A professional engineer and concrete repair specialist said he believes “concrete cancer,” a process that happens when steel rods in building structures rust and expand, might have caused the deadly partial collapse of the Champlain Towers South Condo in Florida on Thursday.

Search-and-rescue efforts by first responders are underway following the partial collapse of the 12-story building in Miami, which left four dead and as many as 159 unaccounted for. Building analysts and experts are seeking to determine the cause of the structural failure.

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