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Cable Strikes | Damage to Underground Service
May 18th, 2021
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 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
Protecting Cables Against Strikes & Restoring Power Post-Strike
Thorne & Derrick have been distributors for 3M Electrical since 1985 and can provide a range of reliable and easy to install Cable Repair Products – this includes Scotch Tapes, Scotchcast Joints and Cold Shrink Tubes to provide effective re-instatement of cable sheath jackets on all types of LV MV HV cables in onshore and offshore locations with safe or hazardous area workplace classifications.
Cable Repair Products
Our range of cable protection covers manufactured by Centriforce provide underground utility protection of LV MV HV cables including Tapetile (11kV) and Stokbord (33kV 66kV 132kV) – contact us to discuss Cable Damage Prevention Products including Dectamesh, the underground detectable warning tape for alerting excavators of the presence of buried cables and to prevent potentially lethal accidents during excavation.
Stokbord
Tapetile
Cable Strikes | Combined Gas and Electric Strike and Ignition
May 18th, 2021
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 a strike on both Electric & Gas service connections to a property.
Incident Overview
Gas Pipe & Electric Cable Strike
What Happened?
Executive Summary – On Friday the 29th November at 14:30 CityFibre were informed of an incident in an FTTH City.
CityFibre’s Principal Contractor (PC) reported a combined gas and electric strike, resulting in ignition of the gas. SGN (Gas Network) and the emergency services were called to support in the incident. SGN and PC worked to make the area safe, no injuries were reported and the road was closed as a precaution whilst the repair was made.
The cables were lowered, trench backfilled and area made safe with full reinstatement undertaken the following morning.
The strike was on both Electric – 35mm & Gas – 25mm service connections to a property. The services had been laid in a combined utilities trench. There were no safety indicative markers such as tiles or tape present in the trench, nor was there any distinct separation or sand split between the two utilities.
Utilities were buried significantly shallower than specified with by NJUG (industry guidelines). The fire was extinguished by 17:00, with PC supporting SGN engineers by hand digging to expose the damaged plant and electricity cables. By 19:00 the electric supply was restored.
A temporary reinstatement was made of the excavation and the PC returned in the morning to permanently reinstate the works.
Key Learning
- Ensure all teams are briefed on the STREET WORKS UK GUIDANCE ON THE POSITIONING AND COLOUR CODING OF UNDERGROUND UTILITIES’ APPARATUS
- Ensure that Safe Dig Techniques are followed as per HSG47
- Ensure service drawings are in date and fully reviewed prior to any excavation work
- Use the CAT & Genny together (in avoidance mode). We recommend the use of the ECAT4+ and version 4 Genny so that Survey results can be recorded electronically. This will aid the identification of correct usage and level of usage. All operators of the equipment must be trained and competent to use.
- Safe systems of work such as risk assessments and method statements are in place and understood.
- All strikes must be reported to [email protected] as detailed in the contractors contract and/or construction phase plan.
Protecting Cables Against Strikes & Restoring Power Post-Strike
Thorne & Derrick have been distributors for 3M Electrical since 1985 and can provide a range of reliable and easy to install Cable Repair Products – this includes Scotch Tapes, Scotchcast Joints and Cold Shrink Tubes to provide effective re-instatement of cable sheath jackets on all types of LV MV HV cables in onshore and offshore locations with safe or hazardous area workplace classifications.
Cable Repair Products
Our range of cable protection covers manufactured by Centriforce provide underground utility protection of LV MV HV cables including Tapetile (11kV) and Stokbord (33kV 66kV 132kV) – contact us to discuss Cable Damage Prevention Products including Dectamesh, the underground detectable warning tape for alerting excavators of the presence of buried cables and to prevent potentially lethal accidents during excavation.
Stokbord
Tapetile
Cable Strikes | Ingrebourne Valley – 415V Cable Strike
May 18th, 2021
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.
Cable Hangers | Cable Ducting | Cable Protection | Electrical Safety Equipment
Incident Overview
What Happened?
On the 2nd July, at approximately 15:35, a service strike occurred when an excavator tracked over an above ground 415V armoured cable. This cable was located in the vegetation clearance area of the satellite compound in Ingrebourne Valley. The excavator (with a grab attachment) was completing vegetation clearance works for site compound set up.
The service strike caused immediate loss of power to the neighbouring site welfare cabins of Brown and Mason. Following the strike the excavator operator stayed in the cab and called for assistance. Brown and Mason representative and their electrician were called to the scene and confirmed power had been lost and the area made safe. The excavator driver was then able to track back to safety and stand down.
The power was supplied by a generator situated in the work area of Package B. Perfect Circle and Socotec Site Management believed the area was free from services. They had received a guidance certification from the site owners which was misunderstood and heavily relied on. The certificate also failed to mention the power generator.
Immediate Causes
Failure to follow PAS 128 correctly, before any works commenced. They did not look at their surroundings and investigate any furniture which could have utility supplies, in this case the generator and cabins.
Had this been undertaken the direction of the over ground cable could have been identified, prompting further careful investigation prior to the works being undertaken.
Ingrebourne Valley 415V Cable Strike
Prior to vegetation clearance work in the vicinity of the generator, no communication took place with site neighbours Brown and Mason to address cable management/direction.
CAT and Genny scanning from the live generator cables did not take place, which would aid the clarification of the cable’s direction.
Lessons Learnt
Too much reliance was placed on service plans and client certification of services. These documents must be treated as guidance only. All services must be identified and traced on all packages.
Appropriate site planning would have identified the generator and cables as a hazard for the works. Works should not have commenced in the area of the generator until cable direction and status (live / terminated) was clarified.
There was a failure to adapt and change methodology for site restrictions caused by the dense vegetation. Where site restrictions affect prescribed and agreed methodology of works, works must stop, be reassessed, re-briefed and signed by those completing the tasks.
Perfect Circle Site Management failed to enforce PAS128 / CAT & Genny usage on site by subcontractors. All services need to be traced out, if vegetation prevents the use of CAT & Genny, stop works and reassess the methodology of works. Reduce vegetation following a safe system of work to aid access and identify services.
PAS 128
PAS defines a hierarchy of detection methods to be used to detect underground utilities:
- Survey type D shall use desktop search techniques to identify existing utility data within the survey area.
- Survey type C shall comprise a site reconnaissance to identify physical features that support the existence of utilities within the survey area.
- Survey type B shall use geophysical techniques to detect and identify utilities within the survey area.
- Survey type A shall comprise exposing the target utility(ies) within the survey area to confirm and record the location and other attribute data following safe digging practises.
Protecting Cables Against Strikes & Restoring Power Post-Strike
Thorne & Derrick have been distributors for 3M Electrical since 1985 and can provide a range of reliable and easy to install Cable Repair Products – this includes Scotch Tapes, Scotchcast Joints and Cold Shrink Tubes to provide effective re-instatement of cable sheath jackets on all types of LV MV HV cables in onshore and offshore locations with safe or hazardous area workplace classifications.
Cable Repair Products
Our range of cable protection covers manufactured by Centriforce provide underground utility protection of LV MV HV cables including Tapetile (11kV) and Stokbord (33kV 66kV 132kV) – contact us to discuss Cable Damage Prevention Products including Dectamesh, the underground detectable warning tape for alerting excavators of the presence of buried cables and to prevent potentially lethal accidents during excavation.
Stokbord
Tapetile
Cable Strikes | 132kV Cable Strike at Sellafield
May 18th, 2021
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.
Cable Hangers | Cable Ducting | Cable Protection | Electrical Safety Equipment
Incident Overview
CDM construction site at Fellside
Summary
The incident happened at the Fellside CDM area; part of a project to build new fuel storage tanks for the New Steam Generation Plant, NSGP. The piling work was ongoing around a live underground 132kV cable, during which an auger struck the cable.
Pile 46 formed through 2 phases of cable
Consequences
- Banksman was put at risk of injury by electrocution
- CHP lost power supply to Gas Turbines 1 and 2 resulting in loss of significant steam raising capability and reducing the steam resilience to site
- Large voltage dip on Sellafield site leading to plant trips and disruption on the site
- The Project was delayed several weeks with additional costs
- Reputational damage to all parties
Direct Cause
Auger penetrated the 132kV cables (HTF1201)
– This cable provides power to the CHP GTs 1 and 2
– Also exports excess power generated by the CHP plant to the National Grid
Root Causes/Contributory Factors
Failure to accurately identify the route of the cable and manage its location.
| Isolation would take 9 months | Confirmation Bias |
| Failure to isolate the cable | Risk Perception |
| Cable not fully exposed as a result of failure to isolate | Risk Perception |
| Cable was in a straight line | Confirmation Bias |
| Misconception of the purpose of the concrete slab | Risk Perception & Confirmation Bias |
View along centre line of excavated slab
Slab position markings in relation to cable
Root Causes/Contributory Factors
Failure to apply adequate document control procedures resulting in the use of a superseded design drawing.
| Document control system limited access to the drawings Not available to the Engineer on the ground |
Error Tap |
| Individuals failed to challenge the different versions of the drawings | Human Performance |
| Lack of escalation when challenged | Human Performance |
Use of Superseded Drawing (C06, not C07)
The centreline of the concrete slab was not laid over the centreline of the tiles or the cable. The pile was sunk as per version C06 of the drawing, rather than the current C07
Learning from this Event
- A lack of independent challenge to assumptions played an important part in influencing the course of events.
- It can be easy to lose sight of how our decisions can inadvertently influence safety.
- How could your work influence safety?
- What techniques and methods would help reduce this influence on safety?
Key Recommendations
The SL process for Excavations amended to a mandatory standard, that services must be isolated and positively identified (i.e. exposed) prior to excavations. If unachievable, then a formal justified mitigation to approved by a principal SAP and signed off by the Chief Engineer.
The ISA collaboration should implement improvements to their assurance and document control arrangements to ensure that the most recent and accurate information is are readily available to end users.
Arrangements equivalent to SL’s own mechanisms for providing independent challenge, oversight and learning should be developed within delivery partnerships. The Intelligent Client organisation to be educated in Human Performance, Human Factors, Nuclear Safety.
SL, PX and the ISA group should undertake collaborative working improvement activities in order to improve sharing of experiences and to foster healthy internal challenge.
Protecting Cables Against Strikes & Restoring Power Post-Strike
Thorne & Derrick have been distributors for 3M Electrical since 1985 and can provide a range of reliable and easy to install Cable Repair Products – this includes Scotch Tapes, Scotchcast Joints and Cold Shrink Tubes to provide effective re-instatement of cable sheath jackets on all types of LV MV HV cables in onshore and offshore locations with safe or hazardous area workplace classifications.
Cable Repair Products
Our range of cable protection covers manufactured by Centriforce provide underground utility protection of LV MV HV cables including Tapetile (11kV) and Stokbord (33kV 66kV 132kV) – contact us to discuss Cable Damage Prevention Products including Dectamesh, the underground detectable warning tape for alerting excavators of the presence of buried cables and to prevent potentially lethal accidents during excavation.
Stokbord
Tapetile
Cable Strikes | 10kV Medium Voltage (MV) Cable Struck By An Excavator
May 18th, 2021
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.
Cable Hangers | Cable Ducting | Cable Protection | Electrical Safety Equipment
Incident Overview
Incident Type: 10kV Electrical Strike
Project/Location: McDonalds Restaurant, Mullingar, Co. Westmeath
Client: Gas Networks Ireland
Incident Date: 24-03-2019
Summary
During planned weekend work a 10kV medium voltage (MV) cable was struck by an excavator. A subcontractor/DLO blended team were tasked with extending the existing gas main at a depth of approximately 1.7m.
Temporary works designs were authorised and planned for the job. Service plans were provided in the job pack and indicated the presence of a 10kV/20kV MV cable. Cable was traced, located and marked. Despite knowing the presence of existing services, the team allowed the excavator to work within 500mm of the various utilities.
The cable was struck by a combination of the bucket of the excavator and material shift towards the ESB cable at a depth of approximately 400mm.
| Action Taken |
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| Lessons Learnt |
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| Follow Up Action Required |
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| Action Holders | Emmet O’Brien, Roisin Kelly & Neil Doherty – BBCLG, ALL SBU Heads of Contract & Operational Management, ALL SBU Heads of Contract & Operational Management |
Protecting Cables Against Strikes & Restoring Power Post-Strike
Thorne & Derrick have been distributors for 3M Electrical since 1985 and can provide a range of reliable and easy to install Cable Repair Products – this includes Scotch Tapes, Scotchcast Joints and Cold Shrink Tubes to provide effective re-instatement of cable sheath jackets on all types of LV MV HV cables in onshore and offshore locations with safe or hazardous area workplace classifications.
Cable Repair Products
Our range of cable protection covers manufactured by Centriforce provide underground utility protection of LV MV HV cables including Tapetile (11kV) and Stokbord (33kV 66kV 132kV) – contact us to discuss Cable Damage Prevention Products including Dectamesh, the underground detectable warning tape for alerting excavators of the presence of buried cables and to prevent potentially lethal accidents during excavation.
Stokbord
Tapetile
