What characteristic distinguishes wet pipe systems from dry pipe systems?

Wet pipe systems are distinguished by the fact that they contain water at all times within the pipes. This characteristic allows for immediate activation and response when a fire is detected, as the water is readily available to be released from the sprinkler heads. The continuous water supply is essential for providing quick suppression of fire, making these systems highly effective in various types of buildings, particularly those where freezing conditions are not a concern.

In contrast, dry pipe systems do not maintain a constant supply of water in the pipes and instead are filled with pressurized air or nitrogen. When a sprinkler is activated, the air pressure drops, allowing the water to flow into the pipes and out through the sprinkler heads. This design is particularly advantageous in environments where the risk of freezing can occur, as it prevents water from remaining in the pipes, thereby reducing the risk of pipe rupture due to ice.

The other choices relate to different characteristics or misconceptions regarding wet and dry pipe systems, but the defining feature remains the constant presence of water in wet pipe systems, which is crucial for their operational effectiveness during a fire emergency.