Models and Methods for Analysis and Improvement of Physical Work Environments
The aim of this thesis concerning work-related personal injuries was to obtain knowledge bases for two purposes. The first was to develop a model, the Ergo-Index, for use when comparing work situations regarding ergonomics and time aspects and choosing the most favourable working method. The second aim was to develop methods for managing personal injury risks at company level. Such tools can be used to motivate improvements in work environments, which will most likely decrease work-related injuries and human suffering, and at the same time increase efficiency.
Five studies were carried out. For the Ergo-Index model, four laboratory studies of work situations were used to investigate 1) fatigue reactions such as endurance time, recovery time, resumption time and pain reactions in some awkward postures, 2) differences between women and men regarding endurance, recovery, pain and physical strength, and 3) differences between skilled and non-skilled persons regarding endurance, recovery and pain. Force measurement, EMG methods, and subjective ratings on the Borg CR-10 scale were used for studying static load levels in university students and staff, hospital staff and construction workers. In the fifth study a procedure consisting of two models for managing work-related injuries was developed. This was based mainly on injury statistics, semi-structured interviews with company managers, construction workers and other researchers; and on existing models and methods.
Several interesting results were obtained e.g. that the same type of mathematical relations could describe the relation between load and endurance time for passive and active muscle loading situations, that pain from muscle tissue limited the endurance also in loading situations with joints near or at the end of their range of motion, that there were significant differences between skilled, experienced workers and non-skilled participants regarding endurance and resumption time, and that no significant differences between women's and men's endurance time and recovery time were found at the same relative load level. The results were used for developing the Ergo-Index. Further, the risk-management procedure enabled economic consequences of work-related injuries at company level to be estimated. This procedure consists of the statistically based cost analysis method (SCA) and the method for analysing work-related risks, improving work environment and estimating total cost (MAWRIC). In an example for a construction company, work-related personal injury costs constituted about 2 % of turnover. Further, the company's total cost for work-related personal injury approximated its total profit. Only 6 % of such costs were accounted for traditionally as sick-leave salaries, social contributions and holiday pay. The rest, i.e. 94 % were indirect costs. Risk-reducing measures can lower both risks and costs. In the example given, the measures taken reduced company costs by about 75 %.
It is concluded that the models and methods presented can be used as tools for analysis and improvement of physical work environment and for increasing management's awareness of work-related personal injuries, hence providing incentives for improvement of the working environment.
work-related personal injuries