Methods for Evaluating Noise Exposures

Understanding noise exposure evaluations, from basic area evaluations to the intricacies of equipment precision and the role of smartphone apps in noise measurements.

• By Gregory Boothe
• Nov 08, 2023

Noise exposures and standard threshold shifts have been present in general industry and construction sites since the Occupational Safety and Health Administration was founded. In fact, many safety professionals will be responsible for dealing with noise hazards at least once in their careers.

Although this is a common challenge, many safety professionals have never received any training on sampling for noise exposures. Understanding the noise sampling process can be very important in accurately evaluating noise exposures and implementing effective controls.

Basic Evaluation of Area

A common approach to evaluating noise exposures is to walk around the facility with a sound level meter (SLM) and record noise levels as area samples. The readings are sometimes used to produce a “sound map” of the facility showing areas where readings were above or below the action level and the permissible exposure limit (PEI), which is the noise exposure OSHA allows for a workday. In some cases, the readings are used to evaluate compliance with the OSHA standard, the need for a hearing conservation program and the need to implement controls including the use of hearing protection. This approach can be acceptable if the readings are representative of the workers’ actual exposures.

Acceptability of area samples typically depends on the mobility of the workers and the homogeneity of sound levels in the work areas. When the workers are mobile throughout the workday, and/or the sound levels change frequently during the work shift, area readings with an SLM may not be representative of actual exposures and another evaluation should be used.

Noise dosimeters are commonly used to measure personal exposures to noise in a workplace when mobility is an issue. The noise dosimeter can be worn by the worker and will provide a time-weighted average (TWA) exposure for the worker wearing the dosimeter. This would include the integration of exposures during breaks. Noise dosimeters are typically more costly than SLMs and can be a disincentive for many companies.

Meeting the Standards

It’s pertinent to understand the performance characteristic of the different types of instruments that can be used for noise exposure evaluation. SLMs and dosimeters used for OSHA compliance must meet the specifications in American National Standards Institute (ANSI) Standard S1.4 (OSHA, 2013). The ANSI standard sets tolerances for performance and accuracy (OSHA, 2013). There are three levels of precision in the ANSI Standard, Types 0, 1 and 2. Type 0 is the most precise and Type 2 is the least precise. Type 0 SLMs are used in laboratories so this article will not discuss them in relation to field sampling.

A Type 1 SLM can be used in the field and will provide more precise noise measurements than most dosimeters. Type 2 SLMs and noise dosimeters are more common for commercially available instruments. The main difference in the two meters is the accuracy. A Type 1 meter has a listed accuracy of + 1 dBA, while a Type 2 meter has a listed accuracy of + 2 dBA. What do these accuracies mean when collecting real-life readings in a workplace? The reading you record from the SLM, or the noise dosimeter, cannot be taken as 100% accurate. There is a range of sound levels associated with each meter that would contain the true exposure.

For example, if you recorded a sound pressure level of 90 dBA using a Type 1 SLM, you might think that your exposure was at the OSHA PEL. However, because the Type 1 meter has a precision of + 1 dBA, the actual level would be between 89 dBA and 91 dBA. The actual level using a Type 2 dosimeter would be between 88 dBA and 92 dBA. With those readings and precision levels you could not be sure if the exposure exceeded the OSHA PEL or not. It is for that reason that the OSHA Technical Manual states that an overexposure using a Type 2 dosimeter would not occur until the TWA reading was 92 dBA, meaning the range would be 90 dBA to 92 dBA (OSHA, 2013). Using the same reasoning, an exposure would not exceed the action level until the exposure was at least 87 dBA for an 8-hour shift.

The noise standard also defines the action level as an exposure of 50% or greater, which can be applied to extended work shifts (OSHA, 2008). For example, the action level for a 12-hour shift would be 82.4 dBA (a 50% exposure). Applying the accuracy of a Type 2 dosimeter the exposure for a 12-hour shift would have to be at least 84.2 dBA to be sure the exposure was above the action level.

Noise Apps: Helpful, but Shouldn’t Be the Standard

Most workers today carry smartphones with them at work. There have been many advancements in technology related to smartphones in recent years, including downloadable apps with safety and health applications. There are many available apps that allow a smartphone to be used as an SLM or dosimeter, with some apps even including an octave band filter. Some safety and health professionals will use an app to collect readings for noise in a facility and base compliance on those readings. Care should be taken when using these noise apps in the field.

First, smartphones are not Type 0, 1 or 2 meters since they do not meet the requirements of the ANSI standard. The accuracy of the smartphone using the noise app is unknown, so the reading cannot be accurately compared to OSHA standards. Smartphones typically cannot be placed within the “hearing zone” as required by OSHA. Many times, the phones are carried inside a pocket during work so the microphone is located behind some fabric, which would affect the reading. OSHA (2013) says that the phone readings can be used for rough estimates but cannot be used to document compliance with the noise standard.

Another issue with smartphones is that they cannot be accurately calibrated. The OSHA noise standard requires calibration of instruments used to evaluate noise exposures (OSHA, 2008). Calibration should be performed before and after each sampling event. Calibration for Type 1 and Type 2 SLMs and noise dosimeters is straightforward, using a portable calibration device emitting a known frequency of noise. The calibration device is placed over the SLM’s or dosimeter’s microphone. There are no validated methods to calibrate a phone with a noise app.

What do these issues mean for a safety professional who is evaluating noise at a work location? If you have a noise app, you can use the phone to screen areas for noise levels, understanding the results are not accurate enough for OSHA compliance purposes. You can use the screening information to identify work areas to evaluate using a Type 1 or Type 2 SLM or noise dosimeter. All noise information from a survey using SLMs or dosimeters should be viewed with the understanding that the results are not exact and actual exposures may vary by as much as 2 dBA.

However, best practices would be to use a conservative approach to evaluating noise exposures because some studies have indicated hearing loss can occur with exposures as low as 80 dBA. The conservative approach would be to take the high end of the noise range for the readings and use those levels to determine if controls including a hearing conservation program should be implemented.

Lastly, it is best to use a SLM or dosimeter rather than a noise app for a more accurate reading and one that meets OSHA standards. This is key when evaluating the work area’s noise level so that you can determine effective controls to ensure the hearing and safety of those who work amid the noise. Afterall, a safety professional’s main role is to ensure the safety and health of workers.

This article originally appeared in the November/December 2023 issue of Occupational Health & Safety.