What are Underground Utility Colour Codes?

Underground utility colour codes are used to differentiate and identify underground utilities to protect it from potential damage during excavation.

There are different types of utilities and in order to tell them apart, either coloured lines or flags, or sometimes both are used. These lines/flags help mark the location and indicate the type of utility that is buried underground.

Utility systems are buried underground due to the nature of their function, as well as convenience and aesthetics.

Excavators are required to check and locate these lines before any digging takes place. Before any excavation work can begin, they are liable to contact the concerned companies and organisations to notify them about the proposed excavation activity so that the existing underground utilities can be determined and marked.


How are Underground Utility Colour Codes mapped?

Different section and location methods are used due to the fact that utilities are made of different types of materials.

For metal pipes and similar cables, electromagnetic equipment with a transmitter and receiver is used. For plastics and concrete, radio location and ground penetrating radars are used.

Utilities such as petroleum products are permanently marked using posts and bollards due to the nature of their content. There are maps to locate these utilities but certain equipment is required in order to have a precise and accurate location.

A specific type of spray paint, which is often a fluorescent colour, is used to mark lines. For flags, a type of logo representing the company or municipal utility is used to identify the ownership of the lines.

Flags are also used as a sort of advertisement by companies installing lines for irrigation purposes for lawns and garden. In which case, the head of sprinklers are usually marked so that landscapers will leave the head open to avoid damage from tractors, construction equipment used for digging holes and fenceposts.

The United Kingdom uses a colour code similar to the US for marking underground utilities like water, gas, electric, telephone and cables. The system is based on convention with no written standard. Contractors will paint different colours onto the pavement to mark areas with underground utilities by using the colour code.

The National Colour Coding System for underground utilities are:

Underground Utility Colour Codes - Diagram

Red – Electric power lines, conduit and cables.

Orange – Telecommunication, alarm or signal lines.

Yellow – Gas, oil, steam, petroleum, or other flammable material.

Green – Sewage and drain lines.

Blue – Drinking water.

Purple – Reclaimed water, irrigation, and slurry lines.

Pink – Temporary survey markings, unknown/unidentified facilities.

White – Proposed excavation limits or route.


Why are Underground Utility Colour Codes important?

The Code of Practise introduced by the Health and Safety Authority states that:

“The aim of the Code of Practice is to improve the level of safety with which excavation work is carried out. In particular, it aims to reduce the incidence of damage to underground services and in doing so to minimise risk to personnel who are involved in this work. The COP is intended to provide practical guidance to utility/service providers, clients, designers, planners, project supervisors (both design process and construction stage), contractors, safety representatives and any personnel who are involved in work where there is a risk from underground services.”


How important is the positioning depths of utilities?

Due to the nature of utilities and the potential danger that could come with damaging them, each type of utility has a minimum positioning depth in order to reduce the risk of damage.

According to Streetworks UK Guidelines on the Positioning and Colour Coding of Underground Utilities’ Apparatus, the following is the recommended minimum depths that these utilities need to be buried underground under the likes of footways and carriageways. The first set of numbers is for underneath footways/verges and the second set is for underneath carriageways.

Electricity HV (High Voltage) – 450-1200mm / 750-1200mm

Electricity LV (Low Voltage) – 450mm / 600mm

Gas – 600m (footway), 750mm (verge) / 750mm

Water Non Potable & Grey Water – 600-750mm / 600-750mm

Water – Firefighting – 600-750mm / 600-750mm

Oil / Fuel Pipelines – 900mm / 900mm (All work within 3 metres of oil fuel pipelines must receive prior approval)

Sewerage – Variable / Variable

Telecomms – 250-350mm / 450-600mm

Water – 750mm / 750mm minimum

Water Pipes for Special Purposes (e.g. contaminated ground) – 750mm / 750mm minimum

Screen Shot 2019-07-25 at 10.24.50

(Diagram taken from the Streetworks UK Guidelines)

All of these depths are measured from the surface level to the crown of the apparatus, and they also note that all pipes, ducts and cables should have warning tape positioned directly above it.

It’s important to remember that these guidelines for positioning depths apply to newly installed utility apparatus, and older services or pipelines may not conform to these guidelines. This also applies to the utility colour code, as markers may not be visible due to age or might look different under poor lighting.

When working around older utilities, it’s even more important to ensure that best practises are being followed to reduce any risk of damage to utilities or workers.


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