|MadSci Network: Physics|
There are two types of fire hydrants used in the U S. of A , on called a wet barrel, used in the south, not prone to freezing due to milder temperatures. This is used mostly in the the southeast and Texas areas where water mains are buried above the frostline. In the Northern areas a dry barrel system is used whereby the water mains are buried at least 3 to 4 feet below soil grade and they are also equipped with a fairly elaborate draining system whereby any water remaining in the hydrant after use is able to drain off beneath the system to keep problems from happening freezing temperatures for many days in a row. Once the water is brought above grade, it can freeze but this danger can be minimized by keeping water moving through the system rather than allow it to stand stagnant or still, thereby allowing it to freeze up. Consult further the NFPA Handbook or the International Fire Service Training Association's Handbook, Essentials of Firefighting. Hope your question is adequatetely answered. thank you for the query Donald E Duggan
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