Using Noise Compliance Measurements to Plan Noise Controls

By: Dan Wilding M.Eng., Acoustics, Contributor

Using software for noise dosimeters and sound level meters that have built-in tools to perform noise analysis allows safety professionals to explore hypothetical noise control scenarios to aid in their decision-making process. (photo courtesy Larson-Davis)

Effective hearing conservation programs need to have two critical parts to reliably protect the hearing health of employees. The first is accurate noise measurements within the facility. The second is the implementation of necessary controls to protect employees’ hearing. These controls can be administrative changes, using personal protective equipment (PPE) or designed engineering controls. This article explores how to use the latest technology to utilize noise compliance measurement data to plan noise control implementation.

Choosing the Best Noise Control

Choosing the correct type of noise control can be difficult, even when noise problems are understood. Administrative changes, such as reducing the time employees are in problematic areas, can reduce production efficiency. PPE may be uncomfortable when worn for long periods of time and often provides less protection than what is measured in laboratory conditions. Engineering controls can be very expensive and often require outside consultation.

New technology advancements for post-processing measurement data can guide the decision-making process for choosing the best type of control with reliable success. This type of analysis can always be done mathematically with a proper understanding of acoustic equations, but for individuals who focus on many aspects of safety and health beyond noise, this is often time-consuming and unrealistic.

Using software for noise dosimeters and sound level meters that have built-in tools to perform this analysis allows safety professionals to explore hypothetical noise control scenarios to aid in their decision-making process. Note that the analysis shown in this article is for demonstration only and does not imply that one noise control approach should be preferred over another.

To illustrate this process, consider a scenario that may be applicable to anyone who deals with noise in the workplace. A noise measurement was taken using a dosimeter for nearly two hours in a noisy environment. The noise dosimeter worn by this employee reported a projected noise dose of 446% based on NIOSH calculations. The projected noise dose calculation assumes that the same noise exposure continues for a full eight-hour period. The NIOSH calculations are being selected for the purpose of demonstration in this article, as they are stricter than the OSHA calculations. Obviously, experiencing this noise level for a full eight hours would expose this employee to significant hearing health risks, as the noise dose is significantly higher than 100%, but how can we use this data to determine what plan of action would be best to protect this employee’s hearing health? While every scenario is unique, using measurement data to explore the effect of various noise control proposals can make the decision process easier.

Scenario Analysis

Since this employee is exposed to a health risk, we want to explore possible solutions by examining how changing different parameters will affect the employee’s overall noise dose. Recent technology advancements for post-processing noise measurement data have allowed simple analysis to be done without requiring outside consultation to determine the best path forward. To use the following techniques, measurements must be performed using an instrument that provides time history data logging with the ability to post-process the data to create modified results. The following screenshot shows the A-weighted noise levels measured by a noise dosimeter, which reached levels as high as 110 dB.

Administrative Noise Control

First, let’s look at an administrative approach. If this noise is coming from a specific area within a facility, then employees in this area could be moved to quieter areas periodically. Let’s assume that we could remove employees from this particular area of the facility for two hours during their shift without affecting production efficiency. This would mean that 25% of their work shift would now be in a quieter area and should reduce their noise dose, but would it be enough?

As part of the scenario analysis, offsets are easily applied to the data, and new projected dose values are automatically calculated using the modified data. In the new screenshot below, this hypothetical offset is applied to a portion of the data. For this demonstration, the quiet area has noise levels 25 dB below the noisy area, so a -25 dB offset is applied.

A modified projected dose is automatically recalculated, and we can determine if this control would be sufficient to protect our employees. The modified results are shown below.

Unfortunately, the projected dose was only reduced a small amount to 398%. This is because such a large portion of the data is still well above the 85 dB Criterion Level defined by NIOSH. This type of control by itself will not protect the employee enough to be a
viable solution.

Modified Results

Virtual Dosimeters

Projected Dose: 398.1% NIOSH

Personal Protective Equipment

Now we can look at PPE as another approach for protecting the employee’s hearing health. With hearing protection devices, noise attenuation results can vary significantly from their published Noise Reduction Rating (NRR) but, for simplicity, we will assume that the hearing protection we have selected will have an effective 10 dB reduction in practice. In similar fashion to the previous example, this scenario can easily be explored with the latest dosimeter and sound level meter software tools. The screenshot below shows a -10 dB offset to the entire measurement.

Modified Results

Virtual Dosimeters

Projected Dose:    37.2% NIOSH

The new projected dose is once again automatically re-calculated and shows an expected 37% projected noise dose over eight hours.

This is a drastic improvement and represents a viable solution to protect employee health.

Engineering Noise Control

As a final approach, we can investigate engineering control solutions. Engineering controls can be expensive but are sometimes the most effective for providing employee safety without sacrificing comfort. Selecting the best engineering control solution can be a difficult process and often requires outside acoustic consultation. However, going through the scenario analysis can certainly guide our decision process.

In our demonstration, there is one particular piece of equipment that seems to be the noisiest; hence, there is interest in putting some type of enclosure around it to reduce the noise. However, it is unknown if that will offer enough protection. A short measurement was performed with that specific machine completely off, which revealed the overall noise was approximately 10 dB quieter. An engineered enclosure around that machine won’t block 100% of the noise transmission, so it is assumed that the noise attenuation will be some amount less than 10 dB.

We can use our scenario analysis to see the effect for various noise reduction amounts and determine if they are adequate. For this demonstration, assume that the enclosure will provide an overall attenuation of 6 dB in our environment.

Modified Results

Virtual Dosimeters

Projected Dose: 107.1% NIOSH

When the -6 dB offset is applied to the entire measurement, a modified projected dose is automatically recalculated, and it predicts a 107% dose.

This -6 dB offset assumption may be slightly incorrect; however, we can see that we would still have a health risk if we didn’t get results significantly better than this estimate. This can be very useful when deciding what level of engineering controls would be needed to have a significant effect.

By utilizing the latest technology for post-processing noise data to perform scenario analyses, industrial hygiene and safety professionals can now easily explore different noise control implementations and decide which fits best for their situation, whether that be administrative, PPE, engineering controls—or  any combination of the three.

About the Author:

Dan Wilding is an Acoustician at Larson Davis, a division of PCB Piezotronics, Inc. Dan has master’s degree in Acoustics from Pennsylvania State University, and his expertise in acoustic testing methodologies, international standards and calibration of acoustic measurement devices has guided the engineering design of sound level meters, noise dosimeters and acoustic couplers. For more information about noise measurement tools and techniques for the occupational safety professional, please visit www.larsondavis.com.

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