Vibration

2. Vibration Sean Mahar, PhD, CIH, CSP, PE

3. Vibration Introduction • Types • Problems • Controls • Measurements • Standards

4. Sean Mahar • BS, Sacred Heart University • MS, Texas A&M University • PhD, University of Iowa • Certified Industrial Hygienist • Certified Safety Professional • Professional Engineer

5. Experience • U of Wolverhampton, 4 years • Ohio University, 3 years • Worksafe Iowa, 3 years • US Navy, 9 years • Tracor, 1 year

6. Educational Objective The student should have a basic understanding of the measurement and control of vibration, including what instruments are used, the relevant exposure limits, but they need not have the practical experience to enable them to carry out a vibrations survey.

7. Definitions and measurements units Units of measurement - understanding of acceleration amplitude Velocity amplitude displacement amplitude

8. Definitions and measurements units Choice of measurement parameters, dynamic range and frequency information required Relationship and implications of mass and stiffness and damping, natural frequency and static deflection

9. Monitoring instruments Vibration transducers Piezoelectric accelerometer. Also aware of existence of proximity probes and velocity pick-up. Meters Elements of a general purpose vibration meter.Also awareness of swept filter frequency analyser and fast Fourier transformanalyser.

10. Making a survey ISO Evaluation of human exposure to whole body vibration: • Equivalent acceleration value • Frequencies of the vibration • Direction of excitement of the vibration • Time of exposure to vibration

11. Making a survey ISO Guidelines for the assessment of human exposure to hand-arm vibration: • Frequency weighted RMS acceleration value • Probability of developing white finger syndrome

12. Exposure limits for vibration • ISO 2631:1997Guide for the eval. of human exposure to whole body vibration. • ISO 5349-1:2001 Guide to meas, and eval. of human exposure to vibration transmitted to the hand • HSG 88Hand -arm vibration

13. Control of vibration Whole-body vibration damping • Use of suspension system for vehicles • Use of suspension system for seats of vehicles with stiff suspensions • Decrease operator's exposure time by job rotating

14. Control of vibration Hand-arm vibration damping • Damping of tool internally • Insertion of damping between tool housing and hand • Remote operation of tool • Decreasing operator's exposure by job rotation

15. Vibration effects and limits Health effects of whole body vibration, vibration dose Sensitivity to vibration at different frequencies, Fatigue - decreased proficiency and exposure limits, reduced comfort

16. Vibration effects and limits Sources of vibration Vibration in buildings, Segmental vibration, hand arm vibration - neurological and vascular effects Vibration from powered hand tools and other processes

17. Vibration effects and limits 8-hour energy equivalent weighted acceleration Relationship between time to development of vascular symptoms and weighted vibration and exposure time

18. Vibration effects and limits BSEN ISO 2631 4:2001 Fatigue - decreased proficiency and exposure limits, reduced comfort BS 6472 1992 Vibration in buildings, 1-80 Hz

19. Vibration • oscillatory motion of a system

20. Vibration • oscillatory motion of a systemmotion - simple harmonic or otherwise system - gaseous, liquid, or solidair molecules vibrating 20 - 20,000 Hz is sound

21. Vibration

22. Vibration Parameters • Displacement • Frequency • Velocity • Acceleration

23. Displacement x(t) = X sin (2 p t/T) = X sin w t = X sin (2 p f t) x = instantaneous displacement (m) X = maximum displacement (m) t = time (s), T = period of vibration (s) f = frequency of vibration (Hz) w = angular frequency (2 p f ) (radians/s)

24. Velocity v = dx/dt = wX cos (wt) = = V cos (wT) = V sin (w + p/2) = V cos (2 pf t) v = instantaneous velocity (m/s) V = maximum velocity (m/s)

25. Acceleration a = dv/dt = d²x/dt² = - w²S sin (wt) = - A sin (wt + p) = - A sin (2 pf t) a = instantaneous acceleration (m/s2) A = maximum acceleration (m/s2)

26. Acceleration, rms

27. Acceleration, rms

28. Crest factor

29. Phase Difference

30. Non-harmonic motion

31. Non-harmonic motion

32. Effects depend on: • frequency (Hz) • displacement (m) • acceleration(m/s2) - a measure of the intensity • resonance - depends upon the natural resonant frequency of either the source of vibration or of the object being vibrated (the human body segments or organs).

33. Vibration Segmental or Hand-Arm Vibration General or Whole Body Vibration

34. Segmental or Hand-Arm Vibration Transmitted to hands and arms from power tools and other vibrating equipment, such as chain saws, chipping tools, drills, grinders, motor bikes.

35. General or Whole Body Vibration Transmitted to the sitting or standing body through transmitting surfaces such as in aircraft, ships, vehicles or working on vibrating floors.

36. Segmental Vibration

37. Symptoms • finger blanching, particularly when exposed to the cold • tingling and loss of sensation in fingers • loss of light touch (difficulty fastening buttons and zippers) • pain and cold sensations between periodic white finger attack

38. Symptoms • loss of grip strength • bone cysts in fingers and wrists • carpal tunnel syndrome

39. Although segmental or local vibration almost always affects only upper limbs, legs can be affected if they come into contact with vibrating equipment.

40. Primary syndrome names • Raynaud's syndrome • Traumatic Vasospastic Disease • Vibration White Finger • Hand Arm Vibration Syndrome

41. Characteristics • sudden block in blood circulation to fingers • fingers become white, pale, cold, and sometimes painful • tactile sensitivity reduced • Symptoms last from minutes to hours, at first reversible

42. www.whitefinger.co.uk

43. Causes • vascular disturbance • (changes in blood vessel walls) • nervous disturbance • (reflex contraction of smooth muscles of blood vessels) • occurs naturally in ~ 1% of pop, 90% of which are female

44. Factors • Physical • Biodynamic • Individual

45. Physical Factors • Dominant frequencies & vibration direction • Years of employment & daily duration • Temporal exposure pattern • Non-occupational exposure

46. Biodynamic Factors • Grip forces • Surface area & mass of hand • Handle orientation & texture

47. Individual Factors • Susceptibility • Vasoconstrictive agents • (smoking, drugs)

48. Frequency dependence

49. Taylor-Pelmear Classification

50. Taylor-Pelmear Classification