Taking down a high-rise office tower raises concerns not only about the safety of the workers involved, but also of all the people in the immediate surrounding area.
Developers faced with desirable urban areas already filled with aging high-rises are more often demolishing or completely remodeling them to create new work or living space.
John Swagart, Clark Construction Group LLC’s vice president for field operations, told Bloomberg Law the biggest misconception is that high-rise demolition is chaotic and uncontrolled.
“There is so much preplanning and effort that has to be done before we get out on site that nobody ever sees,” Swagart said.
And a wrecking ball isn’t an option.
“You’re not demolishing a building, so much as you’re disassembling it,” Steve Smithgall, senior vice president for safety at general contractor
While federal Occupational Safety and Health Act and state rules protect a project’s workers, the safety of people living and working near the demolition efforts is typically overseen by local governments enforcing building codes and environmental regulations.
Dust, Noise, Inconvenience
The immediate impact on surrounding buildings and residents is a concern.
Contractors try to limit dust by spraying water on concrete surfaces that are cut or ground up, a process that also eases compliance with federal airborne silica limits.
Automated noise monitors track how loud the work is, and vibration detectors warn when the work could lead to cracks in adjacent buildings.
Because construction sites are often inherently noisy, Arlington bans outdoor demolition work at night, Shahriar Amiri, chief building official for Arlington County in Virginia, told Bloomberg Law. Interior work can continue if noise limits aren’t broken.
Street and sidewalk closures are coordinated with the local government, Swagart said. One public safety concern determining street closures is whether a crane will need to swing loads over a road.
The public inconveniences of urban projects lead to questions on how long projects will last. There’s no set answer and no average time to remove a floor.
Every building “is unique and has a life of its own,” Kris Manning, vice president for safety at Clark, said.
Still people wonder why a building isn’t just swiftly leveled.
Smithgall observed: “A lot of people just simplistically think all you do is knock down an old building. It’s significantly more complicated than that, especially in a tight, urban setting.”
The Occupational Safety and Health Administration doesn’t track inspections specifically targeting high-rise demolition projects. The agency does have a rule broadly covering demolition. In fiscal year 2018, OSHA inspectors found rule violations during 48 inspections of all types of projects.
The agency has three regional emphasis programs targeting demolition projects, but their focus is predominately on small-scale projects, where contractors were less likely to have conducted adequate engineering reviews or where local building officials alerted OSHA about their concerns.
Find the Building Plans
The overall process of taking down a building is a painstaking one.
“Before a building is demolished, we ask for complete structural drawings and evaluation,” Amiri said.
Another initial step is for the contractor to find and review the blueprints of the building coming down, Manning told Bloomberg Law.
If plans can’t be located, an option is bringing in teams to test how much weight floors can support and gauge the building’s overall structure, Swagart said.
Even when plans are available, they’re not always accurate.
“You have to make sure what you are demolishing is what you planned to see,” Smithgall said.
The Balfour Beatty safety official recalled one project where drawings showed concrete panels were welded to a garage’s superstructure. On site, workers discovered the panels weren’t welded; instead, they were hooked to the structure and held in place by gravity.
“Had we pulled that first-floor garage panel out as we intended, the whole façade would have collapsed,” Smithgall said.
The Final Takedown
While the safety experts say each building poses unique challenges, there’s a common path to successfully taking down or gutting a high-rise.
Manning said that before any demolition starts, the contractor must evaluate whether hazardous asbestos is present and must be removed.
Once the building is asbestos-free, the building’s power and water is turned off and crews begin taking down interior walls; removing doors, fixtures, windows and carpeting; and stripping out air ducts—cleaning each floor down to its concrete base.
How the debris gets to the ground varies. In renovation projects where new elevators will be installed, the cleared out elevator shafts often become disposal chutes. Other projects may use exterior chutes.
For complete demolitions, once the building is down to its framework, specialized machinery is often brought in to begin chewing and cutting away at the concrete and reinforcing steel—starting on the top floor and working down.
“It’s very often done by remote control to minimize exposure to the operator,” Manning said.
A concern Arlington’s Amiri highlighted is ensuring the demolition of upper floors doesn’t dangerously weaken the lower floors and underground parking garages. County structural engineers visit sites at least twice a week.
Smithgall said contractors try to recycle as much of the debris as possible—including concrete—to meet new building standards measuring environmental impact.