NOISE HAZARD EVALUATION

1. NOISE HAZARD EVALUATION

2. Measurement of noise levels to determine if they are hazardous to hearing Hazardous noise is defined as: > 85 dBA steady state noise over an 8 hour period >140 dBP impulse/impact noise Purpose of Noise Hazard Evaluation

3. Purpose of Noise Hazard Evaluation (cont.) • To determine if noise hazards can be eliminated or reduced through engineering controls: • Engineering controls should be the primary means of protecting personnel from hazardous noise • All practical approaches to engineering noise out of the work place or reducing noise levels to below hazard criteria should be explored

4. Purpose of Noise Hazard Evaluation (cont.) • To determine if noise hazards can be eliminated or reduced through engineering controls: • Engineering controls will be applied to military unique workplaces within the constraints of maintaining combat readiness • New equipment being considered for purchase should have the lowest sound emission levels that are technologically and economically possible

5. Purpose of Noise Hazard Evaluation (cont.) • To identify and label noise-hazardous areas and equipment • Signs and labels inform workers when it is necessary to wear HPD’s • Exception: labels are not to be placed on combat equipment and tactical vehicles

6. Purpose of Noise Hazard Evaluation (cont.) • To enroll noise-exposed personnel in the Hearing Conservation Program • Noise level data is a vital element of the HCP • Absence of noise level data does not preclude enrolling personnel in the HCP

7. Noise Hazard Evaluations may be performed by: • Industrial Hygienists – (primary responsibility) • Audiologists • Trained technicians

8. Equipment Used • Sound Level Meter (SLM) – used to screen for noise hazards • if the screening detects noise levels above 84 dB, a dosimeter is then used to determine individual noise dose

9. Equipment Used (cont.) • Dosimeter – measures the average decibel exposure level over an 8 hour day

10. Types of Sound Level Meters A. Type 1 – Precision Laboratory Meter • Very expensive • Allowable variance is +/- 1 dB accuracy B. Type 2 – General Purpose • Allowable variance is +/- 2 dB accuracy C. Type 1 or Type 2 may be used for hearing conservation purposes D. Impulse noise measurements require a special meter with peak holding capability

11. Weighting Networks in Sound Level Meters “A” Scale • Filters out low frequencies • Response curve is similar to sensitivity of human ear “C” Scale • Filters out very little (only the extreme low frequencies) • If a measurement is higher on the C scale than the A scale, the noise has a low frequency component • Used to estimate the effectiveness of ear protectors

12. Operation of a Sound Level Meter • A. Control Switches • On /off switch • Battery check switch • Network selector • Fast / slow meter response selector • Attenuator – dB range selector • Display meter

13. Operating Instructions • Check calibration – demonstrate use of calibrator • Set weighting switch to dBA • Set meter response to slow • Adjust meter range switch until response is seen on display • Hold the SLM at ear level, close to the worker’s most exposed ear • Read dB level on display meter • Record results on NEHC 5100/17214 (Sound Level Survey Form) or other form containing all the information on the NEHC form • Re-check calibration

14. Factors Affecting Validity of Sound Level Readings • Weak battery • Body baffle effect – microphone held too close to your body may cause absorption or reflection of sound • Shielding effect – occurs when measurer’s body or other object is located between the sound source and the microphone • Wind noise – wind velocities above 5 mph may affect measurements; microphone windscreen helps reduce wind noise • Humidity / moisture on microphone or inside meter • Microphone size – larger microphone (one inch) is best for measuring a broad frequency range • Operator errors

15. Inverse Square Law • Doubling the distance from a sound source reduces noise level by 6 dB • This principle is used to define the noise hazard radius

16. Care of the Sound Level Meter • Must be electroacoustically calibrated annually • Calibration must be checked both before and after measurements are taken • Kept in a dry, safe place

17. Time-Weighted Average • Time-weighted average sound level • That sound level, which if constant over an 8-hour exposure, would result in the same noise dose as is measured

18. Dosimetry: Measures Time-Weighted Averages • Time-Weighted Average – average noise level measured over an 8 hour time period

19. Strategies for acquiring TWA’s on noise-exposed personnel • Personal dosimetry • Conservative estimate for group based on sample TWA measurements • Area monitoring • Calculation based on SLM data (possible but not practical)

20. QUESTIONS???