Cable Strikes | Damage to Underground Service

Published 18 May 2021

USAG

Cable Strikes

Utility Strike Avoidance Group

USAG have published a range of documents to assist industry understanding of the root cause and contributory factors behind specific incidents. The aim is to improve industry standards and reduce the number of cable strikes.

Cable damage is often caused by excavating machines – hand held tools such as pneumatic drills, crowbars, pins, picks and forks also expose workers to potential sources of danger when digging around underground cables.

The next in the series is a safety alert thanks to Highway England regarding damage to cable ducting and power cables during trial hole investigation works as part of London Power Tunnels project.


Incident Overview

Date of incident: 3rd June 2020
Time: 16:30
Location/Site: Hurst Site
Principal/Contractor: Hochtief Murphy Joint Venture

Damage to Underground Service

Damage to underground cables


What happened?

The Principal Contractor was undertaking trial hole investigation works as part of London Power Tunnels project to establish positions of existing services to allow a road widening to be installed. This activity was planned, had agreed RAMS and was being performed in accordance with HSG47 including the use of a Vacuum Excavator.

A Cat and Genny survey was performed prior to breaking ground with re-scanning every 150mm as the work progressed.

During these Vac Ex works a concrete block was uncovered and needed to be removed. This was discussed on site between ET operations, Capital Delivery and the Principal Contractor on 2nd June during a site walkover.

When lifting the concrete block, the watcher saw a clay duct stuck to the concrete, so they stopped the activity. The clay duct was embedded into the concrete. As the block was lifted the clay duct shattered, revealing the duct and its contents (5 cables).

To make the area safe the concrete block needed to continue to be moved. Once the block was safely removed it could be seen that there was damage to one of the cables (the outer sheath of a 15mm cable). The approximate position of the concrete block is shown by the red outline on the picture to the right. Immediate actions taken/Initial learning All excavation works where stopped immediately.

All relevant parties informed within timescales Drawings and CAT+Genny surveys are not a guarantee that all services have been identified. Additional actions are required to prove an area is sterile of buried services (e.g. perimeter slit trench using safe digging methods). Investigation underway to understand learning.

Categorisation of the incident: Medium


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