Common Causes of Explosions – Gas Leaks
A report by the Associated Press after the 2010 BP Deepwater Horizon explosion in the Gulf of Mexico revealed the accident was, in part, due to methane gas that had come from the underlying well. Shooting through the drill column, the methane expanded and burst multiple seals and barriers prior to the explosion. There were several other triggers, as the investigation would find, but workers did have evidence of a gas leak that contributed to the incident.
In 1988, an offshore oil explosion involving the Piper Alpha killed 167 people. After the oil platform went on line, it was also modified to collect gas. The rig exploded when a gas leak ignited firewalls designed to protect workers. Crew modules had originally been placed away from high-risk areas but, during an upgrade, gas compression units were put near the main control room. Communication gaps kept workers unaware of the pipework needed, which was sealed without a safety valve. Taking three weeks to bring under control, the fire killed both people on the rig and on standby control vessels.
Oil Rigs and Gas Leaks
Another example is the Brae Alpha rig in the North Sea, operated by Marathon Oil. The installation was the source of a gas leak from discharge pipework. Insulation from there was never removed, and the system hadn’t been inspected since 1983, as of a 2016 report. Even the company has recommended the procedure be done every 12 years. Reports also suggested workers were exposed to a hydrocarbon gas. Measures were under way to remediate the problem and prevent a possible explosion.
A gas leak can, therefore, come from the rock formations under an offshore platform, or from equipment within it. Another North Sea rig was the site of a leak in 2012, in which the source of the leak was determined to be a reservoir 4000 meters below it. The risk of an explosion complicated matters, as was attempting to determine the size of the leak and its source. A safety system included a flare atop the rig, which burned off excess hydrocarbons.
The gases in the reserve, known as the West Franklin Field, are under greater pressure than the Macondo Prospect in the Gulf of Mexico, where the BP Deepwater Horizons rig was located. Estimates of when the leak could be plugged stood at 10 to 12 years. The risks of an explosion if the gas was ignited, and its effects on people weren’t the only factors, as it was estimated that every day, 200 tons of greenhouse gases were escaping.
Gas Hazards and Sources
Other common types of emissions include:
- Carbon Monoxide: A toxic gas that can enter crew quarters and work areas. It can accumulate in air intakes and temporary refuges.
- Hydrogen Sulfide: Also toxic to humans, it can accumulate at the well head and in process and drilling areas, among other parts of the rig. The gas can also enter the HVAC system and accommodation areas.
- Combustible Hydrocarbons: Accumulates in various areas, from the well head to battery rooms, cranes, control rooms, accommodation areas, and ventilation systems.
Combustible gas is a hazard if it is found near gas compressors, oil de-watering plants, turbine and power skids, bottled gas stores, and water treatment areas. The only way to be completely protected is to have sensors and other monitoring systems in place, and emergency procedures should a problem be detected. However, even the monitors must be well-maintained, because the marine environment is highly corrosive (those made of 316 stainless steel are the most resistant).
The risks associated with gas leaks from offshore rigs are bad for public health and the environment, the U.S. Environmental Protection Agency has taken action. As of May 2016, it had finalized standards to reduce the release of methane and other compounds, such as toxic emissions and volatile organic compounds, from rigs and other facilities in the oil and natural gas industry. The new standards also focus on toxins such as toluene, benzene, xylene, and ethylbenzene. Although they focus on health and climate change, the standards address some emissions that can elevate the explosion risks on offshore rigs as well.