MOBILE — With spring brightening the streetscape, Mobile’s fire hydrants seemed to be blooming too — freshly painted in an assortment of hues, some wearing bonnets of blue, others green or orange, their bases yellow or red.
The colors are not decoration, and they are not the whim of a public works crew with leftover paint. They are a code, and Steve Huffman of the Mobile Fire Department explained what it means.
What the colors say
"The hydrants are color coded based on the size of the water main, the amount of water it will supply and discharge, and the pressure to which it is discharged," Huffman said.
The critical number is what firefighters call available flow — how much water a given hydrant can actually deliver, measured in gallons per minute. Under the National Fire Protection Association’s standard, NFPA 291, the hydrant’s top — the bonnet — and its caps are painted according to that capacity:
- Blue: 1,500 GPM or more. Very good flows.
- Green: 1,000 to 1,499 GPM. Good for residential areas.
- Orange: 500 to 999 GPM. Marginally adequate.
- Red: below 500 GPM. Inadequate.
Blue is best; red is a warning.
Why it matters at 3 a.m.
The practical stakes are considerable. "Primarily, we need to know how much water is available from the closest hydrant so that we may select the appropriate size hose lines for the size and complexity of the fire," Huffman said, "but not select lines which would exceed the capacity of the hydrant and thus be ineffective."
That is the crux of it. A hose line too large for its hydrant does not deliver more water — it delivers less, or none. A crew that connects a heavy line to a red-capped hydrant on a residential street has not gained firepower; it has wasted the only minutes that mattered.
Pressure is the second variable, and it is a peculiarly local one. "Water pressure is affected by elevation," Huffman said. "The communities that we serve are spread over many elevations so pressures found in hydrants vary greatly." Mobile runs from near sea level along the waterfront up through the ridges of Spring Hill and beyond, and a hydrant’s pressure varies accordingly. Knowing the range in advance lets a crew implement the correct pumping operation immediately and compensate for low pressure using the pumps aboard the engine.
A system built for a glance
Why paint, rather than a database or a placard? Because of how firefighters actually encounter hydrants.
"It has also been found that the most efficient means to convey this important information to firefighters is to paint the hydrant tops and caps using standardized color codes," Huffman said. "These colors give us a reasonably accurate picture as to how the hydrant should perform. They are easy to recognize, and as fire crews travel the streets performing their various duties, they see these hydrants and get a feel for where the problem areas exist well in advance of a fire alarm being called in."
That last clause is the elegant part. The system does not merely inform a crew at the moment of an emergency; it teaches them their district passively, over months of ordinary driving, so that by the time an alarm sounds they already know which blocks are thin on water.
The base is a different story
Huffman noted that typically only the bonnet and caps carry the flow code. The base of a hydrant may be white, yellow, red or violet in various parts of the country; in Mobile, yellow and red predominate.
"It’s the basic colors of the caps that matter most," he said.
The standard appears in both the International Fire Code and the NFPA code and is recognized nationwide — which means a firefighter from Mobile could arrive in a strange city that follows it and read its hydrants at a glance. Not every city does. But where the code is followed, the language is the same.
So the next time a hydrant on a Mobile street corner appears to be wearing a bright blue hat, it is not decoration. It is telling anyone who knows how to read it that if the house behind it ever catches fire, there will be water enough.