When is the only occasion to flow over 80 psi on a 2 1/2 line?

Flowing over 80 psi on a 2 1/2 inch line is typically associated with the use of a fog nozzle or a fixed master stream device. This is because both of these devices are designed to operate under high pressure to achieve a finer water mist or a more effective water delivery system over a longer distance.

Fog nozzles, in particular, require higher pressures to atomize the water effectively, which enhances cooling and penetration into a fire environment. Fixed master stream devices, such as those mounted on fire apparatus or aerial platforms, also operate at these elevated pressures to ensure sufficient reach and volume for effective firefighting, especially in large-scale incidents.

While other scenarios may involve different pressure requirements, the specific operational characteristics of fog nozzles and master streams necessitate flowing at or above 80 psi for optimal performance in a firefighting scenario.