Thermal runaway reactions are always said to be dangerous on an industrial scale since the reactions go faster in an industry where they tend to reach higher temperatures. As you would already know that Exothermic reactions tend to release quite a large amount of heat, so when the reaction mixture gets very warm, a very very hot exothermic reaction begins.
When you use industrial floor scales, it wouldn't take long to measure how and for how long the reaction needs to run to completion, so although it begins to get very very hot, it's soon over at the speed it started off with. When we see no more heat is being generated by the industrial reaction, and when it'll start cooling once the reaction is over. Did you know that for around 30 years manufacturers of some of the top of the line industrial weighing equipment with the best quality, accuracy, advanced technology and durability have always struggled to sustain it.
When you have got a large volume of raw materials reacting, and that too in an exothermic reaction, it then begins to get hot, and finally it can quickly spiral abd get out of control. What happens is that the heat generated from the reaction can't escape, the reaction goes quicker, which then leads it to release even more heat, which speeds up the reaction even more. So that is how you have a thermal runaway reaction - in such a reaction even vessels cold melt, or explode.
The raw material or even the product might boil away and be lost. At times it might catch fire and lead to very very dangerous situations. So that leads to the conclusion that exothermic reactions have to be run with plenty of coolant available which will help to keep the reaction at a manageable temperature. But on the other hand Nuclear power stations is another example where you don't want it to get too hot.
