We have measured exposure to hand arm vibration for many hand power tools; sanders, drills, grinders and the full shift exposure assessment has been a simple calculation based on the vibration level measured and the trigger time. We have found the HAVi meter to be useful for finding trigger time. Sometimes, when sanding where the vibration level changes due to sanding flat surfaces and edges and corners, we have used an average vibration level measured for a complete part and multiplied by the number of parts sanded in a day.
In the winter of 2014/2015 we had to think again when we were asked to measure hand arm vibration exposure on a vehicle assembly line. The tools in use were a wide variety of pneumatic and battery powered torque wrenches and nut runners. One operator could use up to ten different tools for a couple of seconds at a time over hundreds of nuts during a shift. No one had complained of any ill effects but no measurements had been taken to prove the scale of hazard or risk.
Using information from the report by the Health and Safety Laboratory in the Annals of Occupational Hygiene we planned to make a dedicated trial jig with a number of different size bolts, on which to test the different tools. We decided to measure the vibration level of each torque wrench in two cells, over 4 nuts. The HSL report had found that real life work gave increased vibration levels compared with testing on a jig. Our jig was not possible as the client’s parent company would not allow non standard equipment on site unless it had passed health and safety tests. The company used a torque calibrator on the tools so this was used on tools to establish vibration levels over a number of tightening and loosening cycles. We retested some of the in-situ-tested tools as well to find out how representative this method was for establishing personal exposures. The measured vibration levels were turned into “exposure points” per 100 nuts. We used bolt purchasing data and working procedure methods to work out how many nuts were tightened per day by which torque wrench. This was done for the most popular model on each line.
We found that hand arm vibration was not a high risk and more importantly we could prove this. The company were pleased as they knew that previously they had no defence should any employee make a claim for hand arm vibration syndrome.