Surveyor's guide to unexploded ordnance

When planning any development or construction, one important consideration is what might be beneath the ground, and in the UK, this can still include unexploded ordnance

Author:

Phil Baptie

07 May 2019

Geomatics

Health and safety

Two world wars and more than a century of military land use have resulted in unexploded ordnance (UXO) lying beneath the surface of British cities, towns and rural areas. From the bombs dropped by the Luftwaffe to the grenades, mortars, mines, projectiles and ammunition of our own forces, this can pose a significant risk to those wishing to carry out ground works in certain areas of the UK.

While there is no formal obligation or specific legislation requiring a UXO risk assessment for construction projects in the UK, the need is implicit in the Construction (Design and Management) Regulations 2015. The Health and Safety at Work etc Act 1974 includes information for those responsible for intrusive works such as archaeology, site investigation, drilling, piling or excavation, stating that they have a duty of care to their employees and should carry out a comprehensive assessment of the potential risks, and that mitigation measures are implemented to deal with any hazards.

Thankfully, there have been no recorded fatalities in the UK resulting from the detonation of German high-explosive bombs since the war. However, given the many high-profile discoveries here this may be due more to luck than good planning.

In mainland Europe by contrast, notably in Germany and Austria, a number of Second World War bombs have been detonated during construction work that have resulted in injuries and fatalities. It is not only the cost in terms of potential risk to life and limb that is a concern, though, but also the commercial costs of having to close a busy working site while you deal with unexpected UXO.

Risk management procedure

In 2009, the Construction Industry Research and Information Association produced Unexploded ordnance (UXO): A guide for the construction industry, which outlines the recommended risk management procedure. Crucially, it highlights the need for UXO to be considered as early as possible in the lifecycle of a project, and the importance of a thorough assessment of risk early on.

This risk assessment is the first step in the process. One of its primary goals is to investigate the history of an area to assess the likelihood of contamination from UXO. In heavily bombed urban areas, or those near potential bombing targets, this may include looking at pre- and post-war historical maps, bomb mapping, written bomb incident records, bomb damage maps, Luftwaffe reconnaissance photographs and aerial imagery from the war.

For military sites there are different considerations, such as the following.

Which of the forces used it?
How long was it used?
Was explosive ordnance stored there?
What types of ordnance?
Where are the likely hotspots?

Sites can vary from current and historic firing ranges to military airfields, naval bases, training areas, defensive lines and army camps. Many of these features are no longer visible and it is not always easy to ascertain whether an area was bombed without carrying out detailed research at local and national archives.

This is where a UXO specialist can help – compiling and analysing historical records and data sets, and assessing factors such as the:

likelihood of UXO contamination
probability of the UXO remaining likelihood of encountering UXO
consequences of initiation.

It is usually recommended that the risk assessment is split into two stages, a preliminary and a detailed study. For most UK sites, the risk of encountering buried UXO will be negligible and can be screened out early with a preliminary report and no need for further research or costly proactive risk mitigation measures. Any competent construction professional with access to the relevant information can carry out a preliminary study, which should generally look at basics such as whether an area was bombed, whether there were targets nearby, whether bomb damage was sustained or whether the area was used historically by the military. If there is enough data to discount the risk with confidence, it may be that no further action is required.

If there are indicators of bombing in the area, however, or if military land use is evident, it is likely that a detailed assessment would be required. This assessment should always be carried out by a qualified UXO specialist, and would make use of a range of historical information sources, including local and national archive data to ensure thorough investigation of the history of a site, the precise nature of any recorded bombing, the extent of any bomb damage, and the specifics of any military use. Detailed assessments should also take into consideration what has occurred on site since the war, and the nature of the intrusive works proposed.

Risk mitigation

If a viable risk from UXO is identified, various technologies and methodologies are available to mitigate that risk. These will depend on the nature of the risk and the type of work planned. For greenfield sites such as parks, fields and open, undeveloped land, for example, a non-intrusive UXO survey followed by target investigation can effectively locate shallow anomalies before works begin.

If there is an assessed risk from deeply buried bombs in an urban area, an intrusive magnetometer survey can be carried out to ensure pile and borehole locations are free from unexploded bombs at depth. For open excavations, a UXO specialist can monitor the works and provide safety briefings.

A site-specific risk management plan is recommended to document the steps taken to manage UXO risk, and to prepare for unexpected UXO. Anyone responsible for health and safety on a site can do this, with input from UXO professionals.

It is always better to mitigate the risk of encountering UXO before intrusive works so that any items can be dealt with in a safe and controlled way. Unexpected UXO can present the greatest problems, as there can be a much higher risk of initiation. However, even with a robust risk assessment and extensive risk mitigation measures, the risk of encountering UXO can rarely be entirely negated.

Any UXO risk management plan should therefore always include a list of actions to be taken if a suspect item is discovered.

Report: mark and secure the area and report to site management.
Confirm: the management or foreperson should view the object to confirm it is not a known item.
Inform: advise a specialist UXO consultant or the police.
Cordon: until the police or specialist arrives impose and maintain a cordon.
Control: until the police arrive maintain the cordon and control the site.

Specialist UXO consultants can provide a range of services from risk assessment to training, on-site survey and clearance. They will help and advise on best practice and risk mitigation options, case studies, site history and planned works. No matter the size or location of a site or the complexity of a project, help is available to manage any UXO risk safely, practically and effectively.

Phil Baptie is head of research at 1st Line Defence Ltd

phil.baptie@1stlinedefence.co.uk