Complex sentence: If liquid water comes in contact with a very hot substance (such as lava, or molten metal) it can create a steam explosion which were responsible for many foundry accidents and possibly also for much of the damage in the Chernobyl accident.
Split into simpler sentences: If liquid water comes in contact with a very hot substance (such as lava, or molten metal) it can create a steam explosion. Steam explosions have been responsible for many foundry accidents and may also have been responsible for much of the damage to the plant in the Chernobyl accident.