Assisting the Rescue
Engineers were called to support rescue workers in the attack's immediate aftermath.

Surveying the Damage
Dramatic first impressions of the destroyed complex

Assessing Buildings
To safeguard the rescue workers, engineers analyzed the damage to the structures.

Navigating the PATH
By raft or by foot, the PATH commuter-train tunnels offered access to critical regions in the site.

Understanding the Site
When clearing the site, engineers had to understand its foundation.

Stabilizing the Wall
Engineers secured the WTC foundation and avoided a major flood.

Removing Debris
Taking apart the massive steel structures required technical expertise.

Supporting Structures
Engineers had to reinforce some structures before tearing them down.

Extracting Hazards
WTC 5 and 6 housed potentially explosive stockpiles of ammunition and two 10,000-gallon diesel tanks.

Uncovering Property
The Bank of Nova Scotia was eager to recover its millions in gold and silver.

Supporting the Rescue and Recovery

In the hours following September 11th, New York City officials called in a Who's Who of New York City engineering to assess the structural conditions of buildings surrounding Ground Zero and to help search and rescue workers safely navigate the treacherous ruins.

In this section, engineers from three firms — Leslie E. Robertson Associates (LERA), LZA/Thornton-Tomasetti, and Mueser Rutledge Consulting Engineers (MRCE) — explain some of the engineering that went into this year-long process.

Richard Garlock is an associate of LERA, whose founder Leslie E. Robertson is the structural engineer of record for the World Trade Center complex. Garlock used the firm's years of experience on the site, along with the vast collection of architectural and structural drawings, to advise the rescue and stabilization operations on structural issues.

Dave Peraza is a Vice President of LZA Technology of Thornton-Tomasetti/LZA. Peraza, who has investigated many high-profile building collapses, led the rescue and recovery effort and the emergency inspections of the surrounding buildings. Over 500 engineers, from about 25 firms, assisted in these efforts.

George Tamaro, a partner in MRCE, supervised the construction of the Twin Tower's foundation in 1967. He was called in to determine the condition of the concrete perimeter wall that kept the Hudson River at bay and to devise a plan to stabilize this "bathtub" with tieback anchors.