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Human Vibration

Introduction, Legislation and Standards. Human Vibration. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de. Effects of Vibration at Workplaces. Human Vibration. Hand-Arm Vibration. Whole-Body Vibration.

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Human Vibration

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  1. Introduction, Legislation and Standards Human Vibration Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  2. Effects of Vibration at Workplaces Human Vibration Hand-Arm Vibration Whole-Body Vibration Working with hand-held machines or driving mobile work machines and vehicles may cause damage to bones, joints, muscles and circulatory problems in the hand-arm system as well as disk damage to the spine. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  3. Activities with Potential Health Risk • Hand-Arm Vibration: • Hand-held powered tools used in manufacturing: percussive metal-working tools, grinders and other rotary tools, impact wrenches etc. • Quarrying, mining and construction: rock-drills, stone-hammers, pick-hammers, vibro-compactors etc. • Agriculture and forestry: chain saws, brush saws, barking machines, lawn mowers etc. • Public utilities: road and concrete breakers, drill-hammers, hand-held grinders etc. Whole-Body Vibration: • Tractor driving • Armored fighting vehicles, e.g., tanks • Earth-moving machinery - loaders, excavators, bulldozers, graders, scrapers, dumpers, rollers • Forest machines driving • Mine and quarry equipment • Forklift trucks • Some trucks • Some bus and tram driving • Some helicopters and fixed-wing aircraft • Some concrete production machinery • Some railway driving • Some sports activities etc. Source: Michael J. Griffin / ILO Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  4. Legislation and Standards EC Vibration Protection Directive 2002/44/EC Measurement and evaluation of human exposure to hand-transmitted vibration ISO 5349:2001 Evaluation of human exposure to whole-body vibration ISO 2631:1997 Human Response to Vibration – Measuring Instrumentation ISO 8041:2005 Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  5. EC Directive 2002/44/EC Since the implementation of the EC Vibration Protection Directive 2002/44/EC there has been an obligation on companies throughout Europe to assess the risks of jobs involving vibration. The directive defines minimum requirements for employers and manufacturers of machines. For evaluation daily vibration exposureA(8) is used: where ahv is the total vibration value of the frequency weighted acceleration during the exposure,calculated on the basis of the standards ISO 5349 for hand-arm vibration and ISO 2631 for whole-body vibration Te is the total duration of exposure during one work day T0 is the reference duration of 8 hours Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  6. EC Directive 2002/44/EC The directive lays down the following limit values for the daily vibration exposure A(8): Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  7. EC Directive 2002/44/EC • Once the exposure action value is exceeded, the employer shall establish and implement • a program of technical and and organizational measures intended to reduce to a • minimum exposure to mechanical vibration, taking into account in particular: • Other working methods that require less exposure to mechanical vibration • Appropriate work equipment of ergonomic design, producing the least possible vibration • Provision of auxiliary equipment that reduces the risk of injuries, such as protective gloves or special seats • Appropriate maintenance programs for work equipment • Design and layout of workplaces • Adequate information and training to instruct workers to use work equipment correctly and safely • Limitation of the duration and intensity of the exposure • Work schedules with adequate rest periods • Provision of clothing to protect workers from cold and damp • In any event, workers shall not be exposed above the exposure limit value. If this should • be the case, the employer shall take immediate action to reduce exposure below the • exposure limit value. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  8. Hand-Arm Vibration Standard ISO 5349 General Requirements: • The used measuring equipment must conform to ISO 8041 • Vibration should be measured in three orthogonal directions simultaneously • The sensor must be capable of measuring the highest peak acceleration magnitudes • The sensor should be mounted as close as possible to the center of the handle without affecting normal use of the machine • In the case of machines which need to be held with both hands, measurements must be made on each hand. The exposure is determined by reference to the higher value of the two • Measurand is the interval RMS of frequency-weighted acceleration in m/s² Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  9. Hand-Arm Vibration Standard ISO 5349 Weighting Filter: • The weighting filter Wh represents the relative health risk of certain vibration frequencies for the hand-arm system Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  10. Hand-Arm Vibration Standard ISO 5349 Interval RMS: • Interval RMS values awx, awy and awz should be measured and reported for X, Y and Z separately • To minimize variation, vibration should be measured, if possible, several times during a work day and averaged: where ahwi is the interval RMS of measurement i n is the number of measurements ti is the duration of measurement i • The measuring time shall be sufficiently long to provide representative values for a machine or activity. The duration of one measurement should be more than 8 seconds. The total measuring time should be at least 1 minute. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  11. Hand-Arm Vibration Standard ISO 5349 Total Vibration Value: • Evaluation is performed on the basis of Total Vibration Value ahv, which is the square root of the sum of the squares (vector sum) of the interval RMS values awx, awy and awz: • In certain cases it may be not possible or not necessary to measure the RMS in three axes for the calculation of ahv. The results of uniaxial measurements must be multiplied with a correction factor. The factor can vary from 1.0, if there is only one dominating axis, to 1.7, if all three axes have similar values: where awmeas is the measured RMS value for one dominating axis for three similar axes Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  12. Hand-Arm Vibration Standard ISO 5349 Daily Exposure: • The health risk depends on the duration of vibration exposure during a work day • Daily exposure A(8)is the equivalent continuous acceleration over an eight-hour work period. For the determination of A(8) it is not necessary to measure over eight hours. It is sufficient to make short-term measurements during representative work steps. The results are normalized to eight hours. Daily exposure is calculated as follows: where ahv is the total vibration value of the frequency weighted acceleration during the exposure Te is the total duration of exposure during one work day T0 is the reference duration of 8 hours Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  13. Hand-Arm Vibration Standard ISO 5349 Combined Daily Exposure: • If a daily exposure consists of more than one activity with different vibration magnitudes, daily exposure is calculated: where ahvi is the total vibration value of the frequency weighted acceleration of activity i n is the number of activities Ti is the duration of activity i • To compare the contributions of different activities, it may be useful to calculate partial exposure values: Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  14. Hand-Arm Vibration Standard ISO 5349 • Daily exposure should be measured for both hands separately • Since measurement uncertainty is usually relatively high (e.g. 20 to 40 %), not more than two significant digits should be stated for A(8) Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  15. Hand-Arm Vibration Standard ISO 5349 Measuring Report: The result of measurements to ISO 5349 shall be a report including the following data: • Names of company / contractor and operating person • Purpose of measurement • Date • Location • Temperature, humidity, noise • Description of activities • Work procedure (working time, interruptions, breaks) • Tested equipment (model, serial no., condition, age, weight, rotary speed, handle type), tools and work pieces • Measuring equipment (type, serial no., calibration date, function chaeck • Sensor positions and directions, mounting method • Measured interval RMS in X / Y / Z direction for each activity • Total vibration value Ahv for each activity • Duration Ti of each activity for one work day • Daily vibration exposure A(8) • Partial Daily vibration exposure Ai (8), if measured Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  16. Hand-Arm Vibration Standard ISO 5349 Function Check and Calibration: • It is recommended to perform a function check of the sensor and the measuring instrument before and after each measurement by means of a vibration calibrator • Calibration should be performed in regular intervals, e.g. after 2 years, in order to check that the equipment is within the specification to ISO 8041 Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  17. Hand-Arm Vibration Standard ISO 5349 Practical sensor locations for various machine tools: Chain saw Angle grinder Grinding machine Straight handle Chipping hammer Steering wheel More examples of measuring points can be found in ISO 8662 for various hand-held machines, ISO 7505 for chain saws and ISO 7916 for portable brush saws. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  18. Whole-Body Vibration Standard ISO 2631-1 General Requirements: • ISO 2631-1 covers methods for the measurement of periodic, random and transient vibration with regard to health, comfort and perception • The considered frequency range is 0.5 to 80 Hz • Measurand is frequency weighted acceleration • Applicable for vibrations transmitted to the body as a whole through the supporting surfaces: the feet of a standing person, the back and the feet of a seated person, the buttock or the supporting surface of a recumbent person • Vibration is measured triaxial with a coordinate system originating at the point from which vibration enters the body. The Z axis always runs along the spine : Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  19. Whole-Body Vibration Standard ISO 2631-1 Sensor: • A commonly used sensor design for seat vibration measurement is given in ISO 10326-1. A flat triaxial accelerometer is built into a semi-rigid rubber disk: • Sensors shall be located at the interface between the body and the supporting surface • Most common sensor locations for seated and standing persons are the principal support areas of the seat surface, the seat back and the feet. For recumbent persons the supporting surfaces under the pelvis, the back and the head are used. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  20. Whole-Body Vibration Standard ISO 2631-1 Evaluation Methods: • The selection of appropriate evaluation methods depends on the amount of shocks and transient vibration in the measured signal, defined as the crest factor: • The basic evaluation method shall be used for evaluation. In cases where one of the alternative methods is used, both the basic and the alternative evaluation value shall be reported. Evaluation Methods yes no Crest factor < 9? Basic Evaluation Method (interval RMS) Running RMS Method (MTVV) Fourth Power Vibration Dose Method (VDV) Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  21. Whole-Body Vibration Standard ISO 2631-1 Basic Evaluation Method: • For vibration with low contents of shocks (crest factor < 9) • Measurand is the RMS of frequency weighted acceleration in m/s² where aw(t) is the instantaneous frequency weighted acceleration T is the duration of measurement (integration time) • In the presence of occasional shocks or transient vibration, i.e. high crest factors, the basic evaluation method may underestimate the effects of whole-body vibration. Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  22. Whole-Body Vibration Standard ISO 2631-1 Running RMS Method: • Takes into account occasional shocks and transient vibration by use of running RMS with a short integration time constant of preferably 1 second: where aw(t) is the instantaneous frequency weighted acceleration  is the integration time constant for running averaging t is the time t0 is the time of observation • The result is given as the highest magnitude of the running RMS during the measurement period called maximum transient vibration value MTVV: Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  23. Whole-Body Vibration Standard ISO 2631-1 Fourth Power Vibration Dose Method (VDV): • More sensitive to peaks than the basic evaluation method by using the fourth power instead of the second power of acceleration • The result is called Vibration Dose Value (VDV) which has the unit m/s1,75 where aw(t) is the instantaneous frequency weighted acceleration T is the duration of measurement • When the vibration exposure consists of periods with different VDV, the total vibration dose is calculated from the fourth root of the sum of the fourth power partial vibration dose values • Estimated Vibration Dose: Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  24. Whole-Body Vibration Standard ISO 2631-1 Weighting Filters: • Health, comfort and perception are dependent on the vibration frequency content • Different frequency weightings are required for the different directions • Two principal weightings are Wk and Wd: Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  25. Whole-Body Vibration Standard ISO 2631-1 Weighting Filters: • Additional weightings are Wc, We and Wj: Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  26. Whole-Body Vibration Standard ISO 2631-1 Weighting Filters: Wk (Z standing and seated, vert. recumb.) Wc (Seat back) Wd (X/Y standing and seated, hor. recumb.) Wj (head recumbent) Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  27. Whole-Body Vibration Standard ISO 2631-1 Vibration Total Value: • Combining vibrations of three orthogonal directions by calculating the square root of the sum of the squares (vector sum) of the interval RMS values awx, awy and awz: • The values of the multiplying factors kx, ky and kz depend on the selected frequency weighting Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  28. Whole-Body Vibration Standard ISO 2631-1 Multiplying Factors for Vibration Total Value: Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  29. Whole-Body Vibration Standard ISO 2631-1 Health Guidance Zones: • There are not sufficient data to establish a quantitative relationship between vibration exposure and health risk • The following health guidance zone diagram can be used as a rough orientation: Health risk Caution Zone No known effects Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  30. Whole-Body Vibration Standard ISO 2631-1 Basic Requirements for Human Vibration Meters: • The instrument shall at least display the following quantities:- The interval RMS of frequency weighted acceleration over the averaging time- The interval RMS of unweighted, but bandpass filtered acceleration over the averaging time- The averaging time • The instrument shall display an overload condition which occurred during the averaging time. Overload shall be indicated for all relevant points of the signal path.The overload message must be held during the entire averaging time. • A calibration function for transducer sensitivity must be available • The instrument may also measure Maximum Transient Vibration Value (MTVV) • The instrument may also measure Vibration Dose Value (VDV) • The instrument may also measure Total Vibration Value Ahv • The selected vibration quantity shall be identifiable, preferably by displaying the physical unit • The display shall allow reading with a resolution of better than 1 % • Settling time shall not exceed 2 minutes • The delay between starting a measurement and the acquisition of valid data must not exceed 0.5 seconds Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

  31. Instrumentation Standard ISO 8041 Basic Requirements for Human Vibration Meters (continued): • The instrument has one ore more weighting filters calculated by the product of- band limitation- transition acceleration / velocity- step function • Most important weighting filters are Wh for hand-arm, Wd and Wk for whole-body • Maximum errors:- Mechanical reference signal (80 Hz / 10 m/s² for H/A and 16 Hz / 1 m/s² for W/B) under reference conditions (23 °C, 50 % rel. Hum.)± 4 %- Deviation between the measured acceleration with weighting filter and the acceleration measured only with band limiting filter after multiplication with a correction factor: ± 3 %- Deviation between the measured interval RMS and running RMS: ± 2 % • Linearity error: < 6 % • Linear range: > 60 dB • Cross-talk: < 0.5 % • A battery indicator is required • Measuring error at minimum battery voltage: < 3 % • Environmental: temperature range at least –10 to 50 °C waterproof design (IP42 to IP65) Metra Mess- und Frequenztechnik Radebeul / Germany www.MMF.de

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