Avoiding Danger When Digging Near Underground Services

Construction By Matthew Coombes

When excavating anywhere, it’s essential to consider any underground services that may be present. Striking an underground service can cause significant damage to the service itself, the area surrounding it, and potentially create a significant risk to human life.

  • Electrical cables:
    Striking electrical cables can expose workers to up to 33,000 volts (mains voltage in the UK is 230 volts). This has the potential to cause injury such as burns, electrocution, fatalities, arc flash (a type of electrical explosion).
  • Gas mains:
    Striking a gas main can easily result in a gas leak. If this occurs around exposed electrical cables, equipment with naked flames or sparks, or if the strike itself ignites the gas, then this can lead to a considerable explosion. In addition, striking a gas pipe may crack the pipe underground away from the area of impact.
  • Water mains:
    Although water is not nearly as dangerous as gas and electrical services, it is often pumped at high pressure. Striking a water main can release this pressure in one go, sending debris and stones from the work area flying at high speeds. These can damage equipment and injure any nearby workers.It is also worth considering the effect that a burst water main can have on the surrounding area. Uncontrolled water can quickly erode the ground underneath roads and walk ways, and lead to extensive damage or even sink holes.

Striking any service is often a complicated and expensive event to rectify, taking a large amount of time to fix, and causing large disruptions such as shutting off the service, closing roads or pathways and preventing access to areas around the service such as businesses and homes.

Knowing the unknown


Even the vast open fields surrounding a farm can have underground water, gas and electrical services on their land whether they are public or privately owned, and there is always a chance that the plans for your busy high street don’t match the actual locations of underground services. As such, the risk of striking underground services can often feel like trying to predict the future.

Locating underground services

Plans

Utility providers who have installed services should have clear plans on the location of the services. Using these plans is a great way to plan out the excavation activities, mark where known services will be likely to appear and avoid them.

When carrying out an excavation, contacting the owners/operators of any nearby services which could be affected by the excavation is essential. They should provide you with all of the relevant plans, any additional information and in many circumstances, they will provide a representative to visit the site to assist in identifying services. It’s in their interest just as much as yours that everything goes without an incident/accident occurring.

However, the plans aren’t always 100% accurate. Services can shift with time due to movement in the ground, reference points on the plans such as kerbs can be moved or removed, straight cables may instead snake along, or the plans may not be fully up to date.

For example, Northern Gas Networks Ltd was recently sentenced following a fire and gas explosion at a residential property that unfortunately resulted in the death of the homeowner. The HSE investigation found that the gas main which ruptured did not appear on the Northern Gas Networks drawings and therefore it hadn’t been maintained. This shows us that just because it’s not on the plans, doesn’t mean it’s not in the ground.

Only take plans as an indication, not a guarantee.

Surveying the working area

Before carrying out an excavation, a competent surveyor should be used to help to identify, locate, and mark any relevant services that may be present in the excavation area. This will include comparing the plans provided by service companies with actions on-site such as using on-site portable radar, Cable Avoidance Tool (‘cat and genny’) detection, or digging trial holes by hand/through vacuum excavation*.

If any power, gas, water or other lines are uncovered, you must assume that they are live until it is confirmed by the service provider that they are disconnected.

If substantial risks are identified, it may be that an arrangement must be made to disconnect the supply during the time in which the work is undertaken.
The process for avoiding danger when excavating anywhere boils down to a simple principle:

Don’t know? Don’t dig!

*Vacuum Excavation
In some circumstances, services may be excavated using a vacuum excavator. This is a special vehicle used to excavate an area around live services whilst reducing the risk of service strikes. It uses high powered fans and a plastic nozzle to use vacuum suction to remove the dirt and ground surrounding live services. This type of excavation is typically a much lower risk than using a regular excavator.


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