How could the dive ship Conception, lost off the California coast last week, burn so hot and so quickly that the crew on deck barely had time to jump and the passengers below had no chance of escape?
The official answer will only come after the US Coast Guard and the National Transportation Safety Board complete months of inquiries and technical examinations.
But the loss of the Express Shuttle II in 2004 could be the most similar case to the Conception in terms of how the fire might have started and so rapidly enveloped the ship. And some of the science behind the “Mother of All Bombs” — an American weapon known as the GBU-43/B Massive Ordnance Air Blast Bomb — may help illustrate how the fire formed and spread so quickly.
The Express Shuttle II caught fire near Port Richie, Florida, on its way back to the mainland after dropping off passengers at an offshore casino. The vessel had been inspected earlier by the Coast Guard and found to be in compliance with all requirements. It also had fire warning systems installed.
But unknown to the crew and captain, a fuel line to the diesel engine was not mounted and secured properly — which subjected the line to intense vibration. In the engine compartment, the line broke and began leaking diesel fuel.
Enter the science of the Mother of All Bombs. In that weapon, the bomb first explodes in a small way up to 1,000 feet above the ground and as low as 50 feet.
“When they (first) blow up, they blast fuel into the air,” says Edward Priest, a former Air Force Special Operations combat controller. “That fuel atomizes. Then there’s a secondary explosion that lights the fuel that’s been atomized.”
The result is a blast of “overpressure” that can kill humans thousands of feet away.
But the key word is “atomized.” For the passenger ship leak was not seepage or “pooled fuel.”
Says the NTSB report:
The diesel fuel in the Express Shuttle II”s fuel delivery lines was under a pressure of about 1,800 psi at the valves. When fuel under pressure is released by an equipment failure, the result is usually an atomized spray of fuel over a broad area. ….It is thus highly probable that the fuel from the broken fuel line was released as a spreading mist that contacted numerous engine parts…
And for this reason, as the atomized mist spread on the Express Shuttle II, a smaller version of the Mother of All Bombs may have played out. The atomized mist did not instantly ignite because the engine block, when cooled properly, only hits 180 degrees F — not nearly hot enough for diesel to “autoignite” without flame or electric arc.
So the mist built up and spread without igniting – enough so that some of it was sucked into the engine’s turbo chargers and is thought to have caused the starboard engine to first surge and then conk out.
That was the first clue to the crew that something was amiss.
But they did not understand the real problem. By this time, the ambient air down below was no longer “air” but a deadly mix of atomized fuel and air. The atomized mist filled the engine room unchecked and undetected and crept through the lower holds of the ship.
Said the NTSB report:
“According to the material safety data sheet provided by the fuel supplier, the No. 2 diesel fuel used on the Express Shuttle II will autoignite (ignite by heat without spark or flame) at a temperature of 637° F. “
The mist is thought to have worked its way to the engine exhaust manifolds — which operate at temperatures above 1,000 degrees. The manifolds or some other hot engine part is thought to have touched it all off.
Unlike the Mother of All Bombs, the ignition of the mist did not result in an outright explosion or overpressure wave.
But it did create instantly a white-hot fire. And the fire was not confined to a pool of fuel. This was not just an engine fire. The fire was near instantly widely spread — wherever the atomized fuel had drifted, fire erupted. And the mist had pretty much spread everywhere below decks.
The crew saw smoke from below — their first real warning — and thought to fight the fire but it went poorly.
Said the NTSB:
“The master said they lifted the hatch 1 1/2 to 2 inches and that the flames were “like a blowtorch.” They dropped the hatch back over the opening. The master said the cabin was “so full of smoke you couldn’t hardly breathe.”
All three crew members were forced from the deck and the ship’s cabin. As the fire spread, they gathered at the bow. The flames moved toward them, climbing up the starboard cabin bulkhead and into the pilothouse.
It was at this point that the crew of the Express Shuttle caught its second bit of luck for the day. The first big break was that they carried no passengers — having just discharged more than 70 at the offshore casino.
This second bit? A fortunate coincidence. There was a good Samaritan nearby. But not just any Samaritan. . Says the NTSB report:
“At this point, the operator of a passing recreational boat, who happened to be an off-duty Coast Guard rescue swimmer, came alongside the Express Shuttle II and offered assistance. The master and deckhands abandoned the Express Shuttle II and boarded the recreational boat.”
The entire incident, from discovery to abandon ship, took just 20 minutes.
There are plenty of holes in any argument that the Conception was the exact replay of the Express Shuttle II casualty. It seems the Conception crew had almost no warning, for example. And the Conception owners have an excellent record of maintenance and routine inspections of its engines.
Still if there was the ship equivalent of an FBI profiler, the Express Shuttle II and the Conception might very well be grouped together. The atomized diesel origins of the Express Shuttle II fire seem a match for the ferocity of the fire on the Conception. And the gradual spreading of the atomized mist without ignition so that the ship below was permeated with it also seems a possibility.
Vibration is the enemy of all ship engines, large and small, and in the case, of the Conception, even with a careful crew and owner, just a small fuel line crack could have had huge consequences.
As the investigation begins, the Express Shuttle II is almost certain to be one of the case studies where investigators take a hard look.