Safety At the 1 World Trade Center Project
A multi-layered program uses innovative practices and “checks & balances” to achieve the highest industry standards.
- By Dwayne Carter
- May 01, 2012
As the builder of one of the most visible construction projects in the world, Tishman Construction Corporation (part of AECOM's Construction Services business) is taking thorough precautions to ensure that the 104-story 1 World Trade Center (1 WTC) in lower Manhattan is completed in the safest manner possible and to the highest industry standards. To date, Tishman's team and our partners have been successful, with no major safety incidents on this massive project, where a steady flow of public officials, reporters, dignitaries, and tourists are routine visitors to the site.
Perhaps the biggest challenge any safety director faces on a project of this size and scope is managing the large numbers of people on site. The scale of Tower 1 required Tishman to subdivide typical subcontracts in order to get it built efficiently and on time. As a result, at any given time there can be as many as 1,100 workers on site.
One of the keys to any successful safety program is the relationship between the construction manager and the trade contractors. The safety manager and project trade superintendents need to act as one united safety team, keeping the same goals and expectations in mind from the project's inception.
To solidify these critical relationships, exemplified by the motto "I watch out for you, and you watch out for me," Tishman assigned six full-time New York City Licensed Site Safety Managers to the project who also are Certified OSHA instructors and collectively have extensive experience in high-rise construction, exterior and interior construction, and safety management. Additionally, all trades are required to provide a 30-Hour, OSHA-certified competent person, and high-risk trades must also provide full-time NYC Licensed Safety Mangers.
At Tower 1, before commencing work on the project, each trade must provide a Job Hazard Analysis for all major construction activities, which is used to preplan for safety procedures, identify potential hazards, and institute controls to be used to mitigate the hazards. Each week, the client, Tishman, and all of the subcontractors meet to discuss upcoming operations and specifically any safety issue that must be mitigated. All trades are required to subscribe to Tishman's safety requirements from the time the contracts are signed and are responsible for providing at least one competent person and/or licensed Site Safety Manager for the duration they are on site.
Safety is not simply a corporate value and responsibility at Tishman; it is a priority and requirement for everyone on its job sites. At 1 WTC, all personnel are required to hold a current 10-Hour OSHA certification as per NYC DOB Local Law 41, as well as to attend 10-Hour OSHA, SWAC (Secure Worker Access Consortium) approved, and fall protection training. All scaffold users are required to hold a current scaffold certification as per NYC DOB Local Law 52. Additionally, corporate policy requires Tishman's superintendents and project managers to hold a 30-Hour OSHA certification.
We have a very strict and well-defined fall-protection policy. If a worker from any trade fails to tie off, he or she is automatically removed from the site and not allowed back on until they are retrained, and the contractor pays a fine. If that same person commits a second offense, he/she is removed from the site permanently.
In New York City, due to their trade agreement, ironworkers are required only to follow OSHA requirements, known as Subpart R, which says that ironworkers engaging in steel erection operations are required to use fall protection at a height of 15 feet or greater. The connectors -- those workers who make the initial steel connections -- are required to use fall protection at heights of 30 feet or greater.
In California and Nevada, regulations require 100 percent fall protection, but on the East Coast that is not the case. For the first time ever in New York City, ironworkers are using what Tishman calls the Enhanced Subpart R, a red rope system that mandates 100 percent fall protection and involves the pre-installation of vertical and horizontal lifelines so that workers always have the ability to tie off. Each worker is trained on how to use and inspect the system, including how to tie proper knots. Adherence to the system is strictly enforced on site.
Even with top-notch communications and coordination and the best team of professionals available, you still need an overriding, comprehensive safety program to reduce the chance for human error. At 1 WTC, Tishman applied many lessons we learned when we built the new 7 World Trade Center in 2004. WTC Tower 7 is New York City's first hybrid superstructure and served as the prototype for Tower 1. For starters, Tishman engineered as much of the safety protocols as possible during the preconstruction phase, which proved an effective means of mitigating incidents on site.
The most important and visible element of the site’s safety program is the installation of the city's first "cocoon" system on a steel-frame building, encapsulating the top 16 active floors and climbing with the building as the steel is erected, followed by concrete placement and spray-fireproofing operations. Because this is the first cocoon of any type to be used on a building of this size, we worked closely with DCM Erectors, our steel contractor, to design the system specifically for Tower 1. Full-height vertical netting is also installed on all unenclosed floors until the curtain wall is securely in place. The cocoon system provides protection from falling debris, as well as fall protection for the workers themselves.
The tower's hybrid superstructure calls for a steel-first sequence whereby a temporary steel core is erected, allowing two self-climbing, hydraulic tower cranes to climb above the concrete core shear walls and place the permanent perimeter structural steel. The core concrete shear wall operation follows behind, swallowing the temporary core erection steel and maximizing the structural integrity and life-safety features of the building.
Because the cranes are self-climbing, there is no need for constant disassembly and reassembly of the tower crane mast sections to raise them to the next level (a procedure known as "jumping"). Eliminating the disassembly and assembly process reduces the risk of falling pieces and human injury. In order to balance the cranes and stabilize 10 floors of temporary erection steel at a time, the team developed a system using four fully engineered diaphragm structures composed of 36 shipping containers sitting in the core of the building, and this rises with the steel. In order to minimize vertical "commute" times for workers and prevent hoist congestion, the containers have been specially fabricated to double as usable shanty space and food service facilities; the container approach is called a "hotel" system. As the core comes up 10 floors below the steel, as dictated by the steel-first construction sequence, the "hotels" also serve as a temporary ceiling above the concrete workers, allowing them to continue to pour during inclement weather.
Due to weight restrictions, not all materials can be transported on the hoists. To accommodate certain materials, a self-climbing slider crane that cantilevers off the building is dedicated to the concrete operation. It is used for loading materials onto the building and removing debris from it. There are also three "diving boards," or outrigger platforms, that retract off the side of the building -- on floors with ongoing concrete operations -- for cranes to load material, remove debris, and cycle material to the upper floors for the concrete operation without having to swing into the building. Tishman implemented the use of special, fully enclosed skid boxes for debris removal to allow for the maximum amount of waste to be safely loaded into each, thus eliminating the hazard of falling debris and/or material.
Concrete is being poured almost every day at Tower 1 -- up to four floors at once. In order to maintain the schedule and cycle the material efficiently, Tishman has installed a Consep Hoist, which is a self-climbing type of hoist encompassing the four concrete floors devoted to the concrete operation.
Once the concrete superstructure is complete, a dedicated protection contractor assumes responsibility for safety protection. The contractor builds guardrails, installs full-height vertical netting around penetrations, covers core holes and floor openings, and puts up temporary stairs where necessary. MEP trades are utilizing "hole-in-ones," reusable floor hole covers, which provide a high-visibility, smooth covering for the holes and prevent hazards to workers on the floor below.
1 World Trade Center’s structure passed the 90-story mark at the start of 2012. Construction is expected to be complete by mid-2013. In addition to Towers 7 and 1, Tishman is also building Office Towers 3 and 4, both of which also use a hybrid superstructure, and the Vehicle Security Center at the World Trade Center site, utilizing many of the same safety protocols, such as cocoons and self-climbing, trade-specific material hoists. We hope our commitment to safety at the most visible job sites in the world will help make other projects everywhere safer and enable everyone on every project to make it home safely at the end of the day.
This article originally appeared in the May 2012 issue of Occupational Health & Safety.