Detail the procedures and steps involved in conducting a comprehensive workplace noise survey, including the selection and calibration of appropriate measuring equipment.

A comprehensive workplace noise survey is crucial for identifying noise hazards, assessing employee exposure, and implementing effective noise control measures. This process involves several key procedures and steps, starting with the selection and calibration of appropriate measuring equipment.

The first step in conducting a noise survey is to select the right equipment. A sound level meter (SLM) is the primary instrument used for measuring noise levels. SLMs come in different classes, with Class 1 instruments being the most accurate and suitable for research and high precision work, and Class 2 instruments being more commonly used for general industrial hygiene surveys. The selection of the SLM should be guided by the relevant occupational health and safety standards and requirements of the specific survey. Additionally, a noise dosimeter is often used for measuring the personal noise exposure of individual employees over a work shift. Dosimeters are small, body-worn devices that capture the noise exposure at a worker's ear. When selecting a dosimeter, factors such as the user-friendliness, the measurement range, battery life, and data logging capabilities should be considered. It’s also important to ensure that the measurement range of the equipment is sufficient for the noise levels expected in the workplace, and the frequency response is appropriate. For example, if there is substantial low-frequency noise, a C-weighted measurement should also be taken in addition to the A-weighted measurement. If impulsive noise is expected, the device should have the capability to capture the peak noise level.

Before any measurements are taken, the sound level meter and noise dosimeter must be calibrated. Calibration ensures the accuracy of the measurement and involves using a sound level calibrator. This calibrator generates a stable, known sound pressure level at a specific frequency. The SLM or dosimeter is then adjusted until it reads the same sound level as the calibrator. Calibration is normally done prior to starting measurements and checked again after the survey has been completed, which is termed post-calibration. Any differences between the pre and post calibration readings exceeding acceptable levels will invalidate the noise measurements. For example, a common calibration check would use a 114dB calibrator at 1000 Hz, and any readings outside of a very narrow range (e.g. 114 +/-0.5dB) would indicate that the device was not calibrated correctly, or malfunctioning, and could not be used for valid noise measurements.

Once the measuring equipment is selected and calibrated, the next step is to conduct a preliminary walkthrough of the workplace. This allows the surveyor to identify potential noise sources, high-noise areas, and the work practices of employees. The surveyor must also note the type of activities, how frequently the tasks are performed, and the location of the employees. This will assist in determining the measurement points and duration needed to capture a representative measure of the noise exposure. For example, if there is a stamping press in a factory, the surveyor will want to measure near the press and also some distance from the press. If some workers only operate the press occasionally, and others perform it all day, this difference needs to be captured. The layout of the workplace, including walls and other structures that might affect the propagation of sound, should also be noted.

During the noise survey, measurements should be taken using the selected equipment. When using the SLM, a series of stationary noise measurements should be taken at various locations across the workplace, particularly near known noise sources and at places where employees regularly spend time. The locations and timing should be such that they will accurately capture the noise levels and any variations, so that a full picture can be made of all noise levels across a normal work day. These readings should be taken at a height that represents the location of the worker’s ear. If noise levels vary over time, multiple readings might be required or an average measurement taken over a given time period. If using dosimeters, they should be attached to employees at the beginning of their shift and removed at the end of their shift, so they record the worker's noise exposure over the full shift. Employees should be instructed to avoid tampering with the devices. It's important to carefully document the location, time, and type of each measurement. Also, the activity of the workers should be noted at the time of the measurement.

Once all noise measurements have been taken, the next phase is data analysis. For the sound level meter measurements, this involves calculating the average noise levels at various locations and determining the areas with the highest noise levels. These can be mapped and the results used to define the different noise zones within the workplace. For the dosimeter results, the data will provide the individual Time-Weighted Average (TWA) noise exposures of the workers measured, from which the noise dose is obtained. The results should be interpreted in light of the relevant health and safety standards and workplace regulatory limits. For example, a standard might set limits on an 8-hour TWA, which would require calculation from a series of measurements. The data analysis should also consider peak sound pressures, and a frequency analysis for evaluating the noise and selecting appropriate HPDs.

Finally, a written report should document the entire survey process. This report must include details of the equipment used, calibration data, the measurement locations, the time and duration of measurements, the results, and conclusions, especially when comparing to relevant regulatory limits. The report should also include recommendations for noise control and hearing protection as appropriate. This report provides evidence of the noise levels in a workplace and forms the basis for noise control and hearing conservation measures. The report should also outline the limitations of the survey and any other relevant factors that may affect the findings. The noise survey should be repeated regularly, such as every two years, or whenever any changes are made to the workplace that may affect the noise levels, such as changes to equipment, or changes to operating procedures.