Vibration

 In operating vibrating tools such as impact drills, chippers, pneumatic tools and chain saws, employees frequently complain of hand numbness after the shift. With chronic exposure to these tools employees may develop white finger syndrome or Raynaud's phenomenon. This condition occurs following years of exposure to vibrating tools and will affect blood vessels, nerves, bones, joints, muscles and connective tissues in the hands and arms. The employee can experience a sudden loss of fresh blood supply resulting in a sudden bleaching of the fingers. The hands become particularly sensitive to cold weather, become painful or numb, and it becomes difficult to grip large objects or to have the dexterity to handle small objects. The condition, like so many other things, is dose dependent. That is, the number of times the tools are used and the power spectra or amount of vibration of the tool will determine how long the vibration can be tolerated before the onset of the disorder. The frequency of the vibration that is of most concern is found to be between 8 and 1000 Hz. Over 20 years ago, scientists who were working to understand the effects of vibration on the human body designed a scheme to represent body segments as individual masses supported by springs and dampers.

By dividing the body into segments, it has been possible to mathematically model the response of these segments to various vibrating frequencies under a variety of circumstances. Body parts have their own resonance frequency where they are most susceptible to vibration. For example, the resonance frequency for the abdominal mass is approximately 4 - 8 Hz, the head is most sensitive at approximately 30 Hz. A body part exposed to its resonance frequency is at greater susceptibility for injury. With appropriate transducers, investigators can measure the vibration frequency of various vehicles such as automobiles, aircraft or machinery. By better understanding these frequencies, an estimation of their hazards can be made and preventive mechanisms brought to bear to dampen the frequency, alter its resonance, or protect the operator. Adverse health effects from vibration are directly related to a time-intensity factor. As should appear obvious, an individual is able to tolerate a low-magnitude vibration for a longer period of time than would be the case in a high-magnitude vibration field.  someone can tolerate lower magnitude vibrations for longer periods of time but is most sensitive to vibrations in the 6 - 9 Hz range. At higher vibration frequencies, the body becomes more tolerant within the realm of safety and health.

As we know from our daily activities, vibration can interfere with the ability to interpret the environment around us, particularly the visual environment. Whole body vibration increases both the reading time and reading error of a display. It is interesting to note that our interpretation of a display in a vibration field is worse if only the display vibrates, less severe if only the observer vibrates and least disruptive if both the observer and the display are in the vibration field. Further, once the observer has been exposed to vibration for an hour or longer, his ability to interpret the display is compromised for at least several hours post-exposure. One form of vibration with relatively high magnitude but a very low frequency produces an unpleasant response in most of us -- we call this motion sickness. We tend to be most susceptible at frequencies below 0.3 Hz and, given a sufficient exposure duration such as eight hours, over half of us may experience the full spectrum of near-incapacitating motion sickness.

Popular posts from this blog

Human Factor Introduction

Human Factor -  A  Person working in a maintenance environment requires human factor knowledge as per his job requirement. Human Factor Training  - Aviation safety relies on maintenance. When it is not done correctly , it may cause an incident or an accident.  Mistakes of maintenance personnel is difficult to detect. They are subjected to work in changing working in variety of adverse conditon. Regulatory Requirement : CAR 66 Module 09 Human factor - for get AMEL Human Factor   - Study of human capabilities and limitations in the workplace.   It is about study of the interaction  of maintenance personnel, the equipment used, the written and verbal procedures and  rules followed by them, and the environmental conditions of any system.  Aim of human  factors is to optimise the relationship between maintenance personnel and systems to improve  safety, efficiency, and well-being. HF - Fitting the man to the job and the job to th...
Read more

SHEL(L) Model

Model are used to understand human factor  as a framework around which human factor issues can be structured. SHEL(L),PEAR, Dirty Dozen  S - Software H - Hardware L - Liveware E - Environment                                         Liveware  is at the center of the model, is   the most critical and flexible component in the working  Environment and subject to considerable variations in performance and suffer many limitations.                           Physical size and shape.  In the design of workplace and equipment, body measurements and movements is considerd , which may vary according to factors such as age, ethnicity and gender. Human Factors inputs is provided  in the design process, and data for these inputs are available from anthropometry, biomechanics and k...
Read more

Information Processing Limitation

Human information processing  have limitations.   AMT requires support such as reference  to written material (e.g. manuals). Attention and Perception -  A proportion of ‘sensed’ data may be lost without being                              ‘perceived’.   Failing to  perceive  something  which   someone  has said to you, when you are concentrating on something else, even  though the words would have been received at the ear without any problem.  Information processing system has  ability  to perceive   something (such as a picture,                       sentence, concept, etc.) even though some of the data  may be missing.  Danger - people can fill in the gaps with  information from their own store of knowledge or experience, and this may lead to  t...
Read more