The federal probe into the calamitous collapse at Champlain Towers South in Surfside, Fla., has concluded that the condominium's pool deck failed more than four minutes before the 12-story residential building crashed down. The fiasco, during the night on June 24, 2021, killed 98 occupants.

Investigators from the U.S. Dept. of Commerce’s National Institute of Standards and Technology are still working to finger the initiating event, they reported at a National Construction Safety Team Advisory Committee meeting March 7. The NIST team, composed of structural and geotechnical engineers, materials specialists, social scientists and other specialists, aims to finish its technical work this summer. The goal is to release a draft report for public comment, including recommendations, in May 2025. NIST expects to publish the final report in the fall of 2025.

Analysis of videos shot in and around the 40-year-old structural-concrete building—including two videos obtained in December, as well as interviews with witnesses—helped clarify the timeline of the collapse, according to Judith Mitrani-Reiser, associate chief of NIST's materials and structural systems division and the probe's team leader.

David Goodwin, a NIST research chemist specializing in forensics and a member of the team, said a video with a view into the Champlain Towers South parking garage under the concrete pool deck, when enhanced with help from the FBI, shows fallen debris before the building's collapse. Though still a preliminary analysis, the enhanced video appears to show parts of planter boxes and patio furniture, which had been on the deck, in the garage below. Additionally, one column is not visible where investigators believe it should be, but Goodwin said that could be due to obstructions or poor lighting. 

Social scientist Emel Ganapati, still another member of the NIST team, said some residents in a particular apartment stack of the building described hearing noises on the night of the collapse. They compared the noises to knocking, hammering or furniture being moved above them. 

“The noises reportedly became louder and louder and more intense prior to … the pool deck collapse,” Ganapati said.

Other videos revealed distinct signs of movement and damage in the mid-rise, including a hallway floor that was sagging before part of the building dropped. And video from a nearby building shows the drop initiated on a portion of the south face—the side overlooking the pool—below the third floor level and spread northward from there, according to Jack Moehle, also a NIST structural-engineer investigator. 

“The first two of the videos, along with the eyewitness accounts, provide compelling evidence that the first major collapse was in the pool deck,” Moehle said. 

The NIST team had previously highlighted design deficiencies and construction deviations they found in the pool deck, as well as photos that showed signs of distress in part of the pool deck where planters had been added. Georgette Hlepas, a geotechnical-engineer team member, described how water was seen ponding around some of the pool deck drains and damage from seepage was discovered in the ceiling of the garage below. 

Design Deficiencies

However, the pool deck is not the team’s only failure hypothesis. Further structural analysis also revealed deficiencies in the building design that did not meet building code or common standards at the time it was built, according to James Harris, another structural-engineer member of the team. There were also construction deviations in the tower, such as in columns where reinforcing bars were installed with less overlap between upper and lower sets than the minimum allowed by the building code, which is what had been specified on the drawings. 

Investigators are still working through various hypotheses about what factors may have played roles in the collapse, said Glenn Bell, the NIST team associate lead and a forensic structural engineer.  

“While there is strong evidence that the collapse initiated in the pool deck, we have not yet ruled out a failure initiation in some part of the tower that precipitated the collapse in the pool deck,” Bell said. 

The team also has been testing materials and simulating material degradation to better understand key points of the structure. Investigators have extracted 497 concrete cores and completed hundreds of mechanical tests for compressive strength, modulus of elasticity and splitting tensile strength. They have also extracted 369 steel reinforcing bars and completed 40 tests for tensile properties. 

Bell said the team expects technical work to be substantially complete by the end of July, when work on the report, including recommendations, will begin. 

“For the next six months, the major driver of our investigative activities will be substantial completion of our technical work through the analysis of failure hypotheses,” Bell said. “As we’re zeroing in on the most likely hypotheses, thoroughness and rigor demand that we sufficiently analyze all reasonable possible scenarios.”

This article was updated on March 12.