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Vibration Information for rotating machinery applications.


Hand-Arm Vibration in the Workplace

Wednesday, May 04, 2011

Hand-arm vibration has become a concern in the workplace because of the longterm effects of exposure to vibration, and several forums and regulatory bodies exist to address the issues of hand-arm vibration. I had the opportunity to attend and participate in the Hand-Arm Vibration conference in Bologna, Italy in 2007 where several interesting presentations were held to discuss the effects of vibration on the hand, arms and body. Diseases and ailments such as Reynaud's or white finger syndrome are a significant concern for workers who use power tools on a daily basis. Angle grinders are a good example where vibration risks are involved due to continuous and long term use.

Several standards have been established, including ANSI S2.70-2006 (previously ANSI S3.34-1986), to control the methods used in measuring and interpreting vibration. The European Union has adopted some of these standards as part of their Directive 2002/44/EC.

The EU Directive has set exposure limits based on the vibration of a power tool and the amount of time it is operated per day; for example, a power tool that has a vibration level of 5m/s^2can only be used for a maximum of 8 hours per day by an operator. Power tools that have vibration levels of 2.5m/s^2 or lower have no restrictions on the amount of time they can be used. 2.5m/s^2 is considered a vibration threshold limit below which it is deemed safe to operate tools without facing longterm health risks. A more detailed chart that displays the EU Directive's exposure limits is shown in the figure below:

In my opinion hand-arm vibration should be a significant cause for concern in the any workplace, however it is not apparent with whom the responsibility lies:

  • Should it be the employer, or the manufacturer who takes on this role?
  • Some manufacturers do publish actual numbers to indicate vibration levels of their power tools, but are these numbers accurate and can they be disputed?
  • Who should be ultimately responsible to monitor the information for accuracy?

  • ISO 8041 and EN 60745 outline the measurement methodology for angle grinder vibration. The resultant vibration is a combination of vibration in 3 axes: x, y and z, and is given as:

    This equation alone may not be a fair assessment of the problem; several combinations of values in the x, y, and z axes can produce the same resultant vibration, as shown in the figure below. The vector direction of the vibration may be a major contributing factor if it acts in a direction that directly transfers vibration to a tool operator's hand and arm. It raises the question: should vibration measurements be weighted equally for x, y and z? And which combination is the most severe?

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