Practical Uses for Accurate Noise Exposure Assessment
By Justin Stewart
Recent technology advances found in electronic devices of all types are now finding their way into the most commonly used tool for assessing personal noise exposure levels—the personal noise dosimeter.

Increasingly powerful processors and the availability of low-cost memory have enabled new functionalities that can aid industrial hygienists in capturing more data. More importantly, industrial hygienists can now capture other types of information that increase the quality and veracity of noise exposure data.

Octave Bands and Audio Wave Files
The first dosimeters struggled to record the most basic information needed for compliance purposes and rudimentary diagnosis of when and how the most severe noise exposures may have occurred. Certainly, the advent of continuous full-shift measurement on a minute-by-minute basis and the ability to download that detailed profile of exposure was a giant step forward from non-logging instruments that gave only a cumulative dose at the end of the shift.

With the recent development of more powerful dosimeters, many of the more detailed methods of quantifying the noise/sound environment that were previously available only in very expensive sound level meters are now being integrated into compact, shoulder-mounted dosimeters. Two of these capabilities of particular value to industrial hygienists are octave band measurement and audio ”wave file” recording.

Octave band recording consists of measuring the frequency or ”pitch” of the noise across the OSHA- and ANSI-required range of sound frequencies considered hazardous to human hearing—and breaking this range down into narrower ”bands” of pitch from low to high. Each octave band represents a doubling of frequency from its reference point, and the instrument calculates a decibel (dB) level that corresponds to the energy from just that specific range of frequencies. This approach has been used for decades to determine engineering controls and is also used for informed selection of hearing protection devices (HPDs). There are many available references regarding the proper use of octave band data for these applications, the most prominent being the AIHA Noise Manual.

While knowing the octave bands of the noisiest exposure sources is important, being able to identify the source of a hazardous noise is perhaps even more useful. For decades, IHs have had to try to identify the cause of some unexpectedly high noise doses reported at the end of a monitored shift. Until recently, it took quite a bit of work to sort through the downloaded data to find the times of day at which the subject under test was subjected to higher-than-expected exposures, and then try to interview the worker to determine where they were and what they were doing at those times. Self-reporting of the noisiest activities is not always reliable, and unfortunately, there have been cases where workers may have intentionally or unintentionally placed their dosimeter near an unusual noise source, leaving the IH puzzling over what to do about a captured noise exposure 50, 100, or even 200 percent higher than expected when similar tests or cohort groups have exposures below the Action Level.

Decisions regarding whether to include a worker in the Hearing Conservation Program can often hinge on repeatability and confirmation that the test result is a representative sample. Imagine being able to have the noise dosimeter function as an audio recording device that, when enabled, uses its digital sampler to also record the actual noise signal, as it truly sounds, for later playback as a standard-format audio file on your PC. Now it is possible to record unusual noise events for identification as either true sources of exposure or artifacts induced by the worker outside the normal course of duties (examples may include going to unauthorized areas, playing loud music, or shouting). It is important to note that this capability must be applied with good judgment; there may be limitations on recording actual speech and/or confidential information, and recording may be prohibited in secure installations and certain government agencies. When used correctly, however, the audio recording function is invaluable as a diagnostic tool and for determining the very best ways to apply engineering and administrative controls. It could also help identify the need to perform preventive maintenance to keep machinery running more quietly and smoothly.

Octave band and audio file recording functions have been available in hand-held sound level meters for some years, but these devices are not well suited to personal exposure monitoring per OSHA 1910.95. The inclusion of these functions into personal noise dosimeters is a real benefit to industrial hygienists, especially those who encounter a result with significant deviation from the expected levels or are unsure as to how to locate and apply effective controls to lower the exposure to safe levels.

Motion Detection
Another new development unique to noise dosimeters that helps confirm that a representative sample has been captured is called motion detection. This function uses a miniature accelerometer mounted inside the instrument to detect and record movement. Since dosimeters are worn on the upper body, motion can be detected in real time and a record of worker movement integrated into the downloaded test results. This information adds another dimension to the industrial hygienist’s understanding of the total sampling environment and can be used for a wide range of sample quality-assurance purposes. For example, worker movement can be correlated with high noise environments and can help IHs recognize when a worker has removed the device due to the perceived ”inconvenience” of wearing it during certain operations, especially in tight workspaces.

Some of today’s advanced noise dosimeters have also been designed for wireless data transfer. This means that multiple units can be measured remotely without disturbing the wearer, maintaining the productivity of the work force and enabling the IH to focus on the workers who have the highest risk of noise exposure.

All the technology advances described here can be critical to determining whether your noise exposure sample data is truly representative and as accurate as possible. These new tools give those involved in hearing conservation the means to solve real-life mysteries, especially when sampling results are wild outliers to the expected outcomes.

Used correctly and with proper understanding, these new breakthroughs will result in better exposure data, more informed professional decisions, and reduced probability of noise-induced hearing loss.

Justin Stewart is area sales manager for Casella.

Advanced Noise Dosimeter Functions