Read the N.T.S.B.’s Preliminary Report on the Baltimore Bridge Collapse (2024)

The 24-page report includes investigators’ initial findings into the collapse of the Francis Scott Key Bridge after it was struck by a container ship.

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NATIONALSAFETYSPORTATIONBOARD+AVIATIONHIGHWAYMARINERAILROADPIPELINEMay 14, 2024Marine Investigation Preliminary ReportContact of Containership Dali with theFrancis Scott Key Bridge and SubsequentBridge CollapseLocation:Baltimore, MarylandDate and Time:March 26, 20240129 local time(eastern daylight time)Ship:Dali (Neo-Panamaxcontainership)Accident Number:DCA24MM031IMO Number:9697428Injuries:8 (6 fatal)On March 26, 2024, about 0129 eastern daylight time, the 947-foot-longSingapore-flagged cargo vessel (containership) Dali was transiting out of BaltimoreHarbor in Baltimore, Maryland, when it experienced a loss of electrical power andpropulsion and struck the southern pier supporting the central truss spans of theFrancis Scott Key Bridge (Key Bridge). A portion of the bridge subsequentlycollapsed into the river, and portions of the deck and the truss spans collapsed ontothe vessel's forward deck (see figure 1). A seven-person road maintenance crewemployed by Brawner Builders-which was contracted by the MarylandTransportation Authority (MDTA)-and one inspector employed by Eborn Enterprises,Inc., a subconsultant to the MDTA, were on the bridge when the vessel struck it. Theinspector escaped unharmed, and one of the construction crewmembers survivedwith serious injuries. The bodies of the six fatally injured construction crewmembershave been recovered. One of the 23 persons aboard the Dali was injured.1 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseNERGYMAERSKMAERSKERSKMarine Investigation Preliminary ReportDCA24MM031Figure 1. The Dali, with portions of the collapsed Key Bridge across its forward deck and inthe Patapsco River, on March 28.The US Coast Guard classified this accident as a major marine casualty.¹ TheNational Transportation Safety Board (NTSB), according to its Memorandum ofUnderstanding with the Coast Guard, is the lead federal agency for the safetyinvestigation, and, in response to the accident, traveled to Baltimore.As part of the investigative process, the NTSB invited qualified parties toparticipate in the investigation. While they are not part of the analysis, parties arecrucial in helping the NTSB develop the facts around an investigation. The followingentities have agreed to serve as party to the Dali investigation:•Synergy Marine Group•Grace Ocean Private Limited• Maryland Transportation Authority (MDTA)Federal Highway Administration1 A major marine casualty may include any one of the following: (a) the loss of six or more lives,(b) the loss of a mechanically propelled vessel of 100 or more gross tons, (c) property damage initiallyestimated to be $500,000 or more, and (d) a serious threat, as determined by the Commandant of theCoast Guard with the concurrence of the National Transportation Safety Board Chair, to life, property,or the environment by hazardous materials.2 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseAssociation of Maryland Pilots• Nippon Kaiji Kyokai (ClassNK)•HD Hyundai Heavy Industries Co., Ltd•Maritime & Port Authority of SingaporeMarine Investigation Preliminary ReportDCA24MM031The parties were formed into specialized investigative groups led by NTSBgroup chairs in the areas of nautical operations (ship handling, cargo, andnavigation), engineering (propulsion and electrical), survival factors (search andrescue), bridge structures (design and protection), and recorders (electronicevidence). The Chair of the NTSB traveled with the investigative team and acted asthe agency spokesperson.In addition, the Singapore Transport Safety Investigation Bureau (TSIB), the SriLanka Merchant Shipping Secretariat, and the India Directorate General of Shippingare coordinating with the NTSB as representatives of the substantially interestedstates.21Accident Events1.1 Dali's Main Propulsion SystemThe Dali was propelled by a single, slow-speed, 55,626-hp (41,480-kW) dieselengine manufactured by Hyundai MAN B&W (see figure 2). The engine was directlyconnected to a single, right-turning propeller.To run the main engine, one of the vessel's four diesel generators must beoperating and supplying the vessel with electrical power. The emergency generatoralone cannot be used to restart or run the main engine.The Dali's main engine required compressed air directed into its cylinders tostart and change direction. To change from ahead (moving forward) to astern2 According to International Maritime Organization Resolution MSC.255(84), a substantiallyinterested state is a State: (1) which is the flag State of a ship involved in a marine casualty or marineincident; (2) which is the coastal State involved in a marine casualty or marine incident; or; (3) whoseenvironment was seriously damaged by a marine casualty (including the environment of its waters andterritories recognized under international law); (4) where the consequences of a marine casualty ormarine incident caused, or threatened, serious harm to that State or to artificial islands, installations, orstructures over which the State is entitled to exercise jurisdiction; (5) where, as a result of a marinecasualty, nationals of that State have lost their lives or received serious injuries; (6) that has importantinformation at its disposal that the marine safety investigating State(s) consider useful to theinvestigation; or (7) that for some other reason establishes an interest that is considered significant bythe marine safety investigating State(s).3 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031(moving in reverse), the engine would need to be stopped and then restarted in theopposite direction.The engine was also fitted with alarms and automatic shutdown features toprevent damage to the engine if supporting systems required for its operation, suchas the lubricating oil pump (which controls lubricating-oil pressure) or cooling waterpump (which supplies a flow of cooling water), were lost. If a loss of electrical poweroccurred to either of these pumps, the engine would be shut down automatically. Aspart of a multistep sequence to restart and operate the main engine after a shutdown,the lubricating oil and cooling water pumps would need to be restarted.UNDAI MAN BakNTSBFigure 2. Left: The Dali's main engine room (looking aft), showing the vessel's engine. Right:NTSB investigators examining the lower level of the vessel's engine room (looking forward).1.2 Dali's Electrical Power Distribution SystemThe ship's electrical power was supplied by four alternating current generators,which were each driven by a diesel engine. Generator nos. 1 and 4 were rated for4,400 kW, and generator nos. 2 and 3 were rated for 4,000 kW. The generators wereconnected to a 6,600-volt high-voltage (HV) main electrical bus by the vessel's powermanagement system (see figure 3) that powered various shipboard equipment,including the main engine lubricating oil pumps, the bow thruster (a propulsor on theship's bow that that assists with ship maneuverability), and reefer containers4 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM0313(refrigerated containers that cool temperature-sensitive cargo). ³ The HV mainelectrical bus could be split with an installed main bus tie (HVR in figure 5 on page88), which would isolate two generators on each side of the bus. The bus wasdesigned to be normally operated in a closed-bus configuration (meaning the mainbus tie, which connected the two sides of the bus, was closed); this was the caseduring the accident voyage.西門hhhhHV switchboard and breakersB.B.LV switchboard and breakersELLE154nBBNTSBFigure 3. The Dali's power management system in the ship's engine control room. The HVswitchboard (which houses the HV bus) and breakers (left) and the LV switchboard (whichhouses the LV bus) and breakers (right).A 440-volt low-voltage (LV) electrical bus was connected to the HV bus viaredundant step-down transformers (TR1 and TR2 in figure 5). The LV bus poweredvessel lighting and other equipment, including steering gear pumps and the mainengine cooling water pumps. Breakers were located on either side of the step-downtransformers—HR1 and HR2 on the HV side, LR1 and LR2 on the LV side. The LV bus³ An electrical bus is a physical part of an electrical switchboard. (The term bus is a shortenedform of bus bars, which are the metal bars physically located within the switchboard.) The bus connectsthe power produced by generators to systems/devices that require electrical power. Componentssuch as circuit breakers and transformers help handle the electrical power that the bus distributes tothe systems/devices requiring electrical power.5 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031could also be split with an installed bus tie (LVR in figure 5). The bus was designed tobe normally operated with the LV bus tie closed, which was the configuration duringthe accident voyage. With the LV bus tie closed, one transformer (TR1 or TR2) isdesigned to be used, with its associated HR and LR breakers (see figure 5).1.3 Events of March 26The following timeline depicts the events that occurred in the time leading upto the Dali striking pier no. 17 of the Key Bridge, the bridge's subsequent collapse,and initial search and rescue and recovery efforts for the road maintenancecrewmembers (see figure 4).BaltimoreNTSBBrooklynParkSeagirt Marine TerminalPatapsco RiverDundalkFrancis ScottKey Bridge024 miFigure 4. Area where the Dali struck the Key Bridge, as indicated by the red X. (Backgroundsource: Google Maps)Around midnight on March 26, seven road maintenance workers and oneinspector were working in the southbound lanes of the Key Bridge, which wereclosed to traffic. MDTA Police units were stationed at either end of the bridge toalternate traffic on the northbound lanes to protect the construction crew.6 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031About 0005, an Association of Maryland Pilots senior pilot and an apprenticepilot boarded the Dali, which was about to depart from Seagirt Marine Terminalen route to Colombo, Sri Lanka, with a cargo of 4,680 containers (56,675 metric tonsof containerized cargo). During the master/pilot exchange, the senior pilot askedabout the vessel's condition, and the captain reported that the ship was in goodworking order.4The Dali was assisted by two tugboats.••The Bridget McAllister, a 78-foot-long, 5,080-hp tugboat with a 65-tonbollard pull, was secured on the Dali's port quarter.5The Eric McAllister, a 98-foot-long, 5,150-hp tugboat with a 66-ton bollardpull, was secured on the Dali's port bow.About 0036, the two tugboats pulled the Dali away from the dock. About 0107,the vessel entered the Fort McHenry Channel. Generator nos. 3 and 4 were supplyingelectrical power to the vessel (see figure 5). All three steering pumps, which turnedthe ship's single rudder, were online.4 A master/pilot exchange is required at the start of pilot transits and includes discussion of thevessel's navigational equipment, any limitations of maneuverability, available engine speeds, berthingmaneuvers, intended course and speed through the waterway, anticipated hazards along the route,weather conditions, and composition of the bridge team and deck crew both forward and aft,including bow lookout.5 Bollard pull is a measure of the pulling capability of a vessel at zero speed.7 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031DG4DG3DG2DG1NTSBDGR4DGR3DGR2DGR1HV BUS(6,600 V)HR2HVRTR2LR2LVREGHR1B/TTR1LR1LV BUS(440 V)B/T Bow thrusterDG Diesel generatorBreakersDGR Diesel generator breakerEBUSEBUS Emergency electrical busEG Emergency generatorOpenHR High-voltage breakerHV BUS High-voltage electrical busHVR High-voltage bus tieLR Low-voltage breakerClosedLV BUS Low-voltage electrical busLVR Low-voltage bus tieTR TransformerFigure 5. Simplified one-line electrical diagram of the Dali electrical power distributionsystem. Breakers shown reflect their positions at departure on March 26.About 0045, the senior pilot ordered the main propulsion engine (a 55,626-hp[41,480-kW] diesel engine driving a single propeller) to "dead slow ahead." Once inthe channel, about 0107, the senior pilot also gave orders for the tugboats to be letgo per normal practice. The senior pilot handed control over to the apprentice pilotand remained standing by. The ahead engine orders given during maneuveringwould have generally corresponded to the estimated ship speeds (with the vesselloaded) in figure 6.About 0109, the main engine's speed was increased to "slow ahead." Theapprentice pilot ordered a course of 141° to transit under the Key Bridge.8 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031EngineTelegraphEstimatedShip's Speed (kts)(Ahead)RPMLoaded BallastNAV FULL80.0521.923.5FULL6016.818.1HALF5314.515.7SLOW3510.010.9DEAD SLOW 278.18.8STOPFigure 6. The Dali's main engine maneuvering table, which shows ahead engine orders andthe vessel's corresponding speeds under two operating conditions: loaded and ballast. TheDali was loaded when it departed.About 0125, the Dali was 0.6 miles-or three ship lengths-from the Key Bridgewhen electrical breakers (HR1 and LR1) that fed most of the vessel's equipment andlighting unexpectedly opened (tripped) (see figure 7). This caused the first blackout(loss of electrical power) to all shipboard lighting and most equipment, including themain engine cooling water pumps (which controlled engine cooling water pressure)and steering gear pumps.Generator nos. 3 and 4 continued to run and supply electrical power to the HVbus.Most bridge equipment also lost power, and the voyage data recorder (VDR)lost vessel system data feeds. Bridge audio continued to be captured.9 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM03112NTSB1 A primary electrical breaker that feeds mostof the Dali's equipment and lightingunexpectedly opens (trips). The ship loseselectrical power, experiencing a blackout.2 Main propulsion diesel engine shuts downautomatically after pumps lost electricalpower. The vessel loses main propulsion(its propeller stops).3 Crew restores electrical power to thevessel.4 Call for tug assist. Senior pilot ordersanchor dropped.5 Second blackout occurs.6 VHF marine radio call is made to warn allwaterborne traffic.7 The Dali hits the Key Bridge.356Dolphin no. 27Dolphin no. 1Figure 7. The Dali's route on March 26, between the first blackout, and the Dali striking pierno. 17 of the Key Bridge. The location and approximate size of two of the bridge's "dolphins,"sheet pile and concrete structures protecting the bridge's piers, are labeled in the lowerright.The main propulsion diesel engine was independent of the vessel's four diesel-driven electrical generators; however, the loss of electrical power to the pumpsrequired for its operation resulted in the main engine being automatically shut down,and the vessel lost main propulsion, meaning its propeller stopped.The loss of electrical power stopped all three steering pumps, and, therefore,the rudder was unable to be moved. At the time, the ship was on a heading of 141.7º,a course over ground of 140.8°, and speed over ground of 9.0 knots, with the rudderamidships (0°).At 0126:02, the VDR, which had stopped recording vessel system data whenthe blackout occurred, resumed recording the data. The VDR audio recording hadnot been affected by the blackout. The Dali's heading was 144.3° and course overground was 142.7°. Its speed over ground was 8.6 knots. The apprentice pilot calledthe pilot dispatcher by mobile phone. At 0126:13, the senior pilot, who had regainedcontrol from the apprentice pilot by this point, ordered 20° of port rudder.10 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031According to the crew, the emergency generator started and connected to theemergency bus (its breaker would have closed) shortly after the vessel lost electricalpower. At this time, the NTSB is still investigating the exact time when the emergencygenerator started and connected to the emergency bus. Typical for oceangoingvessels, the Dali had an emergency diesel generator (in addition to the fourgenerators) that could be configured to automatically start and connect to theemergency bus if normal electrical power and lighting were lost. When theemergency bus was powered, emergency lighting, navigation and radio equipment,alarms, and other emergency equipment would have been available, and thedesignated emergency steering pump (no. 3) would have been available to turn therudder at its low-speed setting. (When operated alone using emergency electricalpower, steering pump no. 3 was designed to run at a lower speed, turning the rudderat a slower rate than with all pumps.) However, without the propeller turning, therudder would have been less effective.The crew manually closed breakers HR1 and LR1, reconnecting generatornos. 3 and 4 and restoring electrical power to the LV bus, supplying electricalpower again to the entire vessel.At 0126:39, the pilots called for tug assist. The Eric McAllister was 3 miles awayand immediately answered, heading toward the ship (the tug did not reach the Dalibefore it struck the bridge).At 0127:01, the senior pilot ordered an anchor dropped, and the crew beganthe process to drop anchor. The pilots' dispatcher called the MDTA Police duty officerand relayed that the ship had lost power. The pilots' dispatcher then notified theCoast Guard about the Dali's loss of power.•The Dali crew was able to restore electrical power to the vessel, but, when theship was 0.2 miles from the bridge, a second electrical blackout occurredbecause DGR3 and DGR4, the breakers that connected generator nos. 3 and 4to the HV bus, opened, causing a total loss of vessel electrical power (HV busand LV bus). Having connected to the emergency bus by this time, theemergency generator provided electrical power to the emergency equipmentcontinuously through the second electrical blackout.Generator no. 2, which had previously started automatically because it was instandby mode, connected and restored power to the HV bus via DGR2.At 0127:23, the pilot ordered the rudder hard to port (35°). At this point, themain engine remained shut down and there was no propulsion to assist with steering.11 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031At 0127:25, one of the pilots made a call by very high frequency (VHF) marineradio to warn all waterborne traffic.At 0127:32, about 31 seconds after the second blackout, the crew manuallyclosed breakers HR2 and LR2, restoring power to the LV bus, which was powered bygenerator no. 2. (The crew regained electrical power before the vessel struck the pierbut was unable to regain propulsion.)6At 0127:53, the MDTA duty officer ordered the units stationed at the ends ofthe bridge to close the bridge to all traffic. Once the bridge was closed to traffic, onlythe maintenance crew and the inspector remained on the bridge.At 0129:10, the Dali's starboard bow struck pier no. 17 of the Key Bridge at6.5 knots. Six spans of the bridge (the main spans [17, 18, and 19] and spans 20, 21,and 22) subsequently collapsed into the water and across the ship's bow. A Dalicrewmember, who was on the bow at the time of the accident, told investigators that,as he was releasing the brake on the port anchor, he had to escape from the fallingbridge before he was able to reapply the brake. (Due to ongoing salvage efforts, theamount of anchor chain paid out is still unknown.)As the bridge deck collapsed onto the bow of the Dali, another of the vessel'screwmembers sustained a minor injury while escaping the debris.The road maintenance inspector had been walking the length of the bridgewhen the ship struck it. He ran north and made it to the nearest surviving span beforethe rest of the bridge collapsed. The other seven workers were in their vehicles andfell with the bridge. One worker was able to free himself from his truck and wasrescued by an MDTA Police boat at 0155.About 0134, the Coast Guard issued an urgent marine information broadcast,requesting assistance from passing traffic. The first Coast Guard boats were on sceneabout 0151.Multiple agencies searched for survivors throughout March 26. The CoastGuard suspended the active search that evening, and efforts then transitioned torecovery. Six victims were later recovered by divers.6 After the accident, the crew changed which generators supplied the vessel's electrical power.Generator electrical power was routed to the electrical systems only through HR2, TR2, and LR2 untilApril 9, when NTSB investigative parties and equipment manufacturer representatives beganexamining the electrical system. Testing is ongoing.12 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM0312Dali2.1 Background and SpecificationsThe Dali, a 947-foot-long, steel-hulled general cargo vessel (containership),was built by HD Hyundai Heavy Industries Co., Ltd. in 2015. The vessel's draft ondeparture was 39.9 feet fore and aft, with a cargo of 4,680 containers (56,675 metrictons of containerized cargo). The ship and cargo displaced 112,383 metric tons asloaded at departure.Singapore-based Grace Ocean Private Limited, the vessel's owner, owns55 ships-a mix of containerships (including Dali), bulk carriers, and tankers. As ofMarch 26, Singapore-based Synergy Marine Group, the vessel manager whoprovided the crew and operated the vessel for the owner, managed 55 ships underPanama, Marshall Islands, Hong Kong, Liberia, and Singapore flags, including theDali. The vessel was classed by ClassNK, one of several nongovernmentalclassification societies that establish and maintain standards for the construction andoperation of ships. Through construction and later periodic surveys, classificationsocieties confirm a vessel meets the class's technical rules.2.2 US Port Calls in March 2024Since arriving from Sri Lanka to the United States on March 19, the ship hadmade two other US port calls (Newark, New Jersey, from March 19 until March 21,and Norfolk, Virginia, from March 22 to March 23). On March 23, at 0236, the Dalimoored at the Seagirt Marine Terminal in Baltimore Harbor.2.2.1Electrical Power Loss on Previous DayOn March 25, about 10 hours before leaving Baltimore, the Dali experienced ablackout (loss of electrical power to the HV and LV buses) during in-portmaintenance. While working on the diesel engine exhaust scrubber system for thediesel engine driving the only online generator (generator no. 2), a crewmembermistakenly closed an inline engine exhaust damper. Closure of this dampereffectively blocked the engine's cylinder exhaust gases from traveling up its stack andout of the vessel, causing the engine to stall. When the system detected a loss ofpower, generator no. 3 automatically started and connected to the HV bus.Vessel power was restored when crewmembers manually closed HR2 and LR2.Generator no. 3 continued to run for a short period, but insufficient fuel pressure7 The NTSB is not aware of any other vessel power outages occurring in Baltimore or while inits prior ports, Newark or Norfolk.13 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031caused its speed to decrease, and its breaker (DGR3) opened; a second blackout(another loss of electrical power to the HV and LV buses) occurred. In the meantime,the crew had reopened generator no. 2's engine exhaust damper, and the generatorautomatically restarted and then connected to the HV bus when DGR2 closed.While recovering from this second blackout, the crew switched the busconfiguration to use breakers HR1 and LR1 and the bus's associated transformer(TR1) instead of breakers HR2 and LR2, which had been in use for several months.TR1 and its associated breakers, HR1 and LR1, were in use when the ship departed onMarch 26.The first in-port blackout was caused by the mechanical blocking of the onlinegenerator's exhaust gas stack. The second blackout in port was related to insufficientfuel pressure for the online generator. During both of these electrical power-lossevents, the online generators' breakers (DGR2 and DGR3) to the HV bus openedbefore the HR2 or LR2 breakers opened. During the recovery, the crew put TR1online to feed the LV bus because TR2 had reportedly been in use for several months.The first vessel blackout after departure on March 26 occurred when the HR1and LR1 breakers opened unexpectedly.The NTSB is still investigating the electrical configuration following the firstin-port blackout and potential impacts on the events during the accident voyage.2.3 Electronic Data2.3.1Voyage Data RecorderInternational Maritime Organization rules require that vessels of 3,000 grosstons and above, constructed after July 1, 2014, and engaged on internationalvoyages be equipped with a full VDR system. International Maritime Organizationresolution MSC.333(90) requires that these vessels contain both a fixed and afloat-free VDR capsule that record, at a minimum, 48 hours of data. Additionally, theVDR should store internal data of at least 30 days in the VDR's cabinet. The Dali wasconstructed in 2015 and contained a JRC JCY-1900 VDR.Six hours of VDR data, which tracked events immediately before and after theaccident, were downloaded and reviewed on March 26, immediately following thecasualty. The VDR's hard drive from the VDR cabinet on the Dali was later removedand downloaded by NTSB personnel with the assistance of the VDR manufacturer.The hard drive contained 34 days of VDR data.14 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseOther DataMarine Investigation Preliminary ReportDCA24MM0312.3.2Data from other bridge equipment, including the ship's electronic chart displayand information system (ECDIS) and the pilots' portable pilot unit (PPU), were alsodownloaded. Review of this data continues.2.3.3Integrated Control and Monitoring System and High-voltageElectrical BusThe Dali was equipped with an integrated control and monitoring system(ICMS) that retained information related to machinery and system changes andresulting alarms, including vessel engines and the electrical power managementsystem. The NTSB has managed testing of the vessel's HV electrical bus and itscomponents (including the HV and LV breakers) as the investigation parties and theelectrical bus manufacturer, HD Hyundai Heavy Industries, Co. Ltd., work to identifythe cause(s) of the breakers unexpectedly opening while approaching the Key Bridgeand the subsequent blackouts (see figure 8).NTSBDANGER3093Figure 8. An NTSB investigator examining the Dali's HV switchboard (which houses the HVbus) and applying tamper-evident preservation seals.15 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge Collapse2.4 Alcohol and Other Drug TestingMarine Investigation Preliminary ReportDCA24MM031Coast Guard regulations require employers to conduct drug and alcoholtesting for those directly involved in a "serious marine incident."8 On March 26, at0232, the Dali master and chief engineer tested the entire crew for alcohol, percompany procedure. All tested negative.At 0317, the senior and apprentice pilots were relieved by another pilot fromthe Association of Maryland Pilots. The two pilots were taken ashore where, at 0530,both were administered tests for alcohol and other drugs per Coast Guardregulations. Both tested negative.Between 1617 and 1804, a third-party testing provider went aboard the ship totest the entire crew for alcohol and drugs, per Coast Guard regulations. All testednegative for both. The injured crewmember, who had been tested at 0232 with therest of the crew, had already been taken ashore for medical treatment and was nottested by the third-party testing provider.2.5 Fuel TestingThe ship used three main grades of fuel for the main engine and electricalgenerators: low-sulfur marine gas oil (LSMGO), low-sulfur heavy fuel oil, and heavyfuel oil. The Dali carried an estimated 1.8 million gallons of fuel in dedicated vesselfuel tanks. None of the vessel's dedicated fuel tanks were damaged. The last time theDali crew switched fuel was on the evening of March 21, 5 days before the accident,when they switched to burning LSMGO in all engines upon entering US territorialwaters (12 miles off the Atlantic coast), as required by emission regulatoryrequirements.The Dali took on various amounts of all three types of fuel in Newark, NewJersey, on March 19 after the month-long trip from Sri Lanka. Fuel-sample analysisresults indicated that the LSMGO fuel bunkered in Newark, which was the same typeof fuel in use during the accident events, complied with international standards andregulations. The test results did not identify any concerns related to the quality of thefuel.On March 28, the owner took samples of the LSMGO that was being burned atthe time of the accident. At NTSB direction, the owner transferred the samples to anindependent laboratory. The test results did not identify any concerns related to thequality of the fuel.8 See Title 46 Code of Federal Regulations (CFR) 4.03-2-Serious marine incident.16 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031On April 11, additional fuel samples were taken from all fuel tanks and variousfuel supply manifolds on board the vessel; samples were tested by an independentlab. Fuel-sample analysis results indicated that the LSMGO fuel being burned at thetime of the accident complied with international standards and regulations. The testresults did not identify any concerns related to the quality of the fuel.2.6 Hazardous MaterialsOf the 4,680 containers on board the vessel at the time of the accident, 56were identified as containing dangerous goods (hazardous materials). The containerswere located throughout the ship. The NTSB identified 14 containers, which wererecorded as containing hazardous materials, that may have been damaged when theship struck the Key Bridge or during the subsequent collapse of the bridge deck ontothe ship (see figure 9 and table below). These 14 containers were all located forwardof the superstructure, inboard in bays 5, 6, and 7.9101462911135157131. Alkyl sulfonic acid, liquid2. Alkyl sulfonic acid, liquid3. Alkyl sulfonic acid, liquid4.Corrosive liquid, flammable5. Lithium-ion batteries in equipment6. Perfumery products7. Perfumery products8. Perfumery productsNTSB9. Alkyl sulfonic acid, liquid10. Alkyl sulfonic acid, liquid11. Alkyl sulfonic acid, liquid12. Sodium hydroxide solution and Alcohols N.O.S.13. Environmentally hazardous substance, liquid, N.O.S.14. Environmentally hazardous substance, liquid, N.O.S.Figure 9. Approximate locations of cargo bays (yellow with numbers in white squares) andthe 14 impacted hazardous materials shipping containers (orange circles with white numbers)transposed onto the Dali as seen after the accident. Hazardous material container no. 13 wasin a portable tank, stored in the hold, below the deck.9A superstructure is the area on the main deck of a ship that houses crew stateroomaccommodations and the galley. The ship's bridge sits atop the superstructure.17 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031Table. Hazardous materials in potentially damaged containers.DescriptionQuantityNo. ofcontainersHazardclass¹Alkyl sulfonic acids, liquids128,000 kg682Corrosive liquid, flammable4,626 kg18 (class 3subrisk)³Environmentally hazardous substance,6,804 kg195solid, N.O.S. (copper powder)4Environmentally hazardous substance,18,270 kg1liquid, N.O.S. (alkoxylated long-chain alkylamine)6a. Sodium hydroxide solutiona. 10 kg1b. Alcohols N.O.S.b. 174 kg183Perfumery products7,016 kg3Lithium-ion batteries in equipment922 kg19Notes:1. See Title 49 Code of Federal Regulations (CFR) Part 173–Shippers-General Requirements forShipments and Packagings.2. Class 8 materials are corrosive materials.3. Class 3 materials are flammable and combustible liquids.4. N.O.S. means "not otherwise specified." See 49 CFR 172.101-Purpose and use of hazardousmaterials table.5. Class 9 materials are miscellaneous hazardous materials.6. In a portable tank. Stored below deck.The Dali master activated the vessel response plan at 0212 the morning of theaccident by contacting crisis and emergency management firm Witt O'Brien's, thequalified individual. 10 Resolve Marine responded as salvor, and Marine Spill ResponseCorporation responded as the oil spill response organization according to the vesselresponse plan. The Coast Guard additionally deployed its Atlantic Strike Team and itsSalvage Engineering Response Team. The US Army Corps of Engineers and theUS Navy Supervisor of Salvage and Diving, among many other agencies, alsoresponded. Responders deployed containment boom around the ship, conducted10 A vessel response plan is a document that establishes vessel information for use during an oilspill (or if the threat of oil discharge or other unresolved hazardous conditions is present). Informationincludes designated shore-based resource providers, such as oil spill management and salvage, andprocedures for notifying them. A qualified individual is trained in the responsibilities of implementing avessel response plan.18 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031atmospheric monitoring, and plugged the deck scuppers." According to the UnifiedCommand, no hazardous material from containers has reached the water. Salvors aretransferring the bulk liquid acid to intact tanks and moving containers ashore.3.1 Background3Francis Scott Key BridgeThe Francis Scott Key Bridge was owned and operated by MDTA and wasopened to traffic on March 23, 1977, and carried Maryland 695 over the PatapscoRiver, running from Baltimore to Dundalk, Maryland. The approximately 9,087-foot-long, steel and concrete bridge was comprised of a continuous steel through-trusslocated over the river's navigation channel; the north and south approaches of thebridge consisted of multibeam plate girder spans (see figure 10). The continuousthrough-truss main spans of the bridge had a total length of about 2,643 feet andconsisted of a 1,200-foot-long main span and two 721.5-foot-long back spans. Themain span's navigation vertical clearance was 185 feet, and its navigation horizontalclearance (between the supporting piers) was about 1,100 feet.Continuous steelthrough-trussMultibeam plategirder spansNContinuousthrough-truss spansMultibeam plategirder spansFigure 10. The Key Bridge with its truss and spans labeled. (Background source: MDTA)11 (a) A containment boom is a temporary floating barrier extended used to contain an oil spill.Atmospheric monitoring is the monitoring of an area's air to detect concentrations of certain gases.(b) A scupper is an opening cut through a ship's bulwarks (vertical plating that extends the side of theship above its weather decks) that allows water collecting on a weather deck to flow overboard.19 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031At the time of the collapse, the Key Bridge consisted of four total travel lanes(two northbound and two southbound). The annual average daily traffic for calendaryear 2023 was 34,121 vehicles per day, with trucks comprising 10% of traffic. ¹²3.2 Pier ProtectionWhen the Key Bridge was constructed, four large dolphins-two located on thewest side of the bridge and two located on the east side of the bridge-were alsoconstructed at the same time to protect pier nos. 17 and 18 supporting the bridge'scentral through-truss spans. Dolphin no. 1 was about 491 feet west of the center ofpier no. 17 and 550 feet clear of the centerline of the navigational channel (seefigure 11). The dolphins were constructed with a 25-foot-diameter sheet pile filledwith tremie concrete and capped with reinforced concrete (see figure 12). Attachedat various locations on the dolphin were 17-foot-long rubber fenders.Dolphin no. 1491 feetFort McHenry ChannelPier no. 17XXXDolphin no. 3550 feetDolphin no. 2Pier no. 18Dolphin no. 4700 feet550 feetFigure 11. Locations of dolphins relative to the Dali, the Key Bridge, and Fort McHenryChannel. (Background sources: MAXAR and Google Earth)12 Recent traffic data provided by the MDTA.20 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapsePier no. 18Pier no. 17Dolphin no. 1Pier fendering systemMarine Investigation Preliminary ReportDCA24MM031Figure 12. The Key Bridge and the locations of pier nos. 17 and 18. Insets showdolphin no. 1 as well as pier no. 17's fendering-system surrounding. (Background source:MDTA)In addition to the dolphins, pier nos. 17 and 18 were each surrounded by a100-foot-by-84.5-foot crushable concrete box and timber fender system, as seen infigure 12. These systems were comprised of hollow, thin-walled, concrete boxstructures attached to the piers. The timber portions of the fender were attached tothe outer face of the concrete box and utilized a combination of vertical andhorizontal members. Additionally, steel plates were secured at the base of the verticaltimber members.The Dali struck pier no. 17 and the fendering system surrounding the pier butdid not contact dolphin no. 1 or its rubber fenders. Both fendering systemssurrounding pier nos. 17 and 18 were further damaged during the collapse of thetruss spans of the bridge when components of the truss spans impacted portions ofthe fenders as the components fell into the water.21 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM0313.3 Bridge Inspections and Condition13The Key Bridge was subject to regular inspections in accordance with theNational Bridge Inspection Standards. ¹³ These periodic inspections are intended tomaintain safe bridge operation and prevent structural and functional failures. Inaddition to routine bridge inspections, the bridge's steel-truss design and locationover the Patapsco River required two additional types of inspections be performed.One of these additional inspections focused on the nonredundant steel tensionmembers within the steel truss, and the other examined the bridge's underwatermembers. 14 The last inspection of the nonredundant steel tension members wascompleted in May 2023, and the last underwater bridge inspection was completed inMarch 2021. Data from these inspections and the routine inspections were enteredinto the Federal Highway Administration National Bridge Inventory (which recordsbridge inventory and condition data collected from states, federal agencies, andtribal governments) indicating that bridge inspectors rated the conditions of thedeck, the superstructure, and the substructure as being in satisfactory condition.4Ongoing ActivitiesThe NTSB will continue evaluating the design and operation of the Dali'spower distribution system (including its breakers). Examination of damage to thevessel will continue when the ship is clear of debris and moved to a shoreside facility.The NTSB is working with parties to immediately assess their bridges anddetermine whether pier protection needs to be improved. Specifically, the MDTA isstudying short-term and long-term options for upgrades to the existing protectionsystem for the eastbound and westbound spans on the Gov. William Preston Lane Jr.Memorial Bridge (commonly known as the Bay Bridge) near Annapolis.The NTSB is examining the pier protection improvements that have beenmade on the following bridge collapses resulting from marine vessel strikes that theNTSB has investigated: the Sunshine Skyway Bridge in Tampa Bay, Florida; QueenElizabeth Causeway Bridge near South Padre Island, Texas; and the I-40 Bridge nearWebbers Falls, Oklahoma.13 23 CFR Part 650 Subpart C–National Bridge Inspection Standards.14 A nonredundant steel member is a primary steel member fully or partially in tension, andwithout load path redundancy, system redundancy, or internal redundancy, whose failure may cause aportion of or the entire bridge to collapse; see 23 CFR 650.305–Definitions. In 2022, the FederalHighway Administration started using the term nonredundant steel tension member, replacing theprevious term fracture critical member.22 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseMarine Investigation Preliminary ReportDCA24MM031Interviews, including with bridge experts, waterways management personnel,marine safety and highway regulators, and vessel operators, are planned.Detailed analysis of the VDR bridge audio and further validation of VDRparameters continues.Planned areas of investigation include oceangoing vessels' propulsion andelectrical systems; the frequency and causes of vessel contacts with bridges overnavigable waters; and bridge-strike mitigation measures such as a combination ofvessel-size restrictions, vessel-assist tugs, and bridge-pier protection.The NTSB investigation of all aspects of the accident is ongoing as wedetermine the probable cause.23 of 24This information is preliminary and subject to change.

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Contact of Containership Dali with the Francis Scott Key Bridgeand Subsequent Bridge CollapseDaliOwnerOperatorFlagBuilderBuild yearIMO No.MMSICall SignDestinationGrace Ocean Private LimitedSynergy Marine GroupSingaporeHD Hyundai Heavy Industries Co., Ltd.201596974285630042009V5283Colombo, Sri LankaMeteorological InformationSkyWater temperatureLightObservation timeAir temperatureWind speed andOvercast48°F / 9°CNight0216 local time (eastern daylight time)39°F / 4°C2 kts (calm)directionVisibilityWreckage InformationVessel crew injuriesVessel passenger injuries10 mi1None7 (6 fatal)Ground injuriesTotal injuriesDamageFire8 (6 fatal)SubstantialNoneExplosionNoneLatitudeLongitude39°12.99' N76°31.75' WInvestigationMarine Investigation Preliminary ReportDCA24MM031Investigator in chargeAdditional participatingpartiesSubstantially interestedstatesNoteMarcel MuiseSynergy Marine Group, Grace Ocean Private Limited, Maryland TransportationAuthority (MDTA), Federal Highway Administration, Association of Maryland Pilots,Nippon Kaiji Kyokai (ClassNK), HD Hyundai Heavy Industries Co., Ltd, andMaritime & Port Authority of SingaporeIndiaSingaporeSri LankaThe NTSB travelled to the scene of this accident.24 of 24This information is preliminary and subject to change.

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