THE BSI'S PAS 128.

What is PAS 128? PAS 128 stands for Publicly Available Specification 128, a BSI specification used in the United Kingdom that provides guidelines for locating underground utilities. It is often referred to as a PAS 128 Utility Survey. It offers a framework for managing utility infrastructure during excavation or construction projects. The specification categorizes the quality of location information about underground utilities into four defined levels (PAS 128 Quality Levels) ranging from D (Desktop) to A (Verification). These levels help ensure safety and reduce the risk of damaging underground utilities during construction or excavation work.

Here at Plot. Surveys Ltd, we are able to provide BSI's PAS 128 compliant utility surveys. This specification is a great tool for giving further insight and guidance to clients on the accuracy of detected buried services on their sites.

PAS 128 Quality Levels:

Quality Level - A (Verified)

Horizontal and vertical location of the top, bottom or

centreline of the utility (to be indicated on drawings).

Visually verified position in a manhole chamber or trial hole for example.

Quality Level - B1 and B1P

Horizontal and vertical location of the utility detected by

one of the geophysical techniques used (EML or GPR)

Symmetrical electromagnetic field achieved resulting in peak and null

measurements within B1 tolerance and/or present in GPR

data where both depth estimates and horizontal location

can be confidently established to the required accuracies.

Quality Level - B2 and B2P

Horizontal and vertical location of the utility detected by

one of the geophysical techniques used (EML or GPR)

Symmetrical field achieved resulting in peak and null

measurements within B2 tolerance and/or present in GPR

data where both depth estimates and horizontal location

can be confidently established to the required accuracies.

Quality Level - B3 and B3P

Horizontal location only of the utility detected by one of

the geophysical techniques used.

EML field unable to estimate depth and horizontal

accuracies within B2 tolerances with confidence.

Features present within the GPR data that indicate the

presence of a utility but do not directly correlate to its

position (e.g. trench sides or fill detected by GPR without

positive identification of utility).

Quality Level - B4 and B4P

A utility segment which is suspected to exist (either on

QL-D or QL-C records) but has not been detected and is

 therefore shown as an assumed route.

QL-C

A segment of utility whose location is demonstrated

by visual reference to street furniture, topographical

features or evidence of previous street works

(reinstatement scar).

QL-D

Copy of utility asset record only.

(Desktop search)