What is the difference between a wet pipe and a dry pipe sprinkler system and where is each typically found?

• A. Wet pipe systems have water-filled tubes; dry pipe systems have pressurized air or nitrogen in the pipes with water in the main; wet pipes are common in warmer climates; dry pipes in colder climates to prevent freezing.
• B. Wet pipes are installed outdoors only.
• C. Dry pipes have water-filled tubes; wet pipes have pressurized air or nitrogen.
• D. Dry pipes are never used in buildings.

Answer: (A)

The main idea is whether the sprinkler piping is filled with water or charged with air before a head is activated. In a wet pipe system, the piping itself is water-filled, so when a sprinkler head is heated, water is released immediately into the line and to the head. This makes wet pipe systems fast to respond and simple, and they’re commonly used in heated, climate-controlled spaces where freezing isn’t a concern. In a dry pipe system, the pipes are charged with pressurized air or nitrogen, while the water is kept in a separate storage or in the main supply until a head is activated; when a head opens, water is released into the dry piping and fills the lines, which takes a little longer but avoids freezing in unheated or cold areas. That’s why dry pipes are favored in colder climates or unheated spaces like warehouses or mechanical rooms. The other statements don’t fit because wet pipes aren’t limited to outdoors, the roles of water and air are opposite in the described systems, and dry pipe systems are indeed used in buildings.