Doing any kind of work which involves digging or even breaking the surface of the ground carries with it risk. Underground services can be absolutely anywhere, and they include electricity cables, water pipes, gas pipes, telecoms, sewers, and other possibilities.
The Health and Safety Executive provides a lot of guidance for contractors who need to undertake any sort of excavation work – which is quite a large number of them – and one of the pieces of advice it gives is "Underground services are widespread. Assume they are present unless you have been shown otherwise."
Even that is probably insufficient because you may have seen STATS – maps and data from utility companies in the area – but they are not always accurate! In other cases, although there are underground services present, there are no STATS. It would be better to work on the basis "Assume they are present". Full stop.
That means that before you so much as put a shovel or spade into the ground, you need to undertake a survey in order to see what may be present. Quite obviously, some sites are going to have underground services present, such as residential areas, high streets, roads with streetlamps, and so on. They will have electricity cables, water pipes, telecoms, and sewers, as a minimum but may well have gas pipes, inert gases such as argon and nitrogen, toxic liquids, flammable liquids, fluids under pressure – oh yes, there is a lot going on underground that we really never think about.
Of course, if you have to carry out any excavation, you should obviously contact the local utilities and arrange to see any STATS that they have. However, what you should not do is to take them as gospel. They might be very accurate. Then again, they might not.
The HSE says that a safe system of work has three basic elements. They are planning the work; detecting, identifying, and marking underground services; and safe excavation and safe digging practices. These three elements complement each other, and all are essential when working near underground services.
Even emergency work requires planning and assessment of any risks arising from the work. For instance, suppose a water pipe has broken and an area is being flooded: you need to excavate in order to mend the pipe. However, there could well be electricity cables, gas pipes, and so on, running alongside or under or above the damaged water pipe.
All of this is why it is essential to undertake a survey of the area using the appropriate tools – largely the CAT and Genny. The CAT (Cable Avoidance Tool) on its’ own can only detect certain services and certainly not plastic pipes. This is why it should always be used in conjunction with the Genny which can attach to an underground service pipe or cable and send a signal along it which can then be detected by the CAT.
The CAT and Genny have a number of different modes in which they can be used, and they also have certain limitations. Anyone who is to undertake a survey searching for underground services should first take a CAT course which will cover the use of the tool and also cover its’ limitations. A CAT training course should also go into depth about the use of the CAT and Genny together, because even when combined there may be certain limitations, and the last thing that you need is to produce a result which tells you that there are no services in the area in which you need to dig, only to find out that the information was wrong.
Unfortunately, this happens all the time. One estimate says that in any year there are around 4 million excavations that take place. Whether this is accurate may be open to dispute, but what is not open to dispute is the fact that there are around 60,000 cable or other service strikes every year. A number of these result in serious injury to operatives, and there are around a dozen fatalities every year.
This is despite the fact that responsible contractors undertake a survey before commencing works. It follows that anyone who is going to undertake such surveys needs to first attend a training course which covers the use of the equipment in great detail.