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Baltimore bridge collapse raises question of how long a person can survive in cold water

Authorities are conducting a massive search to find survivors in the frigid Patapsco River after the Francis Scott Key Bridge collapsed early Tuesday.

A massive search is underway for at least seven people in the frigid waters of the Patapsco River near the Baltimore area after a major bridge collapsed when it was hit by a cargo ship.

State and local authorities are in a desperate search in water estimated to be about 48 degrees, raising the question of how long a person can survive in those conditions.

Rescue teams are looking for at least seven people after the 1.2-mile-long Francis Scott Key Bridge collapsed early in the morning on March 26, Baltimore City Fire Department Chief James Wallace said in a briefing with reporters.

The estimate of seven people is a “dynamic count” that authorities have not confirmed yet, as the search and rescue operation continues, Wallace said.

Two people have been rescued. One was in good condition, while another was seriously injured and being treated in a trauma center, Wallace said in a news conference.

How long can a person survive in the cold water?

NBC News Senior Correspondent Tom Costello was on the scene Tuesday morning and said the air temperature was 32 degrees. Multiple reports put the water temperature at about 48 degrees.

Experts at the University of Minnesota-Duluth told Costello that a person would start to feel exhaustion after only about seven minutes in the water.

"Then if you’re lucky, if you have a flotation device and the right gear, you might be able to survive for an hour," Costello said.

“In reality, anything below the temperature of your own body can put you at risk,” Dr. Ryan Stanton, spokesman for the American College of Emergency Physicians, told TODAY about cold water dangers in 2018. “For a lot of people, that range would be from 55 degrees to 70 degrees Fahrenheit.”

At the time of Costello's report, it had been about six hours since the bridge collapsed.

"Survivability is really potentially very, very challenging," Costello said.

"In 50-degree water, you might have as little as 10 to 15 minutes of manual dexterity," Paul Newman, a recreational boating safety specialist for the U.S. Coast Guard, told TODAY in 2018. "If the water is cold, it’s only a matter of time before you lose control of your arms and legs.

"Most people think of hypothermia (drop in body temperature) when they think of cold water, but the reality is that if you don’t have a life jacket, you will not live to experience hypothermia — you’ll drown or go unconscious first,” Newman continued.

Baltimore and Maryland state authorities are scouring the area with helicopters and boats in a search for survivors.

Who was on the bridge?

An unknown number of workers were on the bridge repairing concrete ducts when the ship crashed into it, Maryland Department of Transportation Secretary Paul Wiedefeld said at a news conference.

A group of people gathered at a convenience store near the bridge who said they were family members of workers employed by Brawner Builders Inc. told NBC News that their loved ones had been working on it at the time of the collapse.

Sonar, infrared and underwater drones confirmed there were several cars in the river following the collision, Wallace said.

About 31,000 vehicles a day use the Francis Scott Key Bridge, which was built in 1977, according to the Maryland Transportation Authority.

All 22 crew members aboard the ship that crashed into the bridge have been accounted for and there were no injuries, according to Synergy Group, which operates and manages the ship. The vessel is a 948-foot container ship sailing under a Singaporean flag.