DEVELOPMENT OF A SAFE WEIGHT OF LIFT MODEL FOR MANUAL WORKERS AT ARULOGUN, IBADAN, OYO STATE

Abstract

The Low Back Pain (LBP) problem is prevalent among construction workers involved in the Manual Load Handling (MLH) of sandcrete blocks. Studies have shown that human and environmental based factors affect the weight of lift appropriateness and may lead to musculoskeletal disorders such as low back pain. Ergonomic models that utilise compounded human characteristic factors and environmental temperature to estimate Safe Weight of Lift (SWL) for construction workers are sparse. This study was, therefore, designed to develop a model for determining SWL among manual labourers at varying workplace temperatures. A safe weight of lift model was developed with compounded human ergonomic factors of age, body weight, spinal shrinkage, spine length, lift frequency, and environmental temperature using the principle of strain energy. Subjective sampling technique was used in selecting fifty experienced male bricklayers involved in lifting sandcrete blocks of weight between 20.00 and 22.50 kg for 8-hours daily at Arulogun, Akinyele Local Government Area, Ibadan. For each subject, the compounded human ergonomic factors and environmental temperature were measured using the ZT-160 scale, stadiometer, measuring tape, clock timer and Extech RH/Temperature pen device. The obtained data were used as input into the developed model to estimate the SWL for each subject at varying temperature ranges of 26.00 – 27.90, 28.00 – 29.90, 30.00 – 31.90, 32.00 – 33.90, 34.00 – 35.90 and 36.00 – 37.00°C. These were compared with existing secondary SWL data at the temperature range of 27.00 – 32.00℃. Analysis was subsequently done to determine factors that were significant in estimating SWL. Data were analysed using ANOVA at ∝0.05. The model revealed that a non-linear relationship exists between the SWL and compounded ergonomic factors. The age, body weight, spinal shrinkage, spine length, lift frequency, and temperature were 33.26±7.22 years, 67.50±11.58 kg, 0.02±0.06 m, 0.47±0.03 m, 2.00±0.48 lifts/min, and 30.46±2.51℃, respectively. The safe weight of the lift at environmental temperature ranges of 26.00 – 27.90, 28.00 – 29.90, 30.00 – 31.90, 32.00 – 33.90, 34.00 – 35.90 and 36.00 – 37.00℃ were 6.23±0.82, 5.79±1.45, 7.20±1.84, 8.04±2.74, 5.96±0.00, and 5.87±0.00, respectively. The SWL, which ranged between 3.78 and 12.77 kg implied that sandcrete blocks in this weight range when lifted, were incapable of causing low back pain. The SWL from the model and that of the compared secondary data were 6.10±1.29 and 16.34±6.40. These indicated that there was a significant difference between the model and secondary data, which could be attributed to differences in the environmental temperature at which the secondary data were obtained as compared with those of the model. The model SWL was significantly influenced by the interaction between compounded human ergonomic factors and environmental temperature. An ergonomic model to estimate the safe weight of lifts for manual labourers was developed. The model is a useful tool for decision-making in the area of safety management of male labourers involved in the manual load handling.