One of the suggested ignition sources for the Deepwater Horizon explosion was that the No. 3 engine ingested hydrocarbon gas, went into overspeed, and self-destructed.
The engine was a Wartsila 18V32LN(E) attached to an ABB AMG 0900XU10 generator. Witness accounts and location of damage and injuries are consistent in pointing to an explosion in the vicinity of the No. 3 engine room. Witness accounts are inconsistent in whether power was lost before or after the explosion. There are also witness accounts of lights and computer monitors “popping” before the explosion. Engine room personnel reported consistently that the engines were increasing speed up to the instant of explosion.
The No. 3 engine was protected by three overspeed devices:
A Diesel Engine Speed Measuring System connected to a Simrad Integrated Automated Control System (IACS). If the measured speed is 13% above normal, the IACS cuts both fuel and air supplies.
A Woodward 723 Governor/Actuator that senses engine speed and will move the fuel rack to the zero position and send a shutdown signal to the IACS if speed gets to 15% above normal.
A Mechanical Overspeed Trip Device attached to the camshaft that operates by centrifugal force and which will move the fuel rack to the zero position and send a shutdown signal to the IACS at 18% above normal speed.
The No. 3 engine used engine room air from ventilation inlets, which were 15-20 feet from the source of the escaping hydrocarbon gas. The engine shutdown and ventilation damper closing mechanisms connected to the gas alarms were not set on automatic. The engine air cutoff valves were not connected to gas alarms and were not actuated by the crew.
The assumed composition of the gas was approximately 74% methane, 7% ethane, 5% propane and the rest miscellaneous hydrocarbons.
I have three questions:
The IACS represents a single point of failure for air/gas cutoff. Does anyone out there have any evidence, anecdotal or otherwise, pertaining to the reliability of Simrad IACS units?
The testimony of the engine crew suggests that the engines were controlled through the fuel supply and that air cutoff was a seldom-used feature. Is this conclusion reasonable?
The normal operating speed of the engines was 750 RPM. Would anyone care to speculate on what the destruction RPM of these engines would be, and how rapidly they could reach that speed?
Any and all response will be greatly appreciated.