Colour is not confidence. A red electricity line plotted from a statutory return and a red electricity line traced by EML and supported by GPR should not carry the same weight in a clash detection. Quality levels exist so they do not.
QL-D means the segment is on the drawing because a record said so. That is useful. It is not a surveyed position. QL-C means someone saw supporting surface evidence — a cover, a marker, a scar — and the record became less lonely. QL-B means geophysics produced a horizontal and, where stated, vertical position within a described confidence. QL-A means the apparatus was exposed and measured.
Within Type B, PAS 128 uses B-levels to describe how complete the detection evidence is. A high B-level usually means a continuous trace supported by more than one method. A low B-level may mean the service was expected but not found, and is shown as an assumed route. If your drawing has no B-levels at all, ask why.
A single site can — and usually should — carry more than one quality level. The working area of a Leeds campus spine might be QL-B. The verge outside the hoarding might remain QL-D. Two crossings under a proposed pile cap might be upgraded to QL-A. That mix is cheaper than pretending the whole red line is equally true.
Clients sometimes ask for “QL-B everywhere” because it sounds decisive. On a reinforced Birmingham slab, that instruction can be physically impossible without processed radar and still leave gaps. A competent surveyor will say so. A less competent one will stamp B1 on every line and hope nobody reads the method statement.
The CICES types-and-quality-levels note is the document to attach to an internal briefing. Then read PAS 128 surveys for how we apply those labels, and trial hole verification for when a quality level is no longer enough.
Designers sometimes flatten quality levels in their own models “to keep the drawing clean”. That is how a QL-D gas record becomes a clash that everyone treats as surveyed. If you must simplify for a public-realm sketch, keep the PAS 128 file as the source and say which segments you simplified.
Insurers and principal contractors increasingly ask for the quality-level key, not for a statement that the site was “fully scanned”. A key that matches the visible drawing is also what a competent incident investigation will request. If the key and the lines disagree, the drawing is not finished.
Depths deserve the same honesty. A QL-B vertical figure is an interpretation. A QL-A level is a measurement. Printing both as the same text height on a sheet is how people excavate to a radar number as if it were an invert survey.
Teach the labels once, in a ten-minute site induction, and you will spend less time later explaining why a red line was not a promise. The specification is a language. Languages only work when more than the surveyor is fluent.
When two quality levels meet on one segment — a record that was later detected — the higher evidence should win, and the method statement should say that the upgrade happened. Silent upgrades are how people lose the audit trail.
Do not invent extra letters. If a supplier offers “QL-B+” as a house grade, ask them to map it back to the PAS. House grades are how drawings become incomparable between firms.
Print the key on every sheet, not only on the cover. Cabin walls display sheet 3. Sheet 3 should still explain itself.
If you are new to the labels, read this page once and then look at a real drawing. The second time the letters will mean evidence, not a grade. That is the whole point of QL-D to QL-A.