WAZIPOINT Engineering Science & Technology: Avoiding Danger at High Voltage Underground Power Cable Installation

Thursday, April 27, 2023

Avoiding Danger at High Voltage Underground Power Cable Installation

Avoiding Danger from Excavation and Cable Laying Works at High Voltage Underground Power Transmission Lines 

This article is aimed at all those involved in underground cables power transmission networks project commissioning, planning, managing, and carrying out work on fields or near underground other existing cables and utility services. It will also be of use to the owners, operators of such services, and contractors who execute the excavation and cabling works. It outlines the potential dangers of working near existing underground utility services and gives advice on how to reduce any direct risks to people’s and property’s safety, as well as the indirect risks arising through damage to services. This safety guidance will explain mainly three basic elements of a safe system of work during excavation:

1. Planning the work;
2. Locating and identifying buried services;
3. Safe excavation.

Where this Excavation and Cable Laying Safety Guidance will be applied?

This Cable Laying Safety Guidance is aimed at all of those involved in commissioning, planning, managing, and carrying out work on or near underground services, as well as the owners and operators of such services apply to situations where underground services may be found and disturbed, including:

i. Excavation on the street or footpath works;
ii. Excavation on road works;
iii. excavation, horizontal directional drilling (HDD), and piling;
iv. demolition, renovation of the existing structure, and site remediation;
v. site investigation route surveys;
vi. any other work that involves penetrating the ground at or below surface level.

Find out and plan to manage the dangers 

Negligence or carelessness may cause fatal damage or severe injury to underground services as well as a significant interruption and substantial damage to man or property; it can also delay the project and incur considerable costs.

Common Incidental points are as below:

i. Electricity cables
ii. Gas pipes
iii. Water pipes and sewers
iv. Other pipelines
v. Telecommunication cables

Electricity cables

Maximum injuries happen in excavation work from live electrical cables. Incidents may also arise from aged cables, connections, and terminations which have been damaged but left unreported and unrepaired. Explosive effects of arcing current, and by any associated fire or flames that may result when a live cable is penetrated by excavating tools sharp edge, a cable is crushed severely enough to cause internal contact between the conductors, or between the metallic sheathing and one or more conductors.

Gas pipes

Excavators or any excavating tools may damage gas pipelines.
There are mainly two types of gas pipe damage occurs:
i. damage that causes an immediate leak;
ii. damage that causes a leak sometime later.

Water pipes and sewers 

Water and sewer pipeline damage may not bring fatal or severe damage, but it happened a significant number at each site and causes delays in everyday progress. 

i. A jet of water from a main can be of sufficient pressure and intensity to injure a person. It may also contain stones or other hard objects ejected from the ground around the pipe. 

ii. Leaks of water from underground pipes can affect adjacent services and reduce support for other structures.

iii. Damage to mains pipes can result in flooding, leading to subsequent risks from drowning or the rapid collapse of support to the sides of an excavation; water can enter gas pipes if they are also damaged.

Other pipelines

The danger arising from damage to other pipelines depends on the nature of the conveyed fluid, it may be in some special compound area: 

i. flammable liquids and gases; 
ii. fluids at elevated pressure 
iii. toxic liquids and gases; 
iv. inert gases such as nitrogen and argon.

Telecommunication cables

Damage to telecommunication and fiber optic cable may be expensive to repair and disturbance some relying services.

So, working safely considering the planning of the work; detecting, identifying, and marking properly underground services; and safe excavation or digging practices.

Planning the work considering resources and information limitation

We may aspect to getting information from another utility department as below:

i. Obtain service drawings from utility companies and other organizations with relevant information about the site.

ii. Survey the site to identify the services and other underground structures. Record the location of any services.
iii. Review/assess the planned work to avoid disturbing services where possible.

iv. Allow sufficient time and provide sufficient resources to do the work safely.

v. Emergency work still requires planning and assessment of the risks arising from the work. 

Also, consider always not possible to get all information or correct information. So, you have to do the physical survey or open a significant number of test pits for each site. No alternative to taking a precautionary approach when breaking ground.

Limitation of plans

You may plan to collect information from a local utility company, but plans alone are insufficient to identify and locate the actual position and quantity of various services before starting work. They provide basic information on which to base a thorough site survey and opening test pits are required before work begins.

Plans can give an indication of the location, configuration, and number of underground services at a particular site and should help subsequent tracing by detecting devices or locators, but physically it may not match to information prior collected. However, they are not always drawn accurately to scale and, even if they claim to be, you should not rely on them to obtain quantities, distances, or depths.

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