Contextual information for the case studies
| Case study number | Utility strike context | Utility strike incident |
|---|---|---|
| 1 | There was a error of judgement and a failure to observe fully the permit to dig procedure, and safe digging’ practices were not observed on a construction site adjacent a bridge. The remedial works did not unduly disturb traffic | While diamond drilling concrete slab to enable quiet demolition, the core drill cut through a 25 mm water supply |
| 2 | The night shift supervisor noticed at about 2.30 a.m. that traffic warning sign bulb had gone out. He went to investigate and discovered a damaged cable and stopped works. The operator did not follow the safe system of work. Works in the immediate area were suspended and sandbags were used to make the area safe temporally. The remedial works did not unduly disturb traffic | When excavating the operative lost control of the mini digger and struck an LV street light cable |
| 3 | Workmen were pulling out concrete bedding from kerbs. A cable feeding a lit street sign was encased within the concrete. This came out with the concrete, and a pop sound was heard. The cable was known about due to a taped-off electrical pole socket nearby in the footpath. The remedial works did not unduly disturb traffic | When pulling out concrete kerbs, an electrical lit LV street sign cable embedded in concrete was snagged |
| 4 | Prior to opening the tunnel to traffic, it was confirmed by London Streets Tunnels Operation Centre (LSTOC) that they had a fault on communication to the gantry on the westbound tunnel and could not control the matrix signs on the gantry, which was operated manually to allow the tunnel to be opened to the public. Further investigation revealed that a communication cable that was believed to be part of the disconnected cables was cut. It was later found to be the live communication control cable of the western gantry. The remedial works disturbed traffic flow in the tunnel and surrounding area for near enough a full day | Human error – a live communication cable was accidentally cut The contractor had to contact LSTOC for an update on any faults on the system which will allow time to rectify them before the end of the shift |
| 5 | While attempting to remove a street lighting control cabinet, an LV signal cable was heard sparking in the ground. Despite service plans being available and a Cat scan being carried out, the cable was not identified as it was encased in concrete. The remedial works disturbed traffic in the area for 4 h | The LV cable was encased in concrete and was not detected when using a Cat. As the control cabinet was moved, it became apparent that the cable had been damaged by a mini digger |
| 6 | The operative was breaking/excavating behind kerbs to install a duct for a traffic signal – an LV cable was struck 150 mm below footpath surface in hard ground. The remedial works did not unduly disturb traffic | When installing ducting, the operative lost control of the pneumatic spade and struck an exposed LV cable |
| 7 | The gas pipe was buried approximately 150 mm below the surface material. It was not identified on statutory plans or identified during scanning due to the plastic pipe material. The remedial works did not unduly disturb traffic | During trial hole excavation using a hand breaker, an LP gas pipe was accidentally struck. The works were stopped until the gas pipe was reinstated |
| 8 | The cable was identified on statutory plans, and a Cat was used to verify this. A lump of concrete was lifted using a machine when the duct and cable were damaged. The remedial works did not unduly disturb traffic | While excavating to lay cable ducts, a 4 mm LV street lighting cable was damaged |
| 9 | Apparatus undertakers asked the contractor to dig a trial hole around an existing 6″ (152 mm) water pipe along a footpath. This trial hole was needed to determine a tie-in location for a new rider main. The tie-in works were planned for night time. The work started at 2 a.m. The remedial works did not unduly disturb traffic | There was 60 mm depth of paving and below these slabs approximately 300 mm of concrete. This meant that operatives had to use an air-powered breaker to excavate the trial hole. While breaking the concrete, a 50 mm black LV duct was breached by the air-powered breaker. There was no spark as the cable was not live. The contractor halted the trial hole until a repair was undertaken. UK Power Networks came to site at 3 a.m. and isolated the cable permanently by installing a shrink wrap end cap which proved the cable was dead |
| 10 | The service in question was not shown on the drawing accompanying the permit to dig. Prior to the possible cable strike, there was a black cable in ducting uncovered, of which the ducting appeared to have been damaged. This was also not on the drawing. The remedial works did not unduly disturb traffic | The LV cable in question was surrounded in a sharp sand and cement mixture with no indications such as ducting, sand or hazard tape present. It was struck using a pneumatic spade |
| 11 | Work was being carried out to divert an existing 18″ (0·457 m) HP gas distribution main prior to further works. Uncompacted reinstatement material from previous work carried out by the contractor, which had been supported by this shoring, pressed against the top number of sheet piles, pivoting them and creating a gap which allowed a small volume of material to slump into the excavation. The remedial works severely disturbed traffic and businesses in the area for approximately 3 weeks | While a 12 m length of 500 mm PE HP gas main was being lowered into the excavation, a section of shoring failed |
| 12 | Two utility operatives were excavating a trench at a busy junction in order to lay a duct for a future HV cable when a strike incident happened. The remedial works disturbed traffic in the area | Considering the LP gas pipe to be dead, following checks undertaken by utility operatives from the subcontractor for the main contractor, the operatives decided to break the pipe. The pipe was subsequently found to be live, resulting in uncontrolled loss of gas. The utility operatives from the subcontractor attended the site to seal the broken pipe temporally. A cordon was placed around the work compound to control members of the public, and the local restaurant was warned |
| 13 | While breaking out the slab, a cable was struck by a breaker, causing a flash of light/fire to be emitted. It was soon after found that as a result of the utility strike, power to businesses on two adjacent roads was lost from 9.30 a.m. to 5.10 p.m. (c. 6·5 h). The remedial works did not unduly disturb traffic | While carrying out excavation works to determine a route for the installation of the 180 mm water main, an LV cable was struck by a handheld breaker |
| 14 | While carrying out excavation works for the construction of the mass retaining wall on a busy street, a HP gas main was exposed adjacent to the excavation. The remedial works did not unduly disturb traffic | A floor saw was used to cut the existing asphalt, followed by the breakout of the underlying concrete road base. During the breakout, the gas main was exposed and punctured using a mini digger |
| 15 | Information from the statutory undertaker proved to be incorrect on a construction site. The drawing identified the water main to be at 1·3 m below ground level and was subsequently struck at 1·6 m below ground level. The remedial works disturbed underground train services as well as water supply to two businesses in the area | A 100 mm inner dia. water main was fractured with a mini digger requiring repair. Minor water damage and clean-up were required up to the train platform level |
| 16 | Inaccurate buried service information was utilised to plan and implement excavation works on a construction site, resulting in an inadequate risk assessment and the development of associated control measures. The remedial works affected power in the local area for half an hour, and a nearby theatre performance was interrupted | A handheld hydraulic breaker point pierced the outer protective layer of an 11 kV HV cable, resulting in damage to one core resulting in a short circuit |
| Case study number | Utility strike context | Utility strike incident |
|---|---|---|
| 1 | There was a error of judgement and a failure to observe fully the permit to dig procedure, and safe digging’ practices were not observed on a construction site adjacent a bridge. The remedial works did not unduly disturb traffic | While diamond drilling concrete slab to enable quiet demolition, the core drill cut through a 25 mm water supply |
| 2 | The night shift supervisor noticed at about 2.30 a.m. that traffic warning sign bulb had gone out. He went to investigate and discovered a damaged cable and stopped works. The operator did not follow the safe system of work. Works in the immediate area were suspended and sandbags were used to make the area safe temporally. The remedial works did not unduly disturb traffic | When excavating the operative lost control of the mini digger and struck an LV street light cable |
| 3 | Workmen were pulling out concrete bedding from kerbs. A cable feeding a lit street sign was encased within the concrete. This came out with the concrete, and a pop sound was heard. The cable was known about due to a taped-off electrical pole socket nearby in the footpath. The remedial works did not unduly disturb traffic | When pulling out concrete kerbs, an electrical lit LV street sign cable embedded in concrete was snagged |
| 4 | Prior to opening the tunnel to traffic, it was confirmed by London Streets Tunnels Operation Centre (LSTOC) that they had a fault on communication to the gantry on the westbound tunnel and could not control the matrix signs on the gantry, which was operated manually to allow the tunnel to be opened to the public. Further investigation revealed that a communication cable that was believed to be part of the disconnected cables was cut. It was later found to be the live communication control cable of the western gantry. The remedial works disturbed traffic flow in the tunnel and surrounding area for near enough a full day | Human error – a live communication cable was accidentally cut |
| 5 | While attempting to remove a street lighting control cabinet, an LV signal cable was heard sparking in the ground. Despite service plans being available and a Cat scan being carried out, the cable was not identified as it was encased in concrete. The remedial works disturbed traffic in the area for 4 h | The LV cable was encased in concrete and was not detected when using a Cat. As the control cabinet was moved, it became apparent that the cable had been damaged by a mini digger |
| 6 | The operative was breaking/excavating behind kerbs to install a duct for a traffic signal – an LV cable was struck 150 mm below footpath surface in hard ground. The remedial works did not unduly disturb traffic | When installing ducting, the operative lost control of the pneumatic spade and struck an exposed LV cable |
| 7 | The gas pipe was buried approximately 150 mm below the surface material. It was not identified on statutory plans or identified during scanning due to the plastic pipe material. The remedial works did not unduly disturb traffic | During trial hole excavation using a hand breaker, an LP gas pipe was accidentally struck. The works were stopped until the gas pipe was reinstated |
| 8 | The cable was identified on statutory plans, and a Cat was used to verify this. A lump of concrete was lifted using a machine when the duct and cable were damaged. The remedial works did not unduly disturb traffic | While excavating to lay cable ducts, a 4 mm LV street lighting cable was damaged |
| 9 | Apparatus undertakers asked the contractor to dig a trial hole around an existing 6″ (152 mm) water pipe along a footpath. This trial hole was needed to determine a tie-in location for a new rider main. The tie-in works were planned for night time. The work started at 2 a.m. The remedial works did not unduly disturb traffic | There was 60 mm depth of paving and below these slabs approximately 300 mm of concrete. This meant that operatives had to use an air-powered breaker to excavate the trial hole. While breaking the concrete, a 50 mm black LV duct was breached by the air-powered breaker. There was no spark as the cable was not live. The contractor halted the trial hole until a repair was undertaken. UK Power Networks came to site at 3 a.m. and isolated the cable permanently by installing a shrink wrap end cap which proved the cable was dead |
| 10 | The service in question was not shown on the drawing accompanying the permit to dig. Prior to the possible cable strike, there was a black cable in ducting uncovered, of which the ducting appeared to have been damaged. This was also not on the drawing. The remedial works did not unduly disturb traffic | The LV cable in question was surrounded in a sharp sand and cement mixture with no indications such as ducting, sand or hazard tape present. It was struck using a pneumatic spade |
| 11 | Work was being carried out to divert an existing 18″ (0·457 m) HP gas distribution main prior to further works. Uncompacted reinstatement material from previous work carried out by the contractor, which had been supported by this shoring, pressed against the top number of sheet piles, pivoting them and creating a gap which allowed a small volume of material to slump into the excavation. The remedial works severely disturbed traffic and businesses in the area for approximately 3 weeks | While a 12 m length of 500 mm PE HP gas main was being lowered into the excavation, a section of shoring failed |
| 12 | Two utility operatives were excavating a trench at a busy junction in order to lay a duct for a future HV cable when a strike incident happened. The remedial works disturbed traffic in the area | Considering the LP gas pipe to be dead, following checks undertaken by utility operatives from the subcontractor for the main contractor, the operatives decided to break the pipe. The pipe was subsequently found to be live, resulting in uncontrolled loss of gas. The utility operatives from the subcontractor attended the site to seal the broken pipe temporally. A cordon was placed around the work compound to control members of the public, and the local restaurant was warned |
| 13 | While breaking out the slab, a cable was struck by a breaker, causing a flash of light/fire to be emitted. It was soon after found that as a result of the utility strike, power to businesses on two adjacent roads was lost from 9.30 a.m. to 5.10 p.m. ( | While carrying out excavation works to determine a route for the installation of the 180 mm water main, an LV cable was struck by a handheld breaker |
| 14 | While carrying out excavation works for the construction of the mass retaining wall on a busy street, a HP gas main was exposed adjacent to the excavation. The remedial works did not unduly disturb traffic | A floor saw was used to cut the existing asphalt, followed by the breakout of the underlying concrete road base. During the breakout, the gas main was exposed and punctured using a mini digger |
| 15 | Information from the statutory undertaker proved to be incorrect on a construction site. The drawing identified the water main to be at 1·3 m below ground level and was subsequently struck at 1·6 m below ground level. The remedial works disturbed underground train services as well as water supply to two businesses in the area | A 100 mm inner dia. water main was fractured with a mini digger requiring repair. Minor water damage and clean-up were required up to the train platform level |
| 16 | Inaccurate buried service information was utilised to plan and implement excavation works on a construction site, resulting in an inadequate risk assessment and the development of associated control measures. The remedial works affected power in the local area for half an hour, and a nearby theatre performance was interrupted | A handheld hydraulic breaker point pierced the outer protective layer of an 11 kV HV cable, resulting in damage to one core resulting in a short circuit |
HP, high pressure; HV, high voltage; LP, low pressure; LV, low voltage
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