3M Noise Measurement


Noise measurement forms the foundation for the entire HCP. The noise survey results are the basis for decisions on reducing risk and taking protective action.

Do we need a Hearing Conservation Program (HCP)?

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    If employees at your company work in noisy areas, start by conducting a sound (or noise) survey. 

    In the US, the Occupational Health and Safety Administration (OSHA) requires employers to provide a Hearing Conservation Program (HCP) whenever employees have 8-hour time- weighted-average (TWA) noise exposures of 85 dBA or more.

    Surveys can be simple or complex and may be conducted by people on your health and safety team or by a consultant. There are many different types of noise measurement instruments available depending on the type of noise and the purpose of the survey.

    Measure noise to answer key questions

    • Is HCP needed?
    • Can we control the noise?
    • How much hearing protection do we need?

    Some indications that noise may be a problem in your workplace

    • Employees hear ringing or humming in their ears after exposure to loud sounds
    • The noise is so loud that employees must shout to be heard by a coworker an arms length away
    • Employees notice temporary loss of hearing ability when leaving work

Key Takeaways

    • Hearing Conservation Program (HCP) is required whenever employee time weighted average (TWA) noise exposures are 85 dBA or more.
    • Area monitoring is a useful starting point. 
    • Personal monitoring (noise exposure of an individual worker) is needed when workers are highly mobile and noise levels vary considerably.
    • Detailed noise measurements with an octave band analysis may be needed for developing noise control solutions.
    • Action level (AL)
    • Criterion level
    • Dose
    • Dosimeter
    • Exchange rate
    • Octave Band Analysis
    • Permissible exposure limit (PEL)
    • Sound (Noise) Surveys
    • Sound level meter (SLM)
    • Threshold level
    • Time weighted average (TWA)
    • Weighting

Getting Started with Sound Surveys

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    Step 1. Perform a walkaround survey
    A walkaround survey or “screening” survey can be the first step to knowing where there are noise problems. The purpose is to identify where hazardous noise is present. If noise levels are 80 dBA or more, additional sound surveying is needed.

    Step 2. Conduct sound level surveys in noisy areas
    A sound level survey is a systematic method for measuring sound pressure levels of specific equipment or tasks, in an area, or near a person. Types of Sound Level Surveys include:

    • Basic survey: Helps employer quantify the noise environment, create noise maps of area sound levels, and determine if a more extensive survey is needed. The results can be used to create a sampling plan; an estimate of how many samples need to be taken to accurately describe the noise levels for each area or job description.
    • Extensive survey: Involves gathering detailed information about specific job tasks, areas, or equipment. Results are useful to determine worker noise exposures, make hearing protection assignments, and identify who is in or out of the HCP.
    • Noise control survey: Focuses on identifying and prioritizing options for reducing the noise hazard using engineering or administrative controls.

    Step 3. Create a noise sampling plan
    The results of your basic sound level survey and your observations of how noise fluctuates during the work day can help you develop a plan for how many measurements need to be taken in order to accurately assess the noise exposures in each area and for each task or job description. Generally, more samples are needed when the results of your basic survey are close to the Occupational Exposure Limit (OEL) for noise and when the variability of your noise survey results is high. Fewer samples may be needed if the sound levels in your surveys are well below the OEL and the sound levels are less variable.

    Suggested resources to learn more about sampling strategies for occupational noise exposure: “Quantitative Exposure Data: Interpretation, Decision Making and Statistical Tools” in A Strategy for Assessing and Managing Occupational Exposures, 4th Edition". AIHA Press, 2015. "The Noise Manual, Fifth Edition". AIHA Press 2003

    Step 4. Monitor employee noise exposures
    Measuring the noise exposure of employees requires averaging the sound levels over time. Noise exposure monitoring is often included as part of an extensive sound survey. The purpose of noise exposure monitoring is to determine a worker’s 8-hour time weighted average (TWA) or accumulated noise dose over the work shift (personal noise dose).  It is also used to measure how noise varies over time according to the job task.

Getting Started with Sound Measurement Instrumentation

Learn More About Noise Exposure Instrumentation

Sound measurement instrumentation should be rugged and reliable and include a software system that detects, measures, evaluates, and reports any occupational and environmental safety hazards.

Sound level meters (SLMs) measure sound pressure levels in real time. At least a general purpose meter (Type 2 microphone) and specific instrument settings are needed for occupational sound surveys. SLMs can be basic or have advanced features and capabilities. 

  • Measure and display the sound level in real time. They do not average or store results.

  • In addition to measuring and displaying the sound levels, advanced SLMs can average, or integrate the sound levels over time. This is an important function because risk of hearing loss and noise exposure limits are based on the average sound levels measured. These SLMs meters may also have special filters to measure impulse/impact noise or octave band filters to divide the sound spectrum into smaller segments.

  • Personal noise dosimeters are portable devices worn by workers for extended periods of time throughout the work shift. At the end of the sampling period, the instrument automatically calculates the time-weighted average, noise dose, and other important metrics. Regulations require that employers use representative personal sampling when workers move locations frequently and/or when noise levels are variable.

  • All sound measurement instruments need to be routinely calibrated. It is recommended that instruments be calibrated annually by the manufacturer to ensure the accuracy of the measurement device. Each time a sound measurement instrument is used, it should be checked with an acoustical calibrator, designed for that instrument. The sound level reading should be the same at the beginning and end of each measurement period.

  • Noise measurement instruments are categorized by Type or Class according to the accuracy of the microphones. Type 2 (class 2) general purpose instruments are designed to be accurate to +/- 2 dB . For most hearing conservation program noise measurements, a Type 2 instrument is considered adequate. A more accurate Type 1 instrument may be used by engineers to conduct detailed noise control surveys but is generally not needed for basic sound level surveys.

  • There are many apps for mobile phones and tablets that can be used to measure sound. These apps may be useful for teaching employees about sound levels in your facility and demonstrating how sound levels vary by area and task. However, mobile phones and tablets should not be used for conducting noise surveys as part of an occupational HCP unless a Type 2 microphone is used and the calibration of the device is checked before and after each measurement. To learn more about the accuracy and reliability of these apps, visit NIOSH online

Sound Measurement Instrument Settings

  • 3M Sound Measurement

    The results of a sound level survey depend on the measurement settings used. In the US, OSHA regulations specify that certain settings be used for compliance. Other regulations and some professional organizations recommend a different group of settings for a more protective approach.

    For hearing conservation, a filter setting on sound measurement instruments, known as A-weighting, is used. When this is done, the sounds that are included in the measurement are limited to a range of sound frequencies where human ears are most sensitive and the risk of hearing damage from noise is greatest.

    Slow response
    The decibel reading displayed on a sound level meter is an average of the sound level measured over a certain time. For hearing conservation, a slow response setting is used, meaning that the value on the display is the 1-second average that was measured while the instrument is on.

    Dosimeter settings (OSHA 1910.95)

    • Criterion level: 90 dBA
    • Threshold level: 80 dBA (hearing conservation) or 90 dBA (noise controls)
    • Upper limit: 115 dBA

    Resources to learn more about noise measurement instrumentation and sampling methods:

What is Required?

OSHA does not specify a time schedule for conducting noise monitoring. Instead, employers are required to repeat noise surveys whenever there is a change in processes, procedures, or exposure time that may lead to changes in employee noise exposures. Many companies choose to conduct surveys periodically (once every year or two) to ensure that all exposed employees are included in their hearing conservation programs.

  • Occupational Noise Exposure
    OSHA Requirements in United States 29 CFR 1910.95 Occupational Noise Exposure

    When employee noise exposures meet or exceed the TWA Action Level (AL) of 85 dBA:

    • Develop and implement a noise monitoring program
    • Design a sampling strategy to identify employees for inclusion in the hearing conservation program (HCP)
    • Use representative personal sampling (dosimetry) when workers are highly mobile, noise levels are variable, or there is significant impulse noise
    • Set sound measurement equipment to an A-weighting scale, and a “slow” response setting. Use a Type 2 microphone (or better).
    • Let employees (or their representatives) observe the monitoring. Inform them of the survey results.

    Read OSHA 29 CFR 1910.95

  • Permissable Exposure Limit
    Know The Limits

    OSHA and other agencies have set the Permissible Exposure Limit (PEL) at 90 dBA based on a 5 dB exchange rate for calculating noise dose. This is known as the ‘90/5’ approach to quantifying daily noise exposure.

    Resources for more information on US Federal noise and hearing conservation regulations.

    Read MSHA 30 CFR Part 62

    Read FRA 49 CFR Part 227 & 229

Beyond the Basics

Download Noise Exposure Infographic*** (PDF, 167.21 KB)

Employers may choose proactive policies to better protect exposed workers. Best practices for noise measurement include:

  • 3M Occupational Noise Limits Infographic

    Lower the Limits
    Some employers have adopted the lower NIOSH Recommended Exposure Limit (REL) of 85 dBA TWA and a 3 dB exchange rate for estimating noise dose.  As shown, the maximum allowable daily exposure time is much shorter when the NIOSH approach is used.  Measuring noise exposure this way may lead employers to implement more extensive noise controls and hearing protection solutions to reduce employee noise exposures.

    To learn more about the 85/3 approach to measuring noise exposure and recommended noise measurement methods:

    Plan Ahead
    Keep noise measurement data current by repeating surveys every one to two years. Repeat noise surveys after implementing engineering controls. Calibrate noise survey equipment annually. Conduct calibration checks before and after each measurement to verify the reliability of the instruments.

    Be Thorough
    Conduct enough samples to ensure that the noise measurements are representative of the worker’s exposures. This may require a statistical sampling approach. Document areas and jobs that have noise levels and/or exposures that are less than 85 dBA TWA as well as those at or above the action level.

    Use Your Results
    Create a database of noise survey records that can be easily accessed and maintained over time. Review noise survey results routinely: identify changes in noise levels or job tasks that trigger the need for additional monitoring.

    Get Help
    Consider contracting with a noise specialist for guidance and detailed survey requests that go beyond the expertise of the employer. Engage workers in identifying noise problems and solutions.

    *Noise Exposure Infographic Copyright 3M 2017. All rights reserved

Have You Considered?

  • Noise Exposure Variance
    How much do noise exposures vary?
    • Does each job classification have an assigned time weighted average (TWA)?
    • Have you measured all occasional or seasonal noisy activities?
    • Have changes in the length of work shifts been accounted for?
    • Is it clear which jobs are NOT required to be in the hearing conservation program (HCP)?
  • Noise Exposure Reduction
    Can it be better?
    • Can lower noise limits be adopted as company policy?
    • Did you set your dosimeter to measure  noise exposure with multiple parameters?
    • Can you use the noise survey results to identify projects for noise control?
    • Is noise interfering with workers’ ability to communicate?
  • Noise Exposure Protection
    Who knows the noise?
    • Do workers know their noise exposures and how to protect themselves?
    • Are the noise survey results part of the hearing test records?
    • Are signs posted to alert workers of high noise areas?
    • Do workers know when the next noise survey is?

Resources to Learn About Noise Measurement

  • IMPORTANT NOTE: This information is based on selected current national requirements. Other country or local requirements may be different. Always consult User Instructions and follow local laws and regulations. This website contains an overview of general information and should not be relied upon to make specific decisions. Reading this information does not certify proficiency in safety and health. Information is current as of the date of publication, and requirements can change in the future. This information should not be relied upon in isolation, as the content is often accompanied by additional and/or clarifying information. All applicable laws and regulations must be followed.