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NOISE HAZARD EVALUATION. 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. Purpose of Noise Hazard Evaluation (cont.).

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purpose of noise hazard evaluation
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
purpose of noise hazard evaluation cont
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
purpose of noise hazard evaluation cont1
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
purpose of noise hazard evaluation cont2
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
purpose of noise hazard evaluation cont3
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
noise hazard evaluations may be performed by
Noise Hazard Evaluations may be performed by:
  • Industrial Hygienists – (primary responsibility)
  • Audiologists
  • Trained technicians
equipment used
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
equipment used cont
Equipment Used (cont.)
  • Dosimeter – measures the average decibel exposure level over an 8 hour day
types of sound level meters
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

weighting networks in sound level meters
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
operation of a sound level meter
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
operating instructions
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
factors affecting validity of sound level readings
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
inverse square law
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
care of the sound level meter
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
time weighted average
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
dosimetry measures time weighted averages
Dosimetry: Measures Time-Weighted Averages
  • Time-Weighted Average – average noise level measured over an 8 hour time period
strategies for acquiring twa s on noise exposed personnel
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)