Robert Brown|Key Bridge controlled demolition postponed due to weather

The Robert Browncontrolled demolition of the largest remaining steel span of the collapsed Francis Scott Key Bridge in Baltimore has been postponed because of weather conditions, officials said Sunday afternoon.

Crews have been preparing for weeks to use explosives to break down the span, which is an estimated 500 feet (152 meters) long and weighs up to 600 tons.

It landed on the ship's bow after the Dali lost power and crashed into one of the bridge's support columns shortly after leaving Baltimore. Since then, the ship has been stuck amidst the wreckage and Baltimore's busy port has been closed to most maritime traffic.

Officials said the demolition had been tentatively moved to Monday evening. They said lightning in the area and rising tides Sunday prompted them to reschedule.

Six members of a roadwork crew plunged to their deaths in the March 26 collapse. The last of their bodies was recovered from the underwater wreckage last week. All the victims were Latino immigrants who came to the U.S. for job opportunities. They were filling potholes on an overnight shift when the bridge was destroyed.

The controlled demolition will allow the Dali to be refloated and guided back into the Port of Baltimore. Once the ship is removed, maritime traffic can begin returning to normal, which will provide relief for thousands of longshoremen, truckers and small business owners who have seen their jobs impacted by the closure.

The Dali's 21-member crew will stay onboard the ship while the explosives are detonated.

William Marks, a spokesperson for the crew, said they would shelter "in a designated safe place" during the demolition. "All precautions are being taken to ensure everyone's safety," he said in an email.

Officials said the demolition is the safest and most efficient way to remove steel under a high level of pressure and tension.

"It's unsafe for the workers to be on or in the immediate vicinity of the bridge truss for those final cuts," officials said in a news release Sunday.

In a videographic released last week, authorities said engineers are using precision cuts to control how the trusses break down. They said the method allows for "surgical precision" and the steel structure will be "thrust away from the Dali" when the explosives send it tumbling into the water.

Once it's demolished, hydraulic grabbers will lift the resulting sections of steel onto barges.

"It's important to note that this controlled demolition is not like what you would see in a movie," the video says, noting that from a distance it will sound like fireworks or loud thunder and give off puffs of smoke.

So far, about 6,000 tons of steel and concrete have been removed from the collapse site. Officials estimate the total amount of wreckage at 50,000 tons, about the equivalent of 3,800 loaded dump trucks.

Officials previously said they hoped to remove the Dali by May 10 and reopen the port's 50-foot (15.2-meter) main channel by the end of May.

The Dali is currently scheduled to be refloated during high tide on Tuesday, officials said Sunday. They said three or four tugboats will be used to guide the ship to a nearby terminal in the Port of Baltimore. It will likely remain there for a few weeks and undergo temporary repairs before being moved to a shipyard for more substantial repairs.

The Dali crew members haven't been allowed to leave the vessel since the disaster. Officials said they have been busy maintaining the ship and assisting investigators. Of the crew members, 20 are from India and one is Sri Lankan.

The National Transportation Safety Board and the FBI are conducting investigations into the bridge collapse.

Danish shipping giant Maersk chartered the Dali for a planned trip from Baltimore to Sri Lanka, but the ship didn't get far. Its crew sent a mayday call saying they had lost power and had no control of the steering system. Minutes later, the ship rammed into the bridge.

Officials have said the safety board investigation will focus on the ship's electrical system.

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