Classification of acoustic exposure by time
From the perspective of occupational health, the key criterion for assessing sound vibrations is their stability over the working time. During instrumental measurement using the sound level meter's time weighting in "slow" mode over a standard 8-hour shift, all industrial noises are globally divided into two categories.
Continuous noises are characterized by the fact that the sound level throughout the entire working day changes by no more than 5 dB(A). This is a stable, monotonous exposure.
Intermittent noises demonstrate sound level fluctuations of more than 5 dB(A) over time. This group is more heterogeneous and, in turn, is subdivided into several specific types depending on the nature of these fluctuations:
- Fluctuating over time: the sound pressure level changes absolutely continuously, without clearly defined pauses or steps.
- Intermittent: characterized by a step-like change in sound level (by 5 dB(A) or more at once). At the same time, the duration of intervals during which the sound level remains constant must be at least 1 second.
- Impulsive: represent acoustic impacts. They consist of a single isolated or several short sound signals at once. The key criterion is that the duration of each such impulse is strictly less than 1 second.
Hygienic assessment and characteristics in the workplace
To properly assess the impact of continuous noise on the worker and to check how effectively protective and soundproofing equipment works, hygienists use sound pressure level measurements. These values are recorded in decibels (dB).
The assessment is not carried out chaotically, but in strictly defined octave bands with geometric mean frequencies. These include the frequencies: 31.5; 63; 125; 250; 1000; 2000; 4000 and 8000 Hz. It is this spectrum that makes it possible to build an objective picture of the acoustic load on the auditory analyzer.
In addition to spectral analysis, single-number noise rating is widely used in practice. It represents an assessment of the sound level in dB(A). The essence of this time-weighted value is that it corrects the physical frequency characteristics of sound pressure taking into account the real biological effect of sound on the human body, reflecting how we specifically perceive the acoustic load.
The effect of intensive exposure on the body
Systematic exposure to intensive noise pollution does not pass without a trace. Occupational medicine distinguishes two main groups of reactions: specific (directly affecting hearing) and nonspecific (general pathological shifts).
Specific reactions of the auditory system:
- Adaptation of the auditory system. This is a primary defensive reaction, which clinically manifests as an increase in auditory sensitivity thresholds (a person begins to hear quiet sounds worse).
- Auditory fatigue. A deeper state in which, after the cessation of sound exposure, sensitivity thresholds return to their initial normal level extremely slowly.
- Persistent changes. If exposure continues day after day, elevated thresholds may not have time to recover. As a result, they persist by the beginning of the next work shift, which is an alarming signal.
Pathological changes and nonspecific effects: The acoustic factor affects not only the ears. The severity of general pathological changes depends on a combination of factors: intensity, total duration of exposure, spectral composition of the sound, as well as the presence of concomitant harmful factors in the workplace and the current psychological state of the worker themselves.
The main nonspecific consequences of regular presence in a noisy production environment include: a sharp acceleration of the development of general fatigue, a noticeable decrease in concentration, clinically recorded decrease in the speed of mental reactions, as well as impaired accuracy and coordination of fine and gross movements.
Briefly: answers to topical questions
What frequencies belong to the infrasound range in the industrial environment?
The infrasound range includes sound vibrations with frequencies below 20 Hz (according to some classifications, less than 16 Hz). During hygienic rationing at workplaces, sound pressure levels are assessed in octave bands with geometric mean frequencies of 2, 4, 8, and 16 Hz. The frequencies of 8 and 16 Hz are considered the most pathogenic for the human body.
How does the effect of infrasound differ from the effect of audible industrial noise on the human body?
The main difference is that infrasound is not perceived by the human organ of hearing and is not an adequate stimulus for it.
| Characteristic | Audible industrial noise | Infrasound |
|---|---|---|
| Perception | Causes specific reactions of the auditory analyzer | Causes auditory, tactile, and pain sensations |
| Effect on the ear | Adaptation of the auditory system, auditory fatigue | Pathological mechanical impact on middle ear structures, hemorrhages |
| Systemic effects | Acceleration of fatigue, decreased attention and reaction speed | Dizziness, spatial disorientation, inhibition of the transport function of lymphatic vessels |
In what units is the sound pressure level of infrasound measured and rationed at workplaces?
The sound pressure level of infrasound is measured and rationed in decibels (dB). To assess continuous infrasound, sound pressure levels in octave bands with geometric mean frequencies of 2, 4, 8, and 16 Hz are used. For non-continuous infrasound, energy-equivalent sound pressure levels in the same octave bands are rationed, as well as the equivalent overall sound pressure level, which is measured in dB Lin.
What industrial processes and equipment are the main sources of infrasound?
The main technogenic sources of infrasound are new types of machinery with powerful engines and assemblies. The mechanisms of generation of infrasound vibrations include turbulence, resonance, pulsation, and reciprocating movements of mechanisms.
What collective protection methods are used to reduce infrasound levels in the industry?
To reduce the adverse effects of infrasound, technical and organizational measures are used: elimination of the causes of infrasound directly at the source or its mitigation, as well as regulation of contact time and withdrawal from the exposure zone to a more favorable zone. Hygienic rationing of infrasound levels is also carried out.
To memorize the types of non-continuous noise, use the phrase "Fluctuations Interruption Impulse": Fluctuating (continuously), Intermittent (in steps from 1 sec), Impulsive (impacts up to 1 sec).
What else to study on this topic
- Methodology for working with a sound level meter on the "slow" time weighting
- Performing measurements in octave bands with geometric mean frequencies
- Assessing the effectiveness of protective measures against industrial noise
- Combined action of noise and other concomitant harmful production factors
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