PAS 128: what is it and what you need to know

What is PAS 128?

British Standards Institution (BSI) PAS 128 is the current specification for underground utility detection, verification and location. A collaboration between BSI and the Institution of Civil Engineers (ICE) resulted in the PAS 128 standard which requires accurate, quality information to be recorded to a consistent standard with regards to the location of underground utilities. This removes the element of uncertainty, interpretation and resultant variable risk when end users are referring to utility survey reports.

With more effective planning and consistent collection of associated data for underground utilities, it can be expected that construction works, ground work and utility based works will be carried out in a safer manner. The degree of confidence of each PAS 128 survey is clear, based on the category and level of survey carried out.

Why is PAS 128 needed?

Utility tracing or mapping should take place before any construction work commences, including ground investigation, boreholes and trial pits. These surveys also aid designers in the earlier stages of projects. By detecting utilities beneath the ground, accurate mapping minimises costly and potentially dangerous conflicts, delays and disruptions during construction works.

PAS 128 sets out the accuracy for capturing the data. By assuring quality and confidence in the data, it can aid the project planning and scoping process, as well as assisting in desktop utilities records search and verification.  PAS 128 assures measurable levels of quality for surveys from desk top studies to full verification on site.

Who uses PAS 128?

It is applicable to engineers, construction contractors, project managers and utility owners as well as surveyors, geophysicists and subsurface utility engineers, all of whom are responsible for recording and using information about underground utilities.

What are the different PAS 128 survey types and levels?

When specifying a PAS 128 compliant underground utility survey, there are different levels of detail that may be required. The selection criteria ensures the data collected meets the on-site requirements of the specific project. The PAS 128 survey types are:

• PAS 128 Survey Category Type D: Underground utilities are plotted based only on record data, otherwise known as desktop survey.
• PAS 128 Survey Category Type C: Underground utility are plotted based only on utility record data, but with on-site investigation to match physical indicators above ground with the records as a best fit.
• PAS 128 Survey Category Type B: Utilities are detected by geophysical methods, such as Ground Penetrative Radar (GPR) to get an exact horizontal position and vertical position i.e depth. Category B Surveys are carried out to one of four levels of accuracy with each requiring a different survey type.
• PAS 128 Survey Category Type A: Utilities are verified and positioned by eye, using physical identification, which may include visual inspection, vacuum excavation, or hand dug trial pitting.

Why are PAS 128 surveys beneficial?

Using standards allow organisations to be specific about the scope of the survey and to demonstrate the quality and best-practice methods used.  The standard also requires operators to be trained to Level 2 NVQ or equivalent and so provides improved quality and standardisation.

Underground Utility Detection Surveys completed to a PAS 128 standard are not compulsory. However, the benefits of minimising construction disruption, as well as having a greater level of confidence in utility tracing underground, a PAS 128 surveyor can provide a higher standard and a safer environment.

For more information on SOCOTEC’s Underground Utility Detection Surveys, completed to BSI PAS 128 specification, please contact us.