Copyright 2021 NPR. To see more, visit https://www.npr.org. LULU GARCIA-NAVARRO, HOST: We're joined now by a guest who knows firsthand why this rescue and recovery effort and the investigations are so painstakingly slow. Robert Jensen is a disaster management expert who dealt with the aftermath of 9/11, the Oklahoma City bombing, and the Grenfell Tower fire in the United Kingdom among many other mass casualty events. Welcome to WEEKEND EDITION. ROBERT JENSEN: Thank you. GARCIA-NAVARRO: First, your reaction to this collapse - is there a precedent for something like this in the United States? JENSEN: Yeah. There's unfortunately not many new disasters, and it has happened before. There's - I'm really afraid this will be probably the largest nonintentional collapse of a building. The last big nonintentional collapse was the walkway at the Hyatt Regency in Kansas City in April 1981 that killed 114 people. I don't know what the final number will be because, of course, they're still doing rescue, and they haven't really started recovery.