Differentiate between a wet-pipe and a dry-pipe sprinkler system.

• A. Wet-pipe has water-filled pipes that discharge immediately; dry-pipe has pressurized air or nitrogen in pipes and requires a delay to fill with water when a head is activated.
• B. Wet-pipe uses foam; dry-pipe uses water.
• C. Wet-pipe has pressurized air; dry-pipe has water.
• D. Wet-pipe is only in high-rise buildings.

Answer: (A)

The key idea here is how water is stored and delivered in the sprinkler piping, which determines how quickly water reaches a sprinkler head and how the system behaves in cold environments. In a wet-pipe system, the piping itself is filled with water at all times, so when a sprinkler head is heated and opens, water discharges immediately from that head. In a dry-pipe system, the piping is charged with pressurized air or nitrogen and the water is kept in a separate supply, not in the exposed pipes; when a head is activated, the dry-pipe valve opens and water begins to fill the dry pipes, displacing the air, which introduces a short delay before water reaches the sprinklers. This delay is the trade-off for keeping the pipes dry and less prone to freezing in unheated areas.

The other statements don’t fit because they mischaracterize where water is held or how the systems operate: wet-pipe is not defined by foam, and dry-pipe is not simply water-filled; wet-pipe is not about having pressurized air, nor is it exclusive to high-rise buildings.