Vibration disease from whole-body vibration

Prevention of occupational vibration exposure

Although it is difficult to completely eliminate contact with vibrating machinery, adverse effects can be minimized. To achieve this, a set of organizational and biomedical measures is applied:

• Work and rest schedule: workers need regular breaks after every hour of continuous work. Shifts should be organized so that vibration-exposure operations alternate with tasks that do not require heavy physical exertion.
• Therapeutic and prophylactic measures: employees are prescribed specialized occupational exercises aimed at relieving tension in the spine and hands. Additionally, local hydrotherapy and prophylactic administration of vitamin B1, which improves nerve tissue trophism, are recommended.

Infrasound: physical nature and sources

One of the factors closely associated with mechanical vibrations is infrasound—sound waves with a frequency of less than 20 Hz. They propagate through gaseous, liquid, and solid elastic media, but are not perceived by the human auditory system.

Sources of infrasound are divided into:

1. Natural (geophysical): storms, earthquakes, volcanic eruptions, thunderstorms, and waterfalls.
2. Technogenic: the introduction of powerful machinery and units leads to an increase in the number of professions exposed to this factor. It arises from the same causes as audible noise (turbulence, resonance, mechanical pulsation).

The hygienic significance of infrasound is determined by its unique properties: it is weakly absorbed by the medium, can travel ultra-long distances (especially through specialized channels in water and air), and effectively bends around obstacles due to its long wavelength (pronounced diffraction). Furthermore, due to the phenomenon of resonance, infrasound is capable of inducing secondary vibration in large objects.

Biological effects of infrasound

The primary damaging factor is sound pressure. The oscillations cause both auditory and non-auditory sensations:

• Auditory effects: infrasound is not a normal stimulus for the ear, but it mechanically traumatizes the middle ear structures (tympanic membrane and auditory ossicles), causing hemorrhages. This secondarily leads to inner ear pathologies.
• Non-auditory effects: at low levels, a person experiences tactile sensations; at high levels, severe pain.

At high intensities (from 120 dB), acute reactions develop: nausea, dizziness, disorientation, and a sensation of pressure in the ears. Chronic occupational exposure damages the central nervous system (fatigue, decreased cortical excitability), the cardiovascular system (up to hypertension), suppresses lymph flow, and causes respiratory disturbances, including tachypnea and a sensation of vibration in the chest.

Industrial ultrasound

Ultrasound refers to mechanical oscillations with a frequency greater than 20 kHz. Depending on the transmission method, it can be airborne (propagating through the air) and contact (transmitted when the source touches the body).

The most important physical effect of ultrasound in mixed media (liquid-gas) is cavitation—the formation and collapse of bubbles, accompanied by a powerful release of energy. Low-frequency ultrasound (up to 100 kHz) is actively used in industry for parts cleaning and in medicine for sterilization. High-frequency ultrasound (up to 1000 MHz) is used for flaw detection and diagnostics.

Biological effects depend on intensity: low doses stimulate metabolic processes, while medium and high doses inhibit them. High-frequency ultrasound causes microtraumatization of tissues, which in medical workers can lead to peripheral nerve damage in the hands. Low-frequency ultrasound provokes angiospasm, disrupts capillary permeability, and increases the pain threshold of tissues.

Hygienic standardization and protective measures

Acoustic factors are assessed in decibels (dB). For infrasound, sound pressure levels are measured in octave bands (2, 4, 8, 16 Hz). Ultrasound is standardized depending on the medium: sound pressure is measured for airborne ultrasound, and peak vibration velocity values for contact ultrasound.

Protection of the body against acoustic factors is based on the following principles:

1. Hygienic standardization and regular monitoring of pressure levels.
2. Mandatory preliminary and periodic medical examinations for workers.
3. Engineering solutions: use of remote control, protective shields, and enclosures.
4. Organizational measures: "time protection" (reduction of contact time).
5. Use of personal protective equipment (PPE): double gloves (cotton inside, rubber outside) and warm protective clothing are required when working with ultrasound.

Briefly: answers to topical questions

Class and exam questions

What else to study on this topic

• Classification of infrasound by spectrum character and temporal characteristics
• Mechanism of cavitation generation upon exposure to low-frequency ultrasound
• Specific physical properties of ultrasound: focusing and acoustic shadow
• Differences between magnetostrictive and piezoelectric transducers
• Acute systemic effects upon exposure to infrasound with an intensity exceeding 120 dB

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.