When carrying out any sort of excavation work it is vital to do everything possible to avoid striking underground utilities. They can be absolutely anywhere. Some places are obvious, while others are not. The best thing to do is to follow the advice given in HSG47 by the Health & Safety Executive, and that is unless you know otherwise, you should assume that they are present where you are going to dig. The emphasis on the word “know” is ours.

This is for a number of very good reasons. The first and most obvious thing to do when planning any sort of excavation work is to do just that – plan. That includes obtaining plans of underground services from any or all utilities that may be in the area. However, these plans, also known as STATS, must never be entirely relied upon. There can be errors.

Unfortunately, there is no national set of instructions on how to record STATS, and different utilities may record them in a different fashion. The same utility, for example, electricity, may record them differently in one area from another. They can also be recorded in different formats. Things may not be recorded at all because a contractor cut corners. A utility might be supposed to be located at a certain depth but is in fact not as deep as it should be because, again, a contractor cut corners. The utility may have been in the place that the STATS show originally but could have been moved and the move subsequently not recorded, so the plan is just plain wrong. There may be no STATS at all for a particular service in a certain area. You can begin to see just why it can be fatal – literally – to rely on STATS alone. They should only ever be used as a guide, and even then, treated with a good dose of scepticism.

These are just some of the things that we cover with our underground service location training at Sygma Solutions. Between us, we have over 100 years of combined experience in cable location and utility detection and we are dedicated to passing on our knowledge so that cable strikes are avoided, and workers kept safe.

In order to help identify the different types of utilities, in the UK we use a colour coding system which is similar to that used in the US. Unfortunately, once again there is no set of written rules and the colours are marked by convention rather than anything else.

The colour coding system 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.

A certain type of spray paint, which is often fluorescent, is used to mark the different utilities. Flags may also be used and may have the logo of the utility or company responsible. There can be problems with colour coding because while this applies to recently installed services, older ones may not either be marked or if they are, not in the same colours. Furthermore, the marker may have aged and not be visible or may look different in poor light such as when working after dark in the winter.

There are also minimum depths which apply, and our thanks are due to Street Works UK Guidelines for the following chart. There are two sets of figures, the first of which is for underneath pavements and footpaths, and the second 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

As you can see, there is a lot to learn, and we cover all this and much, much, more in our training at Sygma Solutions.