(Been busy lately – rather shocked that it’s nearly four weeks since my last post.)
I had a question the other day of a type that comes up from time to time: What location classification do you assign to pipeline facilities? It’s a question based on a misunderstanding of location classification principles, but an easily forgiven misunderstanding because AS 2885 is silent on the matter.
The basics of location classification were outlined here, where I said “The primary purpose of the AS 2885 location classes is to draw attention to the greater risk level in more populated areas so that the pipeline can be designed (or managed) appropriately.” In higher location classes there tend to be both more threats to the pipeline (because of the higher level of human activity) and more serious consequences of pipeline failure (because there are more people around to be hurt).
How do you apply that principle to a pipeline facility? The short answer, in my view, is that you don’t. Most pipeline facilities are neither an origin of threats to the pipeline nor part of the consequences of a pipeline failure. Rather, they are part of the source of the hazard (ie. the pipeline). So my starting point in responding to the question of location classification for pipeline facilities is that is often a meaningless question.
Having said that, there are always exceptions. A pipeline site that is normally manned by a few people might be treated in the same way as an isolated house in a rural area because the population density is similar. That doesn’t need a change in location class but might require some additional physical protection of the nearby pipeline (eg. extra wall thickness and depth of cover, which is common practice anyway).
Another argument that might be applied is where the facility is a large compressor station complex. If a pipeline failure at some remote location causes serious supply disruption for a few days pending repair, that’s bad. If a pipeline failure immediately adjacent to a critical compressor station disables the station and cuts off supply to a city for months until the station can be reconstructed, that’s extra bad. I could be persuaded that in this situation the compressor station vicinity should be classified as Heavy Industrial (HI) on the basis that a pipeline failure can have serious flow-on effects (or escalation, using the terminology from AS 2885).
So far this discussion has been about sites that are dedicated to the pipeline. The situation might be different if the facility is, say, a gas processing plant operated by another party, or a power station to which the pipeline is delivering gas, or a refinery to which the pipeline is delivering oil. Those sites are different partly because they are outside the control of the pipeline operator (usually), and partly because a pipeline failure may result in escalation similar to the compressor station example above.
A final comment: No pipeline facility, and no adjacent plant such as a gas processing site, power station or refinery, should give rise to the Industrial (I) location class. As discussed in this post the Industrial location class is for light industry set in a typical urban streetscape, usually with a lot of people around. It has essentially the same population density and level of public access as T1 (Suburban) except the buildings are industrial/commercial/retail rather than residences. It would clearly be wrong to assign this classification to the surroundings of a compressor station, gas plant, power station or refinery unless it is one of the few older facilities that really are located in a heavily built-up urban area (and I can think of just one of those).
The location classification system has its limits. With only four primarily location classes and five secondary classes there will be situations that don’t fit nearly into any of them. As I’ve said repeatedly, the point is to highlight features of the pipeline surroundings that can affect the types of threat and the consequences of failure. If you focus on those things you will get the design right no matter what location classification is assigned.