The Impact of Vibrations Upon the Musculo-Skeletal System

Dipl. Eng. Silviu PLATON

Dipl. Eng. Dan NICULESCU

The National Research and Development Institute on Occupational Safety

1. The vibrations. Risk factor for health and safety

Vibration or oscillation – the movement of a system as compared to its reference condition

Characteristic parameters: Acceleration level (efficient values),

Frequency content (spectral analysis),

Contact point of the human body with the vibration source (global vibrations, forearm – hand vibrations),

Exposure duration.

The human body is submitted to the action of vibrations when:

the machines it travels with are concomitantly vibrating,

the person concerned is to be found in rooms where machines and

installations are operating, Upon certain parts of the human body i.e. muscles, bones,

articulations, there are directly acting those vibrations arising from vibrating machines, various pneumatic tools etc.

The vibrations acting upon the human body may induce:

Disturbance of the physical and intellectual activity – tiredness,

Mechanical damages – fractures arise at certain levels of

acceleration, lung damages, heart damages,

Subjective phenomena – lack of comfort, pain and anxiety,

Generally, three steps of evaluating the vibrations’ effect are

considered e.g. perception, discomfort and intolerance

threshold.

2.Global vibrations, forearm - hand vibrations. Effects upon the human body

GLOBAL VIBRATIONS

The exposure to global vibrations induces a complex distribution of the

oscillating forces and movements into the body,

The location and the nature of the sensations may vary to a significant

extent depending on the vibrations’ frequency, direction, etc.,

The global vibrations transmitted to the whole body may affect:

Acummulation of information through the senses,

Information processing;

Levels of interest, stimulation or tiredness,

deliberate actions.

The sight – represents the perception mechanism that may be easily

influenced by the vibrations’ action as the visual acuity may be damaged even

for unsignificant movements of an image on the eye retina,

The perception in terms of body orientation and position stability may be also

affected.

For the individual exposed to the vibrations’ action within the work system, a

significant importance shall be given to the body contact point with the

vibrations’ source.

Acting directions of the mechanical vibrations transmitted to the whole body through the supporting area

FOREARM – HAND VIBRATIONS

The severity of the biological effects of the vibrations transmitted to

the forearm- hand system, in working conditions, is influenced by

several factors:

Exposure duration and working method Duration of working day exposure and cumulative duration per

working day;

Direction of the vibration transmitted to the hand as well as the extent

and direction of the forces applied by the operator through his hands

to the tool and the body during the exposure i.e. articulations angles

of the fingers, hand, fist, elbow and shoulder.

The surface and the part of the hands/arms exposed to vibrations,

The type and condition of the vibrating mechanisms, of the manual

tools or processed piece,

The operator’s working method and qualification – factors that should

be considered,

Factors related to the working environment - microclimate, noise and

chemical agents,

Raynaud syndrome – usually associated to the vibrations’ action upon

the arm – hand system being also involved in other general or

occupational diseases.

2.1 Effects of the vibrations’ action transmitted to the musculo-skeletal system

The injuries induced by mechanical vibrations upon the musculo-

skeletal system as occupational disease represent one of the oldest

occupational disease that need surgical treatment,

They may be generated by working with vibrating tools, these

vibrations acting upon the extremities,

The consequences of the vibrations appear within muscles,

articulations and bones that are actively participating in carrying out

“pushing” onto the tools and “reception” of the vibrations,

In some cases, diseases related to the elbow, fist and shoulder

articulation are reported corresponding to the clinical image of a

deforming arthrose that should be considered as being amplified and

premature as compared to the normal evolution in age,

The most solicited is the cubitus – humeral articulation followed by the

fist articulation and the scapulo- humeral articulation respectively.

Circulatory diseases –one of the very first issues that should be

considered when speaking of negative effects as a result of the

activities carried out by means of vibrating tools,

Circulatory troubles are manifested through the occurrence of

vascular spasms at finger level immediately followed by skin

cyanosis or tumefaction,

The circulatory troubles appear independently of the fact that

the person exposed to vibrations works within a warm or cold

microclimate.

3. Basic health and safety requirements related to the exposure of workers to the vibrations generated risks

HG 1876-2005 3.1 Limit values of exposure and exposure values beyond which the

action starts

3.1.1 For the vibrations transmitted to the arm – hand system

- the limit value of daily occupational exposure calculated for a

reference period of 8 hrs is 5 m/s2;

- the value of the daily exposure beyond which the action starts,

calculated for a reference period of 8 hrs is 2.5 m/s2.

3.1.2 For the vibrations transmitted to the whole body:

-the limit value of daily occupational exposure calculated for a reference

period of 8 hrs should be 1.15 m/s2,

- the value of the daily exposure for which the action starts, calculated

for a reference period of 8 hrs should be 0.5 m/s2

Employer’s obligations

Establishing and assessment of risks – the employer shall evaluate

the necessity of measuring the risks arising from the exposure to

vibrations,

Employers’ information and training,

Employers’ consultation and participation,

Health surveillance.

HG 1876 transposed Directive 44-2003 of EU

4. Methods of determination and apparatus

SR ISO 2631/1:1997 – for the determination of global vibrations

- evaluation of the exposure level to vibrations is based on the

calculation of the daily exposure expressed as continuous

acceleration equivalent for a reference period of 8 hrs. It is calculated

as the highest value (rms) of ponderated accelerations in frequency

as determined on three orthogonal axis, for a sitting or standing

worker.

SR ISO 5349:1995 – for the determination of the arm – hand vibratations

- the evaluation of the exposure level to vibrations transmitted through

the arm – hand system is based on the calculation of the daily

exposure value for a reference period of 8 hrs expressed as the

average square root (rms) (total value) of the ponderated acceleration

values in frequency as determined versus three orthogonal axis z, x, y

- in case of the equipment that are to be be hold by both hands, the

measurements should made for each hand. The exposure shall be

determined depending on the highest value of the two values found.

Fig. 4.1 – Examples of practical measurement positions for several currently used tools

SR EN ISO 8041-2006 – Operational diagram of an apparatus or system for the measurement of vibrations

Legend1 transducer 8 ponderation in frequency (including band limitation)2 mounting system 9 band limited output signal3 vibrating surface 10 ponderated output signal in frequency 4 cable 11 time ponderation 5 input electrical signal 12 additional processing6 signal conditioning 13 display7 band limitation