By Mike DeNardo

PHILADELPHIA (CBS) – Walkers and drivers in Center City Saturday should be aware — streets around the old PNB building are going to be closed.

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Crews plan to remove an old chiller unit from atop One South Broad Street by helicopter, and install a support system for a new unit.

Patrick O’Donnell, a right of way officer with the Streets Department, says roads around the building will close as early as 6 a.m. and stay closed for hours:

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“Once we do the closure, it’ll be a hard closure for the duration of the helicopter lift. The eastern portion will be 11th Street with the opportunity to open up Market Street to 13th. But it goes as far west as 16th Street.”

The streets are scheduled to be closed through 4 p.m., but O’Donnell says it’s hoped the work can be completed and roads reopened by 1 p.m.

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A similar closure happened last November, when the iconic letters were removed from the top of the PNB building.