Occupational Noise Measurements: Best Practices for Workplace Safety

Noise exposures and standard threshold shifts have been present in general industry and construction sites since the Occupational Safety and Health Administration was founded. Although this is a common challenge, many safety professionals have never received any training on sampling for noise exposures. Assessing the level of noise in your workplace is the first step.

This article outlines the best practices for occupational noise measurements, instrumental in protecting worker's hearing and ensuring compliance with safety and health standards.

Workplace Noise Measurement Techniques

Understanding Noise Measurement Instruments

Basically, there are two different instruments to measure noise exposures: the sound level meter and the dosimeter. It’s pertinent to understand the performance characteristic of the different types of instruments that can be used for noise exposure evaluation. SLMs and dosimeters used for OSHA compliance must meet the specifications in American National Standards Institute (ANSI) Standard S1.4 (OSHA, 2013). The ANSI standard sets tolerances for performance and accuracy (OSHA, 2013). There are three levels of precision in the ANSI Standard, Types 0, 1 and 2. Type 0 is the most precise and Type 2 is the least precise.

Sound Level Meters (SLMs)

Sound level meters (SLMs) measure sound pressure levels in real time. A sound level meter is a device that measures the intensity of sound at a given moment. At a minimum, it measures sound level in dB SPL. At least a general purpose meter (Type 2 microphone) and specific instrument settings are needed for occupational sound surveys. Measure and display the sound level in real time.

Since sound level meters provide a measure of sound intensity at only one point in time, it is generally necessary to take a number of measurements at different times during the day to estimate noise exposure over a workday. To estimate employee noise exposures with a sound level meter it is also generally necessary to take several measurements at different locations within the workplace.

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.

Personal Noise Dosimeters

Personal noise dosimeters are portable devices worn by workers for extended periods of time throughout the work shift. A dosimeter is like a sound level meter except that it stores sound level measurements and integrates these measurements over time, providing an average noise exposure reading for a given period of time, such as an 8-hour workday. With a dosimeter, a microphone is attached to the employee's clothing and the exposure measurement is simply read at the end of the desired time period. Since the dosimeter is worn by the employee, it measures noise levels in those locations in which the employee travels.

At the end of the sampling period, the instrument automatically calculates the time-weighted average, noise dose, and other important metrics. This would include the integration of exposures during breaks.

The best way to take personal noise measurements is to use noise dosimeters.A small badge-type device worn by the employee during a typical work day, is the simplest and least obtrusive option for directly measuring noise dose.

Calibration of Instruments

All sound measurement instruments need to be routinely calibrated. Each time a sound measurement instrument is used, it should be checked with an acoustical calibrator, designed for that instrument. It is recommended that instruments be calibrated annually by the manufacturer to ensure the accuracy of the measurement device.

Types or Classes of Instruments

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.

Mobile Phone and Tablet Apps

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.

Methods for Measuring Noise Exposures

A common approach to evaluating noise exposures is to walk around the facility with a sound level meter (SLM) and record noise levels as area samples. Acceptability of area samples typically depends on the mobility of the workers and the homogeneity of sound levels in the work areas. A sound level meter can also be positioned within the immediate vicinity of the exposed worker to obtain an individual exposure estimate.

Area Samples and Sound Maps

The readings are sometimes used to produce a “sound map” of the facility showing areas where readings were above or below the action level and the permissible exposure limit (PEI), which is the noise exposure OSHA allows for a workday. In some cases, the readings are used to evaluate compliance with the OSHA standard, the need for a hearing conservation program and the need to implement controls including the use of hearing protection.

After appropriate sound level meter readings are obtained, people sometimes draw "maps" of the sound levels within different areas of the workplace. By using a sound level "map" and information on employee locations throughout the day, estimates of individual exposure levels can be developed.

To create a sound map, workers should move throughout the facility using a sound level meter to measure the frequencies in each area. When the map is complete, pinpoint the loudest areas within the facility and determine whether the machines or equipment in those areas need to be replaced. Conducting noise surveys of the facility as a whole will determine the specific areas in which hazardous sound levels are present. Use the sound map to identify each hazardous noise source within the facility.

A simple example of a noise map. It can be hand-drawn in practice. After completing a noise map, identify the loudest areas on the map and the equipment in those areas.

Personal Monitoring

Noise dosimeters are commonly used to measure personal exposures to noise in a workplace when mobility is an issue. The noise dosimeter can be worn by the worker and will provide a time-weighted average (TWA) exposure for the worker wearing the dosimeter.

Area monitoring can be used to estimate noise exposure when the noise levels are relatively constant and employees are not mobile. In situations where personal monitoring is appropriate, proper positioning of the microphone is necessary to obtain accurate measurements. With a dosimeter, the microphone is generally located on the shoulder and remains in that position for the entire workday.

Attach the microphone to the top of the worker's shoulder on the side that is likely to have the highest exposure. If the device does not have a separate microphone this may not be necessary.

Hearing Conservation Program

All University employees whose noise exposures equal or exceeds an eight-hour time weighted average (TWA) of 85 decibels are enrolled in a hearing conservation program. When information indicates that any employee’s exposure may equal or exceed an 8-hour time-weighted average of 85 decibels, the department is to notify the Health and Safety Office to implement a monitoring program. The employee is to be notified when he/she is exposed at or above an 8-hour time-weighted average of 85 decibels.

This revised amendment requires that employees be placed in a hearing conservation program if they are exposed to average noise levels of 85 dB or greater during an 8 hour workday. It is not necessary for every employer to measure workplace noise. Noise monitoring or measuring must be conducted only when exposures are at or above 85 dB. Factors which suggest that noise exposures in the workplace may be at this level include employee complaints about the loudness of noise, indications that employees are losing their hearing, or noisy conditions which make normal conversation difficult. The employer should also consider any information available regarding noise emitted from specific machines.

Components of a Hearing Conservation Program

Annual audiometric testing is performed by a licensed or certified audiologist, at UNC School of Medicine’s Speech and Hearing department. A baseline audiogram is obtained within 6 months of an employee’s first exposure at or above the action level. The baseline audiogram is established to compare against subsequent audiograms.

Audiometric tests are to be pure tone, air conduction, hearing threshold examinations, with test frequencies including as a minimum 500, 1000, 2000, 3000, 4000 and 6000 Hz. Right and left ears shall be individually tested. Employees are to be notified, in writing, of the results of exams.

This audiogram shows normal hearing thresholds in the right ear. Frequency refers to how low or high the "pitch" of the sound is.

Unlike baseline testing, annual hearing tests should be done as close to the end of a worker's shift as possible (no preceding quiet period). Results of annual hearing tests should be compared to results from the baseline hearing test to check for significant threshold shift (STS). NIOSH considers a 15 dB change in hearing threshold at any frequency to represent an STS. If an STS is noted during an annual hearing test, the worker should be retested within 30 days to confirm.

Workers who develop an STS - whether temporary or permanent - should be notified. Steps should be taken to prevent further change in hearing.

You should tell workers they are having their noise exposure monitored and provide them with an explanation of the results. Involve workers in the noise monitoring process. They can provide important information about the work environment, machinery operation, and specific job tasks. Encourage workers to tell you when changes in equipment or production occur.

Engineering and Administrative Controls

When employees are subjected to sound levels exceeding 85 dBA TWA, feasible administrative or engineering controls are to be utilized. Types of administrative controls are rotation of employees, limiting time of certain operations, or restricting areas or work operations.

If possible, consider replacing loud devices with low-noise tools.

Hearing Protection

If feasible engineering or administrative controls cannot be accomplished personal hearing protective devices must be provided and used to reduce sound levels in areas above 85 dBA. The hearing protection used will depend on the operation, employee preference and attenuation required. The safety and health officer is to assist in supplying information on attenuation data and supervise the correct use of hearing protectors.

Employees are given the opportunity to select their hearing protectors from a variety of suitable hearing protectors. The University strongly encourages the use of hearing protection devices while working around noisy equipment. For employees who have experienced a standard threshold shift, hearing protectors must attenuate employee exposure to an 8-hour time-weighted average of 85 decibels or below.

Hearing protection devices are the best form of personal protective equipment for defending employees from hearing loss. Ear muffs should cover the outer ear completely. Tighten the fit by adjusting the headband as needed. Earplugs are inserted into the ear canal to totally block sound from entering. Earplugs come in disposable and reusable varieties and can be purchased in many sizes.

Signs are to be posted in areas where noise levels are above 85 dBA stating that hearing protection is required.

Training Programs

An annual training program is provided for each employee included in the hearing conservation program.

Record Keeping

Employee exposure measurements and assessments are maintained at the office of Environment, Health and Safety. Employee audiometric test records are kept at the University Employee Occupational Health Clinic.

Purchasing or Renting Noise Monitoring Equipment

Noise monitoring equipment may be either purchased or rented. Sound level meters cost about $500 to $1,000, while dosimeters range in price from about $750 to $1,500. Smaller companies may find it more economical to rent equipment rather than to purchase it. Names of equipment suppliers may be found in the telephone book (Yellow Pages) under headings such as: "Safety Equipment," "Industrial Hygiene," or "Engineers-Acoustical."

In addition to providing information on obtaining noise monitoring equipment, many companies and individuals included under such listings can provide professional advice on how to conduct a valid noise monitoring program. Some audiological testing firms and industrial hygiene firms also provide noise monitoring services. Free, on-site assistance may be obtained from OSHA-supported state and private consultation organizations.

Additional Considerations

The amendment requires that when there are significant changes in machinery or production processes that may result in increased noise levels, remonitoring must be conducted to determine whether additional employees need to be included in the hearing conservation program.

Manufacturer's instructions, contained in dosimeter and sound level meter operating manuals, should be followed for calibration and maintenance.

Provide free annual hearing exams to all employees within the hearing conservation program can help catch and address hearing loss before it becomes permanent. Establish workers’ baseline hearing when they are first hired or enrolled in the program.

Suppose a significant threshold shift (STS) is detected when comparing a worker’s most recent hearing exam to their baseline test result. Encourage workers to communicate with you about their experiences with the program.

Why Noise Control Matters

Noise control is vital to occupational safety. Prolonged exposure to chronic loud noise can result in partial or permanent hearing loss. Workplace sound level is controllable, and hearing loss due to occupational noise exposure is 100% preventable. Employers can determine these factors by taking detailed noise surveys of their facilities.

A high rate of employee turnover is a bad look for any business. It results in an unstable and inconsistent work environment. Neglecting to prioritize occupational health in the workplace can result in heavy fines, legal fees, and lower revenue. Fines vary from state to state and can easily surpass tens of thousands of dollars.