Vibration transmitted to operator's back by machines with back-pack power unit: a case study on blower and sprayer machines

To correctly evaluate the vibration transmitted to the operators, it is necessary to consider each body’s point interested by the vibratory stimulus produced by machines. All the body’s part in contact to the vibration, when a portable device with internal combustion engine is used, are: hands, back and shoulders. Some information for whole-body vibration are available in the ISO 2631-1997 standard, which otherwise refers to a seated operator. ‘C’ type standards for the vibration analysis exist for some portable machines with an internal combustion engine which is comprehensive in the machine (chainsaw, brush-cutter, blower). If the engine is not inside the machine, but it is on the operator's back, ‘C’ type standards on vibration measurements are quite incomplete. The IMAMOTER institute of CNR, the DISAFA Department (University of Turin) and the Occupational Medicine Department of the University of Catania started some tests to verify the vibration levels transmitted to an operator working with backed engine devices. Two machines have been examined: a blower and a spraying machine. Two operative conditions have been considered during all the tests: idling and full load. Three operators have been involved and each test has been repeated three times. The spraying machine has been tested both with the empty tank and with 10 litres of water, to simulate the load to be caused by the presence of liquid inside the tank. In this work the comfort condition of ISO 2631-1 standard was considered, using the frequency weighting Wc curve with the weighting factor 0.8 for X axis (back-ventral direction) and the Wd curve for Y and Z axis (shoulder - shoulder and buttocks - head) with weighting factors 0.5 and 0.4 (respectively for Y and Z axis). Data were examined using IBM SPSS Statistics 20 software package. The statistical analysis underlined that the running condition is the main factor to condition the vibration levels transmitted to the operator’s back, while the ballast and the operators are influent when the running conditions are distinguished. Concerning medical investigation, lower back and shoulders are the main critical part of the body interested by vibration transmitted to each operator.