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A number of different metrics are in use for measuring and reporting exposure to noise for hearing conservation including noise dose, time-weighted average level, sound exposure, and sound exposure level. Functions for computation of individual metrics from measurement of acoustic pressure vary widely. Functions defining particular metrics in some instances contain choices of parameters (e.g., exchange rates and threshold levels). In most instances, once a metric has been evaluated for a particular time profile of acoustic pressure, it is not possible to convert it to another metric if the original time function is not retained. In addition to the defining functions, dynamic and frequency response characteristics of measuring instruments have influences on results obtained and can present obstacles to conversion among metrics. Large bodies of data exist which only contain the finally processed metric. The degree to which comparisons can be made because of recent changes in TLV requires inferential interpretation of the values of specific metrics which are produced by time functions that are identified only in a statistical sense. This paper examines the inferential relationships among prominent metrics for various classes of sound-pressure profiles as obtained with measuring instruments meeting ANSI and IEC performance standards.

Sporadic reports of substantial variations in measurements of exposure noise dose in the workplace performed with contemporary dosimeters have generated concern in the community of users. Measurement differences ranging up to many hundreds of percent have been reported. Differences have been observed when several dosimeters of different makes have been used simultaneously as well as in instances where apparently identical dosimeters have been used. Moreover significant differences have been observed in day to day tests on a given worker. These tests have been made with the same dosimeters in an apparently invariant working environment. Careful investigations of the properties of the ambient noise fields and limitations of microphones worn on the body explain, and sometime mitigate, some of the measurement variations. Remaining differences have been attributed by some users to inadequate “accuracy” of the dosimeters. ANSI S 1.25 stipulates that type 2 SLM performance is required for dosimeters. Some individuals have proposed changing to type 1 dosimeters (of even type 0 SLM's). The problems are quite complex and cannot be resolved by simple upgrading or resorting to SLM's. This paper identifies several sources of measurement variability which are introduced by generic configurations of dosimeters. These include: detector performance in the presence of impulsive noise when a 5-dB exchange ratio is used, and uncertainty in achieving threshold cutoff. It is concluded that present standards and applications practices must be changed to achieve improved measurement reliabilities.

The Occupational Safety and Health Administration published the final version of its hearing conservation amendment on 8 March 1983. It states explicitly that contributions from all noise, impulsive, intermittent, and continuous must be included in determining worker noise dose. In addition it is stated that measurements must be made with instruments possessing A-weighting and slow response. Many claims have been made that dosimeters overestimate contributions from impulsive noise (e.g., defense submissions and testimony in the Collier-Keyworth case and Friend of the Court submission by Chocolate Manufacturers Association). The CMA document presents results comparing theoretical computation for waveforms having short pulse components to results obtained with a variety of dosimeters currently in use. The instrument readings are high compared to the theoretical computations; thus it is concluded that dosimeters overestimate. This paper demonstrates that dosimeters complying with the OSHA stipulation to include A-weighting and slow response do not overestimate. Conclusions reached in the CMA brief are critically affected by ignoring the dynamic properties of Slow Response when performing theoretical determination of predicted dose for specified pulsed waveforms. It has been suggested, and in several instances demonstrated, that the discrepancy between computed and measured values disappear if fast response is substituted. Mathematical analysis of the idealized dosimeter transfer function verifies this conclusion. It should be noted that the discrepancy reappears for pulse duration of less than 0.125 s. The issue to be resolved is not one of instrument performance; rather it is whether the stipulation of A-weighted slow response is justifiable.

Noise dosimeters used to monitor worker exposures to noise must have prescribed transient response characteristics to satisfy the requirements of the U.S. Department of Labor, Occupational Safety and Health Administration. In addition, computation of noise dose or average sound level must be based on a 5 dB per time doubled trading ratio. Various individuals have concluded that there is an apparent discrepancy between measured and computed doses when industrial noise contains impulsive components. The discrepancy results when computation neglects the effects of the prescribed transient response characteristics. In particular, “slow” response has a critical effect when trading ratios of 4 or 5 dB are used. A dosimeter is required to produce measurement results which correspond to results that can be computed from SLM readings. This paper shows the relationship between transient response and measured dose resulting from noise containing impulses. Furthermore, experimental results are presented which show that dosimeter and SLM derived results are consistent and correct. Reported results purporting to show that dosimeters give incorrect measurements of impulsive noise are shown to be incorrectly evaluated because theoretically computed reference values fail to account for U.S.D.O.L. OSHA prescribed transient response. The effect of Substituting “fast” response is also presented.