Rescue underway as cold water temperatures create hypothermia risk in Baltimore Harbor

The water temperature was in the low 40s Tuesday morning when the Francis Scott Key Bridge along I-695 in Maryland collapsed into the Baltimore Harbor after a cargo ship struck it. 

Rescue efforts remain underway for at least 20 people believed to be in the water, the Baltimore Fire Department told the Associated Press at around 3:00 a.m. ET. Officials have described the bridge collapse as a mass casualty event. There is no official death toll known at this time. 

A person exposed to cold water temperatures for a prolonged period of time risks suffering from hypothermia. When the water temperature is between 40-50 degrees, exhaustion or unconsciousness can happen within 30-60 minutes. The expected survival time for someone exposed to those conditions is between one to three hours. 

"Our focus right now is trying to rescue and recover these people," Kevin Cartwright, director of communications for the Baltimore Fire Department, told The Associated Press.