Dosimeter Noise Sampling
Noise Dosimeters:
 | Measure accumulated exposure to varying noise levels over time period. |
| Give readouts in % Noise Dose. |
Most Dosimeters also provide:
| Sound Level Meter (SLM) capability. |
| Average Noise Level. (Time Weighted Average) |
| Projected 8 Hr Noise Dose. |
Dosimeter Exercise #1- Calibration
For these exercises you will need a calibrator. This can be
either be a single or a multiple noise level calibrator. You will
need to switch your Dosimeter to 'Sound Level' or 'SLM' mode.
- Insert instrument microphone into the calibrator.
- Turn on instrument and switch it to
Sound Level Meter (SLM) Mode.
- Turn the calibrator to the lowest dB level.
What is the Noise Level ? Your instrument should read within ± 1 dBA of
the level indicated on the calibrator.
- If your calibrator is a multi-noise level calibrator,
repeat the above step for all noise levels on the calibrator.
- If all your instrument readings are within ± 1 dBA of the calibrator
settings, your instrument is now field calibrated and ready for use.
Dosimeter Exercise #2 - Proper Calibrator Fit
-
Turn on the calibrator. (Any Noise level will do).
-
Leave microphone in the
calibrator. The Noise level should, again, be within 1 dBA of
noise level indicated on the calibrator.
-
With the calibrator on,
slowly remove the microphone. What happens to the Noise level?
It should drift down. This illustrates the need for a proper fit between the calibrator and instrument. Calibrators are
usually designed to be used with only one type of instrument. Some calibrators come with special collars or
fittings that allow them to be used with different instruments.
-
Always follow the calibrator manufacturer's recommendations.
Dosimeter Exercise #3 - Noise Dose Accumulation
This exercise illustrates how quickly the noise dose can
accumulate at high noise levels.
- Insert microphone into calibrator.
- Turn on dosimeter.
- Set calibrator to 124 dB (or as high as it will go).
- With dosimeter set to display High-Threshold Noise Dose
%, turn the calibrator on for exactly 5 minutes.
- While waiting, watch how fast the Noise Dose is adding
up. (Note:Some dosimeters may require you to press the 'Noise %' button
continuously to get a running readout.)
- Turn the calibrator off after 5 minutes.
- The Noise Dose would be somewhere around 125% for a
calibrator set to 124 dB and 17% for a calibrator set to 110 dB.
Dosimeter Exercise #4 - Dual Threshold Capability
This exercise demonstrates the ability of a dual-threshold
dosimeter to distinguish between Low Threshold and High Threshold Noise
Doses.
- Write down the High Threshold Noise dose you obtained
from the previous exercise. (Do not clear or reset the dosimeter.)
- Leave microphone in the calibrator and switch the
dosimeter display to SLM.
- If calibrator is multi-level, turn calibrator to the
lowest dB setting.
- Slowly remove the microphone until the dosimeter display
reads 83 dB.
- Try to hold the microphone in this position for exactly
5 minutes.
- Switch the dosimeter display back to High Threshold
Noise Dose %. There should be no increase in the Noise Dose % because the noise being
measured is below the High Threshold Limit
of 90 dBA.)
- Now, switch the dosimeter display to Low Threshold Dose %. This reading
should be slightly higher than the High Threshold Noise Dose because the noise
being measured is above the Low Threshold Limit
of 80 dBA.
The New MSHA Noise Rule
Two Noise Limits are defined in the Part 62 Noise Rule:
| Action Level (AL) |
| Permissible Exposure Limit (PEL) |
Dosimeters are “Dual Threshold” and measure AL &
PEL simultaneously:
| 80 dBA is the threshold for the “Action Level” (AL) |
| 90 dBA is the threshold for the “Permissible Exposure Limit” (PEL) |
New Noise Rule - Action Level
The Action Level is the minimum Noise Dose at which you must take action.
| The Action Level is defined as a 50% Noise Dose (using the 80dBA Low Threshold instrument setting),
which is equal to a TWA8 of 85 dBA. |
| The Action Level Noise Dose includes the all noise between 80 dBA and 130 dBA called the Low Threshold |
| If a miner's Noise Exposure over an entire work shift equals or exceeds the 50% Action Level, the miner
must be enrolled in the company's Hearing Conservation Program as per §62.150 |
New Noise Rule - Permissible Exposure Limit
Permissible Exposure Limit (or PEL) is defined as a 100% Noise Dose, which is equal to a TWA8 of 90 dBA.
The PEL Noise Dose includes all noise between 90 dBA and 140 dBA This is called the High Threshold Noise
Dose.
If a miner's exposure exceeds the PEL :
| Feasible engineering and administrative controls must be applied. |
| The miner must enroll in the company's Hearing Conservation Program as
per §62.150. |
| Double hearing protection must be worn if Noise Dose is higher than 800%
(where the TWA8 = 105 dBA.) |
| No exposures above 115 dBA are allowed (based on a 30 second average
reading.) |
Noise Sampling with a Dosimeter
- Make sure the microphone is inserted into the
Windscreen.
- Clip the dosimeter to the subject’s belt, or put it in
the subject's pocket.
- Clip the microphone to the center of the shoulder,
pointing up. (Pick the subject's “Noisiest” shoulder.)
- If necessary, use clips or duct tape to attach the
microphone cord to the clothing.
- Document, Document, Document
Dosimeter Documentation - Form 7
If you have not already done so, choose one of the options
below to either view in a separate browser window or print.
Always record your Name, Date, Employee Name, Location, Time On, Time
Off, Noise Sources, Noise Controls, Work Activity, Hearing Protectors, Dosimeter
Data, and Calibration
| Throughout the sampling period, record the accumulated Noise Dose as
often as the task changes or at least every 2 hours if the task does not change. |
| Spot check the Noise Levels with an SLM (to verify Dosimeter readings). |
| Record the Final (or Projected) Noise Dose. |
Projected Noise Dose
You can sample for less than 8 hrs, and the dosimeter will calculate what
an 8 hr exposure would be if the noise had continued at the same average level.
| This is called the Projected Noise Dose. |
| It is less accurate than sampling for a full 8 hours. |
| It does not project for 10 hr, 12 hr, or 14 hr, etc. work shifts. These
you must estimate yourself or sample the entire shift. |
Projected Noise Dose Exercise:
- Place the microphone in the calibrator.
- Turn on the dosimeter and the calibrator.
- Switch dosimeter to 'Projected 8 hour Noise Dose'.
- Depending on the Noise Level that the calibrator is set at, you will now
get an 8 hour projected estimate of the Noise Dose for that Noise Level.
CONTINUE WITH NOISE SAMPLING
SECTION
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