INDH 5131 Controls of Occupational Hazards. Noise & Hearing Conservation. Part II. V. Audiometric Testing

Transcription

1 INDH 5131 Controls of Occupational Hazards Noise & Hearing Conservation Part II By: Magdy Akladios, PhD, PE, CSP, CPE, CSHM V. Audiometric Testing Equal Loudness Contours (Fletcher-Munsen Curves) 1

2 Testing All employees exposed to or > 85 dba TWA must be tested No charge to employees Tests the quietest level that you can hear Test time is ~ min. Test environment is quiet Background noise in chamber < 40 db Testing must be conducted by: Licensed or certified audiologist, or ENT MD, or Technician certified by the council of Accreditation in Occupational Hearing Conservation, or A non-certified technician operating automatic tester (must report to audiologist or MD) Audiometer should be checked acoustically, at least annually When?? Baseline: Done within 6-mo of first exposure to or > 85 dba (unless mobile test van, then 1-yr) Annual audiogram to compare to baseline Done to determine if STS existed in either ears 2

3 Testing criteria No exposure to occupational noise > 80 dba for 14 hrs prior to exam Notify employee of need to avoid high levels of non-occupational noise in 14-hr prior testing Provide hearing protection to employee to be tested to attenuate < 80 dba How?? Pure tone (one at a time), air conduction At the center of the Octave Band: 500 Hz, 1,000 Hz, 2,000 Hz, 3,000 Hz, 4,000 Hz, 6,000 Hz Each ear separately Increase SPL at each frequency until subject presses button Do next frequency Results are reported in graphical form by the audiogram Hearing loss Compare to norms and previous results If STS = 10dBA or more reduction at 2k,3k or, 4k Hz: Sensorineural Loss If STS = 10dBA or more reduction equal at all frequencies: Mechanical hearing loss 3

4 Standard Threshold Shift (STS) Change in hearing threshold of an average of 10 db or more at: 2,000 Hz 3,000 Hz 4,000 Hz Adjust for age, gender Audiogram (The Age Factor: Right (RED), Left (BLUE) Example Frequency 2,000 3,000 4,000 Shift in Hearing Age Correction (27 yr old Male) Difference ( )/3 = This is > 10, therefore, STS occurred 4

5 If STS occurred: Retest in 30 days Follow-up is required, unless: MD determines STS not work-related or aggravated by work exposure Workers must be: Fitted with hearing protection Trained in use of PPE Required to use (or refitted, or retrained) Workers must be referred to clinical examination if necessary, or if a medical pathology is expected If STS occurred:... 2 May substitute annual results for baseline if: Expert says STS is persistent (set new baseline) Next audiogram is better than baseline STS is Compensable IV. Sound Measurement 5

6 Types of Sound instruments: Sound Level Meter Noise Dosimeter Octave Band Analyzer Make sure instrumentation is calibrated...!! Sound Level Meter Used for contour mapping 98dBA 95dBA 90dBA 94dBA 96dBA 89dBA SLM: Depends on type of field (i.e., lab, field, high-precision, low precision, etc.) Instantaneous Identifies noisy areas Identifies noisy levels of machines 6

7 While Monitoring Using SLM You ll need to note: Location (distance and direction from machine) dba Name, model of machine Materials, feed speeds, die #, etc. Date, Time Worker comments Info provided by SLM Areas where exposure < 85 dba Areas > 90 dba (100+) Machine levels so that if a 2 nd machine was added/moved, etc., one can estimate new noise levels SLM Specifics Sound level meters can be calibrated with a portable acoustic calibrator Calibrators provide a precisely defined sound pressure level to which the sound level meter can be adjusted (114 db at 1,000 Hz) Calibrate sound level meters immediately before and after each measurement session 7

8 Fast/Slow Fast: 1/8 th sec. Used to estimate the variability in the observed sound where only the limits (upper and lower) are desired. Slow: Integrates over longer time Takes the average to simulate human exposure rather than sudden increase or drop Mandated for use by OSHA Dosimeter Integrated sampling A-weighted Slow response Averaging Body absorbs sound Noise is directional Therefore, keep on collar Dosimeter... 2 Worker not stationary Maintenance Shielding (use wind screen) Get buy-in (supervisors, workers, etc) Placement 8

9 Dosimeter... 3 Before starting: Check battery Check calibration Attach dosimeter Put windscreen over mic After starting: Check on worker(s) Dosimeter... 4 After measurement, record: Make, model, and serial number of dosimeter Serial number and last annual calibration date Pre- and post-calibration levels and date Name and SSN of worker Job title of worker Date of measurement Dosimeter... 5 After measurement, record: Start and Finish time of measurement (duration) Settings of dosimeter TWA measurement Dose measurement LEQ (Sound Level Equivalent) on dosimeter is the average sound Level received over entire shift Review data (does it make sense?) 9

10 Microphone Unobstructed (have to use a wind screen) Class II: OSHA compliance Dosimeter... 6 Definitions: TWA: Sound level that would produce a given noise dose if an employee were exposed to that sound level continuously over an eight hour day Impulse: Impact noise 10

11 Dosimeter Calculations A review + some other cases...! Dosimeter Calculations D = 100 [C 1 /T 1 + C 2 /T C n /T n ] Where: D ~ Dose C n ~ Actual exposure time in minutes T n ~ Allowable time of exposure at particular db in min. T n = 480/[2 (L-90)/5 ] Where: L ~ SPL (L P in dba) TWA = log (D/100) PEL for NOISE (From OSHA 5dB exchange rate) Duration/day dba (Slow response) 8 hrs 90 7 hrs 91 6 hrs 92 4 hrs 95 3 hrs 97 2 hrs hrs hrs hrs hrs

12 Dosimeter Running Time Types of running time: 1. Shift = 8 hrs, Recording > 8 hrs 2. If Shift > 8hrs, Recording = Shift 3. Shift = Whatever hrs, Recording < Shift Running Time Case 1 If Shift = 8 hrs, Recording > 8 hrs: You re in good shape...!! Report what you get on the dosimeter Running Time Case 2 If Shift > 8hrs, Recording = Shift: Dose reading represents what the worker would receive if they had received all the noise in 8 hrs. 12

13 Example If LEQ from dosimeter is 91 dba, time measured is 16 hrs, calculate the TWA for this worker. Solution Dose = (T actual / T allowable ) x 100% T actual = 16 hrs x 60min/hr = 960 min T n = 480/[2 (L-90)/5 ] = T n = 480/[2 (91-90)/5 ] T n = 480/[2 (1/5) ] = 418 min. Therefore, Dose = (960/418) x 100 % = 230% TWA = log (dose/100) TWA = log (230/100) = 96dBA This worker is over exposed Example If the shift is 10 hrs, LEQ is 88 dba over the entire shift. What is the dose and TWA? 13

14 Solution Dose = (T actual / T allowable ) x 100% T n = 480/[2 (88-90)/5 ] T n = 480/[2-2/5 ] = 633 min. = Hrs. Dose = (10/10.56) x 100% = 94.7% TWA = log (dose/100) TWA = log (94.7/100) TWA = 89.6 dba Running Time Case 3 If Recorded only part of the shift: Assume rest of shift is identical to measured portion of shift Need to calculate actual TWA and dose In other words, don t use what is shown on dosimeter...! Dose reading represents what the worker would receive if, for the remainder of the shift, they worked in less than 80 dba (very low exposure) LEQ on dosimeter should be used for the TWA This is the average sound level sustained over the recorded time Actual Dose = Dose from dosimeter x (time of shift/time measured) ie, use scissors way to get actual Dose Scissors way: (An Example) Dose for part of shift Measured Time (64%) (3 hrs) Dose for full shift (X) Time of full shift (8 hrs) 64% x 8 hrs = X x 3 hrs Therefore, X = (64% x 8)/3 14

15 Example You recorded 4 hrs on a 6 hr shift; you assumed that the noise level is constant. The dose on the dosimeter says 64%. What is the 8-hr TWA? Solution Given times, Dose on Dosimeter, No LEQ Recorded 4 Hrs; shift = 6hrs Dose from dosimeter = 64% Dose = Dose from Dosimeter (Actual time of shift/measured time) x 100% Dose = (64 x 6)/4 x 100% = 96% TWA = log (96/100) = = 89.7 dba Example The worker has a shift of 12hrs in a noisy environment. You recorded a dose on the dosimeter over 8hrs to be 91%. Should this worker be in the Hearing Conservation Program? 15

16 Solution Recorded < Shift, Shift = 12hrs Dose on dosimeter = 91% Dose = Dose from Dosimeter (Actual time of shift/measured time) x 100% Dose = (91 x 12)/8 x 100% = 136.5% TWA = log (136.5/100) = 92.24dBA Yes, this worker is overexposed and should be wearing a hearing protection device Dose... W/>1 sample D = 100 [C 1 /T 1 + C 2 /T C n /T n ] Where: C n ~ Actual time T n ~ Allowable time T n = 8/2 (L-90)/5 OSHA T n = 8/2 (L-85)/3 NIOSH Example A worker was sampled for 2 83 DB, 3 92, and 3 90 db. Calculate the Dose. Calculate TWA. 16

17 Solution D = 100 [C 1 /T 1 + C 2 /T C n /T n ] D = 100 [2/ / /8] D = 96% TWA = log (96/100) = 89.78dBA Octave Band Analyzer This is the breaking down of a large frequency range (20-20K Hz) into smaller bands An octave is a frequency band where the highest frequency is twice the lowest frequency (f 2 = 2f 1 ) Helps understand the frequency make-up of noise This is useful to assess the frequency at which the attention of an IH is mostly needed in implementing noise control Octave Band Analyzer... 2 Ranges may be: , , , , ,000 17

18 Octave Band Analyzer... 3 Used to: Select adequate damping material with appropriate Select adequate isolation material with appropriate Transmission Loss (TL) Fletcher-Munsen Curves SPL db vs. Frequency They characterize EQUAL loudness perception by humans for pure tone at different frequencies Adjust Frequency (perceive as louder) Were basis for Low, Medium, and High scales (later called A- B- and C-scales) The A-weighted sound level (dba) Used by OSHA/NIOSH Equal loudness of 40 db at 1,000 Hz (equivalent to what the human ear can hear) Can be measured directly or computed Scales (A, B, or C) are determined by frequency Weighted heavier at 1,000-4,000Hz dba discounts lower frequencies 18

19 C-Scale (dbc) C = No weighting (flat, or equally weighted) Used for environmental noise (EPA) Both are equally weighted at 1,000Hz (A=C) dbc > dba at low frequencies A, B, and C Scales VII. Noise Regulations 19

20 Federal Agencies regulating Noise Exposure OSHA MSHA FRA USCG FHWA DOD OSHA 29 CFR CFR Exchange Rate (or Doubling Rate) = 5 db Impact noise = 140 db OSHA Formulas Where: C n = employee s exposure time at a particular noise level T n = Total time allowed at that noise level D = Total noise Dose 20

21 OSHA Criteria If Dose > 1.0 (100%), TWA >90 dba OSHA Limitations In construction: No protection is required for TWAs of 85 dba 90 dba The specific provisions of the hearing conservation program are not listed in detail Oil and Gas well drilling and servicing operations are not covered 21

22 More on OSHA Limitations Civilian employees of other federal agencies are not covered Farm workers who are employed by farms with <10 workers Crew members on all commercial vessels, trainmen, mine workers, and civilian and military employees of the U.S. DOD 22