Fire hydrants are placed on street corners, usually painted a color that makes them impossible to miss, but most people know very little about them. These fixtures are a part of daily infrastructure that often goes unnoticed until something goes wrong, such as when a hydrant bursts open on a hot day, turning a street into a paddling pool.
What Is a Fire Hydrant?
A fire hydrant is a connection point to a pressurized water main running below the road. It does not generate pressure or boost flow on its own. Instead, it functions as a valve that allows firefighters to adjust the pressure from the existing water network.
Types of Fire Hydrants in the US
In the United States, hydrants come in two main types, chosen largely based on climate. Wet barrel hydrants are used in regions where freezing is uncommon. They remain full of water at all times, with the control valve above ground, making them simpler to maintain and quicker to operate. Dry barrel hydrants are suited for colder climates. The main valve is buried below the frost line, so the barrel stays empty until needed. Turning the top operating nut opens a long internal stem that connects to the underground valve.
What Do Differently Colored Fire Hydrants Mean?
Fire hydrants can be spotted in various colors across cities, but these colors are not random or merely decorative. In the US, many hydrants follow the National Fire Protection Association (NFPA) 291 guidelines, where the color indicates flow capacity: blue for 1,500 gallons per minute (GPM) or more, green for 1,000–1,499 GPM, orange for 500–999 GPM, and red for under 500 GPM. Hydrants are also painted chrome yellow for visibility. NFPA 291 is a guideline, not a law, so not every community uses it. Some hydrants are violet, which usually indicates non-potable water, while a black hydrant means it is out of service.
How Does a Fire Hydrant Work?
When a hydrant is opened, water travels up from the underground main and out through the hose connections. Importantly, a hydrant is designed to be either fully open or fully closed; it does not throttle the flow. This ensures maximum water delivery when needed.
