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Physical Health Hazards - Noise

Physical Health Hazards - Noise. PUBH 3310 October 20, 2010. 1. Supplemental Resources. The Basics of Occupational Safety (course text) Chapter 16, Noise and Vibration Hazards Selected Internet websites, as noted in this presentation. Objectives. Know basics of sound

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Physical Health Hazards - Noise

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  1. Physical Health Hazards - Noise PUBH 3310 October 20, 2010 1

  2. Supplemental Resources The Basics of Occupational Safety (course text) Chapter 16,Noise and Vibration Hazards Selected Internet websites, as noted in this presentation

  3. Objectives • Know basics of sound • Definitions, physics of sound • Understand decibels (dB) • Be familiar with ear anatomy and physiology • Know about hearing loss, causes and effects • Know how noise exposure is evaluated • Be aware of controls basics, especially: • Adding dB • NRR calculations • Hearing Conservation Program requirements 3

  4. Outline • Introduction • Physics of sound • Anatomy and physiology of hearing • Hearing loss • Evaluating noise • Controlling noise • Hearing conservation 4

  5. Introduction • Extent of the problem • 30 million US workers exposed to hazardous noise levels on the job • 1 in 4 will develop permanent hearing loss • Noise Induced Hearing Loss (NIHL) has a significant impact on quality of life • Diminished ability to hear and understand speech and other high-frequency sounds • Noise is a growing social problem, too • Widespread lack of concern • Noise pollution, amplified music, sporting events, etc 5

  6. Introduction • What is Noise? • Unwanted sound • Annoyance • Interfere with speech or communication • Hearing impairment 6

  7. Physics of Sound • Sound • Disturbance that propagates as a wave of compressions and rarefactions through an elastic medium • Vibrating source creates a pressure wave 7

  8. Physics of Sound • Sound (cont.) • The sound wave is a pressure wave C = Compression, R = Rarefaction 8

  9. Physics of Sound • Sound properties: • Velocity, c • Sound travels about 1100 feet per second through the air • More dense materials transmit sound waves a higher velocity • Frequency, f • Vibrations per second • 1 cycle per second = 1 Hertz, Hz • Frequency determines the pitch of the sound • The “A” above Middle “C” = 440 Hz 9

  10. Physics of Sound • Sound properties: (cont.) • Amplitude • The maximum absolute value attained by the disturbance of a wave • Wavelength, λ • The distance for one complete cycle 10

  11. Physics of Sound 11

  12. Decibels • Sound pressure • Our ears can detect changes in atmospheric pressure (sound waves) from < 20 µPa to >20 Pa • Because of this wide range, sound pressure level is expressed in decibels (dB), a logarithmic scale • Io is the reference value, 20 Pa (the threshold of hearing) for sound pressure, where 1 Pa = 1 N/m2 • 3 dB increase is twice the sound level 12

  13. Decibels • “Weighting” • Our ears are more sensitive to frequencies in the 1000 to 10,000 Hz range • Human hearing has evolved to be more sensitive to the frequencies of human speech • Decibel scales are “weighted” to compensate for this increased sensitivity • Instruments used to evaluate noise exposure use the “A” weighted scale • “A” weighting is required by OSHA 13

  14. Weighting 14

  15. Decibels 15

  16. Sound “thermometer” 16

  17. http://www.cdc.gov/niosh/topics/noise/abouthlp/noisemeter_html/hp90.htmlhttp://www.cdc.gov/niosh/topics/noise/abouthlp/noisemeter_html/hp90.html NIOSH Sound Meter

  18. Anatomy and Physiology • Outer ear • Pinna, external auditory canal (ear canal), tympanic membrane (eardrum) • Middle ear • Ossicles (bones) • Maleus (hammer), incus (anvil), stapes (stirrup) • Eustachian tube • Inner ear • Semicircular canals • Cochlea 18

  19. Anatomy and Physiology Outer ear Middle ear Inner ear 19

  20. Anatomy and Physiology • Sound waves are transmitted to the inner ear • Hair cells in the cochlea respond to sound to produce nerve signals 20

  21. Anatomy and Physiology 21

  22. Hearing Loss • Noise-induced hearing loss (NIHL) is a sensorineural hearing deficit • Begins at the higher frequencies (3,000 to 6,000 Hz) • Develops gradually as a result of chronic exposure to excessive sound levels • Hair cells in the cochlea are damaged • Permanent, irreversible 22

  23. Healthy Cochlea The cilia ( sensory hairs) appear normal 23

  24. Damaged Cochlea Loss of cilia as a result of Noise 24

  25. Hearing Loss • Audiometric testing measures hearing loss • Audiograms show dBA loss by sound frequency • “Dip” or notch at 4000 Hz is a typical sign of NIHL • Higher frequency loss affects the ability to understand speech (consonant sounds) • The “notch” may occur from 3000 Hz to 6000 Hz 25

  26. Hearing Loss • A person suffering from Noise Induced Hearing Loss can understand you if you simply speak louder. • True • False B. False. NIHL primarily affects higher frequencies, which makes difficult to hear consonants in speech. Lower-frequency vowel sounds are not affected nearly as much. 26

  27. Hearing Loss • A typical audiogram comparing normal and impaired hearing. The dip or notch at 4 kHz as shown, or at 6 kHz, is a symptom of noise-induced hearing loss 27

  28. Hearing Loss • Noise Induced Temporary Threshold Shift (NITTS) • Hearing loss caused by neural fatigue from excessive noise • Hearing sensitivity generally returns after a few hours or days • Long-term noise exposure leads to permanent hearing loss 28

  29. Hearing Loss • Tinnitus • Ringing of the ears • Most commonly caused by excess noise exposure • Acoustic trauma • Caused by sudden intense noise • Perforated eardrum, damaged ossicles 29

  30. Hearing Loss • Presbycusis • Age-related hearing loss 30

  31. Evaluating Exposure • Sound Level Meter (SLM) • Hand-held instruments • Real-time display • dBA and (usually) dBC • Must be calibrated to assure accuracy • Uses: • Evaluate noise sources • Determine where hearing protection is required 31

  32. Evaluating Exposure • Noise dosimeter • Direct-reading instrument • Worn by employees to determine TWA exposure • Display/download TWA noise levels • Often with datalogging • Must be calibrated to assure accuracy 32

  33. Evaluating Exposure • Background sound level can be estimated by the difficulty of spoken communication • When noise levels are above 80 decibels (dB), people have to speak very loudly. • When noise levels are between 85 and 90 dB, people have to shout. • When noise levels are greater than 95 dB, people have to move close together to hear each other at all. 33

  34. Evaluating Exposure • OSHA PEL • 90 dBA 8-hr TWA, 5 dBA exchange rate (doubling rate) • Exposure at the OSHA PEL will result in hearing loss

  35. Evaluating Exposure • ACGIH Threshold Limit Value • The TLV is more protective (1994) • 85 dBA limit • 3 dBA “exchange rate” • Acceptable exposure duration doubles every 3 dBA (the OSHA PEL is based on a 5 dBA exchange rate) • Exposure at this level should prevent most hearing loss • Employers have a legal requirement to comply with the OSHA PEL • Responsible employers wanting to control employee hearing loss should also comply with the more protective TLV 35

  36. Controlling Noise • Engineering controls (most desirable method of control) • Substituting new quieter equipment for old • Modifying (reducing) the sound creating energy • Change the orientation between the (work on the quiet side) • Isolate the vibrating equipment • Attenuate noise energy as it leaves the surface via insulation • Enclose the source or the personnel • Line surfaces with sound absorbing material • Shield workers with sound barriers 36

  37. Controlling Noise • Isolation of secondary surfaces 37

  38. Controlling Noise • Reduce vibrating surface area 38

  39. Controlling Noise • Sound absorbing materials 39

  40. Controlling Noise • Multiple methods 40

  41. Controlling Noise • Adding noise • “Easy” method • Based on dB difference between two noise sources • Add 3 dB if noise sources are equal • Add 1-2 dB for 0-10 dB difference • Add 0 dB for  10 dB difference 41

  42. Controlling Noise • Adding noise • Example: add 90 dBA and 90 dBA • Equation: • “Easy” method • Difference = 0, so add 3 dBA • 90 + 3 = 93 42

  43. Adding Decibels • 90 dB + 80 dB = ? • 85 dB • 90 dB • 93 dB • 170 dB B. 90 dB (add 0 dB for  10 dB difference)

  44. Controlling Noise • Administrative controls (less desirable) • Restrict number of hours workers are allowed in noisy areas • Train workers to reduce noise 44

  45. Controlling Noise • Personal Protective Equipment (least desirable method of control) • Mandatory PPE for noise  90 dBA • PPE must be available for noise  85 dBA • Estimating noise dose when PPE is used • Hearing protectors are labeled with the NRR (noise reduction rating) • Equation: dBA – (NRR-7) = employee dose while wearing the protector 45

  46. Controlling Noise • Personal Protective Equipment • NRR example: • What is the employee dose where exposure is 95 dBA while wearing earplugs with 29 NRR? • In practice, PPE performance often is not as good as the NRR • OSHA strongly recommends applying a 50% safety factor to the NRR: • dBA – ((NRR-7) x .5) = employee dose dBA – (NRR-7) = employee dose while wearing the protector 95 – (29-7) = 73 dBA dose 46

  47. Controlling Noise • Personal Protective Equipment • Ear plugs • Usually best for continuous exposure situations • Formable (foam) • Premolded • Custom molded • Canal cap protectors • Convenient when noise areas are frequently entered and exited 47

  48. Controlling Noise • Personal Protective Equipment • Ear muffs • May be better for high frequencies • Can be combined with ear plugs for extra protection • Extra protection for combining ear muffs and ear plugs is limited to about 5 additional dBA due to bone conduction 48

  49. Hearing Conservation • OSHA Hearing Conservation Program • Required when exposures reach 85 dBA • Monitoring • Employee notification • Audiometric testing • Additional requirements if “standard threshold shift” (10 dBA hearing change from baseline) • Recorded as “hearing loss” on OSHA form 300 • Hearing protectors • Training • Recordkeeping • Noise exposure • Audiometric tests 49

  50. Conclusions • Noise (unwanted sound) causes hearing loss • The logarithmic “A” weighted decibel scale, dBA, is used to measure noise exposure • NIHL is sensorineural hearing loss caused by cumulative noise damage to the inner ear • NIHL is typified by an audiogram “notch” at 4000 Hz • SLM and noise dosimeter instruments are used to evaluate noise • The PEL is 90 dbA, 8-hour TWA , but this level is not protective • Hearing Conservation Program required at 85 dbA • Doubling noise adds 3 dB • NRR is a measure of the PPE performance

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