The following graph shows the fatigue decreased proficiency boundary for vibration based on the frequency of the vibration, and its acceleration. To obtain "Exposure Limit": multiply acceleration value by 2.

Graph 1:

Graph 2:

How To Determine Exposure Limit

If the measured acceleration is in the vertical direction use graph 1, otherwise use graph 2. Studies have found that the resonance frequency-range of the lower back is 4-8 Hz. Given this information and the measured acceleration value at work, an exposure work time and acceleration limit can be determine. For example, the limit to whole-body vibration acceleration (vertical direction - graph 1) allowed for an 8 hours working day is 0.315 m/s2 if fatigue-decreased proficiency is the criterion and 0.63 m/s2 if health is the criterion (exposure limit).

   Several studies have published vibration levels for various vehicles used in the construction, manufacturing and farming industries. These values are summarized below in order to compare them to the ISO Fatigue-Decreased Proficiency Boundary and Exposure Limits. Some of the vibration values were measured on various terrain types. Most values, however, did not take into account the maintenance level, age of vehicle, and other contributing factors. Thus, caution should be taken when using the value.

COMPARISON OF VIBRATION VALUES FOR VEHICLES RESEARCHED IN LITERATURE

Vehicle Acceleration in the x,y,& z direction Vehicle Acceleration in the x,y,& z direction Forklift truck 0.8 Bulldozer with standard seat 0.52 - 0.64 Tractor on brick paved road 1.76-2.03 Bulldozer with vibration absorption seat 0.43 - 0.80 Tractor on asphalt 1.17 Forklifts 0.4-2.3 Tractor on road 1.1 Caterpillar 0.6 Tractor in field 0.6 Bulldozers 0.4-1.3 Freight container 1.0 Power Shovels 0.5-2.3