‘cumulative strain’.) Hearing loss (over and above age-related) begins with exposure to noises over 67 dB. Factors include noise level, exposure, duration, gender, age, and frequency. Some researchers have developed predictive models, but … We cannot identify sensitive ears prior to hearing loss. ISE 311 - Ch. 24 13 Noise Reduction Office vs industrial environment In offices, coworkers’ conversations are the main source of noise. Consider sound absorbers or masking noise. To reduce cumulative trauma: 1. 2. 3. 4. ISE 311 - Ch. 24 Plan ahead Modify the existing noise source Modify the sound wave Use personal protection 14 Plan Ahead Substitute less noisy processes. Purchase less noisy equipment. Use quieter materials and construction. Separate people and noisy equipment. ISE 311 - Ch. 24 15 Modify the Noise Source Reduce driving force. Change the direction of the noise. Minimize velocity and turbulence of air. POOR ISE 311 - Ch. 24 BETTER 16 Modify the Sound Wave Confine the sound wave. Absorb the sound wave. ISE 311 - Ch. 24 17 Use Personal Protection Reduce exposure duration. Use earmuffs and earplugs. ISE 311 - Ch. 24 18