The influence of moisture and stress is characterised by the Stress-Moisture-Cohesion (SMC) function.  From this function the maximum unconfined stress of a coal sample can be determine. The critical moisture is the moisture at which this maximum occurs. The maximum unconfined stress and the critical moisture are the most important handling properties of a coal product and the ECT allows these to be measured effectively.

In the recent ACARP project 15070 19 Australian coals were tested and it was found that all coals tested had unique SMC functions as shown in Figure 1.