This was a posting on an engineering question board (words in italics are my addition). I don't think they meant it quite the way I interpreted it. But it's good to know the EU has regulations about these sorts of things, 4 hours is a long time.....
Back in the eighties Company........ reported that high vibration amplitudes of Hand Arm Vibration (HAV) combined with high feed forces (the forces required to press the tool to the work surface) can cause micro-fractures in bones and have adverse effects on joints.
In recent years, research seems to have concentrated on vibration exposure assessments. For instance, EU Directive 2002/44/EC states that "As regards hand-arm vibration (HAV), the action level is likely to be exceeded by operators of most main percussive and roto-percussive tools (such as chipping hammer, demolition hammer, rock drill, breaker, impact drill, scabbler, rammer, vibratory rammer), of main rotative tools (e.g. grinder, impact wrench, sander) and main alternative tools (e.g. jig-saw, file). The limit value for exposure to vibration may be exceeded if percussive and roto-percussive tools are used for more than one to two hours a day, or in the case of some rotative tools if used for more than four hours."
Until recently, most risk management guides on the topic HAV concentrate almost entirely on the high vibration amplitudes and barely mention feed forces or the factors that might affect them (posture, work practices, tool design, tool size, task nature, handle design, coupling effects due to gloves [?hands] et cetera).
However, the European Agency for Safety and Health at Work has published "Workplace exposure to vibration in Europe: an expert review" (2008) which notes that with respect to HAV, the authors note that awkward postures, static muscle forces, grip and feed forces should also be taken into account and mention tht there has been progress in force-measurement equipment (as shown by the Vibtool report).
Our lack of data on grip forces and feed forces for using various vibrating hand tools is worrying. Could it possibly be that large gloves (? hands) magnify the grip force needed and amplify injury rates? Does anyone know of any research papers on the topic of the feed forces that are needed to control vibrating hand tools for typical tasks?