HSG47 is the guidebook produced by the Health & Safety Executive concerning the safe working practices that are needed when undertaking any form of excavation. The current edition is the third one and was updated in 2014.

The HSE has a Code of Practice which states that the aim of the Code is to improve the level of safety with which excavation work is carried out. In particular, the purpose is to avoid damage to underground services which will, in turn, minimise any danger to those carrying out such work. It “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.”

There are also guidelines as to the depth of different underground services, and there is a colour coding system as well. The minimum depths at which services should be laid are as follows, but it should be noted that services may well have been laid at a shallower depth. These are recommended minimum depths. The first set of figures for each service is for the depth under footpaths or verges, and the second set is for the depth under 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.

All of the depths are from the surface to the top of the service pipe or cable. All pipes, ducts, and cables should have a warning tape positioned directly above them. What is important to remember is that these guidelines apply to newly installed services and that older services may well not conform to them.

A Colour Coding System

There is also a national colour coding system which is similar to the US system and should be used to identify different services. This should be used to mark the line of a service by spraying paint on the ground after a thorough survey has been carried out. This system is based on convention and there is no written standard. However, if different colours are used by a contractor, it is important that all operatives working on the site should know what each colour means. The colour code is as follows:

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.

At Sygma Solutions, we provide an HSG47 course which goes into great detail concerning the location and identification of underground services using the CAT and Genny. It is vital that all operatives who are going to undertake a survey to locate and identify such services have as much knowledge as is possible so that work is carried out in a safe and secure manner. Our team has a combined experience of over 100 years in the location of services and the use of the tools to find them. We also have experience of working with manufacturers of such equipment, and in addition we service and maintain Mala Easy Locators which use ground penetrating radar to locate services.

Our HSG47 course is split into two sections, one of which is classroom training which can be at our offices, at a venue of your choice, or online. This is followed by training on site so that operatives can put into practice what they have learned in the classroom. In particular, it is vital to understand that the CAT and Genny do have certain limitations, and to understand why they could give a false reading under certain circumstances. All of this knowledge is taught by our expert trainers so that operatives can then carry out surveys with confidence.