Which statement about wet pipe and dry pipe systems is true?

• A. A wet pipe system carries wet extinguishing agents, while a dry pipe system contains only dry extinguishing agents.
• B. A wet pipe system holds water in the pipes, while a dry pipe system's pipes are empty until the valve is opened.
• C. A wet pipe system can only be used for water distribution, while a dry pipe system can never be used to distribute water.
• D. Wet pipe systems are most frequently used in commercial applications, while dry pipe systems are most frequently used in residential applications.

Answer: (B)

Understanding how these systems fill with water is the key. In a wet pipe system, the pipes themselves are filled with water at all times, so when a sprinkler head is activated, water is released immediately through the piping to the head. In a dry pipe system, the pipes are charged with air or another inert gas and held back by a dry pipe valve; when a sprinkler head is activated, the valve opens and water rapidly fills the dry pipes before reaching the heads. This explains why the statement is true: wet pipes always contain water in the lines, while dry pipes are empty of water until the valve is opened and water is sent into the system. The other options either misstate what fills the pipes (both systems carry water, not “wet” versus “dry” extinguishing agents) or make inaccurate generalizations about where each type is used, since both can distribute water and usage patterns depend on factors like climate and building design.