When undertaking any form of excavation, it is necessary to consider whether there may be underground services on the site which is to be excavated or close by. This is for two major reasons, one of which – and the most important – is the possibility of danger to life and limb. The other consideration is of damage to the utility which can cause major problems and also has financial implications which could be considerable. If an underground service is damaged it means that at the very least the contractor will have to stop work on the site while the utility concerned sends out a team to repair it. The main contractor may also impose penalties on the sub-contractor.

In addition, there could be claims for compensation from other people affected by the stoppage. For instance, if the power is shut off it could result in a local factory losing a day's production which could involve large amounts of money. If a worker is injured or even killed – and that does happen occasionally – the claims for damages from the worker or his dependents could run into the hundreds of thousands of pounds.

Another collateral is the damage to the reputation of the sub-contractor concerned which could result in the loss of other contracts. There could also be environmental damage of any description. For all these reasons, extreme caution must be used when carrying out any sort of excavation work, and a thorough survey using every available method must be carried out before a spade is inserted into the ground.

The advice of the HSE is that underground services are widespread and that you should assume that they are present unless you have been shown otherwise. Unfortunately, that advice could lead you to think that if a utility has provided you with plans showing the location of a service then you can simply follow the plan. That is not necessarily the case, because the plans may not always be accurate, nor are they always complete. You should only rely on plans as a guide rather than gospel.

The dangers of underground services strikes cannot be over-stated. The danger of striking an electricity cable and penetrating it with the point of a tool can cause serious injury from arcing current and from any associated flame or fire that may result. Similar damage may occur if a cable is crushed causing internal contact between the conductors or between a conductor and metallic sheathing. Injuries are usually severe, including burns to hands, face, and body, and may be fatal. There could also be other services nearby such as plastic gas pipes, and this could result in explosions and further damage from fire.

Damage to gas pipes directly can also lead to fire and explosion. There can be damage which causes an immediate leak or there could be damage which causes a leak some time later. The damage could be caused while the excavation is taking place, or it could be caused by poor reinstatement leaving a gas pipe poorly supported. LPG is heavier than air, so if a pipe that is carrying it is damaged it can travel long distances underground and can build up in a basement or cellar, or underground car park.

Damage to water pipes is not so likely to cause injury but can do so if a jet of water under pressure spouts out of the ground. It could also carry stones within it from the surrounding earth. In addition, it could lead to flooding. Most sewer pipes are not under pressure, but nonetheless striking them can cause damage to health by exposure to raw sewage, and environmental damage also.

The two tools used for locating underground services are the CAT and the Genny. There are companies that specialise in training surveyors in the use of this equipment, and also in their limitations. Training may be carried out to EUSR standards if the company is recognised by the EUSR and authorised to carry out EUSR CAT and Genny training and EUSR cable avoidance training. Successful completion of such a training course and passing an exam enables the award of an EUSR card which is similar to the CSCS card and will allow the holder to undertake work on sites that require such certification, such as HS2 and many main contractors.