Novel - Occupational Safety and Environmental Measurement Parameters: What is noise? Noise Measurement Methods

One of the most significant physical agents to which employees are exposed is noise. As a physical agent, noise can cause acute damage to the auditory sense, whilst also possessing the potential to adversely affect hearing health in the long term through cumulative damage. Due to these characteristics, noise ranks among the most closely scrutinised occupational hygiene parameters. Before examining noise in detail as an occupational hygiene parameter, it is beneficial to clarify the frequently confused concepts of sound and noise. Sound consists of waves propagating as mechanical vibrations in an elastic medium. Stretched strings, metal plates, or fleshy vocal cords in the human throat can be cited as some sound sources. When these sources vibrate, they also oscillate the surrounding air molecules, thereby generating sound. The propagation of this molecular vibration in air is termed a sound wave, and the velocity at which these vibrations propagate through air is termed the speed of sound. Briefly, noise can be defined as sudden or unwanted sound, or loud sound capable of damaging hearing. Although loud sound affects human health, it may not always be perceived as noise, such as loud music during a concert. In certain circumstances, sound may also be defined as noise even without high loudness or potential physical harm, because it disrupts concentration during tasks requiring mental focus. High-intensity sounds resulting from various types of impacts and explosions are termed “instantaneous noise” or “impact noise”. Impact noise does not exceed 1 second in duration, but its adverse effects can be severe. As can be understood from the definitions above, sound and noise are subjective concepts that cannot be delineated with absolute rigidity, and these terms can often be used interchangeably. We can state that every noise is a sound, but not every sound is noise. What is Sound? Sound Parameters Fundamental parameters are used to define sound. Let us touch upon these briefly; Frequency: Frequency is the number of vibration cycles occurring per second. The cycles per second of vibrating objects and air movement can differ. The faster the particle oscillates, the higher the frequency. Frequency is denoted by the symbol “f” and its unit is hertz (Hz). For higher frequencies, this unit is expressed as kilohertz (kHz) (1000 Hz = 1 kHz). For a healthy human, the normal audible range is accepted as 20 Hz – 20000 Hz (20 kHz). The human ear is more sensitive to mid-frequencies, which lie in the range of 500 Hz – 4000 Hz, representing the conversational frequency range. Sounds falling below and above this frequency range cannot be perceived by the human ear, but exposure can result in adverse effects such as headaches and fatigue. Sound Pressure: Sound pressure (or acoustic pressure) can also be termed noise intensity. Sound pressure propagates as a wave by creating variations in atmospheric pressure. The intensity of noise depends on the magnitude of pressure generated by the sound wave. Sounds are heard as a result of the human ear reacting to sound pressure. As vibrations at the sound source increase in magnitude, the resulting sound pressure also rises. The unit of sound pressure is the pascal (Pa); however, since this unit involves quantities in the millions, the decibel (dB) unit corresponding to Pa is used in noise measurements. A healthy human ear is sensitive to sound pressures between 0 and 140dB. As can be understood from the definitions above, noise affects human health depending on sound pressure (= level) and sound frequency. Sound level is measured in units called "Decibels (dB)", and frequency in units called "Hertz (Hz)". What are the Risks of High Noise Exposure? Excessive sound temporarily damages hair cells in the inner ear, leading to temporary hearing loss. Continued exposure to this high sound level over extended periods inflicts permanent damage to the hair cells, causing permanent hearing loss. Even without prolonged exposure, sudden and loud sounds such as intense/impact noise or gunfire can also cause hearing loss (acoustic trauma). In certain instances, extreme sound levels can rupture the eardrum. The harmful effects of noise may not be confined to workplaces. For instance, listening to loud music through headphones or exposure to excessively loud sounds in entertainment venues can also damage the sense of hearing. Occupational Health and Safety Recognized Noise Limit Values To implement measures against the harmful effects of noise, the "Regulation on the Protection of Employees from Noise-Related Risks" was drawn up, defining noise exposure limit values. Under the regulation currently in force, these limit values are as follows: Lower exposure action value; 80 dB(A) – Hearing protectors must be made available Upper exposure action value; 85 dB(A) – Hearing protectors must be worn Exposure limit value; 87 dB(A) – Hearing protectors must be worn alongside environmental control measures In addition to defining limit values, the Noise Regulation specifies allowable durations of stay at various maximum noise levels. Let us examine these values; For impact noise, the ceiling is 140 dB; this limit must not be exceeded. In preparing the Regulation, standards of the American ACGIH (American Conference of Governmental Industrial Hygienists) were taken as the baseline; values stated in the table above may vary across different international standards. Occupational Health and Safety – How is Noise Measured? To protect against noise, whose mechanisms of action and adverse health effects are outlined above, accurate and precise measurements must be carried out first. Two distinct types of instruments are used for sound measurements in workplace environments: ambient sound level meters and personal noise dosemeters. Ambient sound level meters are hand-held instruments; they can also be used fixed via tripod-style support units. With these instruments, the intensity and sound frequency of the sound emitted from the sound source into the environment are measured. Depending on the measurement purpose, there may be versions of the instrument that only measure sound pressure, as well as versions that perform frequency analysis on an octave-band basis. With these instruments, parameters such as instantaneous sound level, average sound level, peak (impact noise), and time-weighted average (TWA) can be measured. Ambient sound level meters are divided into two categories, Type 1 and Type 2, depending on their microphone sensitivity. If environmental noise measurements are to be carried out, instruments with Type 1 microphone sensitivity should be selected. If measurements are to be carried out solely for occupational safety, instruments with Type 2 microphone sensitivity are sufficient. After performing measurements with these instruments, practical and secure software is required to download the measurement data to a computer environment and perform detailed graphical and tabular data analyses. Personal noise dosemeters should be wireless, lightweight, and easy-to-use instruments sized to be clipped onto an employee's collar. The primary purpose of these instruments is to measure an employee's noise exposure. A Type 2 sensitivity microphone is used in these instruments. With noise dosemeters, just as with the sound level meters mentioned above, parameters such as instantaneous sound level, average sound level (Leq), peak (impact noise), time-weighted average (TWA), and % dose can be measured. Since the instrument operates clipped onto the employee's collar, the values recorded here are personal data. After taking measurements with noise dosemeters, practical and secure software is required to download the measurement data to a computer environment and perform detailed graphical and tabular data analyses. To simulate the response of the human ear, A-weighted filters are used in sound level meter instruments, and the unit of measurement is specified as dB(A). For the impact noise mentioned above, measurements are carried out via C-weighted filters, and the unit of measurement is expressed as dB(C). How Is Calibration of Noise Measurement Instruments Maintained? Before starting measurements with ambient sound level meters or noise dosemeters, performing a calibration check of the instrument is essential. Through this procedure, it is verified that there is no drift in instrument values and that it measures accurately before beginning the measurement. The calibration check procedure must also be repeated after measurements. Thus, by checking whether any drift has occurred in instrument values throughout the measurements, the reliability of the measurement performed is confirmed. Conclusion Noise, which is one of the most critical health & safety parameters both in our daily lives and in working environments, can have its adverse effects reduced and its risks minimised by taking necessary precautions. For this purpose, it is vital to work with accurate, reliable instruments that have sound technical capability and comply with standards, as well as with organisations that not only supply these instruments but also provide complete technical support for them. It should be kept in mind that if a healthy working environment is targeted and protective measures for employee safety are valued, the first step of efforts toward these objectives is to perform measurements using the correct methods and the correct instruments. Author: Hamdi YÜKSEL All text and visual content on our website belong to the authors of www.novel.com.tr. No content on the website may be copied, modified, or utilised in other print or digital media (websites, blogs, magazines, books, etc.) without written permission. Our rights are protected under the provisions of the Law on Intellectual and Artistic Works No. 5846. Note: All images used may be subject to copyright by their respective owners. 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