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A fire water network is one of the most critical infrastructures in any facility. Its ability to deliver water at the required pressure and flow rate during an emergency determines how effectively a fire can be controlled. While design, installation, and testing are essential, regular flushing of the network is equally important to keep the system healthy and dependable.
Over time, foreign materials such as dust, rust flakes, sand, microbial growth, and construction debris can accumulate inside the pipelines. If not removed, these deposits can cause blockages, corrosion, or reduced hydraulic performance.
Flushing helps by:
Removing debris and sediments from the system.
Ensuring unobstructed water flow during emergencies.
Maintaining pipe health by reducing corrosion from stagnant deposits.
Improving reliability of hydrants, monitors, and sprinklers.
Complying with design codes and fire safety standards like NFPA, IS, and OISD.
Simply put, flushing keeps the fire water network clean, operational, and ready for any fire emergency.
Though both terms are often used interchangeably, they serve different purposes:
Flushing Line
A larger outlet provided at critical points in the network.
Used to discharge high volumes of water at high velocity.
Primarily for cleaning the network during commissioning and maintenance.
Purging Line
Usually smaller in size, located at dead ends of pipelines.
Provided to remove trapped air pockets and drain stagnant water.
Operated more frequently compared to flushing lines.
In short, flushing cleans the network; purging prevents stagnation and air lock.
The number and location of flushing points depend on the layout and length of the fire water network. General basis of design includes:
At all dead ends of the network.
At the lowest points of the system where sediments are likely to settle.
At major loops or junctions to ensure full circulation during flushing.
For long straight runs, flushing points should be provided at suitable intervals (commonly every 200–300 meters, depending on pipe diameter and layout).
This ensures that every part of the network can be effectively flushed.
The flushing point size is typically designed to achieve a flushing velocity of at least 1.5 m/s to 2.5 m/s inside the pipe (as per good engineering practices and NFPA/OISD guidelines).
Generally, the flushing valve/outlet size is not less than 80 mm (3”).
For larger diameter mains, flushing points may be 100 mm or 150 mm to ensure adequate velocity.
Each flushing outlet is usually connected with a valve and a short pipeline extended to a safe drain or open area.
Flushing is not just a commissioning requirement but an ongoing maintenance practice to ensure the health, reliability, and effectiveness of a fire water network. Providing properly sized flushing points at strategic locations ensures compliance with codes and, most importantly, readiness of the system during a fire emergency.
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