1 / 84

Noise Measurement

Noise Measurement. Training Module. Table of Contents. Physics of Sound (Hearing loss, terminology) OSHA (Regulations) Sound Level Meters Noise Dosimetry. Noise Measurement and Dosimetry Learning Objectives.

gerald
Download Presentation

Noise Measurement

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Noise Measurement TrainingModule

  2. Table of Contents • Physics of Sound (Hearing loss, terminology) • OSHA (Regulations) • Sound Level Meters • Noise Dosimetry

  3. Noise Measurement and Dosimetry Learning Objectives • Explain sound pressure level, frequency & respective units of measure • Describe level average, time weighted average & dose • Explanation of criterion, threshold & exchange rate • Proper placement & care of microphones and instrumentation • Explain hearing conservation regulations & OSHA requirements as it pertains to noise measurement • Hands on calibration, function & measurement with the noise dosimeter, sound level meter and octave band analyzers

  4. Section IPhysics ofSound 1-20

  5. Sound vs Noise?

  6. Why Measure Noise? I. Determine if the employee(s) are at risk for Noise Induced Hearing Loss (NIHL) & should be in a Hearing Conservation Program (HCP) • Differentiate between on-the-job & off-the-job noise exposure • Determine most effective hearing protection • Engineering Controls • Administrative Controls • Compliance with applicable Standards

  7. Why Measure Noise? • Prolonged exposure to noise causes permanent and debilitating hearing loss • Mostly between 4 – 8 kHz • Lose ability to understand speech in many situations • Typically affects consonant reception • Individual losing hearing is often the last to know!

  8. Why Measure Noise? • Long term health effects due to adrenaline release • More accidents in high noise environments • Measurable decrease in productivity • Measurable decrease in work accuracy • Increased fatigue

  9. Noise Induced Hearing Loss • Intensity + Duration • Damage occurs in the cochlea • Results in loss of comprehension, not loudness • Permanent

  10. Definition of Sound Fig. I-3 Compression & Rarefaction of air molecules

  11. What does Sound look like? Adapted from Acoustics Animations – Dr. Dan Russell – Kettering University Applied Physics http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html

  12. Compression & Rarefaction ofAir Particles in a Sine Wave

  13. Four Characteristics Of Sound • Frequency (measured in Hz) • Intensity (measured in dB) • Speed (measured in feet or meters/second) • Wavelength (measured in feet or meters)

  14. Frequency • Measured in Hertz (Hz) • kHz for 1000xHz • Relates to the pitch of the signal • Is a measure of the cycles completed in one second

  15. Frequency – (Pitch) Fig. I-4 1Hz and 10Hz Sine Waves

  16. Typical Frequency Examples • Lathe 50 to 1100 Hz • Compressed air 500 to 8000 Hz • Circular saw 300 to 12000 Hz • Cars 8 to 1100 Hz • Violin 300 to 9000 Hz

  17. Frequency Response & Weighting • The human ear is capable of responding to frequencies ranging • from 20 Hz to 20 kHz • The ear is less efficient at high and low frequencies • In the range from 500 Hz to 4 kHz a normal human ear is very sensitive

  18. Frequency Response & Weighting Fig. I-6 “A” and “C” Weighting Curves

  19. 2 Sine Waves: Same Frequency Same Time Duration Different Intensity One is TWICE as loud as the other Sound Pressure Level Fig. I-7 Sine Waves with different sound pressures Measured in decibels (dB)

  20. deciBels S P LdB SPL SoundPressureLevel Relates to measurements of the environment deciBels H LdB HL HearingLevel Relates to intensity of audiometric test tones UnderstandingdeciBels (dB)

  21. 100 dB 100 dB + = 103 dB Doubling Sound Source • Add 3 dB • 10 dB  perceived as “twice” as loud

  22. Addition of Decibels If the difference between two levels to be added is: - 0 to 1 dB, then add 3 dB to the higher number - 2 to 3 dB, then add 2 dB to the higher number - 4 to 7 dB, then add 1 dB to the higher number - 8 dB or more, then add 0 dB to the higher number • Decibels are logrithmic values • They can not be directly added or subtracted

  23. Changing Distance From Source • Outside • Doubling distance • Decrease SPL 6 dB • Room • Very Near Source • Twice the distance decreases SPL by 6dB • Far from source • No change with change in distance NOTE: These are general guidelines. Each case may vary.

  24. Octaves Fig. I-11 Octave Bands • Focus on the frequency content of the overall noise signal • Important for noise control efforts

  25. Occupational Noise Characteristics Fig. I-12 Mixture of Source Signals • In the real world of occupational noise the overall sound is a mixture of many simultaneous sources with a variety of frequencies and intensities.

  26. Types or Characteristics of Sound“Measure all continuous, variable and impact/impulse sound” A fan is an example of a continuous noise source A forklift driver is an example of a variable exposure An explosion or gunshot are examples of an impulsive noise A hammer striking a nail would create an impact noise signal

  27. Response Time • Slow 1 second rise and fall • Fast 0.125 second rise and fall • Impulse 35 millisecond rise 1.5 second fall • Peak 50 microsecond rise and fall

  28. Various time responses

  29. Peak Max

  30. Types of Hearing Protectors • Muffs • Plugs Foam formable Pre formed Custom • Others Plugs on a head band Noise cancellation

  31. Hearing ProtectionNRR Noise Reduction Rating

  32. NRR Devaluation • NRR- 7 dBAdjustedAttenuationthen divide this value by 2to determine if hearing protector’s are adequateto forego noise control • The OSHA method is described well on the OSHA Noise & Hearing Conservation e-Tool website http://www.osha.gov/dts/osta/otm/noise/hcp/attenuation_estimation.html

  33. Hearing Protection NRR - 7 2

  34. NIOSH subject fit Model • Muffs NRR less 25% • Formable Plugs NRR less 50% • All Other Plugs NRR less 70%

  35. GRAPHIC ILLISTRATION • Assume you need 10 dB reduction • Assume NRR is 24 for all • De-rate muff by 25% • De-rate formable by 50% • De-rate anything else by 70%

  36. Plugs + muffs • REMEMBER: • Earmuffs over earplugs provide a maximum of 5dB additional attenuation no matter what the muff rating.

  37. Critical Terminology Criterion - If exposed to SPL on average for eight hours, it would result in a maximum allowable exposure. [90dB for 8 hrs] Threshold – dB level below which, all SPL’s are assigned a value of zero. [80dB] Exchange Rate - Results in a doubling or halving of the maximum allowable exposure.

  38. Critical Terminology Average Level (LAVG and Leq) - If present continuously, would generate the same amount of energy as the varying levels that are present in the environment measured in decibels. Time Weighted Average (TWA) - A level average with an assumed fixed sample period of eight hours measured in decibels. Dose - The allowable daily exposure value. A maximum allowable exposure is equal to 100% dose. [90dB x 8hrs = 100% Dose]

  39. A Basic Concept… • TWA = Lavg @ exactly 8 hours • DOSE = Follows the same line! Lavg TWA 8 hours

  40. Dose / Lavg over time

  41. Exercise I

  42. Exchange Rates • SOUND LEVEL METERS • 3dB exchange rate • When averaged, Leq (level equivalent) • NOISE DOSIMETERS • 5dB exchange rate • When averaged, Lavg (level average)

  43. Criterion and 5 dB Exchange rate • 90dB x 8hrs = 90dB TWA = 100% Dose • 95dB x 8hrs = 95dB TWA = 200% Dose • 100dB x 8hrs = 100db TWA = 400% Dose • 100dB x 4hrs = 95dB TWA = 200% Dose • 100dB x 2hrs = 90dB TWA = 100% Dose • 100dB x 1hr = 85dB TWA = 50% Dose

  44. Section II OSHA 21-25

  45. The Occupational Noise Exposure Standard • Derived from the Walsh-Healey Public Contracts Act. • 1971 adopted under the Occupational Safety and Health Act. • Permissible Exposure Level (PEL) of 90 dBA. • Noises with a higher level than 90 dBA can be sustained for periods of less than 8 hours. • Sounds with average levels less than 90 dBA can persist for periods of more than 8 hours.

  46. Permissible Noise Exposure Hours per Day Sound Level dBA slow response 8 90 6 92 4 95 2 100 1.5 102 1 105 0.5 110 0.25 or less 115

  47. Hearing Conservation Amendment • Published in the Federal Register on March 8, 1983. • The Hearing Conservation Amendment requires the employer to perform five key tasks: • Measure Noise • Audiometric Tests • Hearing Protectors • Education & Training • Record Keeping

  48. Table G-16a (abbreviated) A-Weighted Duration Sound Level (Hours) Measuring Threshold 80 32 H.C. Action Level (50% exp.) 85 16 8 Hour Criteria 90 8 95 4 100 2 105 1 110 0.5 115 0.25 120 0.125 125 0.063 Minimum Upper Range 130 0.031 24 Section II

  49. Measuring Method for OSHA Surveys Original Rule H.C.A. Weighting/Response A/Slow A/Slow Exchange (Doubling) Rate 5 dB 5dB Criterion (LC=100%) 90dB 90dB Threshold (Cut Off) 90dB 80dB Limit 90dB/100% 85dB/50% (PEL) Action Level

  50. Conclusion • The focus of the Occupational Noise Exposure Standard and the Hearing Conservation Amendment, is to set minimum requirements to protect hearing for those workers in a noisy environment. • The Keys to Success • Positive attitude on the part of the management • Clear communication of the value of hearing • Hearing protection takes care of the problem of noise for the short term, but the key to real hearing protection is education and communication.

More Related