Choosing the Right
Noise Exposure Assessment Tool
By Dave Cmar
Most industrial hygienists and others involved in physical hazard risk assessment have at some point in their careers been asked to evaluate noise exposure risk. There are many tools to evaluate this risk, Industrial Hygiene assessment doctrines tend to favor the use of a personal noise dosimeter, some people are satisfied with area measurements, and still others use a detailed tasked based approach with an emphasis on source and control identification. Which one is right for your facility? On the surface this seems straightforward. OSHA appears to provide clear directives as part of the Occupational Noise Exposure Regulation 1910.95 which states:
Where circumstances such as high worker mobility, significant variations in sound level, or a significant component of impulse noise make area monitoring generally inappropriate, the employer shall use representative personal sampling to comply with the monitoring requirements of this paragraph unless the employer can show that area sampling produces equivalent results.
This would seem to make it simple; if the sound levels are stable and the worker is stationary – use area monitoring. If not, attach a dosimeter. Unfortunately, this ‘two-sizes’ fits all approach is not always appropriate.
The key to identifying the appropriateness of an exposure assessment tool is to first define the purpose. Once again, OSHA provides guidance as to the minimum purpose of exposure assessment:
The sampling strategy shall be designed to identify employees for inclusion in the hearing conservation program and to enable the proper selection of hearing protectors
What OSHA does not provide, are guidelines to address (balance) other equally important considerations such as budgets and resource allocation or the use of survey data beyond compliance. e.g. to determine priorities and benefits for engineering controls. When it comes to developing a strategy OSHA really provides very little concrete guidance to assist in the ‘nuts and bolts’ of determining the strategy for assessing noise exposure risk. The onus falls on the EHS professional to construct a strategy that is at minimum defensible, if OSHA were to challenge the results during a site visit or inspection.
This brings us back to the determining the purpose of the sound survey. The available ‘tools’ for exposure assessment are best summarized in the matrix below:
The matrix shows a complex relationship between Assessment Types, and Documentation Levels and how these relate to concepts such as real-world issues such as Cost and Complexity. How and why you go about conducting a sound survey is not simply about compliance with government regulations but also many more factors including:
- Available Sound Measurement Equipment
- Expertise of Personnel Conducting the Survey
- Need for Re-monitoring and updating results
- Workforce Flexibility (Ability to Link Jobs to People)
- Consideration for Retrofit Engineering Controls
- Confidence in Data for Legal Purposes
None of the methods described in the chart above can be characterized as good or bad. They can all be equally effective if applied for the correct purpose. Undocumented area levels are more than sufficient in many cases to validate stable low-noise conditions that may exist in many of today’s new, modern high-tech facilities. It is also an appropriate tool for determining the potential need for conducting personal monitoring. It allows you to set the parameters of a survey scope if an outside service is needed due to limited in-house expertise and equipment.
On the opposite end of the scale Task-Based Exposure Assessment (T-BEAM) can be a very powerful tool to collect data that can be utilized not only for HCP inclusion but also for source identification, validation of process improvements, determining retrofit control priorities and providing a strong supported dataset for use in legal defense against hearing loss claims. While obviously a wealth of information is created, it also requires a higher level of expertise to execute correctly, which generally increases the costs.
Although there most assessment strategies can be classified within this matrix, assessment strategies and the results are as varied as the number of people applying them. Choosing the one best suited for any individual situation is simply a matter of understanding the principals behind the application and the proper definition of survey purpose.
Many industrial establishments are familiar with the concept of the ‘Noise Map’ which is also synonymous with the ‘Sound Survey’. This type of communication tool has it’s origins in area monitoring, which is the basic tool for exposure assessment (and the only tool available prior to the introduction of lower cost dosimeters and Sound Level Meters (SLM)). The use of a ‘Noise Map’ and the assignment of area levels to employees are simply an extension of the area monitoring method of surveying. They can be very useful in generalizing risk potential for people where sound levels or employee interactions with sources tend to have very low variability. It is also effective as a screening tool to target personal monitoring where conditions are more variable or there is doubt as to the actual exposure of a particular job or person. The use of area monitoring can greatly reduce costs especially for industrial establishments with many areas of low exposure risk. It also has the advantage of being simple enough for people with limited exposure assessment/acoustics background to obtain reliable information for decision making. This is important for companies with limited resources for in-house expertise and equipment.
Dosimetry is the standard method that most industrial hygienists define as ‘personal monitoring’ and in fact this is what the OSHA field inspectors are instructed to use to assess exposure. Dosimetry can be an effective for assessing mobile work exposures. When utilizing dosimetry, a surveyor must take to ensure that the results are representative of job exposure. This can most easily be accomplished through direct observation of all sampling. This is can be an expensive endeavor if this approach is taken for a large manufacturing facility, with several types of jobs that may require personal monitoring. Another way to validate dosimetry data is through the use of statistical averaging. Statistical averaging is a valid assessment method in some North American jurisdictions such as Ontario which allows the option of an 8 hour Time Weighted Average (TWA8HR) or a TWA based upon a 40 hour work week. This approach while also commonly used in the United States, does pose a dilemma for OSHA compliance, as OSHA does not specify frequency of exposure. If one of the valid daily samples were to indicate a time weighted exposure above 85 dBA, by definition the person should be included in a HCP.
While these methods yield fairly reliable data, they are seldom actually used in practice. More common is the unobserved dosimetry sampling, where employees are given dosimeters at the beginning of a shift and picked up at the end of the shift. There is an obvious cost advantage to this approach and it does not necessarily require a great deal of expertise to apply. When there is little variation in exposure levels throughout the day, it is generally easy enough to identify artifact levels from the histogram and the data should yield enough info for basic HCP inclusion decisions.
Targeted dosimetry falls between the two methods on the documentation range and is useful where area monitoring and task-based assessment do not adequately address mobility and variability. By utilizing some of the controlled sampling methodology from task-based assessment, targeted dosimetry can be helpful in providing better data for HCP inclusion, decisions and minimizing cost by only documenting information necessary to achieve defensible results.
Task Based Exposure Assessment (T-BEAM)
The alternative personal sampling methodology is known as Task-Based Exposure Assessment. The engineering roots of this methodology are evident by it’s bent towards utilizing controlled sampling methodology to allow a surveyor to collect a multitude of data for various uses including source and control determination, as well as HCP inclusion. The Task Based exposure uses modeling to determine risk potential. It has elements common to Industrial Engineering time-motion studies as well as acoustical source modeling. The combination provides a very powerful tool to rapidly determine risk potential while at the same time provides significant information that makes the assessment easily defensible from a legal standpoint. This typically requires a much higher level of expertise in order to implement successfully. Because the actual sampling is based on controlled elements and requires inputs from workers, process/supervisory personnel as well as actual sound level emissions, the surveyor must be capable of ensuring that the model inputs are valid. This poses a significant problem for companies with neither the time nor resources to consistently utilize this approach. One method for addressing this problem is to simplify the model inputs. This can be a hybrid of the Task-Based approach which can utilizes workstation measurements, areas samples and short term dosimetry (grab samples) and then incorporates them into a model along the lines of classical Task-Based measurement. This simplification in the documentation minimizes the cost and expertise required to document exposures.
The explanation of the monitoring methods address issues of equipment expertise, cost and documentation. However, there are some considerations that affect survey strategy not necessarily solved strictly by examining method selections.
Need for Re-monitoring and updating results
When choosing a monitoring strategy, a forward planning mentality forces one to look at how re-monitoring and updating of the results are handled. It can be extremely costly to repeat a complete survey of a facility on a frequent basis, especially for large facilities. Establishing baseline data that can be easily verified is one way of minimizing cost. This should be paired with methods to easily identify changes that trigger re-monitoring. By addressing this early on in planning for sound surveys, it allows monitoring to be targeted only when needed. This way it is less important as to the frequency that re-surveying takes place, because it will only occur when it is absolutely necessary. This ensures that scarce resources for noise control and hearing conservation are allocated with a focus on problem solving not re-identifying existing problems or non-problems.
Workforce Flexibility (Ability to Link Jobs to People)
One of the primary aims of the sound survey is to identify people for inclusion in a HCP. This goal is more easily accomplished when people have specialized jobs and classifications that match with directly the job exposures assessed during a sound survey. This concept breaks down very quickly with today’s flexible workforces. The current trends toward cross-training employees and maximizing resources through overtime and job rotations forces many companies to include employees in HCP using a very ‘broad brush’ approach. This should have a serious affect on sound survey strategy. The survey methods are primarily aimed at measuring equipment noise emissions. The personal monitoring takes into account a worker’s interaction with the equipment. However this is within the context of a defined serious of tasks – not specific employees interactions. This disconnect between job exposures and employee exposures requires that HCP inclusion decisions rely more heavily on the ability of a company to track an individual’s work history on a dynamic basis. This falls outside the scope of a sound survey. The consequence of this is that it allows for a simplification of the sound survey, because the survey now focuses on physical changes to equipment that may affect noise emissions and secondarily administrative changes to job tasks that may also affect exposure. This simplification can also be applied to facilities that follow a total HCP inclusion process.
Consideration for Retrofit Engineering Controls
One of the selling points of the Task-Based approach is the ability to yield data for use in determining engineering controls. It should be noted that this generally refers to retro-fit controls. This is important because many facilities have moved away from retrofit controls as a priority and now focus on new-equipment controls and purchase specifications to lower noise levels. This is especially true in the automotive industry which has significantly lowered sound levels in their plants through increasingly rapid model and equipment changes. In this case collecting the additional data on a global basis during a survey would simply be a waste of resources as very little of it would actually be utilized.
Companies that are conducting a survey for the first time, however, may want to consider addressing controls as part of the initial survey because it is an opportune time to collect data for this purpose. The key really is to be firmly in control of the purpose of the survey and set the scope and methodology accordingly.
Confidence in Data for Legal Purposes
How you intend to use the data in the future can play a large role in determining the appropriate method for a survey and therefore the cost. The documentation level necessary for adequate legal defenses against unwarranted hearing loss claims can be substantial, and often the burden of proof lies with the employer. However for companies with mature effective hearing conservation programs, the additional cost may not be justified. This is an issue that should be discussed with both management and the legal consul for a company to ensure that documentation level meets both current and future needs of the company.
Take Control of Your Risk Assessment Strategy
Understanding and taking control of your noise monitoring strategy is the only way to ensure that you achieve the desired balance between reliable data, cost and documentation. Whether you utilize internal or outside expertise to conduct your survey, do not allow apathy or others to determine the scope and methodology. Take control, set the objectives and parameters so that the data collected is targeted to help in the way your business operates.