NOISE HAZARD EVALUATION

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NOISE HAZARD EVALUATION
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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
• gt 85 dBA steady state noise over an 8 hour period
• gt140 dBP impulse/impact noise

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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

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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

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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

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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

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Noise Hazard Evaluations may be performed by

• Industrial Hygienists (primary responsibility)
• Audiologists
• Trained technicians

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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

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Equipment Used (cont.)

• Dosimeter measures the average decibel exposure
  level over an 8 hour day

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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

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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

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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

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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

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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

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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

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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

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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

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Dosimetry Measures Time-Weighted Averages

• Time-Weighted Average average noise level
  measured over an 8 hour time period

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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)

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QUESTIONS???