evaluation of noise pollution levels due to four-wheel harvesting machines in bystanders and machine drivers

background: one of the most widely used equipments in harvesting hay and grains are four wheel mowers. the aim of the present study was to determine the levels of noise exposure in drivers and bystanders in different states, speeds and gear of four wheel mowers (bcs model 622).   methods: the iso 5131 and iso 6814 standards were used to assess noise exposure in drivers and bystanders, respectively. experiments were done in totally randomized block models in the form of 2 × 3 × 4 factorials (2 moving blade conditions, 3 states of various motor rpm’s and 4 gear states) and three repetitions. sound pressure levels were measured both at the driver’s ear level and the bystanders. in conditions where in the level of exposure was above permissible noise limits, octave band analysis was performed. data analysis was performed in excel and spss 16.   results: drivers were exposed to noise pollution higher than the permissible level (according to the acgih standards) at 3000 rpm. factors affecting noise level exposure in the driver and bystander included engine speed, gear ratio and cutting blade speeds and were all significant at the 0.01 level.   conclusion: routive use of harvesting machines leads to adverse auditory effects. this fact highlights the necessity of controlling noise emission from this machine through engineering, technical and managemental practices.