Subindices for Hazardous Substances

The Chemical Inherent Safety Index deals with the hazards which are related to the chemical properties of substances in the process. The Index has been divided into subindices for reaction hazards and hazardous substances. 

The Inherent Safety Index (ISI) deals with both main reaction(s) and those side reactions taking place in the reactor and which are meaningful. It also deals with chemical interaction which describes unintentional chemical reactions which can take place among chemicals in the plant. 

Since the possible violence of reactions lies in the heat liberated and the temperature which may be reached, the energy change during the reaction has been selected to present the reaction safety in the ISI. This is a feasible approach since the formation enthalpies are known for most substances. 

The enthalpy released or absorbed in a process can be described by Equation 6 for constant volume conditions and an isobaric process. While determining the safety subindex Irm the heat release of the main reaction is calculated for the total reaction mass (i.e. both the reactants and diluents are included) to take account the heat capacity of the system which absorbs part of the energy released  

From the safety point of view it is important to know, how exothermic the reaction is. The classification used by King (1990) is following the reaction is extremely exothermic ( 3000 J/g), strongly exothermic ( 3000 J/g), moderately exothermic ( 1200 J/g), mildly exothermic ( 600 J/g), thermally neutral ( 200 J/g) or endothermic. These values have also been used for 

---