The control room of any hydrocarbon processing facility, whether it’s an oil refinery, a natural gas liquefaction plant or an oil drilling rig, is the brain of the facility. Instruments in the control room receive temperatures, pressures and flow rates from sensors at important points in the process, then return signals to control valves which influence those parameters by fractionally opening or closing to keep the correct values at those points. Operators keep an eye on the process, watching for imbalances or improperly working instruments.
During the design phase of the facility, process engineers determine and decide for each of those control valves whether they should be open or closed in the event of a power failure. Some should fail open in order to vent material to a flare system and prevent dangerous pressure build up. Others should fail closed to prevent material from entering a vessel or tank. All these controllers and sensors are wired to the control room, where they are electrically powered. Depending upon the size and complexity of the facility, there may be thousands of electrical connections and miles of wires in the control room.
Outside the control room, any electrical connections are contained inside sealed junction boxes to prevent sparks or arcs from igniting any gas that might be present. By universally accepted safety standards, control rooms are kept at positive pressure, that is, air is continuously blown into the room to prevent dangerous gases from entering. In case of power failure, air tanks are provided to help keep gas from entering the control room. Control room doors are self closing, blast proof steel, with air tight weather proofing seals.
In the case of the Deepwater Horizon drilling rig that recently exploded in the Gulf of Mexico, threatening ecological disaster along the eastern Gulf Coast, those safety design measures failed to prevent the explosion. The latest word has it that a “gas bubble” came up the production pipe, overwhelming the valves at the top of the well, and spread until it found an ignition source.
A significant clue as to why the safety systems failed came in a release of information this week. This is purely my speculation based upon that release.
It was reported that a group of company dignitaries had visited the platform that very day to celebrate its safety record. One can easily imagine the executives and assistants being shown en masse around the tight quarters, gawking at valves, pipes and pressure vessels crammed into the platform. They would certainly have been shown the control room, and the safety doors would have been propped open while the group entered and left. The investigation is ongoing, but I am sure that one of those safety doors was left open or partially open, allowing that gas bubble release to enter the control room, setting off the disaster. We may never know, but that’s my bet. And it's a warning that, whatever we do or say, whenever humans are involved, no system is fail safe or fool proof.