Planning A Safe Work Environment – Underground Services Safety
Duties as a client
Clients have a duty to make reasonable inquiries about underground services and pass relevant information to the designer(s) and contractor(s). Your own files and other records may contain information on underground services.
If they do, remember that it may have been obtained for previous work and may be out of date. The most up-to-date information should be included in the tender information.
A client who is unable or unwilling to obtain this information must allow the contractor sufficient time and resource to do so instead. Clients need to consider how contractors have addressed the risks from underground services.
Duties as a designer
Designers have a duty to reduce or ‘design out’ the risks arising from damage to underground services. Having reduced the risks to a level as low as reasonably practicable by design, information should be provided to those doing the work about the risks that remain.
In most cases, the best way of informing contractors and individuals doing the work is by providing this on working drawings. You will need to know if there are underground services present so that you can amend the design to avoid them where possible.
For building work, re-siting the services away from the work is often a reasonably practicable means of avoiding the risk. Ask the service owner/operator to do this and include adequate notice.
Other options to re-siting the services may include:
- repositioning or redesigning structures or parts of structures to ensure that services are avoided during the work.
- arranging for the supply to be disconnected during the work; or, if none of these are possible;
- choosing methods to avoid the services; for example, by using ground beams to bridge or span the services.
For electricity cables more than other services, there may be a need to make them dead for the work to proceed safely. Contact electricity companies as early as possible to allow them to isolate supplies. Plan project schedules to allow sufficient time for this to happen.
If the cable cannot be made dead, an alternative safe way of doing the work will be required. Permanent structures such as buildings should generally not be built over services, nor should services be encased in concrete as this may introduce additional risks to construction workers and can prevent future access to the services.
If it is not possible to avoid building structures over any service, make arrangements with the utility to relocate the services in a duct or something similar.
Consider the location of underground gas pipelines when planning building, excavation, landfill or other such work. Such activities may either cause damage to the pipelines or deny access to them for maintenance purposes. Make suitable arrangements for future access and maintenance before undertaking the work.
Consider ancillary work, including the erection of perimeter fencing and walling, or the position of temporary and permanent roadways onto the site that may affect underground services at the site perimeter. Early identification and planning are essential if you are to control risks during the entire construction phase of the project, including enabling works.
Installing new services near existing services
New underground services often have to be laid in ground which contains existing services. Where it is reasonably practicable to do so, the designer planning the new installation should aim to site it so that it is separated from all existing underground services by the distances specified by the Authority Having Jurisdiction or AHJ.
It is important to have information about existing services to help select a route for the new service that avoids them. The risk of contact with existing services can be reduced by choosing a route with a low density of underground services. For example, a cable television duct might be routed at the side of a road if there is a reduced cable density there.
Designers of pipelines should also be aware of the guidelines which advises that the parallel running of similar pipelines in the street should be avoided. Liaison with the owners of services is important as they are in a position to provide information to the designers to enable them to make such decisions.
Where you cannot achieve the recommended separation, there should be as great a separation as is reasonably practicable. Where the installation of a service would obstruct access to an existing service you should use all reasonably practicable means to avoid this.
In particular, avoid the practice of laying multiple ducts directly above other services. This may require diversion of services or the installation of accessible shared service ducts or chambers.
If the utility or its contractors laying the new service have had to reduce the separation, they should inform the owner/operator whose service has been affected so that they can then amend their records for future reference.
Case study
A self-employed sub-contractor was burnt when he struck a 415 V electrical cable with an electrical breaker he was using to break up some concrete. The client had chosen to build over the cable rather than have it diverted.
The cable had been protected by a conduit and its location was known. The client did not tell the contractor of its location before starting work and the contractor did not ask. The cable was diverted following the incident.
Some specific situations: New housing developments
Underground services within the confines of partly completed housing developments are especially prone to damage from ongoing construction work. Each utility company should keep to its agreed position. A common trench may help to control the position and separation of underground services.
Special arrangements may be necessary to restrict vehicle and mobile plant crossings to locations where temporary protection for the services has been provided.
Where new services such as electrical or gas supplies are being installed, it may be possible to reduce risks by not installing or commissioning them until other groundworks and work on the installation have been completed.
