Occupational Noise

Acoustic noise measurements

Occupational noise is a type of acoustic noise that results from work activities. Typical noise sources are machines, tools, and other work equipment generating loud noise. Occupational noise levels are typically measured in decibels and expressed as a percentage of the daily exposure limits as noise dose. The most popular approach to occupational noise measurement is to take 8-hour measurements with wearable sound level meters called noise dosimeters. This way, the overall amount of sound exposure over 8 hours is obtained and transformed into a noise dose.

Employee noise exposures

To protect workers from occupational noise, employers must implement engineering and administrative controls. Engineering controls involve making changes to the way equipment is used or designed. Administrative controls involve changing the way work is done to reduce exposure to occupational noise. For example, an employer might provide earplugs or earmuffs for workers who are exposed to occupational noise. Employers must also create a hearing conservation program if workers are exposed to occupational noise levels that exceed the permissible exposure limit. The hearing conservation program must include annual audiometric testing and training on how to reduce exposure to occupational noise.

Noise Measurement Method

Assessment

Workplace noise measurement PDF

Learn about methods of workplace noise measurement with the use of octave band analysis. In noisy areas, sound measurement instruments are used to perform noise surveys. The equivalent sound level is the measure of noise that takes into account the fact that our ears respond to sound frequencies differently. In general, noise levels above 85 dB can cause hearing damage. Hearing loss is also affected by noise frequencies. That's why it's important to know how to measure noise levels and how to use octave band filters. By using the right sound measurement instruments, you can make sure that noisy areas are kept safe for both workers and the general public.

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Noise Measurement Techniques

Standards

Occupational noise measurement and control in the United States

In the United States, OSHA 1910.95 is used to determine occupational noise exposure. The Occupational Safety and Health Administration (OSHA) has established noise exposure limits to protect workers from the harmful effects of occupational noise. OSHA’s permissible exposure limit for occupational noise is 85 dBA for an eight-hour workday as noise exposure above this level can result in hearing loss.

ISO9612 and the EU Noise Directive in Europe

Occupational noise measurement in the United States is almost identical to measuring noise in Europe. In both cases, the objective of noise exposure testing is to keep employees from suffering hearing damage. Both in Europe and US, the noise exposure is shown as a decibel level extrapolated to 8 hours. The calculation is extrapolated if the measurement lasts less than 8 hours, e.g., 7 hours, and it is calculated as though it had lasted 8 hours. The only significant changes are in the indicators: US regulation uses noise dose, whereas EU uses L_EX noise exposure level. As a result, it is critical to understand how exposure is determined as well as the limits it is compared to.

Noise Dose

The noise dose results in the percentage of a daily permissible limit for noise exposure, as defined. The OSHA standard 1910 specifies that the dose is the indicator of 8-hour noise exposure and offers instructions on how to calculate it based on the sound level.

L_EX 8h-eight hours of exposure

The daily noise exposure level (LEX, 8h) has been established by ISO 1999 as the most important indicator of noise exposure in Europe. The L_EX, 8h is an 8-hour extrapolation of L_Aeq measured over the working hours.

Noise exposure limits

Following the OSHA 1910.95 standard, it is necessary to provide hearing protection for workers whenever noise exposures equal or exceed an 8-hour time-weighted average sound level (TWA) of 85 decibels measured on the A scale (slow response) or, equivalently, a dose of fifty percent.

The OSHA 85 decibel limit is the EU Noise Directive’s upper action value, which sets up limits for L_EX, 8h:

87 dBA as the daily limit
85 dBA as the upper action value
80 dBA as the lower action value.

Exposure to the peak noise limit

Together with L_EX, 8h, the L_Cpeak should be measured, which limits are, accordingly, 140, 137, and 135 decibels C-weighted, following the EU Noise Directive.

A, C, and Z-weighted noise measurements

IEC 61672 specifies frequency weighting as a difference between the frequency-weighted level indicated on a meter’s display and the corresponding input signal. The goal of the use of frequency weighting is to build an electronic circuit whose sensitivity varies with frequency like that of the human ear. Hence, frequency weighting is a function of frequency.

The A-weighting is most frequently utilized since it processes the incoming signal similarly to how the human ear does. The C-weighting uses less attenuation at low frequencies and is typically used for peak measurements. A Class 2 sound level meter should have at least an A frequency weighting. Class 1 sound meters should also have C weighting. Frequency Z-weighting is optional as it is used mostly for frequency spectrum weighting.

Low-frequency noise measurements

Low-frequency noise is called infrasound. By ISO 7196, the term “infrasound noise” refers to noise in frequency spectra between 1 and 20 Hz. Infrasound is linked to all forms of human activity, including social and workplace settings. Infrasound can originate from both natural and man-made sources. Examples of natural sources include earthquakes, waterfalls, and sea waves. In the work environment, sources of infrasound include vehicles, industrial machinery, compressors, ventilators, or air conditioning. Humans can hear infrasound sounds, but they can also sense them through vibration receptors that are located all over the body. The infrasound measurements are performed with a G-weighting filter or with the use of a 1/3 octave analysis.

Ultrasonic Noise Exposure

The nominal frequencies of technological ultrasonic devices, or sources of ultrasonic noise in the workplace, such as ultrasonic washers and ultrasonic welding machines, are in the range of 18 kHz to 40 kHz. Ultrasonic noise, which is defined as noise with high audible and low ultrasonic frequencies between 10 kHz and 40 kHz, is listed as a factor that is damaging to health in the workplace. The infrasound measurement is performed in 1/3-octave bands from 10 kHz to 25 kHz (or up to 40 kHz).

Noise measurement devices

Equipment

Noise dosimeter

A personal sound exposure meter integrated with the microphone, meeting the specification of IEC61252, is often called a “noise dose meter” or “noise dosimeter”. A noise dosimeter is used for employee noise exposure assessment.

Integrating sound level meter

Sound level meters meet requirements for Class 1 or Class 2 of IEC 61672-1. Class 1 is recommended especially in low temperatures or when noise is dominated by high frequencies. Sound level meters are used both for noise exposure measurements and noise surveys.

Post-processing software

PC software for the noise measurement data post-processing and reporting according to noise measurement standards such as OSHA or ISO.

Sound Calibrator

The sound calibrator meets the requirements of IEC 60942:2003, class 1, providing one or more frequencies within the range of interest. Calibrators are used to check noise measurement equipment before and after the noise measurements series.

What equipment is the best to measure noise levels?

When should noise dosimeters or sound level meters be used to measure exposure?

A sound level meter such as SV973 measures sound pressure levels at a single point in time, which is useful when sound is steady‑state with little variation in level. But when noise levels vary considerably in level and duration, it’s difficult to accurately estimate exposure using a sound level meter. A sound dosimeter such as SV 104 should be used instead.

Exposure monitoring with noise dosimeters

A noise dosimeter measures sound levels continuously over time and integrates them into a single value, the sound dose. A dosimeter provides a more accurate estimate of noise exposure when sound levels fluctuate and/or exposure durations vary, and can alert the user in real-time to the need for hearing protection based on the accumulated noise exposure. Noise dosimeters are easy to operate and can be used for a wide variety of applications. Therefore, it is the preferred method following ISO 9612.

When should Class 1 Sound Level Meters be used?

The ISO 9612 recognizes handheld sound level meters as well as personal noise dosimeters. A noise dosimeter, meeting IS0 61721 and IEC 61672-1 standards, is the preferred device. In the case of measurements in low temperatures or when noise is dominated by high frequencies, class 1 instruments such as SV 971A are recommended.

Noise dosimeters calibration and periodic verification

Noise dosimeters should be calibrated before and after each series of measurements. Additionally, they should be verified in the accredited laboratory at least once every 2 years.

Occupational noise

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