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Fire hydrant color codes and flow classes, NFPA 291.

What a hydrant's color means, the four NFPA 291 flow classes and their ranges, and the class of any hydrant from its flow at 20 psi residual pressure. Free from FireInspection360, the fire prevention platform built by fire inspectors.

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A red fire hydrant flowing water across a lawn into the street during a flow test

The class for a hydrant's flow

NFPA 291 classifies a hydrant by the flow available at 20 psi residual pressure, projected from its flow test, and recommends painting the bonnet and caps in the class color.

Enter the hydrant's available flow at 20 psi residual pressure, from its flow test, to read its NFPA 291 class and the color it should be painted.

Class	Flow at 20 psi	Bonnet and cap color
Class AA	1,500 GPM or more	Light blue
Class A	1,000 to 1,499 GPM	Green
Class B	500 to 999 GPM	Orange
Class C	less than 500 GPM	Red

NFPA 291 is a recommended practice; the water purveyor or fire department that owns the hydrant sets its own marking scheme. Verify the class against the flow test on file.

How it works

A hydrant's color is a flow rating, painted where an engine crew can read it at night.

NFPA 291, the recommended practice for fire flow testing and marking of hydrants, gives a hydrant one of four classes from the flow it can deliver while holding 20 psi of residual pressure in the main: Class AA at 1,500 gallons per minute or more, Class A from 1,000 to 1,499, Class B from 500 to 999 and Class C below 500. Each class has a color for the bonnet and the outlet caps: light blue, green, orange and red. The barrel stays a single high-visibility color, chrome yellow by tradition, so the class color reads as a mark and not as the hydrant itself. Some utilities add the year of the last test, the main size or a private-hydrant marking, and a few paint whole hydrants by ownership; the class color is the part NFPA 291 recommends.

The flow behind the color comes from a flow test: a static pressure read on one hydrant, then a residual pressure on the same gauge while one or more nearby hydrants are flowed through a pitot gauge, and the total flow projected to what the main would give at 20 psi. Twenty psi is the floor because below it the main can draw contaminated groundwater in through leaks, and because a pumper needs positive pressure at its intake. A hydrant painted green from a 2009 test may be orange today: pipe roughens, valves get closed, and development adds demand upstream, which is why the practice recommends retesting on a cycle.

For a fire department the classes answer a question that comes before any fire: does the water in front of this building meet what the building needs? The required fire flow from IFC Appendix B, against the class of the hydrants within reach, is the comparison a plan reviewer makes on a new warehouse and a company officer makes on a preplan.

How FireInspection360 keeps the classes current

Every flow test recorded in FireInspection360 projects the 20 psi flow with the same hydraulics, stamps the hydrant's class, and paints it on the map in the class color. The hydrant inspection cycle brings each one back on schedule, and the fire flow map holds every building's required fire flow against the hydrants that can reach it.

See hydrants, flow tests and the fire flow map

Related tools: the hydrant flow test calculator and the required fire flow calculator.

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