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.
