Fire hydrant design: which statement below is incorrect with respect to spacing, pressure, and availability?

Introduction:
Fire hydrant systems must meet criteria for spacing, pressure, and duration during emergencies. However, hydrants are not meant for ordinary continuous consumption; they are emergency outlets designed for intermittent, high-rate withdrawal during fires.

Given Data / Assumptions:

• Typical urban hydrant spacing is 100–150 m for accessibility.
• Minimum residual pressure at a hydrant commonly targeted ≈ 1.5 kg/cm^2.
• The contentious statement suggests prolonged constant-use supply through hydrants.

Concept / Approach:
Hydrants are emergency fixtures, not consumer delivery points. Design guidance sets residual pressures and flow durations for firefighting scenarios, but “constant use” is not an objective for hydrants. They are isolated via valves and used only during incidents or testing.

Step-by-Step Solution:
Affirm spacing convention (100–150 m) as reasonable for urban grids. Affirm residual pressure ≈ 1.5 kg/cm^2 as a planning minimum. Identify the incorrect statement: long-duration constant use via hydrants contradicts the emergency-only intent.

Verification / Alternative check:
Municipal manuals specify hydrant operating pressures/flows for firefighting duration (e.g., a few hours) but explicitly restrict routine domestic/industrial draw from hydrants.

Why Other Options Are Wrong:

• 100–150 m spacing: Standard practice in many jurisdictions.
• Minimum pressure ≈ 1.5 kg/cm^2: Common planning benchmark.
• None of these: Incorrect because one statement is demonstrably wrong.

Common Pitfalls:

• Conflating hydrant design duration (for firefighting) with “constant use.”
• Ignoring that hydrant outlets are normally locked/valved off.

Final Answer:
Water at 1.0–1.5 kg/cm^2 is made available for 4–5 hours for constant use.