when a pressurized container such as the waterside of a steam boiler ruptures, it is always followed by some degree of steam explosion. a common operating temperature and pressure for a marine boiler is around and at the outlet of the superheater. a steam boiler has an interface of steam and water in the steam drum, which is where the water is finally evaporating due to the heat input, usually oil-fired burners. when a water tube fails due to any of a variety of reasons, it causes the water in the boiler to expand out of the opening into the furnace area that is only a few psi above atmospheric pressure. this will likely extinguish all fires and expands over the large surface area on the sides of the boiler. to decrease the likelihood of a devastating explosion, boilers have gone from the "fire-tube" designs, where the heat was added by passing hot gases through tubes in a body of water, to "water-tube" boilers that have the water inside of the tubes and the furnace area is around the tubes. old "fire-tube" boilers often failed due to poor build quality or lack of maintenance (such as corrosion of the fire tubes, or fatigue of the boiler shell due to constant expansion and contraction). a failure of fire tubes forces large volumes of high pressure, high temperature steam back down the fire tubes in a fraction of a second and often blows the burners off the front of the boiler, whereas a failure of the pressure vessel surrounding the water would lead to a full and entire evacuation of the boiler's contents in a large steam explosion. on a marine boiler, this would certainly destroy the ship's propulsion plant and possibly the corresponding end of the ship.