What is the usual diameter considered inadequate and unreliable for street mains in the context of fire protection water supply?
- Less than 6 inches (152 mm)
- Less than 4 inches (102 mm)
- Less than 8 inches (203 mm)
- Less than 10 inches (254 mm)
Answer: A) Less than 6 inches (152 mm)
Reference: FIRE PROTECTION HANDBOOK 20th
15-64 SECTION 15 ■ Water Supplies for Fixed Fire Protection
A connection from a reliable public waterworks system of adequate capacity and pressure is the preferred single or primary supply for automatic sprinkler systems. In determining its adequacy, one must consider not only the normal capacity and pressure of the system but also the minimum. pressures and flows available at unfavorable times, such as the summer months; periods of heavy demand on the system, such as those created by large industrial areas; or periods of impairment caused by flood or by ice conditions in winter. These conditions are typically referred to as seasonal lows.
The size and arrangement of street mains and feeders from public water supplies are also important. Connections from large mains fed two ways or from two mains on a grid system may provide an excellent supply. Street mains less than 6 in. (152 mm) in diameter are usually considered inadequate and unreliable. Feeds from dead-end mains are also undesirable. Water meters, if required, should be of types listed for the fire service. Flow and pressure tests under varying conditions of demand are generally necessary to determine the amount of public water available for fire protection
Explanation
This passage highlights additional considerations regarding the size, arrangement, and testing of street mains and feeders for supplying water to fire protection systems. Here’s a breakdown:
1. **Connection from Large Mains**: Emphasizes the importance of connecting fire protection systems to large mains, especially those fed from multiple directions or through a grid system. Such arrangements enhance the reliability of water supply during emergencies.
2. **Inadequacy of Small Mains**: Street mains with a diameter less than 6 inches (152 mm) are typically considered inadequate and unreliable for providing water to fire protection systems. Larger mains ensure sufficient water flow and pressure for firefighting needs.
3. **Avoidance of Dead-End Mains**: Feeds from dead-end mains are discouraged because they may not provide adequate flow or pressure, particularly during high-demand situations.
4. **Water Meter Requirements**: If water meters are necessary, they should be specifically approved for use in fire service applications. This ensures accurate measurement of water usage without compromising firefighting capabilities.
5. **Importance of Flow and Pressure Tests**: Flow and pressure tests should be conducted under various demand conditions to accurately assess the amount of water available for fire protection purposes. These tests help determine the system’s capabilities and identify any limitations that need to be addressed.
In summary, the passage stresses the importance of selecting appropriate water supply sources, avoiding limitations such as small mains or dead-end feeds, and conducting thorough tests to ensure the reliability and adequacy of water for fire protection systems.