Four bolts held the fuel supply line to the flange assembly. When three of them failed, oil sprayed on hot engine surfaces.
After three of the four screws holding the fuel line in place broke, the line began spewing fuel. The oil ignited when it sprayed onto a hot exhaust manifold less than a foot away, causing more than $3 million in damage.
“It appears that vibration worked on them until they finally failed,” said the report’s author, Ken Olsen, a casualty analyst with the Coast Guard’s Office of Investigations and Analysis in Washington, D.C. “We suspect they may have become loose over time.”
The fire broke out aboard Nordic Empress on June 15, 2001, about 140 miles northwest of Bermuda, while the ship was en route to New York with 1,566 passengers and 650 crewmembers (PM #58).
The fire seriously damaged the two diesel engines that drive the ship’s port propeller. Each of the ship’s two propellers is served by a Wartsila power plant, comprising two diesels arranged in father/son pairs: a 6,607-hp, V-12 engine and a 4,405-hp straight-8.
The fire began in the vicinity of the fuel lines supplying the port V-12 engine. The failed line carried oil, preheated to about 260Â° F, to one of the engine’s two hotboxes – assemblies of fuel pumps, manifolds and racks that control the supply of fuel to the cylinders. Once the three screws failed, the pressurized fuel line began spraying fuel over the engine and the surrounding area.
“The spraying fuel ricocheted and atomized under the piping cover,” the report said. “It was guided by the cover’s aft edge to the nearby exhaust pipe and manifold. It instantly autoignited lighting off the remaining fuel spraying out in all directions from the openings in the cover. The fire engulfed the entire front of both engines serving the port propeller shaft.”
Automation controls, remote sensing equipment, cabling and pumps were severely damaged by the fire. The two starboard engines were not damaged directly. After the fire was put out, the ship’s engineers were able to operate them after re-cabling several main engine auxiliary motors. The ship then returned under its own power to St. George, Bermuda. No one was injured.
The failed screws and their associated flange assembly were installed in 1999 when the engine underwent safety modifications designed to avert the kind of fire that broke out. In early 1995, Wartsila Diesel, the designer of the ship’s engines, issued a technical bulletin noting that engines of this type had experienced “serious fuel leakage in the low pressure fuel supply” and that “a few of the leakages have led to a fire.”
To correct this problem, the company recommended modifications of some of the components of the fuel oil system. One of those modifications involved the flange assembly where the screws failed on Nordic Empress. Under the original design, the piping was secured with a two-screw system. Wartsila urged replacement of this connection with a four-screw system in its technical bulletin. Wartsila representatives completed Nordic Empress’ conversion to a four-screw connection in early 1999.
The 1995 Wartsila technical bulletin also recommended that the fuel supply system be inspected after 2,000 hours of operation to ensure that the screws were in place and had not loosened.
Although Olsen is sure that the failed screws started the chain of events that led to the fire, he is unable to say exactly what caused them to fracture without a scientific metallurgical analysis. One possibility is that the screws were not properly tightened down in the first place. Another is that they may not have been properly checked for tightness at regular intervals afterwards. Olsen said he does not know if the 2,000-hour inspections were ever performed.
Olsen believes that the screws used in the conversion were of different lengths and quality. Wartsila recommended the use of 30-mm M8 hex socket screws. But two of the remaining segments of fractured screws found later in the engine room and believed to have come from the broken fuel flange assembly, were 23 mm and 36 mm in length. The variations in length and quality meant that each screw might have required different torques for proper installation.
“Tightening too close or beyond the screw’s yield strength may result in failure or torque loss, while tightening to a lower range of the yield may result in insufficient preload for sealing and insufficient residual load to maintain the seal,” the report said.
In its conclusions, the report stated, “The use of different screws would have demanded more specific and varying tightening procedures, thus increasing the likelihood of improper installation.”
The Coast Guard conducted its investigation at the invitation of Liberia, where the ship is registered. Almost all the passengers were U.S. citizens.
While the report does reach conclusions about the cause of the fire, it does not make any specific recommendations. But the actions needed are evident. “It is sort of obvious in the conclusions,” Olsen said, indicating the need to check screws. “Visual inspections are inadequate. Operators may want to put a wrench on them,” he said.
In addition to assessing the causes of the fire, the report also assessed the performance of the crew. It gave the crew high marks for its handling of passengers to ensure their safety.
“During the emergency, the master, officers and crew of Nordic Empress managed the passengers exceptionally well. The mustering process took place without injury in an orderly and controlled manner,” the report said.
The crew was also praised for reacting properly in the crucial early stages of the emergency. “Proper decisions and actions in accordance with good maritime practice were taken by these crewmembers,” the report said.
Firefighting procedures employed were “generally appropriate and effective in containing and extinguishing the fire within the main engine room,” the report said.
Using a computerized Damatic control and monitoring system, the second engineer secured the fuel supply systems. The crew initially entered the engine room with a hose to fight the fire but quickly realized it was spreading. They retreated from the engine room, closed the watertight doors and activated the Flexi-fog water mist system. The mist system, which operated for about 15 minutes, extinguished the fire.
Crewmembers used water hoses to cool down the engine room, but after about half an hour, flames erupted over the smaller of the two port engines. That fire was quickly put out with water from the hoses. About an hour and a half later, inspection crews found cables burning in an overhead utility passageway. The engine room was evacuated once more. This time the Halon system was activated, and after a few minutes, the water-mist system was re-engaged. Three hours after the initial alarm, the cable fire was reported out.
In the aftermath of the fire, Royal Caribbean has conducted a comprehensive review of its firefighting and prevention programs and is pursuing a number of initiatives. The plan includes:
“Safety is a continuous journey,” said Harri Kulovaara, Royal Caribbean’s senior vice president of marine operations.
Although he was pleased with the way the ship’s firefighting equipment – especially the water mist system – operated and the way the crew performed in the emergency, he said that the cruise ship line is determined to draw important lessons from what happened.
For example, the cruise line’s analysis indicated that about a barrel of oil spilled from the fuel lines even though automatic shut-off valves at the fuel tanks operated properly. The company has decided to install additional automatic valves on the supply and return lines close to the engine. The idea is that those valves will isolate fuel in the lines, between the tank and the engine.
These valves “will reduce the amount of oil going into a fire,” Jens Lassen, the line’s vice president of fleet management, explained.
Even though the fire on Nordic Empress started because of three failed screws, Kulovaara suspects there was a human element associated with their failure. Changing the human element in the engine room of the future is at the heart of what Royal Caribbean hopes to accomplish to prevent future casualties.
“I think our engine rooms overall are very good,” Kulovaara said. Still he hopes to “raise the culture to an even higher level so we don’t accept a single drop of oil anywhere.”