Onset A Concept without Scientific Base

There may be great temptation to derive safe process conditions directly from the temperature at which a peak is detected in a dynamic DSC experiment. As an example, a so-called 50 K rule can be found in industrial practice. In fact, such a rule is equivalent to considering that at 50 K below the onset in DSC, no reaction occurs. This is scientifically wrong and may lead to catastrophically erroneous conclusions for two reasons  

There is no defined onset temperature or starting temperature for a reaction. The reaction rate simply increases exponentially with temperature or decreases by lower temperature according to Arrhenius law. 

For example, a first-order reaction with an activation energy of 75 kj moT1 is detected at 209 °C with an instrument having a detection limit of 10Wkg at 

150°C with an instrument having a detection limit of 1 Wkg-1, and at 109°C with an instrument having a detection limit of 0.1 Wkg-1. Thus, it becomes obvious that the distance rule must be replaced by a more scientifically sound concept, as with the time to maximum rate based on reaction kinetics. 

The probability of triggering a secondary decomposition reaction may be assessed using the time-scale as defined in Section 3.3.3. The principle is that the longer the time available for taking protective measures, the lower the probability of triggering a runaway reaction. The concept of Time to Maximum Rate (TMRld) was developed for this purpose and is presented in Section 2.5.5. The TMRld under adiabatic conditions is given by 

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