Hand and arm vibration differences between operatives

Hand and arm vibration measurements in industrial environment can sometimes show some unexpected results. I have recently carried out measurement of hand and arm vibration on two operatives in a small production facility. The company involved specialises in the manufacture of intrinsically safe electrical equipment. The site consists of one open plan unit, welfare facilities and offices. There are approximately 23 permanent employees and variable number of temporary staff. However, only two employees are regularly subjected to significant levels of hand and arm vibration.

hand and arm vibration tool

The operatives under assessment were Dynablade Inc Model 50005 RPM 20K air powered abrasive tools for product finishing. The work consists of abrading edges of stainless steel metal boxes of varying sizes and removing welding residue. I have collected the production information from the factory management and carried out evaluation of the working patterns and number of process pieces of products and thus likely vibration exposure. My exposure time estimates were based on 1 month production data. The two operatives working in the linishing area processed almost 12000 items over 20 working days giving 280 items per operative per day. The process items were then divided into four equally large item groups with 70 items per group per day. The average time spend to process item of each type was measured during normal operation. The processing time of boxes base plates is on average 27 seconds, box body is 45 seconds, box lid is 37 seconds and box side panel is 4 seconds.

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After initial investigation i have progress to carry out hand and arm vibration measurement using precision Larson Davis HV100 Vibration Analyser. My measurements were carried out in accordance with the relevant hand and arm vibration standards.

I have carefully measured each operative performing a variety of tasks. After I have crunch the calculation I have found out that one of the operatives was showing relatively low vibration exposure levels and other one was exceeding the vibration action value despite the fact they both used identical tool and work pieces. As these results would be confusing to the client further investigation was necessary. Firstly I have carried out vibration measurements on both tools under no load conditions. The measurements showed that both tools exhibited very similar vibration levels. Secondly I have retested the operatives but this time I have asked them to exchange to work tool. The measurement in this case showed that the employees exposed to high vibration levels remain to be exposed to high levels. This was a clear indication that the vibration exposure problem was not with the tool but with the working technique of this particular operative. The employer was advised to retrain the operative to reduce his vibration exposure.

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