Buried service strikes – How unlucky are you?
How lucky, or unlucky, you are regarding buried service strikes depends on what you did beforehand to minimise the risk. Understanding whether what went wrong was avoidable or ‘just one of those things’ requires an approach with a built-in audit trail. The Health and Safety Executive’s guidance HSG47, Avoiding danger from underground services, sets out a safe system of work, but it is challenging to convince every client to give it the little space it needs in a ground investigation, especially when an increasingly commoditised surveying market always has someone who will cut corners and costs.
If you follow HSG47’s description of a safe system of work, you will know what to expect on-site from the record drawings and positively identifying the location of each service through a detection survey and/or trial holes. Then you can carry out the work using safe methods, though not everyone hand digs; it takes time. Not everyone gets a full set of service records; they cost money and might not come through before the start of site work. The detection survey is sometimes not done; it too takes time and requires geophysical expertise that might need to be contracted in. HSG47 requires it though and that it be done by individuals “with sufficient experience and technical knowledge… using the appropriate survey tools and equipment”.
To understand what that means, look at the appropriate British Standard, Specification for underground utility detection, verification and location, PAS 128. For detection surveys (referred to as Type B), the specification requires that two geophysical detection methods are used so that all services, not just the metallic ones, can be detected. This is typically electromagnetic location detection (CAT and genny) and ground penetrating radar. Not all detection technologies are the same. Work with the geophysicists to determine the best equipment and survey design given the specific site and ground conditions expected – HSG47 says you should.
It requires a particular mind-set, but not necessarily an increase in cost, to put everything in place. An enlightened client that requires all records drawings be available on-site; verifies that this is the case through work permits; commissions a PAS 128 detection survey in which all the geophysical data are recorded and retained; and documents where all the services identified on-site are located, has an audit trail that can be followed if anything goes wrong. This gives protection and recourse, and, equally, enables contractors and consultants to demonstrate that they followed best practice.
This approach pays dividends through actionable lessons after a strike and by dramatically reducing the number of incidents. If you have suffered delays and losses from a service strike when HSG47 and PAS 128 were not followed, expert witness services are available…
- George Tuckwell is director of geoscience and engineering with RSK