A MODEL FOR ESTABLISHING A SAFE WEIGHT OF LIFT
Some of the causes of lower back disorders, the associated human agony and industrial losses have been traced to manual lifting. Hence, the objective of this work is to formulate a mathematical model for predicting a safe weight of lift with respect to the lower back of an individual worker. A safe weight of lift (SWL) was defined as that weight whose axial component compressive force perpendicular to the disc plane is incapable of causing plastic deformation of the disc. The intervertebral disc cartilage, being the weakest component of the lifting body structure, was the focal point for analysis. 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 load (V); horizontal length of load from the ankles (H); vertical displacement of load (D); angle of lift (q) and the lifters 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 breadth and depth of the trunk were measured. Also measured were the heights just before the start and after the close of work in order to determine the height shrinkage. 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 taken also from the literature. Taking measurements from eighty four individuals, 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 0.014m and maximum permissible shrinkage of 0.21m, the SWL and SWLMax values, were significantly different (at 95％ level confidence) from the corresponding RWL and the MAWL values. Hence, the mathematical model incorporating the lifters anthropometric dimensions for predicting SWL appeared realistic.
Lower Back Height Shrinkage Manual Lifting Safe Weight of Lift Strain Energy
Ismaila S.O. Charles-Owaba O.E.
Department of Mechanical Engineering, University of Agriculture, P.M.B 2240, Abeokuta, Ogun State, N Department of Industrial and Production Engineering, University of Ibadan, Oyo State, Nigeria
国际会议
17th World Congress on Ergonomics(第十七届国际人类工效学大会)
北京
英文
1-6
2009-08-09（万方平台首次上网日期，不代表论文的发表时间）