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Problematic Exposure Monitoring –

Assessing Skilled Trades and

Maintenance Workers


By John Rioux


The purpose of noise exposure assessment is ultimately to help industry preserve their employee’s hearing health.  The assessment is used to determine whether an employee is at risk for occupational noise induced hearing loss, and allows the employer to take appropriate actions as required by law to protect against hearing loss.  For employees working standardized production jobs this is usually a fairly straight forward exercise.  This becomes problematic when the people charged with conducting the exposure assessments are faced with employees working in jobs with high mobility and highly variable work day activities, such as maintenance and skilled trades personnel.


How do you assess noise exposures for your skilled trades and maintenance people?  Is it something you have given much consideration in determining your monitoring program strategy?  The major problem lies in accuracy and repeatability of determining and documenting their actual TWA.  The variability in worker activities, locations and exposure to different sources give a wide range of possibilities for any given day’s noise exposure.  A quiet day in an isolated workshop can produce a TWA(8) under 70 dBA while a day spent making repairs stamping press room may produce one greater than 95 dBA. 


OSHA standard 1910.95(d)(1) monitoring requirements state:



When information indicates that any employee's exposure may equal or exceed an 8-hour time-weighted average of 85 decibels, the employer shall develop and implement a monitoring program.



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.



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 article will:


· Review some of the traditional methods of documenting skilled and maintenance worker exposures,

· Examine the ramifications of inadequate exposure assessment, and

· Offer some suggestions for an improved exposure assessment decision making model that is both cost-effective and defensible.


Assessment Methodologies

Assessing noise exposure is familiar to most safety and hygiene professionals and is even straightforward for most manufacturing jobs.  But when applied to skilled trades, the conventional wisdom as to how to meet these requirements begins to break down. 


Area Measurements/Monitoring - Area measurements or monitoring is often used as an initial ‘broad brush’ approach to determine if further sampling (personal monitoring) is necessary.  It can be effective in assessing risk for mobile employees that do not generate noise from their direct activities such as supervisory personnel who are constantly moving throughout a defined area with relatively stable noise levels.  It is also cost effective, as it can be done independent of the actual employees being assessed.  This type of sampling, however, is often inadequate for skilled trades personnel because in addition to their noise generating activities, the duration and location of their movements are not always predictable.  The information from area sampling can be used as part of an assessment strategy, but it can not be used as a stand alone methodology.


Personal Dosimetry – Personal dosimetry is the standard by which OSHA assesses the validity of exposure assessments.  OSHA states that the burden of proof lies with the employer to show that whatever assessment methodology is used, it will be validated against full shift personal dosimetry.  (Remember, the primary intent of OSHA’s on-site sampling is only to determine if specific employees are exposed to excessive sound levels, not to define the boundaries of an employer’s Hearing Conservation Program.)  The inherently variable nature of the maintenance worker job raises some issues with this exposure monitoring methodology. 


When conducting personal dosimetry according ‘by-the-book’ industry standard this would require obtaining enough ‘random’ and ‘independent’ samples in order to generate a statistically valid geometric mean TWA, which can then be used to represent the employees’ exposure.  This would likely include full shift samples taken during low and high noise exposure activities.  The resultant mean may be below the action level, but in actuality a person may have daily exposures that may exceed it.  Because of the wide variation in exposure levels this has a potential to over or under assess an employees exposure, resulting in possible omissions from a company’s hearing conservation program. 


The potential time and cost associated with trying to conduct a ‘by-the-book’ personal dosimetry assessment makes the practice unworkable, and in reality it is vary rarely utilized.  Many companies conduct as little as one round of sampling and assign that exposure level to individuals or group of employees, without ever considering if the sample is actually representative of employee exposures.  An employee’s exposure may not be re-examined until the next sampling period which could be a year or more away.  Additionally, the vast majority of dosimetry sampling is largely unobserved during the shift, which raises questions about potential artifact in the data.  This is rarely accounted for and would be difficult to determine after the fact due to the natural variability in sound levels.  This is an inherently inaccurate and even dangerous means of determining an exposure level. 


Task Based Exposure Assessment - In task based assessments the auditor accumulates noise level data from equipment/tools or activities that an employee may use and from the area(s) in which they work.  Through an interview process, the auditor determines the representative duration of the equipment use as well as representative durations for time spent in different areas of a facility.  A model is then created using noise level and duration information to compute a TWA using the C1/T1 methodology described in 1910.95(b)(2), Table G-16.


This procedure approaches assessment from a risk potential perspective and attempts to derive an exposure based on a predictable ‘worst case’ exposure day.  The procedures’ results should be viewed as conservative since by design is will not under assess exposure levels.  It practice, it will likely result in the majority, if not all, of your skilled trades employees being included in your HCP.  From a compliance perspective this is more desirable than excluding at risk workers, but more employees in the HCP comes at a higher costs due to increased testing, training and hearing protection.  It may also burden companies with future liabilities for potential work related hearing loss, since employees are included in the HCP based upon exposure levels from activities they are capable and expected to be performed but not necessarily measured for each specific employee.


One of the draw-backs of task based assessment is that it generally does not always document typical daily exposures.  This has the potential to be an issue as OSHA does not specifically state how many times a person needs to be exposed to levels over 85 dBA TWA.  A literal reading would require employee inclusion in a HCP after a single days exposure to levels of 85 dBA TWA or greater.  Considering that noise induced hearing loss is considered to be a cumulative trauma, this leaves the door open to questions as to whether monitoring alone can be used to justify hearing conservation program inclusion.


Hybrid Model for Exposure Assessment


Each of these methodologies essentially yields data that provides a ‘pass/fail’ approach to hearing conservation program inclusion.  By strictly adhering to one methodology or the other the assessment is often either cost prohibitive, negligent, or inaccurate.  Since much of the process relies on the judgment of the person(s) assessing the exposures, it is imperative that they understand the strengths and limitations of various assessment methodologies.  Equally important will be their understanding of the job details, organizational culture, manufacturing processes and workplace rules & regulations specific to the facility in which the employees perform their jobs.  The combination of this knowledge will enable them to quickly and effectively provide worker exposure assessments.


To improve the information used in decision making here are some ideas to assist in assessing validity of your assessment model.  As a general rule of thumb – Utilize all the resources at your disposal.  This may include both hourly and salary personnel, medical staff, noise data, and software.


Interviews – Gather information from as many different sources in the plant as possible.  This may be the Safety Coordinator, Union Representative, Medical personnel, Facilities Engineer, Supervisors, etc.   These people generally have a vast range of knowledge about the activities of their employees.  They can answer questions that relate to the typical activities of the maintenance workers.  A ten minute meeting with these people can save hours of needless sampling time and also provide validation for your assessment model.


Tool Sound Level Documentation - The noise level output of tools and equipment that employees use is an important component to the exposure level.  It may be beneficial to create a living library of this data that can be used repeatedly in exposure assessments.  This can considerably reduce the time it takes to create exposure assessments; it also provides a means to quickly compare various tools and minimize the variability in exposure assessments.  This data can be used in both exposure assessments and independently to assist in educating employees to the dangers of hearing damage that may occur during their use. 


Taking a hybrid approach to exposure assessment involves drawing from the best attributes of the methods described above.  Models can be created that are simple, flexible, repeatable and defensible.  They may incorporate elements of area monitoring, task based assessment and verification using targeted dosimetry sampling.  Rather than exhaustively searching for the ‘perfect’ assessment, a company would be wise to focus its resources on other preventative components such as education and training.



Mr. Rioux has a Masters degree in Industrial Hygiene from Wayne State University, is an Associate with Phase To, Inc., and has over 10 years of experience in the hearing conservation arena.  Mr. Rioux can be contacted at (517) 886-9379 and at johndrioux@phaseto.com.


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