China
Africa
Explore chapters and articles related to this topic
The Environment
Published in Céline McKeown, Office Ergonomics and Human Factors, 2018
Acoustic waves can be described as fluctuations in pressure, or oscillations, in an elastic medium. The oscillations produce an auditory experience which is sound. This is achieved because the ear converts the acoustic waves into nerve impulses, which move to the brain along the auditory nerve. The brain processes this information and imposes some sense on it, resulting in perception of sound and identification of auditory patterns. How loud a sound is considered to be is determined by its frequency and its sound pressure level (SPL). Frequency refers to the complete number of cycles that occur in one second. It is expressed in Hertz (Hz) and gives the sensation of pitch. The amplitude of the sound wave corresponds to the intensity of the sound and provides the sensation of loudness. The human ear is normally sensitive to a range of frequencies between 20 and 20,000 Hz; this is referred to as the audible spectrum. We are likely to hear at our best between 1000 and 4000 Hz, which is the frequency band in which speech is transmitted. Auditory thresholds—the point at which we can actually hear something—are much lower at higher frequencies. Noises at lower frequencies have to be much louder to be heard. Noise is measured in decibels (dB). An A-weighting, written as dB(A), is used to measure average noise levels. A C-weighting, written as dB(C), measures peak, impact, or explosive noise. Table 9.1 indicates typical noise levels encountered in a number of situations.
Human Hearing and Noise Criteria
Published in David A. Bies, Colin H. Hansen, Carl Q. Howard, Engineering Noise Control, 2018
David A. Bies, Colin H. Hansen, Carl Q. Howard
Many occupational noise guidelines recommend a maximum noise exposure limit of LAeq,8h = 85 dBA, which is typically measured using an instrument such as a sound level meter or a noise dosimeter. However, if an instrument is not available, a commonly used subjective technique to judge if the ambient noise level is greater than 80 dBA, and therefore consideration should be given to wearing hearing protection to lessen the likelihood of hearing damage, is if when two people standing about 1 m apart have to speak very loudly to communicate (see Webster (1970) and Section 2.11.1). In addition to the potential for hearing damage, there can be a reduction in the efficiency of workers at elevated noise levels. The German standard, VDI 2058 Blatt 3 (2014), describes the mechanisms that lead to a decrease in work efficiency and an allocation of tasks of different complexity.
Vibration Control
Published in Lewis H. Bell, Douglas H. Bell, Industrial Noise Control, 2017
Lewis H. Bell, Douglas H. Bell
One of the most common sources of noise in industry is the noise generated from vibrating machinery. For example, a 5-hP motor rotating at 1800 rpm is rather quiet, but if it is bolted directly to a metal table, the noise level can rise easily to 90 dBA at a distance of 5 ft. In this instance, the metal tabletop acts as a sounding board and radiates the vibratory energy transmitted from some form of rotational unbalance of the motor. This sounding board effect is frequently found in industrial environments or buildings where floors or machine platforms are constructed of diamond deck, metal grills, hardwood, and even concrete. The excitation can originate not only from rotating equipment but from vibrators, tumblers, shakers, pressers, etc. It should be emphasized that noise is not the only undesirable effect. Floor vibration, for example, can be a serious problem to adjacent equipment, where close tolerances are maintained in machine tools or especially where optical devices are used.
Research on influencing factors of coal mine safety production based on integrated fuzzy DEMATEL-ISM methods
Published in Energy Sources, Part A: Recovery, Utilization, and Environmental Effects, 2023
Qi Yuan, Xingkai Zhang, Hongqinq Zhu, Baozhen Zhang, Jin Chen
A mechanized coal mining face includes equipment and facilities such as shearers, scraper conveyors, brackets, belt conveyors, crushers, power switches, and connecting cables. Equipment is unsafe if it is in a state in which accidents have occurred or may occur. For mechanical equipment, unsafe conditions may occur in various ways (e.g., rotation, sliding, noise, vibration) by negatively affecting worker health and productivity. For example, vibration can harm equipment, facilities, and workers by causing human dysfunction and reducing the response capacity. High intensity and frequency noise affects not only hearing but also affects workers’ attention and productivity, which can easily lead to accidents. The working space of a fully mechanized mining face is relatively narrow, which increases the influence of mechanical factors on safety. Meanwhile, as the mining difficulty increases, the safety requirements for technology also increase; this requires improving the quality and specifications of the equipment and the sensitivity of safety protection devices. The level of safety management has a significant impact on the safety of equipment and facilities, such as the overall arrangement of production units, maintenance and control of electromechanical equipment and the completeness of equipment operation logs. Therefore, analyzing the influencing factors of equipment and facilities is significant to improving the safety of a coalmine system.
Mechanical and acoustic absorption characteristics of UHMWPE weft-knitted structures of flexible porous laminated composites
Published in The Journal of The Textile Institute, 2022
Ruosi Yan, Xingteng Zhang, Mengjin Wu, Zhengkun Zhang, Tuo Liu, Lixia Jia
Acoustic absorbing materials can be used in noise reduction to achieve a satisfactory noise reduction effect. Previous research on acoustic absorbing structures have revealed that the different structures of acoustic absorbing materials, such as perforated orifice, fiber hybrid composites, and organic foam exhibited superior acoustic absorption performance (Choe et al., 2018; Hassani et al., 2021; Yang et al., 2019). Porous acoustic absorbing materials with low density and high porosity are the most widely used types of acoustic absorbing materials. Porous acoustic absorbing materials convert the energy of incident sound waves into heat to absorb incident sound waves (Ayub et al., 2018). Fiber hybrid composite structures are categorized as porous acoustic absorbing structures. Presently, plant and chemical fibers (Berardi & Iannace, 2015; Dieckmann et al., 2018) have broad applications in the field of acoustic absorption and noise reduction. Therefore, it is essential to explore the different fibers applied in the field of acoustic absorption and noise reduction.
Noise at sea: Characterization of extended shift noise exposures among U.S. Navy aircraft carrier support personnel
Published in Journal of Occupational and Environmental Hygiene, 2019
Nicholas Schaal, Kevin Lange, Maria Majar
Controlling noise exposures can be achieved by a combination of engineering, administrative, or personal protective equipment controls. Because personal protective equipment is generally considered the least preferred method of controlling worker exposures, engineering controls such as wall and ceiling sound absorption, partitions, and acoustic panels in off-duty spaces such as berthing and leisure areas could allow for reduced noise levels and provide better opportunities for auditory recovery. However, design and use of these controls on an aircraft carrier may be a challenge due to high cost of implementing throughout the ship, space restrictions, and effects on shipboard flammability. Feasibility determinations of engineering control implementation should be further assessed. Administrative controls to include reducing from a 12-hr work shift to 8-hr work shift would allow a simpler method of comparing exposures to OELs and would allow an opportunity to reduce individual noise exposures. However, low/variable aircraft carrier staffing and workload when at-sea makes additional administrative controls difficult to implement.