“Our units responded immediately within minutes and found several persons in varying degrees of injury from broken bones to three that were partially buried under the rubble,” Fire Chief John Alston, Jr. said during a news conference.

A total of 36 workers were at the site and all were accounted for, officials said. Firefighters pulled six workers out of the rubble and two escaped on their own, officials reported.     

Workers were placing concrete on the building when “a portion of the second floor collapsed onto the first floor and then into the basement,” New Haven Mayor Justin Elicker told the Associated Press. 

Rescuing the workers as the concrete dried made the job particularly urgent, he added.  

Alston said workers told first responders the concrete was being placed at a faster rate than they could spread and when it pooled too much in one area, this caused the collapse.

Elicker says the property under development is owned by Yale and, when complete, will be a 112-unit, seven-story residential building by Stamford, Conn.-based RMS Cos. Calls to RMS for comment have not been returned. 

The U.S. Occupational Safety and Health Administration has “responded to the site and is investigating,” says an agency spokesman.  

Alston told the Associated Press that emergency officials had recently been talking about responding to building collapses following the Iowa event.  

“They did some excellent work under some harrowing conditions,” Alston says of the New Haven first responders.