The implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher spacetime yields, higher temperatures, and a confined reaction volume comprises new risks, such as runaway reactions, decomposition, and incomplete conversion of reactants. Simplified spreadsheet calculations enable an estimation of the expected temperature profiles, conversion rates, and consequences of potential malfunction based on the reaction kinetics. The analysis illustrates that the range of optimal reaction conditions is almost congruent with the danger of an uncontrolled reaction. The risk of a spontaneous reaction with hot spots can be presumed if strong exothermic reactions are carried out in micro-designed reactors. At worst, decomposition follows the runaway reaction with the release of noncondensable gases. Calculations prove that a microreactor is not at risk in terms of overpressure as long as at least one end of the reactor is not blocked.

The intensified technologies offer new prospects for the development of hazardous chemical syntheses in safer conditions: the idea is to reduce the reaction volume by increasing the thermal performances and preferring the continuous mode to the batch one. In particular, the Open Plate Reactor (OPR) type "reactor/exchanger" also including a modular block structure, matches these characteristics perfectly. The aim of this paper is to study the OPR behaviour during a normal operation, that is to say, after a stoppage of the circulation of the cooling fluid. So, an experiment was carried out, taking the oxidation of sodium thiosulfate with hydrogen peroxide as an example. The results obtained, in particular with regard to the evolution of the temperature profiles of the reaction medium as a function of time along the apparatus, are compared with those predicted by a dynamic simulator of the OPR. So, the average heat transfer coefficient regarding the "utility" fluid is evaluated in conductive and natural convection modes, and then integrated in the simulator. The conclusion of this study is that, during a cooling failure, a heat transfer by natural convection would be added to the conduction, which contributes to the intrinsically safer character of the apparatus.

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The implementation of process intensification by multiscale equipment will have a profound impact on the way chemicals are produced. The shift to higher space‐time yields for partial oxidation processes using micro‐designed reactors comprises the risk of having a permanent explosive atmosphere in the reaction section. In Part I, it was concluded that spontaneous reaction with hot spots can be presumed if highly exothermic reactions were performed and may cause ignition of an explosive atmosphere. The risk analysis of the situation, based on public information in the literature, leads to the conclusion that microreactors are inherently safe regarding the initiation and propagation of an explosion inside a microchannel by an uncontrolled reaction. The situation is the opposite when a propagating explosion enters the same micro‐designed reactor from one of the outside openings. The external explosion may enter the micro‐designed equipment and destroy it when the same starting conditions are present.

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