What type of fire sprinkler system has pipes that are filled with pressurized air or nitrogen?

The type of fire sprinkler system characterized by pipes filled with pressurized air or nitrogen is the dry pipe sprinkler system. In this system, the pipes are not filled with water; instead, the water supply is held back by a valve that remains closed until the system is activated by heat from a fire. When a fire occurs, the pressurized air or nitrogen escapes, causing the valve to open and allowing water to flow into the pipes and out through the sprinkler heads.

This design is particularly advantageous in environments where the risk of freezing pipes is a concern, such as unheated buildings or areas exposed to cold temperatures. The presence of air or nitrogen in the pipes prevents water from sitting in them and potentially freezing, which could lead to system failure during a fire emergency.

Other types of systems, such as wet pipe systems, have water constantly in the pipes, and alternate suppression systems may use other methods of fire suppression not involving gases in the pipe. A blockage prevention system is a concept primarily aimed at preventing obstructions within pipe systems but does not specifically relate to the characteristics of fire sprinkler systems.