How does a dry pipe system operate?

A dry pipe system operates using pressurized air or nitrogen in the pipes, which maintains the system in a ready state until activated. When a sprinkler head opens due to heat from a fire, the pressure in the dry pipe is released, allowing water from the supply line to flow into the pipes and out through the opened sprinkler head. This mechanism is particularly beneficial in environments where the risk of pipe freezing exists because it prevents water from sitting in the pipes until it's needed, thus reducing the likelihood of freezing and related issues.

The other choices highlight methods of operation not applicable to a dry pipe system. For instance, having water constantly present in the pipes is characteristic of a wet pipe system, while manual release of water by a firefighter does not align with the automated nature of a dry pipe system. Lastly, the automatic spraying of water upon smoke detection describes a different operational principle, often associated with pre-action or deluge systems, which utilize additional detection mechanisms before releasing water. Therefore, the characteristics of the dry pipe system are accurately reflected in the correct choice pertaining to its operation with pressurized air until a sprinkler head opens.