(Adds FBI criminal probe in first paragraph)

By Lisa Shumaker

April 15 (Reuters) -

The FBI has opened a

federal criminal investigation

into the deadly collapse of Baltimore's Francis Scott Key

Bridge as work continues to clear the wreckage after last

month's collapse.

In March, a container ship crashed into one of the bridge's

support pillars, sending the span crashing into Baltimore 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 cargo ship.

President Joe Biden visited Baltimore and pledged 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.

Dive teams have recovered three bodies so far:

* Maynor Yasir Suazo-Sandoval, 38, of Honduras

* Alejandro Hernandez Fuentes, 35, of Baltimore, originally

from Mexico

* Dorlian Castillo, 26, of nearby Dundalk, originally from

Guatemala.

Three other bodies remain trapped beneath the underwater

debris in the 50-foot-deep (15 meter-deep) waters. They are 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, the

container ship Dali was heading out of Baltimore Harbor along

the Patapsco River on its way to Sri Lanka. At 1:24 a.m. (0524

GMT), the ship experienced a power failure and all its lights

went out.

Three minutes later, at 1:27 a.m. (0527 GMT), the vessel

struck a pylon of the bridge, and nearly the entire structure of

the span crumbled into the water in seconds.

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

2007, when a design error caused the Interstate 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 lack structural engineering redundancies

that are common to newer bridges, making them less vulnerable to

catastrophic collapse.

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

vessel collision into the Sunshine Skyway Bridge in Tampa Bay,

Florida, killed 35 people, and prompted bridge designers to

provide 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.

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 rebuilding.

After the 2007 bridge collapse 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 build 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

(3.4 meters) and 14 feet (4.3 meters) deep. Major cargo ships

need a depth of at least 35 feet (10.7 meters).

Closing the Port of Baltimore for just one month would cost

Maryland $28 million in lost business, according to economic

analysis firm 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 ship's length is 948 feet (289 meters) - as long as

three football fields - and was stacked high with containers.

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 meters) above the river. It opened in 1977 and crosses the

mouth of the Patapsco River.

The bridge is named for Francis Scott Key, who wrote the

words to the U.S. national anthem, 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 AFFECT 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 cars 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 Daniel Wallis, Bill

Berkrot and Jonathan Oatis)