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Important Levels:

^Measuring Threshold tHearing Conservation Begins-50% Dose

^Eight-Hour Criteria Level

§Minimum Upper Range a = Table G-16a (Abbreviated)

Important Levels:

^Measuring Threshold tHearing Conservation Begins-50% Dose

^Eight-Hour Criteria Level

§Minimum Upper Range a = Table G-16a (Abbreviated)

LTL—Low threshold level, when set at 80 dB, measures only 80 dB and above; assumes 0s below that level. Used for OSHA hearing conservation compliance.

HTL—High threshold level, when set at 90 dB, measures only 90 dB and above; assumes 0s below that level. Used for OSHA engineering control compliance.

Criterion LEVEL—90 dB, when measured for eight hours, reads 100% dose.

5dB Exchange RATE—Used by OSHA; every 5 dB increase or decrease either doubles or halves the dose.

A WEIGHTING—Used by OSHA (and others); reads the way the human ear hears sound. Basically the low frequencies and some high are not read as loud as they acoustically are.

LAVG—Average sound level for the actual time measured based on other than a 3 dB exchange rate, ie. 5 dB-OSHA, 4 dB-DOD, or a 3 dB exchange rate with a threshold. Useful for short-term samples or for making projections.

LEQ—Average sound level for the actual time measured based on a 3 dB exchange rate and no threshold.

TWA—An eight-hour dB average regardless of the sample time length. For example, in a four-hour sample measurement, TWA assumes the last four hours are 0s and averages them in the overall reading, making the average dB level lower than it should be. Appropriate to use if someone works other than an eight-hour day, ie. twelve-hour shifts. TWA takes twelve hours of exposure and condenses it into eight giving the appropriate TWA for eight hours. Not appropriate to use for short samples. (Note: LAvg is always greater than TWA in samples less than eight hours. Samples of exactly eight hours result in equal LAvg and TWA, and samples longer than eight hours produce TWAs that exceed LAvg.)

DOSE—The accumulated exposure obtained, expressed in percent allowable over eight hours.

SEL—A one-second average of a noise occurence that is any duration in length. (Used to compare several noise events with different time durations.)

tracting the NRR value of a device (furnished by the manufacturer) from the LAvg. Histograms, or sound-level-time history, in the printed format are quite useful. The benefits of histograms include identification of noise patterns— and significant break in patterns—during the workday. Patterns help identify sound sources which require corrective action to lower total exposure to the worker. The histogram identifies the exact time when a significant break in these patterns occurs. This information is the basis of documentation presented at compensation hearings.

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