Analysis: ‘Sour’ toxins could spell death for sealife around platform

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THE Elgin platform is an example of human achievement in extracting an energy source that 25 years ago would have been unthinkable.

Like the Deepwater Horizon in the Gulf of Mexico it carried risk – not the depth of water (93 meters rather than the 1,500 meters of the Gulf), but the depth of the geology (5,000 meters below the seafloor) and the nature of the material extracted.

At these depths the gas is not only hot (200C) and under high pressure (seven tonnes a square inch), it is also “sour”, meaning it has high levels of carbon dioxide and hydrogen sulfide.

Total’s expertise was in its ability to reach this gas and bring it to the surface, and to safely remove the contaminants before piping it ashore for commercial use. On Sunday, gas started to escape. Now begins the task of assessing what went wrong and the impact. Being so far offshore it is unlikely to present a threat to coastal regions. A six-mile light slick has been observed and two to three-mile exclusion zones implemented for both sea and air around the platform.

The slick will be “gas condensate” – a light, volatile material condensing on the cool sea surface – which will quickly break down and have minimum impact. Of more concern is the hydrogen sulfide, which if dissolved in sea water would prove toxic to marine life.

As with Deepwater Horizon, this is uncharted territory. The gas is flammable, corrosive and toxic, so the challenges in dealing with it will be as great as those with the extreme subsea pressure in the Gulf. This will not be a major environmental incident, but it will cause damage close to the platform.

• Dr Simon Boxall is an oceanograher at the National Oceanography Centre at Southampton University.