Digging Foundations for a Garden Gym: Checking for Buried Services and Overhead Lines Before Work Starts

A garden gym needs a base, and a base usually means digging. So do cable trenches, fence posts and drainage. Buried gas pipes, electricity cables and water mains are often invisible and are not always where a homeowner expects them. This article summarises two Health and Safety Executive (HSE) publications: “Avoiding danger from underground services” (HSG47, third edition, 2014) and the leaflet “Avoiding concealed services and overhead power lines”. The HSE covers Great Britain. HSE guidance is aimed mainly at work activities and, as the publication itself notes, following it is not compulsory unless specifically stated, but its principles apply to anyone breaking ground for a project.

Why buried services are a serious hazard

HSG47 says damage to underground services can cause fatal or severe injury as well as disruption and environmental damage. It describes several hazards:

• Electricity cables: injuries are usually caused by the explosive effects of arcing current and any resulting fire when a live cable is penetrated by a sharp tool. Typically, injuries are severe, potentially fatal, burns to the hands, face and body, and electric shock is possible but less likely.
• Gas pipes: damage can cause leaks that lead to fire or explosion, either immediately or later. HSG47 says leaking liquefied petroleum gas (LPG) presents a greater risk than natural gas because it is heavier than air and does not disperse readily.
• Water pipes and sewers: a jet of water from a main can be forceful enough to injure a person, and can carry stones from the surrounding ground. Leaks can undermine support for other structures.
• Telecommunication cables: damage may be expensive and disruptive, but the risk of personal injury is normally very low.

Assume they are there

HSG47 applies to any work that involves penetrating the ground at or below surface level, including excavation and drilling. It states that underground services are widespread and should be assumed present unless shown otherwise. It also says a safe system of work has three elements: planning the work, detecting, identifying and marking services, and safe excavation.

Getting information before digging

The guidance says anyone planning work that may disturb underground services must contact the owners or operators for information about their location and status, and that there is often more than one owner. It lists who they may be:

• most electricity service cables belong to the regional distribution network operator, though some belong to other bodies;
• most gas pipes are operated by public gas transporters, with exceptions such as new developments served by independent gas transporters and properties fed from bulk-stored LPG, where pipes may belong to the property owner.

HSG47 notes that “one-call” services exist to simplify identifying who may have services in an area, and that some are free while others charge. It adds that plans alone are not enough. They are not always drawn accurately to scale, depths may have changed with re-grading, cables may have been moved without the owner’s knowledge, service connections are often not marked, and the absence of records should never be taken as proof that an area is free of services.

Detecting and marking

The HSE leaflet says to use cable avoidance tools and service plans, and to mark the route with paint or wooden pegs. HSG47 says trial holes should be used to positively identify a service and its depth, and that identified services should be marked with waterproof crayon, chalk or paint on paved surfaces or with wooden pegs in grass. Steel pins, spikes or long pegs, which could damage shallow services, should not be used.

Digging safely near a service

Both publications give distances and methods:

• the HSE leaflet says not to use mechanical excavators or power tools within 0.5 metres of the suspected route;
• HSG47 says that where practicable hand-held power tools should only be used 500 mm or more from the indicated line of a service buried in or below a hard surface, followed by careful hand digging to expose it;
• HSG47 recommends digging alongside a service rather than directly above it, and exposing it finally by horizontal digging, where force applied to hand tools can be controlled better;
• spades and shovels, preferably with curved edges, should be eased in with gentle foot pressure and not thrown or spiked into the ground;
• for gas, HSG47 says not to use mechanical excavators within 500 mm of a gas pipe, and that polyethylene (PE) gas pipes and service connections, which will not be marked on plans, should be located by hand digging first.

If a gas leak is suspected, HSG47 says not to attempt repairs.

Drilling and overhead lines

The HSE leaflet advises that if the location of concealed cables is unknown, the electricity supply should be turned off before drilling into walls or floors. For overhead power lines it says plant should not approach closer than 15 metres, plus the length of the jib, where the line is suspended from steel towers, or 9 metres plus jib length where it is on wooden poles, and that the electricity supplier can be asked to shroud, make dead or reroute lines. These distances relate to plant such as excavators and cranes, so a hired mini-digger or a delivery vehicle with a lifting arm should be kept well clear.

The bottom line

Before breaking ground for a garden gym base, trench or fence post, HSE guidance says to assume buried services exist, gather records from the owners, treat plans as a starting point only, detect and mark routes, and dig by hand near them. Mechanical tools should stay at least 0.5 metres from a suspected route, and overhead lines call for large clearances. Related guidance on this site covers permitted development for an outdoor gym and hiring a builder in England.

Sources

• Health and Safety Executive, “Avoiding danger from underground services” (HSG47, third edition, 2014)
• Health and Safety Executive, “Avoiding danger from underground services” (HSG47, full text)
• Health and Safety Executive, “Avoiding concealed services and overhead power lines: What you need to know as a busy builder” (CIS65)