Vibration and protection against it. Occupational Safety and Health

OCCUPATIONAL SAFETY AND HEALTH
Free library / Occupational Safety and Health

Vibration and protection against it. Occupational Safety and Health

Occupational Safety and Health

Occupational Safety and Health / Legislative basis for labor protection

vibration called mechanical oscillatory motion, which consists in moving the body as a whole. Vibration, unlike sound, does not propagate in the form of compression / rarefaction waves, but is transmitted only during mechanical contact of one body with another.

Vibration practically does not occur in nature, but, unfortunately, it occurs very often in technical devices. In addition, vibration is specially used in engineering, for example, in vibrational transportation.

There are three main mechanisms for excitation of vibration. The first is related to the forces of inertia and the curvilinearity of the path; it, for example, causes the vibration of ground transport, which increases significantly when moving along the unevenness of the agricultural background. The second is due to unbalanced impact forces; it, for example, causes vibration during forging, stamping, riveting, etc. The third is related to the mismatch between the geometric center and the center of mass of the rotating system and causes vibration in mechanisms where there are rotating parts.

The vibration that affects a person through the supporting surfaces affects the entire body and is called a common. (The surface on which a person stands, sits or lies is called a support.) The general vibration that captures the whole body is observed in all modes of transport and when working in close proximity to the source of vibration (industrial equipment).

Vibration that does not act through the supporting surfaces, covers only part of the body and is called local. Almost all of it is hand-borne vibration and occurs where vibrating tools or workpieces come into contact with hands or fingers.

A special subtype of general vibration is motion sickness associated with low-frequency vibrations of the body and some types of its rotation in transport.

The influence of general vibration is usually most noticeable in the range from 0,5 to 100 Hz. Local vibration transmitted through the hands has a harmful effect at higher frequencies - 1000 Hz or more. Frequencies below 0,5 Hz can cause motion sickness.

The real vibrational motion, as a rule, consists of many simple harmonic vibrations and has a complex spectrum. Knowing the spectrum is necessary to assess the effect of vibration on the human body, which depends on the vibration frequency.

A person reacts to vibration depending on the total duration of its impact.

The greatest impact of general vibration affects the processes of receiving incoming information (mainly visual due to vibrations of the eyeballs and head) and the processes of information transmission (continuous monitoring of the activity of oscillating hands).

Long-term exposure to very intense general vibration (for example, tractor drivers) can adversely affect the spine and increase the risk of vertebral and disc changes.

Methods and means of collective protection against vibration. To combat the vibration of machines and equipment and protect workers from vibration, various methods are used. The fight against vibration in the source of its occurrence is associated with the establishment of the causes of the appearance of mechanical vibrations and their elimination.

To reduce vibration, the effect of vibration damping is widely used - the transformation of the energy of mechanical vibrations into other types of energy, most often into thermal energy.

To prevent general vibration, the installation of vibrating machines and equipment on independent vibration-damping foundations is used.

To weaken the transmission of vibration from the sources of its occurrence to the floor, workplace, seat, handle, and the like, vibration isolation methods are widely used.

Vibration isolation is the reduction of the degree of transmission of vibration from the source to the protected objects.

Vibration isolation can be assessed through transmission ratio:

K_n = 1 /f/f₀ - 1, where:

f и f₀ - the frequency of the disturbing force and the natural frequency of the system in the presence of a vibration isolating layer (Hz).

The higher the frequency of the disturbing force compared to its own, the greater the vibration isolation. At f < f₀ the perturbing force is entirely transferred to the base. At f = f₀ there is a resonance and a sharp increase in vibration, and when f > 2 f₀ vibration isolation is provided, proportional to the transmission coefficient.

Vibration isolation is used for vibration protection against the action of floor and manual mechanisms.

Vibration damping is the damping of vibration due to active losses or the conversion of vibrational energy into its other forms, for example, into thermal, electrical, electromagnetic.

The most effective means of protecting a person from vibration is to eliminate direct contact with vibrating equipment. This is done through the use of remote control, industrial robots, automation and replacement of technological operations.

Reducing the adverse impact of vibration of hand-held mechanized devices on operators is achieved both by reducing the intensity of vibration directly at its source (due to design improvements) and by means of external vibration protection, which are elastically damping materials and devices placed between the vibration source and the operator's hands.

Workers use special footwear with massive rubber soles as personal protective equipment. To protect hands, mittens, gloves, liners and gaskets are used, which are made of elastic damping materials.

An important factor in reducing the dangerous effects of vibration on the human body is the proper organization of the work and rest regime, constant medical monitoring of the state of health, therapeutic and preventive measures, such as hydroprocedures (warm baths for hands and feet), massage of hands and feet, vitaminization and others

Authors: Fainburg G.Z., Ovsyankin A.D., Potemkin V.I.

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