Noise Surveys from the Trenches

Noise Surveys from the Trenches

Make tackling hazardous noise easier with the right tools and knowledge.

As industrial hygienists, we anticipate, recognize, evaluate and control many agents (chemical, biological and physical) that can affect the lives of workers. Noise is one of the most ubiquitous of these and a nemesis of many OEHS professionals. In my 15-year industrial hygiene career, I have performed hundreds of occupational noise evaluations and am happy to share my perspective to help promote a better understanding of workplace noise hazards, noise risk assessment with monitoring and how to choose the best tools. 

With approximately 22 million workers exposed to hazardous noise each year, it is not necessarily a challenge to identify occupations at risk for hearing loss. Employees in agriculture, manufacturing, mining, oil and gas extraction, transportation, utilities and related industries are at particularly high risk of hearing loss due to equipment used, inherent risks and specific environments. An exposure and compliance benchmark used by OEHS professionals in the U.S. is what OSHA and the National Institute of Occupational Safety and Health (NIOSH) considers loud, hazardous noise at 85 decibels (dB) or higher, or if a person must raise his/her voice to speak with someone at arm’s length (approximately three feet away). If only noise exposure assessment was as simple as comparing exposures to a benchmark! 

The noise level most likely to induce hearing loss and the occupations at highest risk have been determined from scientific evidence and studies. But the line from that noise level to performing actual noise surveys is not linear. Structuring a noise survey appropriate to local work environments is the real challenge and determining strengths and applicability of data from each measuring instrument is key. Let’s start with a look at noise measurement through the tools of sound level meters and noise dosimeters.

Noise Surveys – The Available Tools 

Sound Level Meters (SLMs). Handheld SLMs are used to measure the noise level of a specific task and/or area and are offered in Class 1 and 2. The OEHS professional remains in the area to be monitored while workers perform their tasks. 

  • Class 1 SLMs measure sound over a wider frequency range and meet the requirements of IEC 61672-1:2002 or its equivalent. Typically, they are used for environmental, building acoustics or road vehicle evaluations.  
  • Class 2 SLMs don’t have the more comprehensive frequency range, however, they do have wider tolerances and are used for occupational noise evaluations (more on this later).  

Many manufacturers produce high-quality SLMs. When deciding on the right one, consider application, features that promote ease of use, cost and accuracy.  

Noise Dosimeters. Noise dosimeters are used to assess personal noise exposure and are the primary instrument for compliance measurements. The worker wears the dosimeter while performing his/her duties during a shift.  

Advancements in technology have transformed personal noise dosimeters from a bulky cabled unit to today’s miniaturized instruments worn in the hearing zone as defined by OSHA. Measured parameters include dose, time-weighted average (TWA) based on the dose and more (e.g., PEAK, Lavg). Dosimeters can take separate measurements (studies) for different job tasks and/or work shifts. The newest models can store individual noise sessions or studies to enable analysis and comparison/contrast among occupations. Manufacturers offer dosimeters with different features. 

An important feature in today’s world is the ability to monitor noise measurement from a mobile device via an app or computer software. Downloaded data provides the whole story of a specific study and identifies noise sources contributing to overall exposure. In addition, good observations by the OEHS professional, such as description of the tasks performed during the shift, are required to support results.  

Selecting the best noise dosimeter depends on specific needs and the desire for features that facilitate accurate measurement, including: 

  • Reliability of the battery and microphone 
  • Ease of use 
  • Automatic calibration and clear access to calibration status 
  • Flexibility and simplicity in setting parameters  
  • Easy access to and readability of data (important for sites with limited lighting) 
  • Remote monitoring capability 

Remote monitoring is especially important when performing a survey during a midnight shift, in low lighting or for occupations where it is difficult to contact the worker during dosimetry (e.g., crane operators). With remote monitoring, the OEHS professional can easily determine if the unit is working properly.  

The Good, Bad & Ugly 

Let’s drill down into the good, the bad and the ugly of noise surveys. The chief objective is to record data so that it can be used to achieve the ultimate goal of protecting workers’ hearing. Based on experience with hundreds of noise surveys, the following considerations stand out as being crucial to a successful occupational noise survey. 

Research applicable standards and develop a plan. Some research is needed before looking at the data. Investigate applicable occupational noise exposure regulations and guidelines. The regulations used depend on the type of industry, country, region or state and length of work shift. It is important to know what occupations will be monitored and when the noise dosimetry should be performed. Communicate this plan to the company’s management to facilitate understanding.  

Set a noise dosimeter to the correct criteria/parameters. This includes the exchange rate, frequency weighting, response, criterion level and threshold. Many instruments now offer presets to help the user. Always double-check presets (or your own customized settings), especially if you need to make changes depending on the regulation you are following. 

Pre- and post-calibrate the dosimeter. In industrial hygiene air sampling, you pre- and post-calibrate the air sampling pump and use the average to calculate the volume of the sample. For noise, even though you don’t need to calculate air volume, you must always calibrate the instrument before and after the survey. This ensures the system’s algorithm calculates dose and TWA is accurate within set parameters. Remember that survey results may be used during litigation. If pre- and post-calibration records are not shown, the data will not be acceptable. 

Place the dosimeter in the employee’s hearing zone. OSHA defines the worker’s hearing zone as the “two-foot diameter sphere around the head.” At times, the noise source may be coming from one area of the workplace or task. It is important to identify which area and its physical relationship to the employee’s work position. This information can help determine dosimeter placement in the worker’s hearing zone. 

Use the dosimeter’s windscreen. The windscreen is an important component of both the noise dosimeter and the SLM. It minimizes interferences and/or background noises that may affect the actual noise exposure of the employee or area. It also protects the most sensitive and important part of the instrument—the microphone—from harsh conditions (i.e., abrasive blasting).  

Never forget the human factor. Explaining to employees the purpose of the noise dosimeter and what to expect is key to avoiding actions that can invalidate monitoring data. Having a high-level understanding of the instrument’s purpose drives acceptance. Despite your best communication efforts, there are just some employees who can’t help themselves (i.e., play with the unit like a video game console or hide it in unexpected places, such as in a microwave, or tell you that the noise dosimeter was making noises). These situations are best handled by talking to the employee and supervisor and trying to find a way to save the dosimetry data, if possible.  

Use an SLM and a noise dosimeter together during a noise survey. Each instrument provides valuable, unique information. The combination results in more complete information that better pinpoints noise controls. It is best practice to obtain sound level measurements with an SLM frequently during noise dosimetry. An SLM will document noise at specific points in time and from sources in the area. Its values will validate dosimeter readings and provide insight into how and when exposure is occurring. Note that SLMs cannot be used as noise dosimeters, conversely, noise dosimeters cannot be used as SLMs; this is a common mistake made in noise surveys. They work together but not interchangeably.  

Take detailed field notes during a survey. This will facilitate a better understanding of events during the work shift. Noise instruments will record exposures but it’s the OEHS professional’s observations that are crucial to providing context to the data and identifying concerns, noise sources and other information to better apply the industrial hygiene hierarchy of controls. Record readable observations. When it comes to litigation, not only are noise data and calibration documentation important but notes taken during the noise survey may also be used. 

You Have Successful Noise Survey Data. Now What?  

Evaluate collected data from dosimeters, SLMs and observations in light of the applicable regulations and guidelines. Identify which tasks have the highest noise exposures and exceed applicable regulations. Determine noise sources that are causing elevated exposure. Even for exposures that fall below regulations, it is good practice to determine if there are elevated noise sources that need addressed.  

Create a report of findings that discusses elevated noise exposures and recommends controls. Engineering controls may include shields, barriers, acoustical enclosures and sound-absorbing materials. If these are not feasible, document the reasons and proceed to administrative controls and/or PPE. Examples of administrative controls include rotating employees and programming machines to operate at a certain length of time during shifts. PPE should not be the first option when mitigating exposures. If the only option, choose hearing protection devices with the appropriate noise reduction rate (NRR–located on the hearing protector package). The higher the NRR, the more protective. Consult the OSHA Technical Manual Section III, Chapter 5, Appendix E to help determine the best NRR based on the noise data.

Performing noise surveys can be challenging for OEHS professionals, particularly if performed infrequently. It is my hope that this article provides insight into some of the pitfalls of noise surveys and promotes consideration of the technical as well as the human aspects of a survey. With knowledge and the best monitoring tools, we can handle our nemesis noise and protect workers from hearing loss. 

This article originally appeared in the September 1, 2022 issue of Occupational Health & Safety.

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