A quatitative approach for establishing safe weight of lift

The objective of this work was to formulate a mathematical model for predicting a safe weight of lift. Considering the intratruncal pressure, post-work height shrinkage of the worker and strain energy of the intervertebral disc, the SWL function was derived in terms of the Young Modulus of elasticity (E) of the articular cartilage (endplate of the disc); velocity of lift (u); acceleration due to gravity (g); vertical location of the load (V); horizontal length of the load from the ankles (H); vertical displacement of the load (D); the angle of lift ("theta") and the lifter’s anthropometric dimensions. To evaluate the function for a particular individual, the value of the length of the spine from the first thoracic to the last lumbar vertebrae, the heights just before the start and after the close of work were measured to determine the height shrinkage. Additionally, the breadth and depth of the trunk were measured. A range of values of the function parameters: V, H and D were adopted from National Institute for Occupational Safety and Health (NIOSH), while E and U were also taken from the literature. SWL values were computed and compared to those of the Recommended Weight Limit (RWL) of NIOSH and Maximum Acceptable Weight of Lift (MAWL) from the literature. At an average height shrinkage of 0.014 m and a maximum permissible shrinkage of 0.21 m, the SWL and SWLMax values were significantly different (at 95% level confidence) from the corresponding RWL and the MAWL values