My source of information for this article is a Scientific American article.
This extraordinary story began on October 23rd 2015 at the Canyon Gas Storage Field “the largest underground Methane storage in the Western United States”. Evidently large quantities of gas are stored underground. The leak is in a 7inch pipe at a depth of 3000ft.
The operator, the Southern California Gas Company, does not know what caused it, but has a plan to stop the leak that involves drilling an interception well and plugging the leak with mud and fluids before a permanent plug of cement is added. This could take some months to complete.
At face value and assuming this information is valid, I can assume that the storage facility involves a significant length of interconnected small bore pipes located deep underground. It is interesting then to subject this design concept to consideration from a risk engineering perspective – the sort of perspective that is to be found pretty much throughout the book.
The Event here is the point in time when a leak began. It appears that no-one knows the Mechanism of this. Options are obviously that the pipe contained a manufacturing defect, or the pipe was subject to overpressure, or the pipe strength deteriorated due to corrosion or the pipe was damaged and so on. Obviously detailed engineering knowledge of the design and installation is needed to be able to hypothesize usefully. I have little doubt that much engineering effort went into structural design criteria, metallurgy, pipe protection, pipe material quality, X-ray inspections etc.
However, an Event is clearly a possibility that arises from containing gas under pressure. We may hope that the design team were aware of the significance of a leak as it does not take much imagination to conceive of the Outcome and the Likely Worst Consequence (LWC) in this case. What happened is pretty much the LWC – 72000 tons of Methane at the time of writing the Scientific American article. According to the article, this gas is 25 times worse than Carbon Dioxide as a greenhouse gas. It takes 12 years to break down in the atmosphere. 2000 residents have been evacuated and two schools have had to close.
Due to the isolated location of any leak, it is easy to understand that some time will pass before its location can be found and a strategy evolved to plug the leak – as we have seen. As a result, it is easy to understand that the LWC is actually a very likely Consequence.
In such circumstances, the cautious risk engineer would include design features that enable the amount of gas leaked from a rupture to be controlled by the inclusion of excess flow sensors or decreased pressure sensors (or both) and valves that can be operated to limit the loss of gas, by isolating the length of pipe that has the problem. Such ‘soft landing‘ techniques are very common in the petrochemical industry. Chapters 7, 9 and 11 include discussions on control measures suited to the Outcome pathways. See for example Table 7.2 and control measure AOC2 – Actively interrupt energy flow.
From a distance, it is very hard to understand why these control measures were not made use of in this case.
It really is little wonder that environmental and citizen action groups don’t have much confidence in the ability of business to manage significant risks.
I think engineers have to step up to this challenge and if they have, they need to ensure that their view is expressed in such articles as that published by Scientific American.