Noise in Industry - Fundamentals and Assessment Tools for Occupational Ergonomics - page 621

pulse. It is important to note that the rms-based IMPULSE dynamics setting is unsuitable for measure-
ment of TRUE PEAK SPLs.

31.4.1.1.5 Analog vs Digital Readouts
With regard to the final component of an SLM shown in Figure 31.4, the indicator display or readout,
much debate has existed over whether an analog (needle pointer or bar “thermometer-type” linear
display) or digital (numeric) display is best. Ergonomics research indicates that while the digital
readout affords higher precision of information to be presented in a smaller space, its Achilles heel is
that the digits (particularly the least significant position) become impossible to read when the sound
level is fluctuating rapidly. Also, it is more difficult for the observer to capture the maximum and
minimum values of a sound, as is often desirable using the FAST response, or the maximum impulse
peak attained, with a digital readout. On the other hand, if very precise measurements down to a fraction
of a decibel are needed, the digital indicator is preferable as long as the meter incorporates an appropriate
time integrating or averaging feature or “hold” setting so that the data values can be captured by the
human eye. Because of the advantages and disadvantages of each type of display, some contemporary
SLMs include both analog and digital readouts.

31.4.1.1.6 Sound Level Meter Applications
It is important to note that the standard SLM is intended to measure sound levels at a given moment in
time, although certain specialized devices can perform integration or averaging of levels over an extended
period of time to provide a long-term descriptor of the noise. When the nonintegrating averaging SLM is

used for noise exposure measurements in the workplace, it is necessary to sample and make multiple
manual data entries on a record to characterize the exposure. This technique is usually best limited to
area sampling, not individual employee measurements, because it is difficult for the observer to hold
the microphone near the employee's ear and to closely shadow the employee as he or she moves
about the workplace. Furthermore, the sampling process becomes more difficult as the fluctuations in
a noise become more rapid and/or random in nature.

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31.4.1.2 Dosimeter
The “audio-dosimeter” or more simply, “dosimeter,” is a battery-powered, highly portable device that is
derived directly from an SLM but also features the ability to obtain special measures of noise exposure
(discussed later) that relate to regulatory compliance and hearing hazard risk. Dosimeters are very
compact and are generally worn on the belt or in the pocket of an employee, with the microphone gen-
erally clipped to the lapel or shoulder of a shirt or blouse. The intent is to obtain a noise exposure log or
record over the course of a full or partial workshift, and to obtain, at a minimum, a readout of the time-
weighted average (TWA) exposure and noise dose for the period measured. Depending upon the fea-
tures, the dosimeter can log the time history of exposure, providing a running histogram of noise
levels on a short time interval (such as 1 min) basis, compute statistical distributions of the noise
exposures for the period, flag and record exposures that exceed OSHA maxima of 115 dBA continuous
or 140 dB TRUE PEAK, and compute average metrics using 3 dB, 5 dB, or even other time-versus-level
exchange rates. The dosimeter eliminates the need for the observer to set up a discrete sampling scheme
or follow the worker, both of which are necessary with a conventional SLM. However, it is important that
the observer establish rapport and gain the confidence of the worker wearing the dosimeter, and convey
at least the following information: (1) to behave normally as to the work activity, (2) to not tamper with
the dosimeter or microphone, (3) to return the device when visiting restrooms or entering damp areas,
(4) to return the device if there is a need to approach large transformers or other magnetic fields, and (5)
to understand the purpose of the dosimetry. Since they are designed to be worn on the noise-exposed
employee, dosimeters are typically thought of as devices for personal measurements, but they may
also be tripod-mounted or held by an observer for area or survey measurements and are very useful
for obtaining community noise measurements as well.