Factors affecting the consumption of working time and the strain on the worker in some

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Sokoine University of Agriculture


The purpose of the study was to formulate an ergonomic model for forest work to serve as frame of reference for theoretical and empirical analysis, to examine the correlations of independent variables in play in forest work such as human, conditions and working method variables with consumption of working time and the physical strain on the worker. The investigation was confined in the empirical material to the cutting of roll-seedlings and the lifting of seedlings in the nursery-, and to the cutting of pulpwood by two working methods, i.e. mediumheavy and heavy work. The final aim was to formulate and test hypotheses of forest work science, postulate new hypotheses and outline an overall theory on the basis of systems analysis. An additional special object was to study the application of the principle of comparative time study in an empirical material and to apply the same principle in pulse rate investigations. This is termed the principle of comparative work study. The work performance was illustrated by a system scheme (Fig. 1). The scheme comprised the following main groups of elements: worker’s inclination for work, working capacity, reflexes and instincts, decision process, environmental factors, working methods and habits, work performance, output, earnings, and effects on the worker. The model was made up parallclly from abstract and concrete concepts, the aim being to make it suitable for the set of concepts of the theory of work study and the level of theory formulation. The model included the feedback from the effects on the worker-sample element group to the worker’s qualities. The literature on forest work studies in which some correlations introduced in the model were investigated is reviewed in Chapter 23. Owing to the great number of output studies they were treated as an example. The greatest part of the research activity has been analysis of the relations between environmental factors — and of them primarily the work difficulty factors — and the work output. The previously outlined system formula is examined in Chapter 24 as a cybernetic, probabilistic system in which the elements as such were conceived to embrace complex linkages and to be of the black-box type. The information transfer of these sample elements was illustrated by only one channel and information was consequently analysed merely as a symbolical expression of space and event. The decision process and the effects of reflexes and instincts were examined as the self-regulatory mechanism of the model. Feedbacks were established both within the worker and between the worker and environment. Principles influencing the formulation of the theory' of work science were postulated on the basis of the general properties of the system, such as threshold values, correlations, the principles of isomorphism and homomorphism: — If a correlation proves to be significant it is relevant at least in the population represented by the material and possibly also in other populations. — On the other hand, if no significant correlation is established between some independent variables there may nevertheless be a significant correlation in some other population or after some threshold values. — Il is useful for development of the theory' to explain the trend of the correlations and the internal conformities to law and mechanism of the elements. — It is assumed hypothetically that the constancy of the relative per-worker working time and strain value is influenced by the difference between the worker’s capabilities that the working methods and working conditions require and by his attitude to the working methods under comparison and his experience. — model taken from nature through simplifications is the more servicable the more deterministic it is. — Empirical work study generally' observes coded messages by indirect means and it is therefore seldom possible to demonstrate direct physiological causal relationships; what results is explanations of the ”either-or” or ”both-and” type. The system description of the work was developed in Chapter 25 by hypothetical insertion in the model of elements formed by the set of concepts of work study principles (Fig. 2). The concepts are: speed of work, physical strain, ratio between physical strain and maximal performance, total strain during the working day, psychic strain, relative consumption of time, average consumption of time, deviation of consumption of time, average strain, deviation of strain, relative strain, and attitudes to work. The quantitative and abstract levels of the concepts of the model were studied using the M-67-meta theory. Fig. 3 shows the concept hierarchies and the measuring features of the concepts. In processing the measuring features for formulation of the theory in the empirical part, concepts of the same quantitativencss arc used which are sub-concepts of the high real theoretical concepts: the worker’s capacity' and inclination for work, effects on the worker, performance, output and environmental factors. Fig. 4 shows the processes as a being model: performance — output and performance — effects on the worker, the worker’s resources (capacity for work) and feelings (inclination for work) and working conditions (environment) which influence the interrelations of these processes. The Jiving organism state of equilibrium. It logical theories that if a was found to be a system which seeks to preserve a was assumed from reference to physiological and psychofactor causes a greater deviation in the equilibrium of the organism than the conditions of other factors, that factor dominates the behaviour of the organism. This theory was applied in the empirical part to explain the phenomena established. In the empirical part the effect was examined of different factors on the consumption of working time, the physical strain on the worker, and the application of certain work study principles in the nursery to the cutting of roJlseedlings, the lifting of pine seedlings and the logging of pulpwood in grapple piles alongside the strip road (working method 2) and a 4-m wide zone for which the bunch size required was reduced (working method 1). The material and the measurements made are described in Chapter 32. The most important results were as follows. Owing to the paucity of degrees of freedom which interfered with testing they were distributed into statistically significant correlations and hypothetical correlations: — Consumption of working time was explained significantly in regression analysis by so-called work difficulty factors, working method, moving speed which illustrates the speed of the work, the time of the working day, the ordinal number of the working day and some independent variables that portray the worker.


PhD Thesis


Ergonomic model, Forest, Forst management, Working time-forest