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Case Studies
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Bretby Maintainability Index
The Bretby Maintainability Index was developed in the late 1980’s as a fast and cost effective method for identifying where
specific design changes could be made to optimise the ‘maintainability features’ of a
piece of equipment and provide an estimate of the likely impact of any change on the
overall maintenance demand. HSEC have now updated the Index to provide a tool
for determining how new designs need to be improved to reduce down time and
improve machine availability and also reduce any health and safety risks to those
maintaining it.
We have developed an extension module to the Bretby Maintainability Index, which
comprises a risk assessment that addresses the potential for unintentional human
errors that are primarily influenced by aspects of the design. The outcome identifies
the most likely errors and their prime causes so that areas requiring design
improvements are highlighted.
Main Features of the Index
The index is structured to highlight those aspects of a task or operation which
are disproportionately demanding or time consuming, likely to predispose errors
or which have potential safety implications.
The concept behind the index is that any task can be assessed and scored against
a series of factors relevant to gaining access to perform each operation and
actually performing the operations themselves.
Each task is assessed independently against all the relevant factors in the index
and allocated appropriate point scores which reflect issues such as the
available access, the various actions and manipulations which have to be made,
the magnitude of the forces and effort which need to be applied, the amount of
carrying and lifting etc.
The total points scored in this way are then modified to take into account the
different maintenance intThe scores not only represent figures of merit for the individual tasks but they
can be added together or combined to provide an overall maintainability profile
for the machine or item of plant. The point scores can also be directly
translated to represent the number of hours per week or year etc demanded by the
tasks. The process is also designed to delineate any health and safety problems
of specific concern and the scores are weighted to account for any such
difficulties.
The Main Uses of the Index
The BMI can be used as a predictive/evaluation tool within the design process, as
a purchasing aid for product selection and to identify desirable and cost
justifiable retrofit changes to existing stock.
Publications
Mason S, Rushworth AM, 1989, Improving machinery availability through the
application of a new maintainability index. Mineral Resources Engineering, Vol
2, No. 3, 249-261
Mason S 1990 Designing mining machinery to facilitate
maintenance, The Mining Engineer, June 1990.
Mason S 1990 Improving plant and
machinery maintainability, Applied Ergonomics March, 1990
Mason S 1991 Improving
mining machinery maintainability, Mintech 91 - The Annual Review of
International Mining Technology and Development, 1991.
Rushworth AM, Mason S
1992 The Bretby Maintainability Index - a method of systematically applying
ergonomic principles to reduce costs and accidents in maintenance operations,
Maintenance, Volume 7, Number 2, June 1992.
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