Surfside condo collapse investigators provide key insights into possible causes of the disaster. Here are the top takeaways

By Elizabeth Wolfe, CNN

(CNN) — Federal investigators on Thursday shared updates on their probe into the cause of the catastrophic 2021 condominium collapse in Surfside, Florida, providing key insights into the factors that may have led to the deaths of 98 people under a mountain of rubble.

Investigators have identified hundreds of possible points of failure in the building, eventually narrowing down about two dozen hypotheses of what could have triggered the collapse, officials with the National Institute of Standards and Technology said in a presentation on their progress.

The probe has revealed that the building’s swimming pool deck – located at ground level above an underground parking garage – collapsed at least four minutes before the rest of the building, confirming earlier witness reports. Potential structural failures in the pool deck or columns supporting the tower are among the top issues now being looked at as teams probe the cause of the disaster, investigators said.

Part of the Champlain Towers South building crumbled to the ground in the pre-dawn hours of June 24, 2021, turning what was formerly a thriving residential building into a devastating scene as residents became crushed or trapped under a massive pile of twisted metal and concrete.

It took about a month for search and recovery crews to find and identify all 98 victims, who ranged in age from 1 to 92 years old. The tragedy affected families all over the world, including in Argentina, Paraguay and Colombia. In some cases, entire families were killed.

The tragedy may have been decades in the making. Investigators have determined Champlain Towers’ integrity had likely been compromised when it was being built in the 1970s, noting that the design and construction of some parts didn’t meet standard building code requirements at the time.

“It becomes clear that the design and construction did not meet all the safety standards of its day,” Surfside Commissioner Marianne Meischeid told CNN following the release of the preliminary report. “I would be most interested in knowing if this was a very isolated defect, or was it common to a particular era of development?”

But the search for answers is far from over, as investigators must continue to meticulously examine the evidence and rule out the long list of possible scenarios. Their final findings are expected to be released in a report next year.

The agency investigates major building failures and disasters – including that of the World Trade Center on 911 – but does not determine criminal culpability. Instead, it can recommend changes to building codes to improve future safety standards.

Surfside Mayor Shlomo Danzinger told CNN the findings are “a poignant reminder of the imperative need for proactive measures and continuous maintenance in the realm of condominium safety.”

“The tragic incident in Surfside, has brought into sharp focus the potential consequences of neglecting these crucial aspects, and underscores the call for a proactive stance in the realm of condominium safety,” Danzinger added.

Here are the key takeaways from Thursday’s investigation update.

Parts of original building weren’t up to code, investigators say

When construction of Champlain Towers finished in 1981, parts of its structural design didn’t meet the required building code, particularly in the pool deck and tower columns, investigators said in their presentation.

“We’ve discovered several places where the construction did not meet the requirements of the drawings, the building code or common practice,” said James Harris, one of the probe’s project leaders.

Deficiencies were found in the building’s steel reinforcement placements, concrete alignment and strength of the columns and floor concrete, according to the presentation. Officials noted several areas of the pool deck had “severe” strength deficiencies.

In the months leading up to the collapse, the building was also facing major structural repairs. Condo association president Jean Wodnicki described some of the issues in a letter to homeowners in April 2021, noting that the “concrete deterioration is accelerating.”

At the time of the collapse, the condo association had approved an assessment that detailed $15 million worth of repairs – a process they began more than two years after receiving a report about “major structural damage” in the building, CNN has reported.

Pool deck buckles minutes before tower collapse

Before the chaos erupted, one resident reported being woken up by a family member concerned about “metallic noises” reverberating in the building – and just moments later watched as the pool deck fell into the underground garage below it, said Emel Ganapati, who’s co-leading evidence collection efforts for the investigation.

The slab supporting the pool deck collapsed more than four minutes before the tower came crashing down, according to investigators. The connection between the slab and its support columns may have failed, causing the slab to drop into the garage, they said.

“There were indications of severe distress in the pool deck at least three weeks before the collapse,” investigators said in the presentation.

Residents had reported hearing “knocking” and “hammering” sounds leading up to the incident that may indicate the slab’s reinforcement had fractured, it said. Evidence also revealed the slab had been sagging, exposed to water and corroded in some areas.

Over time, the landscaping planters decorating the pool deck had also become weighed down with more filling and paving than originally designed, increasing the weight load on the slab, according to the presentation.

Together, all of these deficiencies created “critically low margins against failure” at the time of the collapse, it said.

Still, investigators noted, “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 may have occurred before the pool deck collapse.

Failure of tower’s columns is also a possibility

Investigators said they have identified several scenarios in which the columns supporting the tower’s southern edge could have failed, forcing their load to be distributed elsewhere and triggering the collapse.

Signs of imminent disaster can be seen in video footage which shows “severe structural movements” in the tower before the drop, and roaring and rumbling sounds could be heard in one of the upper story corridors before the floor started to sag and warp, according to investigators.

The initial structure failures that caused the eastern part of the collapse likely happened below the third floor, investigators said, noting that video footage shows the facade of the building moving “uniformly downward” during the fall.

The tower columns could have been compromised in several ways, including corrosion, water exposure and poor installation, the presentation noted.

Dozens of hypotheses still remain

Though investigators said they have identified strong evidence to support the most likely causes of the collapse, they must still meticulously rule out dozens of other hypotheses through extensive evidence analysis and testing.

Among the other possible – but less likely – causes are that the foundation settled unevenly or was build on topography that developed sinkholes or other weaknesses, officials said.

Once the probe is complete, the National Institute of Standards and Technology plans to release a multi-volume final report on its findings as well as an online presentation tailored to the public by fall 2025, it said.

“There are millions of high-rise condominium units in Florida alone, many of them aging structures near the ocean,” its website says. “While a NIST investigation is intended to identify the cause of the Champlain Towers South collapse, it could also uncover potential issues in other similar buildings nearby and throughout the nation.”

The report may also bring much-needed answers to victims’ families, who have seen safety legislation and hefty legal settlements but have been waiting years for clarity on why the tragedy happened in the first place.

CNN’s Jamiel Lynch, Nouran Salahieh and Joe Sutton contributed to this report.

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