The area classification of the pipeline is based upon population density. This is used to determine the Location Class (section 1.2.1b) of the pipeline and the basic Design Factor (section 1.2.1c).
The method to be employed in determining the location class is laid out in section 840.2 of ASME B31.8 - 1992 edition.
In general a zone 200m (220 yards) wide is considered either side of the route of the pipeline. The pipeline route is divided into sections of 1 mile so that the individual sections will include the maximum number of buildings for human occupancy. Each separate dwelling unit in a multiple dwelling unit building is to be counted as a separate building.
The location classes for Design and Construction according to ASME B31.8 are as follows:
Number of buildings intended for Human Occupancy
10 or fewer
more than 10 but fewer than 46
more than 46
more than 46 and including multistorey buildings and where there may be many other utilities
Note. Where a collection of buildings indicates that the location class is identified as class 2, 3 or 4 then that location class shall continue for 0.2 km from the last building (section 840.2 a 2 in ASME B31.8 - 1992 Edition).
In addition to the classification above, section 840.3 of ASME B31.8 -1992 indicates additional criteria to be applied for concentrations of people in location class 1 and 2 areas and the consequences of failure near a concentration of people such as found in a place of public assembly, eg a Mosque, school, hospital, hotel, holiday village etc. This means that all these places within location class 1 and 2 areas should be classified as location class 3. This should also apply to normally occupied buildings in location class 1 and 2 .
When the pipeline route is being classified for the purpose of determining the design factor for pipeline construction or afterwards as part of the pipeline surveillance activities all consideration must be given to the possibility of future development.
Whilst identifying Location Classes and recognising the requirement for pipelines to work at different stress levels in different location classes ASME B31.8 does not place any restriction on the proximity of a pipeline to a building or group of buildings. This can lead to buildings being built close to pipelines or pipelines being constructed close to buildings. Section 1.2.2 of this document provides advice on the proximity limits.