In this blog we are taking an in-depth look at UXO risk assessments, exploring what they are, why you might need one and how you can order a risk assessment at Brimstone UXO.

What is a UXO risk assessment?

A UXO risk assessment evaluates the range of ways that allied and enemy action could have led to UXO contamination on an area of land. This is the first step towards mitigating the risk of UXO on any project that includes planned ground intrusions and therefore should take place in the pre-construction phase. UXO risk assessments should be undertaken for both land and offshore based projects.

At Brimstone, we offer 2 types of risk assessment:

  • Preliminary UXO Risk Assessments
  • Detailed UXO Risk Assessments

Our team of experienced researchers use a wide array of resources to conduct the risk assessment, before creating a bespoke UXO report. This outlines the risk level for the area of land in question and if there are any recommendations for further UXO risk mitigation.

Uxo risk assessments at brimstone

Do I need a UXO risk assessment?

At Brimstone, we recommend that every construction and site investigation project, regardless of whether it is commercial, humanitarian or governmental, should acquire a UXO risk assessment before commencing any groundworks. This is because UXO contamination in the UK comes from a variety of sources, from unexploded bombs dropped by the Luftwaffe (German Air Force) to contamination from Allied military activity such as weapons manufacturing or training exercises. It can be found across the country, including in areas you might not expect!

While there isn’t any legislation in the UK defining the steps you must take to check for UXO before beginning any construction or development work, there are legal obligations under the Health and Safety at Work Act 1974 and the Construction Design and Management Regulations 2015 to ensure the health and safety of employees.

There is also CIRIA C681, which is an industry guide for the management of risk associated with UXO. The guidance is primarily for construction professionals and focuses on WWI and WWII aerial bombardment, though it’s broadly applicable to other forms of unexploded ordnance. It is split into four key sections: Preliminary UXO Risk Assessment, Detailed UXO Risk Assessment, Risk Mitigation and Implementation. We always recommend clients follow the CIRIA C681 guidance, which enables you to reduce the risk of an unexpected UXO encounter and keep your project as safe as possible.

UXO risk assessments not only ensure the safety of construction workers and the public but also prevent expensive, unexpected costs and delays from disrupting your project further down the line.

Preliminary UXO Risk Assessments

When it comes to UXO risk mitigation, a Preliminary UXO Risk Assessment is usually the first step for construction and development projects. Also known as a Stage 1 UXO Risk Assessment, this is a qualitative screening exercise to assess the likelihood of discovering UXO on your project. Completed by our experienced research team, we take an overview of your proposed site and investigate any military activity on or near your land through primary and secondary historical sources. We use this information to assess the UXO risk on your site and identify if further, more in-depth research is required.

This is achieved by looking for evidence of any world war bombing incidents on or adjacent to your site, as well as evidence of damage occurring, before we expand our search to gain an idea of any activity that occurred in the wider area. We will also look to establish if the land was used for any kind of military training or manufacturing.

With a 24-hour turnaround, a Preliminary UXO Risk Assessment is the most cost-effective and fastest way of determining UXO risks for your site.

While this type of risk assessment is suitable for most projects, if you already know your site is on former military land, you’ll need to jump straight to the next stage, which is a Detailed UXO Risk Assessment.

Detailed UXO Risk Assessments

If your site is a former military site, or the Preliminary UXO Risk Assessment identified possible UXO contamination on site, you will need a Detailed UXO Risk Assessment. Also known as a Stage 2 UXO Risk Assessment, this takes an in-depth look at the range of ways WWI and WWII action, along with Allied activities, could have led to UXO contamination on your site. It also considers how modern construction methods and human factors affect the likelihood of encountering UXO.

The factors our researchers will look at are similar to those in the Preliminary UXO Risk Assessment, however, at a Detailed stage, one of the main focuses is on whether an unexploded bomb could feasibly strike the site and remain unencountered until the present day. We consider the local bombing density, whether the site was bombed and if this caused damage, and whether the wartime conditions on site were conducive to the detection of UXO. We also look at any post-WWII developments that have taken place on the site. A similar process is applied for Allied unexploded ordnance.

A Detailed UXO Risk Assessment involves using additional sources of information to calculate critical factors, including estimated bomb penetration depths and the types of UXO contamination present on your site. This approach involves extensive research and analysis, giving you a more granular look at UXO risk mitigation options.

We have an extensive in-house archive featuring bomb maps, damage maps and written records, however, if a site is located in an area for which we hold no original bombing records, our researchers will take a trip to the national or relevant local archives. In addition to this, we always try to obtain WWII-era photographic coverage of the site and any historic OS mapping where possible.

What is a uxo risk assessment?

Expedited Detailed UXO Risk Assessments

An Expedited Detailed UXO Risk Assessment is an alternative to our Detailed UXO Risk Assessments, and was launched in 2023 following customer feedback and extensive work by our research team. It is still considered a Stage 2 UXO Risk Assessment and undergoes the same extensive research process, but it has a faster turnaround time and contains more concise information which makes it easier and quicker to understand.

In an Expedited Detailed UXO Risk Assessment, all site-specific information is front and centre. Background information and UXO industry context are provided in a separate supplementary document, and figures such as images and maps are not included (unless you request them separately).

The EDRA has been designed to benefit both new and existing customers, with the research presented in a way that will better suit some of our clients. The information is arranged in a way that is easier to understand, is more concise, and conveys the key information and outcomes as a priority over the more detailed contextual and background details. This means you won’t have to read through the entire document to get the information you need (unless of course, you want to!)

Quantitative Detailed UXO Risk Assessment

Finally, we also offer Quantitative Detailed UXO Risk Assessment at Brimstone. This considers bombing density and cubic metres of ground disturbance to calculate the likelihood of encountering UXO on your site. Using novel mathematical models, we are able to provide you with a probabilistic rating for your site.

Third Party Peer Review

We find that the quality of UXO risk assessments across the industry can vary, with blanket risk ratings applied to entire sites or important resources neglected by researchers. At Brimstone, we offer a peer review service, which involves us looking at risk assessments provided by other UXO companies, evaluating their sources and analysis. If we can, we will provide you with more realistic and appropriate UXO risk mitigation options, giving you confidence that you’re proceeding in the safest and most cost-effective manner.

Uxo risk assessments at brimstone uxo

What happens with the UXO risk assessment results?

Once the UXO risk assessment has been completed, we provide our clients with a bespoke report outlining the findings and any recommended further action.

For a Preliminary UXO Risk Assessment, this is a 2-page document that highlights any sources of UXO that could potentially contaminate the site. It covers what those sources could be, what the site history is and any risk mitigation factors. As the purpose of a Preliminary UXO Risk Assessment is to determine whether further research is required via the completion of a Detailed UXO Risk Assessment, the report will outline if this is required or not.

A Detailed UXO Risk Assessment is a longer document, covering site history, a breakdown of the potential sources of UXO, the types of ordnance you might encounter (German and Allied), UXO risk mitigation circumstances, key findings, the risk rating, and any recommendation for further risk mitigation. It will feature a range of imagery and maps, along with data sheets and other useful information.

If there is a risk of UXO identified, we may recommend a UXO survey be undertaken. This involves exploring beneath the surface to detect buried ferrous objects that might be items of ordnance. The survey you receive will depend on your site characteristics and proposed ground intrusions. (If you would like to learn more about UXO surveys, we took an in-depth look at them on our blog here.)

Another UXO risk mitigation recommendation might be for on-site supervision. This could be in the form of a Watching Brief, where one of our engineers supervises your excavations and visually checks for the presence of UXO or items relating to military activity. Another option might be Borehole Support, where our engineer can clear your positions as the borehole deepens. You can learn more about our on-site support services here.

If the UXO risk assessment deems your site as low risk, there may be no further recommendations for UXO risk mitigation.

For peace of mind, you may want to consider a UXO Safety Awareness Brief, or Toolbox Talk as they’re also known. This involves one of our engineers providing a briefing that covers general risks and hazards, basic UXO identification and actions to take in the event of a UXO encounter. These can be delivered onsite, or online. We also offer an online UXO CPD awareness course aimed at those working in the construction industry.

How to order a UXO risk assessment at Brimstone

At Brimstone, we have completed thousands of UXO risk assessments for a wide variety of projects across the UK. Our experienced research team have spent the last 6 years developing our extensive in-house archives and refining our processes, ensuring we excel in client expectations and deliver fast, cost-effective and reliable risk assessments.

If you require a UXO risk assessment for your upcoming project, we’d love to hear from you! You can reach out to our Commercial Team by calling 020 7117 2492 and selecting option 1, or by emailing us at

For us to fully understand your requirements, the team will request a few key pieces of information, such as the site location, a redline boundary and details of your proposed development works. This allows us to tailor our assessments specifically to your site.

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