The runaway scenario can serve as a basis for the assessment of thermal process risks. In this context, the time to maximum rate (TMRad), i.e., the time between cooling failure and thermal explosion, can be a measure of the time in which safety measures must be taken. This paper highlights the discussion of TMRad by presenting the catalytic decomposition of hydrogen peroxide with potassium iodide. The experimental procedure is easily practicable and imposing for the students. An overview of the theoretical background is given before presenting the experiment. (C) 2003 Elsevier Science Ltd. All rights reserved.