The explosion is always due to an over pressure. The real problem is coming from a loss of level, if you lose the level of water in your heat exchanger, your t

The explosion is always due to an over pressure. The real problem is coming from a loss of level, if you lose the level of water in your heat exchanger, your top tubes are dry and over heat. If at that time you add water again (because maybe the operator suddenly see the level loss), the water in contact vaporizes immediately and you get over pressure and explosion. If you have a level loss, you need to stop the heat, cool down the complete heat exchanger and start again. This is a very error prone procedure because the immediate reaction as an operator is to add water on a level loss. In most industrial plants now, on a level loss, the complete unit is doing a safety shutdown.