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NOISE HAZARD EVALUATION

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Title: NOISE HAZARD EVALUATION


1
NOISE HAZARD EVALUATION
2
Purpose of Noise Hazard Evaluation
  • Measurement of noise levels to determine if they
    are hazardous to hearing
  • Hazardous noise is defined as
  • gt 85 dBA steady state noise over an 8 hour period
  • gt140 dBP impulse/impact noise

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 HPDs
  • 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 workers
    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 measurers 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 TWAs 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
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