(Updates with president's visit in paragraph 3)

By Lisa Shumaker

April 5 (Reuters) - Work is underway to begin clearing

the wreckage of Baltimore's Francis Scott Key Bridge more than a

week after a faltering cargo ship crashed into it, sending the

span collapsing into the harbor and killing six construction

workers who were thrown into the water.

Replacing the bridge will likely take years, but authorities

have opened two temporary channels to allow some shallow-draft

vessels, such as barges and tugboats, to move around the

stricken container vessel.

President Joe Biden visited Baltimore on Friday, pledging

federal help to rebuild the span, an idea some Republican

lawmakers have resisted.

WHAT IS THE DEATH TOLL IN THE BRIDGE COLLAPSE?

The six victims of the bridge collapse were all immigrants from

Mexico and Central America who were fixing potholes on the road

surface of the bridge when it collapsed early on March 26.

Divers recovered the bodies of two men from their sunken

pickup truck the following day. They were identified as

Alejandro Hernandez Fuentes, 35, of Baltimore, originally from

Mexico, and Dorlian Castillo, 26, of nearby Dundalk, originally

from Guatemala.

Authorities have suspended efforts to recover the remains of

the other four men from the 50-foot-deep (15 m) waters

surrounding the twisted ruins due to treacherous conditions.

They are Maynor Suazo from Honduras; Jose Lopez from Guatemala;

Miguel Luna from El Salvador; and another whose name has not

been released. Two other workers were rescued from the channel

shortly after the collapse, one of whom was hospitalized.

The ship's pilot and crew had reported a loss of power

before impact and dropped anchor to slow the vessel, giving

authorities barely enough time to halt traffic on the bridge,

which likely prevented greater loss of life.

WHEN DID THE BALTIMORE BRIDGE COLLAPSE?

Shortly after 1 a.m. EDT (0500 GMT) on March 26, a container

ship Dali was heading out of Baltimore Harbor along the Patapsco

River on its way to Sri Lanka. At 1:24 a.m., the ship

experienced a power failure and all its lights went out.

Three minutes later, at 1:27 a.m., the vessel struck a pylon

of the bridge, and nearly the entire structure of the span

crumbled into the water within seconds.

The disaster may be the worst U.S. bridge collapse since

2007, when a design error caused the I-35W bridge in Minneapolis

to plunge into the Mississippi River, killing 13 people.

WHAT FACTORS PLAYED A ROLE IN THE BRIDGE COLLAPSE?

Bridges such as the one in Baltimore are classified as "fracture

critical" by the federal government - meaning that if one

component or "member" of its primary structural frame fails, all

or most of the span will collapse. There are more than 16,800

such bridges in the U.S., according to the Federal Highway

Administration.

The head of the National Transportation Safety Board said

"fracture critical" spans structural engineering redundancies

that are common to newer bridges and thus make them less

vulnerable to catastrophic collapse.

The Key Bridge opened in 1977 - three years before a similar

vessel collision of the Sunshine Skyway Bridge in Tampa Bay,

Florida, killed 35 people, and prompted bridge designers to

implement better protections for foundation piers.

HOW MUCH WILL THE BALTIMORE BRIDGE COST TO REPLACE?

Federal officials have told Maryland lawmakers the final

cost of rebuilding the bridge could soar to at least $2 billion.

To fully replace the bridge, Congress would need to approve

funding and there are growing signs of friction about using

federal dollars to fund the bridge's reconstruction.

President Joe Biden has said he wants the federal

government to pay to rebuild the bridge. The Transportation

Department on March 28 awarded $60 million in "quick release"

emergency funds to aid in clearing debris and begin the process

of rebuilding.

After the bridge collapse in 2007 in Minnesota, Congress

allocated $250 million.

Insurers could face billions of dollars in claims, analysts

said, with one putting the cost as high as $4 billion, which

would make the tragedy a record shipping insurance loss.

HOW LONG WILL IT TAKE TO REBUILD THE BALTIMORE BRIDGE?

Rebuilding could be a lengthy process and will depend on whether

any of the remaining structure can be salvaged. It took five

years to construct the original bridge from 1972-1977.

WHEN WILL THE BALTIMORE PORT REOPEN?

The U.S. Army Corps of Engineers said it expects to open a new

channel for commercial shipping by the end of April and restore

port access to full capacity by the end of May.

Authorities opened two temporary channels to allow essential

vessels to go around the stuck vessel. The channels are 11 feet

(3.35 m) and 14 feet deep. Major cargo ships need a depth of at

least 35 feet.

Closing the Port of Baltimore for just one month would cost

Maryland $28 million in lost business, according to IMPLAN.

WHAT TO KNOW ABOUT THE CARGO SHIP DALI AND ITS STRANDED CREW

The Dali was leaving Baltimore en route to Colombo, Sri

Lanka, with a crew of 21 plus two pilots on board. All were safe

and accounted for. The 21 crew members were still on the ship

more than a week after the accident, provisioned with enough

food and water for a 35-day voyage, the U.S. Coast Guard said.

The ship measures 948 feet (289 m) - as long as three

football fields. It was stacked high with containers but capable

of carrying twice as much cargo. Safety investigators recovered

the ship's "black box" recorder, which provides data for the

vessel's position, speed, heading, radar, bridge audio, and

radio communications as well as alarms.

The same ship was involved in an incident in the port of

Antwerp, Belgium, in 2016, when it hit a quay as it tried to

exit the North Sea container terminal.

An inspection in June 2023 carried out in San Antonio,

Chile, found the vessel had "propulsion and auxiliary machinery"

deficiencies, according to data on the public Equasis website,

which provides information on ships.

According to Singapore's Maritime and Port Authority, the

vessel passed foreign-port inspections in June and September

2023.

The registered owner of the Singapore-flagged ship is Grace

Ocean Pte Ltd, LSEG data show. Synergy Marine Group managed the

ship, and Maersk chartered the vessel.

WHAT DO WE KNOW ABOUT THE BRIDGE THAT COLLAPSED?

The fallen bridge was one of three highway routes traversing

Baltimore Harbor - the two others are tunnels beneath the harbor

- and handled 31,000 cars per day, or 11.3 million vehicles a

year.

The steel structure was four lanes wide and rose 185 feet

(56 m) above the river. It opened in 1977 and crosses the mouth

of the Patapsco River.

The bridge is named for U.S. national anthem author Francis

Scott Key, who wrote the words to the "Star Spangled Banner" in

1814 after witnessing the British bombardment of the U.S.

garrison at nearby Fort McHenry from Baltimore Harbor.

HOW WILL THE BRIDGE COLLAPSE IMPACT THE BALTIMORE PORT?

Shipping traffic was suspended at the port, the 17th largest in

the country, idling some 15,000 workers whose jobs directly

depend on port operations.

The flow of container freight to Baltimore can likely be

redistributed to bigger ports. However, there could be major

disruptions in shipments of cars, coal and sugar.

Baltimore is the busiest U.S. port for shipments of car and

light trucks, handling at least 750,000 vehicles in 2023,

according to data from the Maryland Port Administration.

In 2023, the port was the second busiest for coal exports.

It is also the largest U.S. port by volume for handling farm

and construction machinery, as well as agricultural products

such as sugar and salt.

(Writing by Lisa Shumaker; Editing by Steve Gorman, Daniel

Wallis and Bill Berkrot)