Noise measurement is a fundamental part of the Hearing Conservation Programme (HCP). Noise survey results are the basis for decision-making on reducing risk and taking protective action.
If employees at your company work in noisy areas, start by conducting a sound (or noise) survey.
The European Physical Agents (Noise) Directive 2003/10/EC outlines the duty of employers to protect their employees from risk of exposure to noise. There are three different exposure action values defined in the Directive.
Lower Exposure Action Value (LEAV) LEX,8h = 80dB(A) and 135dB(C) Peak
Upper Exposure Action Value (UEAV)LEX,8h = 85dB(A) and 137dB(C) Peak
Limit Value (LV) LEX,8h = 87dB(A) and 140dB(C) Peak
Depending on the level of risk involved, employers are required to take action to reduce the risk of noise exposure. Hearing protection must be made available to employees at LEAV, and strictly enforced at UEAV.
The role of hearing protectors is clearly defined in the context of achieving the Limit Value.
Noise surveys can be simple or complex, and must be conducted by a competent person, such as 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
Some indications that noise may be a problem in your workplace
• Action level (AL)
• Exchange rate
• Octave Band Analysis
• Exposure Action Values and Limit Values
• Sound (Noise) Surveys
Step 1. Perform a walkaround survey
A walkaround survey or 'screening' survey can be the first step towards identifying high-risk noise areas. Their purpose is to identify where hazardous noises are present. If measured noise levels are 80 dB(A) or more, further measurements may be required to assess the risk of exposure.
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:
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 permitted exposure level 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 permitted level and the sound levels are less variable.
Refer to your national regulation for guidelines on risk assessment and sampling requirements.
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 LEX,8h exposure 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.
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 sound levels, advanced SLMs can average, or integrate 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 devices 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, this instrument automatically calculates the time-weighted average, noise dose, and other important metrics. It is common practice for employers to 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 or an accredited third-party 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.
The results of a sound level survey depend on the measurement settings used. Check your local regulations for any specific requirements.
For the purpose of selecting appropriate hearing protectors, sound level measurements using A-weighted and C-weighted filters incorporated in your measuring device are often sufficient. These measurements can provide valuable information on the noise characteristics. Consider the following examples.
Example 1: When the difference between the C-weighted and A-weighted sound is less than 2 (LC – LA ≤ 2), the sound is dominated by high/medium frequencies.
Example 2: When the difference between the C-weighted and A-weighted sound is greater than 2 (LC – LA ≤ 2), the sound is dominated by medium/low frequencies. The higher the difference, the greater the low frequency content.
This information can be very useful when selecting hearing protectors for different applications.
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.
The C-weighted filter corresponds best to the subjective reception of sounds at high sound pressure levels and is normally used for measuring sounds dominated by low frequencies. This filter is also used for measuring peak impulse sound when set on fast 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.
The European Council Directive 2003/10/EC does not provide specific guidelines on how frequent noise measurements should be repeated. Typically, risk assessment (which may include noise measurement) are repeated 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 programmes.
Employers may choose proactive policies to better protect exposed workers. Best practices for noise measurement include:
Lower the Limits
Some employers have opted to implement exposure limits below the Lower Exposure Action Value as an additional safeguard to better protect workers from developing NIHL.
Keep noise measurement data up-to-date by repeating surveys every one to two years or sooner, if and when any changes in equipment or personnel occur. 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.
Conduct enough samples to ensure that 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 LEX,8h 80 dB(A) as well as those at or above LEX,8h 85 dB(A).
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.
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
This information is based on selected current national requirements. Other country or local requirements may differ. Always consult user instructions and follow national 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 national laws and regulations must be followed.
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