If a dead end main is at least ______ in diameter and has sufficient ______, a fire hydrant should be installed at the end of the pipe.

• A. 8 in, pressure and flow
• B. 6 in, pressure and flow
• C. 4 in, pressure
• D. 6 in, velocity and flow

Answer: (B)

The main idea is that a hydrant at the end of a dead-end main must have enough hydraulic capability to serve a fire without the line’s pressure dropping below what the hydrant and attack lines need. A minimum of six inches in diameter gives the pipe enough capacity to carry the required water flow while keeping friction losses and pressure loss manageable along the length of the dead end. The phrase “sufficient pressure” means there must be enough residual pressure at the hydrant to operate the fire stream, and “sufficient flow” means the line can deliver the necessary gallons per minute for firefighting. If the main is smaller than six inches, the pressure could fall too low or the flow could be inadequate under fire demand. Larger diameters, like eight inches, meet the requirement but aren’t needed as a minimum, while a four-inch main wouldn’t reliably meet typical fire flows. Mentioning velocity isn’t the governing criterion here; the critical factors are pressure and flow.