The results expected from a longwall face can best be estimated from the ideal production rate, determined by the capacity of the equipment and the conditions in which it is installed, the effective operating hours, and the utilisation._x000D_
The effective operating hours are determined by a number of scheduling factors which include the proportion of manned time to calendar time, the effective shift factor (effective time to manned time) and the move times._x000D_
Analysis of the results achieved on the last 121 completed longwall panels in Australia (1984 onwards) shows a significant trend between 'actual tonnes/manned hour' and 'ideal production rate' (the measure of the capacity of the installation)._x000D_
Using 1982 'state of the art' longwall equipment, (the average in use in the seven year period), it should be possible to produce around 2.7M tonne/year ROM from a mine with one longwall. Few mines are achieving this._x000D_
A review of production scheduling factors and general natural hazards affecting some mines suggests three things._x000D_
1. Whilst some increase in average effective hours has followed the CIT decision, further improvement is possible at many installations._x000D_
2. Many mines subject to general natural hazards, such as high gas make and high general stress, have found effective solutions and achieve the same utilisation as the overall average._x000D_
3. A small number of faces within such mines have been severely affected, some less so. The most severe effects of natural hazards appear to be very site specific. This emphasises the need for detailed investigation of the causes, and development of means of predicting their presence. Only then can either satisfactory technical solutions be found to overcome the problems or prior decisions be chosen not to mine badly affected panels.