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Taking action to avoid cable strikes


Construction Drilling  

Striking underground utilities or cables during borehole drilling or ground excavation is at best highly disruptive and, at worst, fatal.

Clients’ deadlines and their lack of understanding of the issues and timescales involved in acquiring utility plans and making an effective study of underground services has led the site investigation industry into a worrying situation in which profitability is often directly at odds with health and safety.

Frequently, contractors face the tough decision of choosing to go ahead with boring without making a thorough examination of the ground or risking the loss of their commercial edge by taking time to gather information.

The guidance set out by the Health and Safety Executive in HSG47, ‘Avoiding danger form underground services’, provides a clear set
of procedures that, if followed, would help to minimise strikes in most situations.

However, these guidelines tend to address street works and construction sites and do not address the specific needs of the site investigation industry, which generally digs exploratory holes of limited size or drills small-diameter boreholes.

The approach that the Association of Geotechnical and Geoenvironmental Specialists (AGS) has taken is to produce its own set of guidelines, which provide an excellent and, importantly, relevant summary of those set out by the Health and Safety Executive.

But there is still no sure-fire method or tool that can provide 100% assurance that an incident will be avoided.
Every cable or utility strike is one too many, and yet they are still relatively common occurrences. The lack of accuracy of most service plans and the presence of unexpected utilities, such as thrust-bored cables in natural ground, further compound the challenges of avoiding strikes.

There now needs to be serious discussion on the topic in which people from across the industry share ideas on best practice techniques.

RSK Group plc has made a significant contribution in this area by pioneering the development of vacuum excavation.

The technique involves using high-pressure compressed air and water jets to loosen and remove shallow soil, and high-powered suction to removes the remaining debris.

We routinely use the technique to drill pilot holes on live forecourts and even on Tier 1 Control of Major Accidents Hazards sites.

RSK’s staff are well trained in the technique, and its implementation, along with their in-depth knowledge of the Health and Safety Executive guidelines and best practices, has considerably reduced the number of utility strikes.

Even though RSK is advanced in terms of research, techniques and staff training, we still have incidents.

There is need for a comprehensive strategy starting from examining available records, thorough examination of the site and its surroundings followed by non-intrusive investigations using cable avoidance tools (CAT) and ground probing radar (GPR).

Only then should consideration be given as how to commence excavations, whether by safe methods such as vacuum excavation or by hand. However, even when it appears that all avenues have been explored, incidents can still occur.

It is time for the site investigation industry to initiate a hub for debate on this subject, then ideas for technology and techniques could be pooled and we could work towards a solution.

RSK, for its part, has set up a dedicated team to provide service mapping for its clients (RSK STATS Geoconsult’s SafeGround). All our supervising engineers are trained to use CATs and signal generators, and we make good use of vacuum extraction and GPR techniques.

Even when we have used a specialist service mapping contractor, we still insist upon regular CAT scanning at all stages of digging, and where possible, always dig a 1.2m trial hole, preferably using vacuum excavation, to minimise the risk of a cable strike.

We have produced our own on-site guide to cable and pipe markers to make the identification of utility indicators easier when performing a site walkover.

We are also adopting a permit-to-dig process that is only signed off when the project manager and drilling operative are satisfied all the possible risk mitigation actions have been taken.

In addition, we now aim to brief all our clients on the challenges posed by underground utilities and the additional time required to ensure that an investigation can proceed safely.

It is a question of building up information, as there is clearly no single answer to the issue of cable or utility strikes.

We would like to work with the Health and Safety Executive and our clients and industry peers to consolidate best practices. A series of workshops could be just what we need to achieve this.

Hopefully, we can work together and make cable and utility strikes a thing of the past.

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