A symbolic reference to the year America signed the Declaration of Independence. With its spire attached, the new World Trade Center became the tallest building in the Western Hemisphere, and the third tallest building in the world. The 104-story super-scraper stands on the northwest corner of the 16-acre World Trade Center site, occupying the location of what used to be the original 6 World Trade Center.
Designed by David M. Childs of Skidmore, Owings & Merrill, the new building is the result of the collaborative efforts of the Durst Organization and the Port Authority of New York and New Jersey. One World Trade Center has redefined the New York skyline and set new design and construction standards as an architectural icon for the United States.
Notably, the One World Trade Center building also emerged as one of the safest buildings in the world. Its advanced superstructure is designed around a reinforced concrete shear-wall core, which is surrounded by a redundant steel moment frame. According to designers and structural engineers, this particular structure provides excellent resistance to wind and gravitational loads.
Construction included 45 thousand tons of structural steel, which is six times as much as was used in the construction of the Eiffel Tower. The podium, which sits at the base of the building, was constructed using hefty blast-resistant walls, and much of these highly advanced safety systems exceed the requirements of the New York Building Code. The structure itself can withstand almost three times more pressure than any other building in New York.
The spire, which is comprised of 18 steel sections, three communication rings, and a maintenance platform, sits at the top of the building. After transporting pieces of the spire to the roof of the building, workers had to install each section separately over a period of three months. The spire will provide a television and radio antenna, and it’s LED-powered light will serve as a beacon, producing visibility up to 50 miles away. Once the final section of the spire was bolted into place, the building officially became the tallest in the United States.
To ensure the safety of workers who will perform routine maintenance atop the massive tower, builders, engineers, and the Port Authority partnered with Rigid Lifelines to design and supply 1,975 linear feet of total fall protection track, and the highest self-retracting lanyards in an occupied building. Rigid Lifelines designed two systems for the One World Trade Center building—a horizontal system for the rings and a vertical system for the spire. Each system was specifically designed to ensure that workers have 100 percent fall protection from the moment they leave the top floor to the moment they touch the flashing beacon light.
The 2.6-million-square-foot building will host an observation desk, world-class restaurants, and office space, and the tower is slated to open for business in 2014. Port Authority Chairman David Samson called the building, "A national symbol of hope and strength in the face of tragedy." New York Governor Andrew Cuomo referred to the completion of the spire as, “A milestone at the World Trade Center site that symbolizes the resurgence and resilience of our state and our nation.” One thing is for sure; One World Trade Center has emerged as the shining icon of New York’s infamous skyline, and arguably one of the most desirable office addresses in the world.
In June of 2012, the One World Trade Center building was nearing completion. By June 21st, the tower's steel had risen to the 104th floor, and by mid July of 2012, construction crews began installing parapet steel at the top of the building. It was around that time when DCM Erectors—a member of the Davis Group, who provided the steel and constructed the tower’s skeleton—began to inquire about fall protection systems for the 400-foot spire that they were installing at the top of the massive tower.
That’s when DCM contacted Rigid Lifelines to obtain information about their fall protection systems. According to a DCM representative, they had been searching for reputable companies with extensive experience designing unique and comprehensive fall protection systems. Rigid Lifelines’ National Product and Sales Manager, John Kemp, answered the call and set up a series of high profile meetings with the builders, stakeholders, union workers, steel erectors, contractors, and executives involved with the new World Trade Center building.
Arnie Galpin, Engineering Manager for Rigid Lifelines, and Dave Pisotti, one of the engineers who was intimately involved with the project, met with the Port Authority, structural engineers, and builders to review existing drawings and to outline federal laws in regard to equipment standards, legal obligations, and potential fall protection solutions. Arnie and his engineers forged a collaborative effort with builders, working closely with the structural engineers tasked with constructing the new World Trade Center building to design and install a cost-effective system that would meet their specific needs. After proposing a fall protection system for both the vertical track on the spire and the horizontal track for the rings at the base of the spire, Rigid Lifelines was awarded the contract.
According to Arnie Galpin, Rigid Lifelines’ engineers worked closely with the client to make sure their needs were fully met. Due to the unique structure of the World Trade Center building, engineers had to design a system that was heavily customized to ensure that each worker would have 100 percent fall protection from any position on the spire. This required a system that enabled workers to transition in and out of the spire, while remaining protected at all times.
Because all work environments differ, it is important to determine which fall protection products will provide maximum protection for a particular job. In most cases, it’s a matter of selecting the right product that is best suited to provide protection or totally eliminate hazards. However, in this particular case, engineers identified potential fall hazards that were completely unique. Those hazards required a customized safety program that included an innovative design and resulted in an original system.
Builders for the World Trade Center had initially inquired about the use of a cable system to protect their maintenance workers from fall hazards. But, Rigid Lifelines’ engineers recognized the importance of a specific type of vertical track, which would allow workers to transition in and out of the spire. The project also required a system that could protect multiple workers at once, unlike a standard vertical cable system, which can only hold one worker at a time.
Rigid Lifelines knew that the scope of this project would be huge. Not only did they have to create a system that was completely unique and one-of-a-kind, they had to design one that operated flawlessly and covered a tremendous amount of space. The 1,975 linear feet of track designed by Rigid Lifelines was constructed in separate parts, each functioning as its own track system. Each piece was spliced together, which provided a seamless transition from one section to another and resulted in a unified system that is easier to climb and much safer to use than a cable.
When a worker is attached to a lifeline on a track system, the potential fall distance is only a few inches. In comparison, if a worker falls while he is attached to a cable or rope system, the threat of impact injury due to swing fall is greatly increased. Furthermore, each time a worker falls using a cable or wire rope, the system stretches, which means it has to be replaced. Rigid Lifelines’ track systems include high quality, durable materials that require very little maintenance and ensure each and every worker is 100 percent protected at all times. And it’s a good thing. As Dave Pisotti pointed out, “In an extreme situation like this, no one wants to climb that high to fix the one thing that is preventing him from a potentially catastrophic fall.”
To protect workers who will perform routine maintenance atop the newly constructed One World Trade Center, steel workers and builders collaborated with Rigid Lifelines to design and install 1,975 linear feet of total fall protection track and the highest self-retracting lanyards in an occupied building.
Engineers at Rigid Lifelines were tasked with the difficult job of matching the structural design of their fall protection systems with the distinct and comprehensive needs of the spire and the workers who would be climbing it. Working closely with the building’s structural engineers, Rigid Lifelines reviewed their existing drawings, made recommendations, optimized the use of space and materials, and ultimately constructed a comprehensive fall protection system worthy of the tallest building in the United States.
In total, Rigid Lifelines designed two systems for the One World Trade Center building—a vertical track system for the spire, and a horizontal track system for the rings, which sit at the base of the spire. Since the track systems are meant to provide fall protection for maintenance workers who need to access the building from the 104th floor, all the way up to the beacon at the top of the spire, the building required a distinct design and some serious innovation to construct a system that would guarantee complete coverage.
The horizontal rings mark the start of the fall protection system. While the tower includes five sets of rings at the base of the communication spire, the first two rings are part of a building maintenance fall protection unit that was not designed by Rigid Lifelines.
This particular system is used for window washing and building/ façade maintenance. However, the top three rings include 402 linear feet of fall protection track designed by Rigid Lifelines. Maintenance workers will use these particular rings to access communication level platforms for routine maintenance and repairs. The rings were constructed out of galvanized carbon steel, and each one supports six workers at a time using a standard eyebolt trolley.
The horizontal track system design consists of an uninterrupted circular rigid rail system on all three rings. Workers are attached to a trolley on each track with a heavy-duty fixed length lanyard that was designed to prevent them from moving too far from the track on the fall protection system. The first two rings provide fall protection with a device to stop or arrest a potential fall. The third (top) ring provides fall prevention that limits access to the potentially dangerous areas around the edge of the platform.
The rigid nature of the horizontal lifeline allows workers to move laterally around the spire without needing to reposition their anchorages. On the first and second ring, the lifelines were designed to be under-hung. But engineers at Rigid Lifelines had to design special hangers to suspend the track from the existing structure on the top ring. Because the third ring could not be under-hung, engineers designed a hanger standoff that is side mounted six inches off the platform ground and supported from above.
In addition to the horizontal fall protection system designed for the rings, Rigid Lifelines also had to design a system that would allow workers to access maintenance points from the base of the spire to the top of the beacon light.
The vertical track was constructed using a copper-nickel blend, which provides durability, corrosion resistance, and the ability to form complex shapes. This was especially important to the design of the system, because workers have to transition in and out of the spire as they climb.
The vertical track fall protection system is comprised of several sections, beginning with the interior ladders, which are both enclosed inside the mast. As workers climb, the interior ladders transition to steel pole steps on the outside of the spire. There are three sections of pole steps, and each section includes a vertical rigid rail fall protection system designed by Rigid Lifelines. Workers only need to disconnect and reconnect from the system one time to transition from the South ladder to the North ladder, but they have to disconnect five times between outside pole sections.
There are three rest platforms around the spire that are 40 feet apart. Each rest platform includes a guardrail to prevent workers from falling over the edge. To start, the vertical rail runs 42 inches above the first platform and ends 42 inches above the last platform. The vertical fall protection system was designed so that workers can disconnect from the track and connect to a temporary anchorage until they are safely behind the gate on the platform assembly. Workers can access the rest platforms through a manhole that is fitted with a swing gate which closes over the hole once they are standing on the platform. Once the gate is closed, workers can undo their temporary lanyard, since the guardrail will protect them. In order for a worker to move from a rest platform, he must reconnect to the vertical track system and climb up the pole steps on the outside of the spire.
The third and final section of the vertical track fall protection system was designed to meet the unique specifications of the beacon light assembly. Engineers at Rigid Lifelines had to devise a clever solution to account for limited space inside of the assembly. This section of the spire includes 30 feet of interior ladder, which is extremely narrow and difficult to navigate. In order for workers to access this section of the spire safely, Rigid Lifelines had to incorporate a weather and wind resistant retraction system for self-retracting lanyards so workers can access the lights within the beacon assembly. The self-retracting lanyards on One World Trade Center are made from 100 percent stainless steel, which makes them more sturdy and reliable than other lanyards, even after consistent exposure to the elements.
The unique design and grand scope of the One World Trade Center building required a personalized system that was completely customized to meet the comprehensive needs of the facility. As a result, Rigid Lifelines developed an extensive fall protection system that allows workers to connect and disconnect from anchorage locations as they move from one section of the 400-foot spire to another. When used correctly, the system provides workers with total protection from fall hazards by either connecting them to a portion of the system or by granting them access to a gated area with guardrails. Working collaboratively with the builders and engineers involved with the construction of One World Trade Center, Rigid Lifelines was able to establish a superior fall protection solution that enhances worker safety and exceeds federal equipment guidelines and regulations.