In many industries worldwide, the effects of downtime are becoming aggravated by the increasing adoption of just-in-time (JIT) processes and total quality-management (TQM). Reduced stocks associated with JIT mean that minor breakdowns are now much more likely to stop or inhibit production. The growth of mechanisation and automation means that reliability and availability have become key issues in sectors as diverse as healthcare, electricpower generation stations and chemical processing. Thus, during recent decades, the cost of maintenance has risen in absolute terms and as a proportion of total expenditure. In some industries, it is now the largest contributor to the total cost. Maintenance reactions are dependent on many factors, such as failure rates of the plant’s components, the associated costs of downtime and the expected lives of critical items of equipment. Maintenance strategies have evolved (in highly industrialised countries) taking into account quality, cost, flexible delivery and customer satisfaction. Maintenance is regarded as a proactive profitfocused activity; the aim being to narrow the difference between actual and ideal maintenance costs, i.e. reduce the cost of unreliability. Recent developments [4] are: -