Title: NOISE HAZARD EVALUATION
1NOISE HAZARD EVALUATION
2Purpose 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
3Purpose 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
4Purpose 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
5Purpose 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
6Purpose 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
7Noise Hazard Evaluations may be performed by
- Industrial Hygienists (primary responsibility)
- Audiologists
- Trained technicians
8Equipment 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
9Equipment Used (cont.)
- Dosimeter measures the average decibel exposure
level over an 8 hour day
10Types 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
11Weighting 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
12Operation 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
13Operating 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
14Factors 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
15Inverse 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
16Care 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
17Time-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
18Dosimetry Measures Time-Weighted Averages
- Time-Weighted Average average noise level
measured over an 8 hour time period
19Strategies 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)
20QUESTIONS???