NIST Transfers Evidence From Champlain Towers South to Miami-Dade Police Department

The National Construction Safety Team has reached an important milestone in its investigation into the 2021 partial collapse of the Champlain Towers South condominium in Surfside, Florida, with the transfer of evidence custody to the Miami-Dade Police Department (MDPD). The transfer became possible once the team from the National Institute of Standards and Technology (NIST) completed its extensive review, measurement and testing of critical building evidence extracted from the collapse site.

"Our team members were in Surfside within 48 hours of the partial collapse of Champlain Towers South, working in collaboration with the Miami-Dade Police Department and others to help ensure the identification and preservation of potential evidence that could explain the collapse," said investigative lead Judith Mitrani-Reiser. "Since then, we have conducted extensive testing of concrete slabs, columns and reinforcing steel so that we could understand the condition of the building and the forces acting on it at the time of the tragedy."

Immediately After the Partial Collapse

NIST staff members arrived in Surfside on June 25, 2021, and five days later NIST announced it would conduct an investigation under the National Construction Safety Team (NCST) Act, which gives NIST the authority to investigate building failures. The goals of these investigations are to establish the likely technical cause or causes of a building failure; recommend, as necessary, specific improvements to building standards, codes and practices; and recommend any research and other appropriate actions needed to improve the structural safety of buildings.

NIST's investigations under the NCST Act are fact-finding efforts. NIST is not authorized to find fault, responsibility or negligence when investigating a building failure.

Georgette Hlepas, Kamel Saidi and Judith Mitrani-Reiser (left to right) review a computer model of Champlain Towers South. Models like this one are used to determine where pieces of evidence came from before the collapse.

Taking care not to interfere with the search and rescue operations, NIST's experts collaborated with the MDPD to develop guidance for first responders on which building elements would be important to set aside for a potential investigation into the technical cause of the collapse. Procedures for preserving this potential evidence were developed in cooperation with the Miami-Dade Homicide Bureau, the Miami-Dade Fire Department, structures specialists with the urban search and rescue task forces, and the many contractors working on the site. At the same time, remote sensing of the site helped local and federal experts determine where potential evidence was located.

"The collaboration, coordination and cooperation with everyone on site was key to ensuring we would have the evidence needed to understand what caused this tragedy," said investigation associate lead Glenn Bell. "We were able to obtain over 600 pieces from the site that have provided valuable insight into Champlain Towers South."

Immediately following the collapse, the Miami-Dade Homicide Bureau began conducting a death investigation and maintained custody of all evidence. NIST was provided access to the evidence while it was in MDPD custody, and when the evidence custody and control transferred to NIST on Jan. 28, 2022, the MDPD maintained access to it.

A Safe, Secure Location for Evidence

By the end of July 2021, all of the evidence was moved to secure locations, where it was carefully cataloged so that it could be tracked throughout the investigation. In March 2023, a portion of the evidence was moved to a second warehouse so that NIST, MDPD and their contractors could efficiently work with all the pieces as needed to support their investigations.

Finding additional space to securely and safely store the evidence took several months, as the facilities had to meet certain criteria for security, scale and accessibility. The process of preparing the materials for the move and then securing them in their new location took several weeks. This included having a board-certified industrial hygienist conduct air sampling for asbestos fibers to ensure the safety of those accessing the materials.

The additional space gave team members room to extract concrete cores and reinforcing steel from the evidence and allowed them to begin the next phase of evidence analysis. After completing this phase, the physical evidence was condensed, and organized by type, into a single warehouse. MDPD contractors managed the move, which was overseen by NIST staff.

This 3D scan of Champlain Tower South evidence was captured by exactly 1,700,569,894 points in the lidar point cloud seen in the flythrough (so ~ 1.7 billion). The point cloud was stitched together from over 120 different lidar scans acquired inside the warehouse (the black circles in the video represent the camera locations) over a two-day period.

In addition to the NIST and MDPD investigations, the civil litigants involved in a lawsuit related to the collapse hired their own experts to make observations, take measurements and conduct nondestructive testing. NIST provided them with access to the evidence in February and March 2022, before the civil litigation settlement was finalized in June 2022.

Analyzing the Evidence

The investigation team scanned the contents of each warehouse with an imaging technology called lidar after every milestone related to transporting or moving the evidence. Maps developed from these scans were shared with MDPD and its contractors so they could easily identify and track pieces, and NIST also used the scans to remotely inspect the evidence, and to plan its work. NIST also scanned many of the individual specimens using handheld 3D imaging technology to create more accurate 3D representations that could be analyzed further on a computer.

With the evidence secure, cataloged and accessible, NIST's team members began extracting samples of concrete and steel reinforcing bars for testing to learn everything they could about how the building was built, how its materials and construction may have deviated from its original design, how its components had aged, and if any changes had been made to the structure over its 40-year life.

Judith Mitrani-Reiser, Kamel Saidi and Daniel Gopman (left to right) examine microscopic images of a damaged hard drive recovered from the collapse site.

The concrete testing included compression and tension tests that revealed how well the samples would hold up to pushing and pulling forces. Researchers carefully studied the cement and aggregate making up the concrete, and how it had aged. They also measured how water moves through the concrete. This movement depends on how the cement was formulated and impacts the potential corrosion of the reinforcing steel within it. Tension tests of the steel reinforcing bars helped determine the strength and deformability properties of the bars, and the impacts of corrosion. Learn more about NIST's testing.

Despite extensive searching and inquiries, NIST has not been able to locate as-built drawings for Champlain Towers South. The team has therefore relied on the physical evidence to provide insight into how the building was constructed.

An added challenge that has made the physical evidence so important is the lack of video showing exactly what happened. Champlain Towers South had approximately 24 functional security cameras at the time of the collapse that were recording to a digital video recorder (DVR) within the building.

A NIST researcher carefully removes the magnetic disk from a damaged hard drive recovered from the site of the Champlain Towers South building, which partially collapsed on June 24, 2021. Twenty-five hard drives from the building were recovered and analyzed to determine if any belonged to the digital video recorder that stored footage from the building's security cameras. Unfortunately, the hard drives were too damaged to read, even with the most advanced forensic techniques available.

NCST members hoped to find the security camera DVR hard drive among the evidence collected, which had been sorted by the MDPD into "bulky" and "fine" materials. They conducted multiple searches of the bulky material from the collapse site using drones, personnel on the ground, aerial lifts, and powerful cameras. Unfortunately, no DVR devices were found in the bulky materials. The MDPD and NIST did identify a total of 25 hard drives among the fine materials. The NIST team analyzed these drives to determine whether any of them could have come from a DVR. Experts ultimately determined that the damage to the magnetic media was too extensive and that none of the drives were recoverable.

What the Testing Revealed

Corrosion in reinforcing steel is expected, but it can become an issue if it is too extensive. By carefully examining reinforcing steel in the Champlain Towers South evidence, NIST's experts were able to document the type, degree and variability of its corrosion. This has provided critical information about potential degradation and strength of the overall structure at the time of collapse.

The team was able to "reverse engineer" the materials and concrete mixture used in the original construction by conducting microscopic and chemical analyses of concrete samples extracted from the evidence. This allowed team members to quantify the degree of aging and deterioration in the concrete samples. These analyses also made it possible for them to closely recreate the concrete from Champlain Towers South and use it to build large-scale replicas that are representative of critical structural members and connections from different parts of the building that were likely involved with the collapse initiation or its progression. These replicas are being tested to failure in structures laboratories at the University of Washington and the University of Minnesota. Data from these tests will be used to inform computer simulations that will play a key role in determining the probable initiation and progression of the partial collapse and its technical causes.

The recovered evidence also revealed various ways in which the building's materials had changed or been changed over time. This included cracking and spalling (cracking or chipping) of concrete, corrosion of steel reinforcement, prior attempts to repair cracks and spalls in the concrete, the addition of new materials and finishes to the building (including concrete planters and landscaping vegetation on the pool deck), and mineral deposits indicative of water leakage through the structural elements.

The investigation team began its work with about two dozen hypotheses of how the collapse may have initiated. Team members systematically considered all the hypotheses so that they could eventually rule out the most unlikely causes and fully understand the most probable.

"To be confident we have determined the most likely cause or causes of this terrible tragedy amongst the many possibilities, we are collecting and analyzing all the evidence we can for and against each hypothesis," said Glenn Bell. "We are leaving no stone unturned."

The investigation's six project teams continue their efforts (see details below), with the goal of completing technical work in 2025. The entire investigative team has already begun drafting the investigation's findings and recommendations. The draft report must pass through several stages of review, starting with technical review within NIST and then a review by external subject matter experts. Following these technical reviews, the report will undergo several types of policy review before a draft report is released for public review, which is planned for the spring of 2026.

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