By Pat Ciarrocchi

PHILADELPHIA (CBS) — On bitterly cold days, when walking through Center City, you can see tall pipes, emitting steam on some street corners. They’re evidence of Veolia – the third largest utility in Philadelphia and the one that makes steam.

I got rare access to the Veolia plant, in the Grays Ferry neighborhood where it’s mission is to keep the most vulnerable warm this winter.

For decades now, driving along the Expressway, just beyond the Grays Ferry exit, I’d notice rising above a sprawling complex – brick stacks of one generation, standing next to the gleaming steel of another.

Deep inside, I learned that Mike Smedley, the Veolia VP for the Mid-Atlantic region thinks about one thing when he hears steam being generated.

“Efficiency and warmth,” said Smedley. “ We heat about 500 buildings in downtown Philadelphia.”

On brutally cold days, like the ones we’re anticipating, ninety trained and licensed workers are looking at every pipe, every valve, every gauge to make sure Philadelphia’s steam utility pumps out its lifeline to customers and those inside those buildings.

Smedley’s client list includes, the universities, the hospitals, commercial buildings, museums, apartment buildings.

“The majority of our steam is used for heating but it also has other purposes such as sterilizers for the hospitals. Humidity control for the museums. Domestic hot water. For heating domestic hot water in apartments and commercial buildings.”

In the hardhat territory, Smedley walked with me across what felt like steel catwalks – to get a good look at towering generators, boilers and turbines. They’re housed in a plant, first built in the 1900’s, when Philadelphia was finding its industrial footing.

I admit, through my safety glasses, I kept looking ahead. The floor was grated, allowing  you a dizzying view of sub-basements below.

Today, next to the hulking boilers that run on natural gas are the remnants of twenty boilers built in the 1920’s. They were originally coal fired, then converted to oil and ultimately taken offline in the 1970’s as technology evolved.

Setting apart this steam plant from others is that it became a co-generator – both steam and electricity, in the 1990’s.  That allows more than an 80 percent efficiency in its operation. Useful heat that would escape to the atmosphere from the 225 foot stacks along Christian Street can now be redirected into a boiler to produce steam.

The steam reaches 450 degrees, and is pressurized to push through a 41 mile underground distribution network, that’s monitored in a control room.

A $60 million dollar upgrade in 2012 transformed the plant into what they branded as “Green Steam.”

“We’ve effectively taken 430,000 tons of greenhouse gases out of the air,” said Smedley. “That’s the equivalent of 70,000 vehicles off the road. ”

So, on cold days, as the equipment at Veolia is pushing, and the stacks are steamy, and the heat is rising just remember in 31 more days it will be Spring.