Occupational vibration

Terminology: sound and noise from different perspectives

For a competent hygienic assessment of the working environment, it is necessary to clearly distinguish between the concepts of sound and noise, relying on physiological, physical, and hygienic approaches. Each of these disciplines treats acoustic phenomena in its own way.

Physiological approach From the physiological perspective, sound is viewed as a specific sensation. This sensation is formed directly in the worker's auditory organ when it is exposed to the changing pressure of surrounding elastic medium particles. That is, physiologically, sound is our nervous system's reaction to an external stimulus.

Physical approach In physics, these phenomena are described through mechanical parameters.

• In a general sense, noise represents mechanical vibrations of particles in any elastic medium (whether gas, liquid, or solid). These vibrations are always the result of a specific disturbing force.
• When considering the vibration structure, sound refers to strictly regular, periodic wave processes.
• In contrast, physical noise is characterized as a non-periodic process. These are completely random, chaotic oscillatory movements with no strict regularity over time.

Hygienic approach The sanitary-hygienic discipline combines these concepts. In hygiene, noise is treated as any combination of sounds varying in frequency and intensity that is subjectively unpleasant to a person and has a pronounced irritating character.

Main sources and occupational risk groups

Acoustic vibrations and mechanical disturbances in the workplace never arise on their own. They are always inextricably linked with the execution of specific technological processes and the operation of production facilities.

Sources of noise generation:

1. Directly operating industrial equipment (machine tools, presses, engines).
2. Forced ventilation systems ensuring air exchange in workshops.
3. Specific vibrations arising during technological processes. These include aerodynamic and hydrodynamic phenomena (discharge of gases under pressure, movement of liquids in pipes), as well as mechanical interactions (impact of parts, intense friction, and surface sliding).

Due to the widespread occurrence of such technological operations, certain risk groups are formed among workers. Smithing staff working with impact tools, agricultural machinery drivers (tractor and combine operators), and personnel of various repair shops are most susceptible to the negative impact of the acoustic factor.

Physical characteristics and frequency classification

Strict physical parameters are used for an objective assessment of the acoustic environment. Any sound wave is characterized by three basic quantities:

• Frequency: measured in hertz (Hz) and determines the number of vibrations per second.
• Wavelength: measured in standard units of length (meters) and shows the distance between two adjacent wave crests.
• Intensity: measured in decibels (dB) and reflects the energy characteristic perceived as loudness.

Depending on frequency characteristics, all acoustic oscillations are classified into three large groups. Normal human hearing can perceive only a narrow range of sound vibrations — from 16 Hz to 20 kHz. Anything outside this framework does not cause an auditory sensation, but may have other physiological effects. Vibrations with a frequency of less than 16 Hz are called infrasound, and high-frequency oscillations exceeding the 20 kHz threshold belong to ultrasound.

Acoustic phenomena and sound field formation

The propagation of sound waves in space obeys strict physical laws. Processes such as wave reflection from obstacles, refraction during transition between media, diffraction around obstacles, and interference (superposition of waves) constantly occur in the industrial environment.

The concept of the sound field inside an enclosed industrial room is of particular hygienic importance. This field is not homogeneous. It is formed by two components: the direct sound of the source itself (machine or unit) and a multitude of secondary sounds that are repeatedly reflected from walls, ceilings, and floors. In the process of these reflections, sound energy is gradually absorbed by surfaces.

The key indicator here is the reverberation time — the period spent on the complete decay of sound after the source is turned off. Wave propagation laws and the reverberation index are critically important for hygienists when designing noise protection measures.

Hygienic classification of noise

To standardize standardization approaches, a sanitary classification has been developed. According to current standards, industrial noise is divided according to two main criteria: temporal characteristics (dynamics of change over time) and spectrum character.

When considering the classification by spectrum character, two polar types are distinguished:

• Broadband noise: characterized by a continuous spectrum whose width captures more than one octave. Such noise contains many different frequencies without a clear dominance of any single one.
• Tonal noise: distinguished by the fact that pronounced discrete tones (peaks at certain frequencies) are clearly heard and registered by instruments in its spectrum.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Temporal characteristics of noise (continuous, intermittent, impulse)
• Hygienic standardization and maximum permissible levels (MPLs) of sound pressure
• Specific effects of infrasound and ultrasound on the body
• Methods and means of collective protection against occupational noise

Other topics in "Chapter 6. Fundamentals of Occupational Hygiene and Physiology"

Prepared by WhiteCoat Pro faculty in accordance with the medical school curriculum. For educational purposes only.