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VI-12 . The average area per hydrant required in Carbondale is, from Table VI-J, 120,000 square feet, or a circle having a radius of 200 feet. Ideally, h;drants should therefore be spaced no further apart than about 400 feet. 10 high density areas, a few additional hydrants may be necessa'.y. In low density residential areas, spacings up to 500 or 600 feet may b,. acceptable. The actual fire flow requi rement is dependent upon: 1. Type of building construction 2. The amoun t of fi re loading (by bui lding contents) 3. Whethe ,. 0 r not the bui lding is sprinklered 4. Sepa ra' ion between structures 5. If the roof has shake shingles, additional fi re flow is requ ired. . To demonstrate how these variables interact, the following table was de- veloped for two building types. Case A is for a 20-unit condominium, 3 stories high, with an average of 850 square feet per unit. Case B is for a 60,000 square foot shopping center. As can be noted from Table VI-K, there can be significant financial benefits for water systems if the building construction can be restricted in such a manner so as to limit fire flow requirements. . Reliability design criteria cannot be specifically defined and are princi- pally a matter of judgment. Examining a system's reliability requires weighing costs of reliability design versus the probability design versus the probabi I ity of fai lure and the consequences. There are possibi I ities of power outages affecting pump supplies, intake freeze-ups or blockages, as well as breaks in any of the transmission lines. Reliability design criteria should include: I. Obtaining a sufficient portion of the water supply from two or mo re independent sources. 2. Providing two finished water transmission line systems designed so that anyone outage would not critically reduce the total supply capabilities.