Over the last several weeks, residents may have noticed red fire hydrants disappearing from local sidewalks.

But officials say this isn't the work of a metal scrapping bandit, and will have no impact the effectiveness of area firefighters.

Rather, the removal of the bulky, antiquated hydrants is part of a move to update the hydrant system, protect equipment, save money on costly repairs, and avoid confusion among firefighters rushing to a blaze.

Philadelphia Fire Department Commissioner Lloyd Ayers said response time would not be hampered by removal of the hydrants, which are rarely used.

The hydrants - red in color and gauged for a higher pressure than most - are being removed, he said, because they are relics of a bygone age and have outlived their usefulness.

The archaic hydrants are part of a system that has been out of use since 2005.

"Those date back to the late 1800s...early 1900s," said Ayers. "They served the mill districts."

Ayers said the hydrants are being removed in an effort to save taxpayer money.

He said the unused system would take about $40 million to overhaul and put into service if the fire department intended to use it again.

He estimated removal of the high-pressure hydrants would save the city about $2.2 million a year in maintenance costs.

Ayers said cracks and leaks in the system required yearly repairs, and that costly sinkholes are sometimes created by the leaky, aging pipes.

"It would have cost $40 million if you really wanted to overhaul the system," said Ayers. "But, it would have been for naught because it was only used two times between 1997 and 2005. We hardly ever used it."

Unlike the orange hydrants seen throughout the city - designed largely for residential blazes - Ayers said that the red high-pressure hydrants were part of a system made to tackle fires at the multitude of factories and warehouses that once dominated the city's riverwards.

The system was put in place in an area with a high concentration of industrial buildings, encompassing Allegheny Avenue to Chestnut Street and Broad Street to Richmond Street.

Unlike residential hydrants, which propel water at about 40-pounds of pressure per square inch, these hydrants push water at about 250-pounds per square inch.

At the time they were installed - the system began construction in the early 1900s and was completed by 1910 - the fire department needed that extra pressure to get water onto fires in large buildings, said Ayers.

"You needed (that pressure) to get a lot of waterpower in place at one time," he said.

But, with the development of "pumper trucks," the need for high-pressure hydrants had passed. The modern trucks can pump water from any hydrant and add additional pressure if needed to propel the water to almost any distance needed.

Ayers said there were concerns that the added pressure of the red hydrants might even damage equipment if firefighters mistakenly hooked them to an engine.

He said that, unlike the residential hydrants, the high-pressure hydrants are fed by a system that pulls water directly from the Delaware River - a method that also often sucks up sediment that can damage modern firefighting equipment.

After determining the system needed an overhaul in the 1990s, Ayers said, the fire department decided to halt use of the high-pressure system. The Fire Department is now working with the Philadelphia Water Department to remove the obsolete hydrants.

"We will still maintain the same capabilities," he said, adding that the removal of the red hydrants will not impact the existing hydrant system.

The high-pressure system had been unused for so long thanks to updates to the city's building code, according to Executive Fire Chief Daniel Williams.

He said 90 percent of all fires in large buildings - like the warehouses and factories the high-pressure hydrants were designed for - are currently stopped by the building's own sprinkler systems.

"We have a whole new way of fighting fires now," said Williams.

However, Fishtown resident John Donlen said that, while he understands the system is unused, he became concerned after seeing several hydrants removed along Girard Avenue.

Donlen said he liked having the historic hydrants on his street, and he wanted to know why the fire department had only now decided to pull up the equipment.

"It just doesn't make sense," he said. "Do you see why a company would take out those hydrants without a reason?"

When asked why the hydrants were being removed, Ayers pointed to the repair fees that the city often incurred to maintain the unused system.

"A lot (of the ongoing costs to the system) was leaks. It also caused mud holes and sink holes," said Ayers. "(Our equipment) evolved and we had to stop and think about how much we were spending."

Still, Donlen contended that if the system was unused, it shouldn't have water running through it that could cause a leak.

Chief Williams reiterated that the removal is needed because the red hydrants could confuse firefighters in a hurry to stop a blaze.

He said the fire department does yearly evaluations of all the hydrants throughout the city to help firefighters on duty to remember where hydrants are located.

Citywide, he said, there are three types of orange hydrants, each with color-coded tops (or bonnets) to indicate the diameter of the pipe needed to connect a hose to the hydrant.

"We train so that visually, immediately you know what you're looking at," said Williams.

He said the unused red hydrants could slow up firefighter response time.

Reporter Hayden Mitman can be reached at 215-354-3124 or hmitman@phillynews.com