A post a couple of weeks ago on measurement length and “No Rupture” resulted in unexpected comment on how the measurement length is interpreted for determination of location classes. The problem arises because AS 2885.1-2007 somehow omits a clear definition of the area to be considered when you are deciding on location classification. I guess the intention was so clear to the committee that we failed to realise the oversight. Most people have managed to read the committee’s mind correctly but the recent comments revealed that others came to a different conclusion. After double checking with some other committee members and also the issue paper written early in the process of preparing the 2007 revision I can set the record straight …
The location class shall be determined by the land use within one measurement length either side of the pipeline.
(A secondary requirement is that a higher location class shall extend into a lower location class for one measurement length beyond the land use boundary. That is clearly spelled out in Clause 4.3.3(a) and was also subject to some debate, but I don’t want to dilute the point above by discussing it further here.)
The first thing I do when starting location classification is use either Google Earth or the project GIS to create a zone defined by lines parallel to the pipeline and one measurement length either side of it. Anything outside that zone is of not much interest, everything inside it is important.
Having said that, land uses close to the borderline can’t necessarily be ignored, depending on the circumstances. If the measurement length is 1000 m, a feature at 1001 m is not “safe”. On the other hand, a small cluster of houses at the very edge of the zone in an area that is otherwise R1 might not change the location class to R2 or higher, whereas the same cluster close to the pipeline might.
But I don’t want to create confusion with subtleties – the basic principle is to look at land use within one measurement length either side of the pipeline.