Introduction
Unexploded Ordnance (UXO) in certain areas is a significant risk during construction. Many areas in the UK were heavily bombed during WWII, and some bombing also took place during WWI. The risk of UXO in areas that were known to be targets for bombing (e.g. London, Southampton, Bristol, Liverpool & other major cities) must be carefully assessed. Activities involving excavations, including the demolition of existing buildings and site clearance works, can potentially unearth UXO.
500lb WWII UXO found on site of former school in Bath (BBC news)
In May 2016, contractors using a mechanical excavator unearthed a 500lb unexploded German Luftwaffe bomb that was lying just 1 metre below a playground of a former school in Bath.
This triggered a response by the Police and the Army’s Royal Engineers’ Explosive Ordnance Disposal (EOD) team who safely removed the UXO to a nearby Torr Quarry site near Shepton Mallet where it was destroyed.
https://www.bbc.co.uk/news/uk-england-somerset-36291645
Bath WW2 bomb scare: Hundreds of homes evacuated – BBC News
Assessing the risk of UXO on a development site
There are several companies that offer support in assessing the risk of UXO on a development site. They all follow a similar process in terms of assessment of risk at different stages.
Stage 1 – Desktop assessment / UXO risk mapping
The initial ‘high level’ assessment can be carried out as part of the standard legal searches undertaken during the purchase of a property or site for development. A Landmark UXO assessment report (or similar) should be ordered as part of the searches in any area known to have been bombed in WWII.
PreliminaryBombSearchSample.pdf (landmark.co.uk)
A preliminary risk assessment will interrogate historical data, including maps, library resources, archives (including the records that were taken during WWII of bomb strikes) to identify whether the address of the proposed works is at risk of UXO being present.
The National Archives
One of the most reliable data sources is that found in the National Archives. They include bomb census reports completed by the Research and Experiments Branch of the Ministry of Home Security. They typically include the following information:
- Date the bomb landed
- Details of whether the bomb exploded
- Description of damage
- Size and type of bomb
- Details on air raid warnings
- Details of casualties
Details typically also include a sketch map showing the point of impact of the bomb.
Detailed Investigations
If the desktop study identifies a potential risk, then further detailed investigations are required:
Stage 2 – site investigation
Typically entailing the use of ground penetrating radar technology and ferrous metal detection, various techniques are deployed by different companies including the use of drones and vehicle-towed or hand-drawn equipment that are used to scan below the ground where proposed excavations are to take place.
When piling or other deep excavations are proposed, intrusive surveys are required. These can entail drilling in specific locations with specialist survey equipment that ‘looks ahead’ where piled foundations or deep basement structures are planned. This work is overseen by an Explosive Ordnance Disposal (EOD) specialist, qualified and experienced in the identification and disposal of UXO.
Stage 3 – On-site monitoring and UXO disposal
Where risk of UXO is identified as high and/or investigation works cannot rule out the absence of UXO, typically an EOD Specialist will attend site and monitor the excavation works. In the event UXO is uncovered, the EOD specialist will deal with the disposal of the UXO. If found to contain explosives then Home Office protocols will be enacted with MoD specialists attending to dispose of the UXO safely. https://rmsuxo.com/uk-land-uxo-services
Construction Industry Research and Information Association (CIRIA) C681
There are no defined regulations for the identification of and management of the risk of UXO. There is however, clear useful industry guidance from CIRIA that is accepted as ‘industry best practice’. CIRIA is an independent not-for profit organisation that supports the UK construction industry. CIRIA provides a clearly defined process for the management of risks associated with UXO from WWI and WWII aerial bombardment. It is also broadly applicable to the risks from other forms of UXO that might be encountered.
It is seen as the leading source of guidance on the management of UXO and assists construction consultants and their clients to fulfil their duties under CDM in relation to the identification and management of significant risks in construction projects.
https://www.ciria.org/CIRIA/CIRIA/Item_Detail.aspx?iProductcode=C681
Summary
UXO presents a significant risk to development, particularly on brown field sites in areas that were known to be heavily bombed in WWII. As with all below-ground risks, a methodical approach is required to identify and manage the risk of UXO, thereby minimising risk to personnel and neighbouring property.
