Contractors who undertake any type of work which involves digging or excavation of any sort must always take every precaution to avoid striking any type of buried services. The problem is that these can be located anywhere, even in places where your head might tell that you that they could not possibly exist, and striking them often causes serious injuries and is sometimes fatal.
There are approximately a dozen deaths in the UK every year as a direct result of cable strikes and other utility strikes, which should give pause for a moment's contemplation. Despite precautions taken by contractors who use the services of surveyors before commencing any sort of work, there are nonetheless around 60,000 cases of damaged utilities every year, which is something else to think about. If contractors are so careful, how is it that there are so many accidents?
One reason may be that a contractor contacts utility companies in the area and they supply STATS, or maps showing where their utilities run, and the contractor then relies on them. This can be fatal. STATS are not always correct or up to date. They should only EVER be used as a guide, never as gospel. They should simply be a starting point for further investigation.
Take a very simple example. A builder constructs a new housing estate next to a main road. The electricity company connects that estate to the grid, but for whatever reason does not update its' STATS. Along comes a contractor who needs to repair a water pipe running along underneath the pavement, and simply doesn't realise that there is now a live cable running underneath it to the housing estate.
This is why the use of the CAT and Genny to undertake a full survey is so critical in order to establish whether or not there are any underground services directly beneath or close to the proposed excavation. Surveyors also need to understand the limitations of the equipment, because they do have limitations. For instance, the CAT can only detect certain signals from metallic cables and may not be able to detect them at all if there is no power running through them, or if there is only a very low voltage. A typically quoted example is a street where a survey is undertaken when it is dark, and the street lights are on. Fine, the CAT should find them. However, if you return the next morning in daylight and undertake the same survey it almost certainly will not detect them.
That is why the Genny is needed to attach a signal (Genny is short for Signal Generator) to many underground services which the CAT can then pick up.
Here is another problem. Some of the older CATs and Gennys can only detect the position of an underground service, but not its' depth. Later models can detect the depth, and that might inspire a surveyor to give the all-clear when there is in fact a service running there.
Why? Because some of the equipment can only detect depth to a limited extent. This means that it may show all-clear when used at the surface because it can only detect depth to, say, one metre. So it simply doesn’t show a service that is at a depth of one and a half metres. If you need to dig down two metres you are going to be in big trouble, because you believe there is nothing there!
What you need to do, when carrying out any excavation and you have a clear reading, is to proceed cautiously and dig down about a foot. Then you undertake another survey with the CAT and Genny which may show you that there is indeed a service there, but the equipment couldn't detect it from ground level.
You can begin to see why undertaking excavation of any type can be so hazardous. This is why it is essential that all operatives engaged in undertaking surveys for buried services simply must take a recognised course from a company that specialises in the use of the CAT and Genny and is fully conversant with all the latest models. Possibly more important is the fact that a specialist in running these courses will also be able to demonstrate the limitations of the equipment, and so avoid a disaster because a user thought the area was clear.