🌿 Whole-body vibration — daily exposure A(8)

Environment PN-EN 14253

Overview

Whole-body vibration penetrates the organism through the feet of a standing person or through the pelvis, the back and the sides of a seated person — from the seats and the floors of vehicles, construction and agricultural machines and from vibrating floors, platforms and working platforms in production halls. Those exposed are above all drivers, tram drivers, train drivers and operators of construction and road machines. The effects concern in particular the lumbar section of the spine and the internal organs, whose natural frequencies of vibration lie in the range 2–18 Hz; they are accompanied by functional effects — a lengthening of the reaction time, disturbances of coordination, fatigue.

The standard PN-EN 14253+A1 gives practical guidance on the measurement and the calculation of occupational exposure to whole-body vibration with reference to health; it is based on the assessment method of ISO 2631-1, which defines the measurement of periodic, random and transient vibration transmitted to the whole body through the supporting surfaces in the range 0.5–80 Hz (health, comfort, perception), the basicentric axis systems, the frequency weightings Wk and Wd and the crest factor criterion. ISO 2631-1 does not contain exposure limits — in Poland the admissible values for the daily and for the short-term exposure are given by the regulation on the maximum admissible concentrations (NDS) and the maximum admissible intensities (NDN), and the action level by the regulation on occupational health and safety in work involving exposure to noise or to mechanical vibration (following Directive 2002/44/EC).

Method principle

The frequency-weighted r.m.s. acceleration of vibration is measured in three perpendicular directions x, y, z at the surface of contact of the body with the source: on the seat under the ischial tuberosities, on the backrest, under the feet. For health the weighting Wk is applied for the z axis and Wd for the x and y axes on the surface of the seat. Unlike with hand-transmitted vibration, the vector sum is not calculated; instead the dominant component is determined — the greatest of the values 1.4·awx, 1.4·awy, 1.0·awz; the factors 1.4 reflect the greater sensitivity of the organism to horizontal vibration. For each direction the 8-hour exposure A(8)l = kl·√(1/T·Σ awli²·ti) is calculated, T = 480 min, and the greatest of them is taken for the assessment. Where the total time of exposure t ≤ 30 min (or where individual activities last ≤ 30 min), the short-term exposure aw,max is determined in addition. The basic method (r.m.s.) is sufficient for a crest factor ≤ 9; at a higher one (shocks, transient vibration) ISO 2631-1 requires in addition the running r.m.s. value or the vibration dose value VDV.

Applications

• Workplaces of drivers, of operators of construction, road and agricultural machines and of fork-lift trucks; train drivers, tram drivers
• Workplaces at stationary machines on vibrating floors, platforms and working platforms
• Comparison with the NDN (A(8) = 0.8 m/s², exposure ≤ 30 min: 3.2 m/s²) and with the action level of 0.5 m/s²; for young persons 0.19 and 0.76 m/s², for pregnant women the work is prohibited
• Assessment of seats and of vibration isolation and planning of the working time under exposure
• Documentation of the exposure for the assessment of occupational risk and for preventive medical examinations

Key parameters

Standard

Standard number

PN-EN 14253+A1:2011 (wersja polska; wprowadza EN 14253:2003+A1:2007 [IDT])

Title (PL)

Drgania mechaniczne — Pomiar i obliczanie zawodowej ekspozycji na drgania o ogólnym działaniu na organizm człowieka dla potrzeb ochrony zdrowia — Wytyczne praktyczne

Title (EN)

Mechanical vibration — Measurement and calculation of occupational exposure to whole-body vibration with reference to health — Practical guidance

Step-by-step procedure

1. Analysis of the workplace

   Establish the activities carried out under exposure (driving over various surfaces, operation of the machine, operation of stationary devices), their daily durations and the posture of the worker (seated / standing).

2. Setting of the transducers

   Place the pad with the triaxial accelerometer on the seat under the ischial tuberosities (the person sits normally) or the accelerometer on the floor/platform at the place of support of the feet. Set the axes of sensitivity in accordance with the basicentric system of the body; a deviation of up to 15° is permissible. Check the measuring chain with the calibrator.

3. Measurement

   Measure under the typical conditions of operation of the vehicle or the machine, during the typical activities. The time of measurement is to ensure statistical correctness and representativeness of the exposure; analyse periods of a different character separately. Record the weighted r.m.s. values awx, awy, awz and the crest factor.

4. Check of the method

   If the crest factor exceeds 9 (shocks, impacts), besides the r.m.s. value determine and give in addition the running r.m.s. value or the vibration dose value VDV in accordance with ISO 2631-1.

5. Dominant component and A(8)

   For each activity multiply the components by the factors (1.4·awx, 1.4·awy, 1.0·awz). Calculate for each direction A(8)l = kl·√(1/480·Σ awli²·ti) [ti in minutes] and take the greatest value as the daily exposure. Where the total time of exposure t ≤ 30 min or where individual activities last ≤ 30 min, determine the short-term exposure aw,max.

6. Assessment and test report

   Compare with the NDN (0.8 m/s² and 3.2 m/s²) and with the action level of 0.5 m/s²; take into account the special groups (young persons, pregnant women). In the test report give the location of the transducers, the axes, the time of measurement, the weightings used, the crest factor and the durations of the activities.

Required equipment and apparatus

Health and safety (OHS)

• Measurements in vehicles and machines in motion — the person measuring takes a safe place, and the apparatus is fastened so as not to hinder the operator
• The seat pad must not change the manner of sitting or hinder the operation of the pedals and the levers
• On vibrating platforms and working platforms secure the cables and the apparatus against sliding off

Frequently asked questions