this increases energy costs and can lead to poor quality steam, reduced efficiency, shorter plant life and an operation which is unreliable. At worst, it can lead to catastrophic failure and loss of life. While variations in standards may exist in different countries, stringent legal, testing, training and certification is applied to try to minimize or prevent such occurrences. Failure modes include: Overpressurization of the boiler Insufficient water in the boiler causing overheating and vessel failure Pressure vessel failure of the boiler due to inadequate construction or maintenance. Doble boiler The Doble steam car uses a once-through type contra-flow generator, consisting of a continuous tube. The fire here is on top of the coil instead of underneath. Water is pumped into the tube at the bottom and the steam is drawn off at the top. This means that every particle of water and steam must necessarily pass through every part of the generator causing an intense circulation which prevents any sediment or scale from forming on the inside of the tube. Water enters the bottom of this tube at the flow rate of a second with less than two quarts of water in the tube at any one time. As the hot gases pass down between the coils, they gradually cool, as the heat is being absorbed by the water. The last portion of the generator with which the gases come into contact remains the cold incoming water. The fire is positively cut off when the pressure reaches a pre-determined point, usually set at , cold water pressure; a safety valve set at provides added protection. The fire is automatically cut off by temperature as well as pressure, so in case the boiler were completely dry it would be impossible to damage the coil as the fire would be automatically cut off by the temperature. Similar forced circulation generators, such as the Pritchard and Lamont and Velox boilers present the same advantages. Applications Steam boilers are used where steam and hot steam is needed. Hence, steam boilers are used as generators to produce electricity in the energy business. It is also used in rice mills for parboiling and drying. Besides many different application areas in the industry for example in heating systems or for cement production, steam boilers are used in agriculture as well for soil steaming. Testing The preeminent code for testing fired steam generators in the USA is