adding "smoke free and fire free" areas to the building, as well as a complete sprinkler system serving all floors. Neither of these features had previously been used in a structure in Chicago. Even though regulations did not require a fire sprinkler system, the building was equipped with one from the beginning. There are around 40,000 sprinkler heads in the building, installed at a cost of $4 million. When it was completed, the Sears Tower was heated electrically, unlike older structures that used gas heating. It included 145,000 light fixtures and a cooling system capable of 17,000 tons of refrigeration. Furthermore, the tower contained fire-suppression and communications systems for emergency use, which were powered by diesel generators. If there was a fire in one section of the building, the building's smoke-detection system would close off the fresh-air intake openings in that section, discharging smoke outdoors. Fifteen above-ground stories, as well as three of the basement levels, contain mechanical equipment. Above the Skydeck on the 103rd floor is a seven-story mechanical penthouse. Elevators and escalators The Sears Tower was planned with 103 elevators, including 14 double-deck elevators. The office stories are served by 97 elevator cabs; due to the presence of the double-deck elevators, these occupy 83 shafts. As designed, one bank of single-deck elevators connected the lobby to the lowest 28 stories. Banks of double-deck elevators traveled to "sky lobbies" at the 33rd/34th and 66th/67th floors, where passengers could transfer to local elevators. The 34th through 103rd stories were served by local elevators that operated from the sky lobbies. Two elevators also ran directly from the lobby to the Skydeck on the 103rd floor. , the elevators carried 5.8 million passengers per year. Six of the elevators are used for freight. One of the freight elevators served all stories, traveling to a height of . During a fire or another emergency, this elevator would be reserved for the Chicago Fire Department. Other elevators would be controlled from the 33rd floor. During a fire, elevators would be dispatched to the affected floors to assist with evacuation. The building also had 16 escalators, including a set of double-height escalators that traveled from the main lobby to the lower mezzanine. Another set of escalators connects the 33rd and 34th stories. Interior Base When the building was completed, the main entrance was on Wacker Drive to the west. There was a plaza on the