Evolution 6 — Master Stream + Attack Line

Overview

Combines a master stream with a handline, pushing total flow demand toward the pump's rated capacity. The operator must balance pressure across two very different discharge configurations — a high-flow deck gun and a low-flow attack line — while monitoring intake for supply collapse. This is where throttle discipline and situational awareness are truly tested. The deck gun at 500 GPM plus an attack line at 150 GPM puts total demand at 650 GPM. On a 1,500 GPM pump that is manageable, but the hydrant must be able to keep up. The operator must constantly evaluate whether the supply can sustain the demand, and be prepared to prioritise one line over the other if conditions deteriorate.

Training Objective

Simultaneously supply a deck gun master stream and a handline attack line, managing total flow demand near the pump's rated capacity. Both lines must maintain target pressure. If supply becomes marginal, the operator must demonstrate priority-based flow management.

Skills Practiced

• Combined master stream and handline management
• Near-capacity pump operations and awareness
• Pressure balancing across high and low flow lines
• Supply collapse recognition and response
• Priority-based flow management — knowing which line to reduce first
• Total flow demand calculation before opening lines
• Throttle management at high RPM with multiple demands

Setup

Hydrant supply feeding both a deck gun (500 GPM) and a 1¾" handline (150 GPM). Total flow demand of 650 GPM approaches the hydrant's practical limit. The operator must manage two very different pressure requirements from a single pump.

Scenario

A large commercial fire requiring both defensive master stream application on the exterior and an interior attack line for search operations on the first floor. The operator must keep both lines flowing at target pressure. The IC may order the interior line shut down if conditions deteriorate — the operator must be ready to adjust.

What to Expect

This evolution operates near the pump's limits. Opening the attack line after the deck gun is flowing will cause a noticeable pressure drop on the master stream. The simulation scores pressure accuracy on both lines and monitors for unsafe intake conditions. Expect intake pressure to be marginal — the operator must watch it constantly.

Tips

• Establish the higher-demand line (deck gun) first and stabilise before opening the attack line
• Calculate total flow demand before starting — 650 GPM needs a hydrant that can deliver at least 800 GPM
• Be prepared to reduce the attack line if intake pressure drops critically — the master stream is the priority in a defensive operation
• Communication with the crew is essential when operating near capacity — they need to know if you are struggling
• Small throttle adjustments only — at high RPM, a 5% throttle change moves the needle significantly
• If you hear cavitation, reduce the lower-priority line immediately