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Unit 5-calculation-example

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Presentation for unit 5 of HPEO 408.

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Unit 5-calculation-example

  1. 1. UNIT 5 NOISE CALCULATIONS HPEO 408 Occupational Health Hazards
  2. 2. <ul><li>Two common exchange rates used in industry (3 dBA and 5 dBA) </li></ul><ul><ul><li>Also called “doubling rate”, “trading ratio”, “time-intensity tradeoff”, and “equal-energy rule” </li></ul></ul><ul><li>3 dBA exchange rate </li></ul><ul><ul><li>More conservative than 5 dBA exchange rate </li></ul></ul><ul><ul><li>Theoretically total daily dose is more important than actual exposure levels </li></ul></ul><ul><ul><li>Equal amounts of sound energy will produce equal amounts of hearing impairment regardless of how it is distributed over time </li></ul></ul><ul><ul><li>Therefore, a 3 dBA increase/decrease in noise levels equals doubling/halving of the sound energy </li></ul></ul><ul><ul><ul><li>Use this to calculate permissible limits (allowable exposure times) </li></ul></ul></ul>EXCHANGE RATE
  3. 3. <ul><li>The allowable time a worker can be exposed to noise </li></ul><ul><li>Changes based on noise level and exchange rate </li></ul><ul><li>To calculate permissible limits we can make a permissible limits table (next slide) </li></ul><ul><li>For example: </li></ul><ul><ul><li>If we start an exposure limit of 85 dBA for 8 hours, we know if we double the exposure (i.e. 85 dBA + 3 dBA = 88 dBA) </li></ul></ul><ul><ul><li>Then the permissible time would be halved (i.e. 8 hours/2 = 4 hours) </li></ul></ul><ul><li>Note there are more complex equations available but for this course we will be using the tables to determine permissible limits </li></ul>PERMISSIBLE LIMITS
  4. 4. <ul><li>Halving </li></ul><ul><li>Doubling </li></ul>PERMISSIBLE LIMITS (3dBA EXCHANGE RATE) Noise level (dBA) Permissible Time (hours) 61 2048 64 1024 67 512 70 256 73 128 76 64 79 32 82 16 85 8 Noise level (dBA) Permissible Time (hours) 85 8 88 4 91 2 94 1 97 0.5 100 0.25 103 0.125 106 0.0625 109 0.03125
  5. 5. <ul><li>Noise level is the ‘loudness’ of the noise exposure </li></ul><ul><li>Dose is a percentage of allowable total daily noise exposure </li></ul><ul><ul><li>Combines intensity (noise level) and exposure time </li></ul></ul><ul><li>For example: </li></ul><ul><ul><li>8 hr exposure at the exposure limit is the maximum therefore; </li></ul></ul><ul><ul><li>8 hr @ 85 dBA = 100% dose </li></ul></ul>“ NOISE LEVEL” VS. DOSE
  6. 6. DOSE CALCULATION Where: C n = Duration of time exposed to noise level n T n = Permissible duration of exposure of noise level n
  7. 7. <ul><li>Assume a worker spends: </li></ul><ul><ul><li>6 hours on a production line with a noise level of 85 dBA </li></ul></ul><ul><ul><li>1 hour performing cleanup with an average noise level of 88 dBA </li></ul></ul><ul><ul><li>1 hour in the lunch room with an average noise level of 73 dBA </li></ul></ul><ul><li>Calculate daily dose </li></ul><ul><ul><li>Step 1: determine permissible exposure times for each activity (T n ) from permissible limits table </li></ul></ul><ul><ul><ul><li>85 dBA = 8 hours </li></ul></ul></ul><ul><ul><ul><li>88 dBA = 4 hours </li></ul></ul></ul><ul><ul><ul><li>73 dBA = 128 hours </li></ul></ul></ul>DOSE CALCULATION EXAMPLE
  8. 8. DOSE CALCULATION EXAMPLE CONT.
  9. 9. TWA ESTIMATION FROM DOSE?
  10. 10. <ul><li>WorkSafeBC – How to conduct noise survey’s </li></ul><ul><ul><li>http :// www.worksafebc.com/publications/health_and_safety/by_topic/assets/pdf/occupational_noise_surveys.pdf </li></ul></ul><ul><li>WorkSafeBC noise calculations </li></ul><ul><ul><li>http://www.worksafebc.com/publications/health_and_safety/by_topic/assets/pdf/basic_noise_calculations.pdf </li></ul></ul><ul><li>Methods for dealing with non 8-hr work shifts (i.e. L ex ) </li></ul><ul><ul><li>http ://www2.worksafebc.com/publications/OHSRegulation/GuidelinePart7.asp#SectionNumber:G7.2 </li></ul></ul>REFERENCES FOR NOISE CALCULATIONS

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