Your Guide to CIRIA C681: Managing UXO Risks in Construction
Unexploded ordnance (UXO) poses a genuine threat to construction and development projects across the UK. Whether it’s the result of wartime aerial bombardment, military training, or leftover munitions manufacturing, UXO contamination can cause significant delays, increase costs, and create serious safety risks.
CIRIA C681 is the industry-standard guide designed to help construction professionals manage UXO risks effectively. It offers a clear framework to reduce the likelihood of unexpected UXO encounters and keep projects running safely and smoothly.
In this blog, we take an in-depth look at CIRIA C681, its four-stage risk management process, and how Brimstone UXO supports clients in applying it to their projects.
What is CIRIA C681?
CIRIA C681 is the industry guide for the management of risk associated with UXO. It was published in 2009 by the Construction Industry Research and Information Association (CIRIA), an independent, not-for-profit organisation dedicated to improving standards and safety in the construction sector.
The guide was developed in response to the increasing number of UXO discoveries on construction sites, particularly in areas heavily bombed during World War II. Its purpose is to help developers, contractors, and consultants assess, mitigate, and manage UXO risks in line with their legal obligations under the Health and Safety at Work Act 1974 and CDM 2015 regulations.
Although CIRIA C681 focuses primarily on the hazards of WWI and WWII aerial bombardment, its principles are broadly applicable to other forms of UXO, including landmines, artillery shells, and military training ordnance.
Why is CIRIA C681 important for construction projects?
During the Blitz, approximately 450,000 bombs were dropped on Britain. It is estimated that around 10% failed to detonate, leaving a legacy of buried UXO. Beyond the impact of wartime bombing, other sources of contamination include military testing ranges, defensive operations, and ordnance manufacturing sites, many of which were repurposed for civilian use.
Despite the risks, there is no UK legislation that specifically requires developers to conduct a UXO risk assessment before breaking ground. However, employers have a legal duty to protect the health and safety of workers, making UXO risk assessments and mitigation measures essential on potentially contaminated sites.
CIRIA C681 provides a standardised, best-practice framework for identifying and managing UXO hazards, helping construction professionals meet their legal obligations and safeguard their workforce.
The four stages of CIRIA C681: a step-by-step breakdown
The CIRIA C681 process outlines a four-stage approach to UXO risk management:
1. Preliminary UXO Risk Assessment
The first step is a preliminary risk assessment to determine whether UXO poses a credible threat to the project. This involves researching the site’s history to identify any past military activity, such as bombing raids, training exercises, or weapons testing.
Brimstone UXO conducts thorough research using primary and secondary sources rather than relying on automated systems, ensuring accuracy and reliability. Our team typically delivers a risk rating and report within 24–48 hours, allowing your project to move forward without unnecessary delays.
If the site is deemed low risk, no further action is required. However, if the site has a moderate or high UXO risk, the next stage is necessary.
2. Detailed UXO Risk Assessment
A detailed UXO risk assessment is carried out if the preliminary assessment indicates a potential risk or if the site has a known military history.
At this stage, Brimstone’s research team investigates the site in greater depth, using detailed historical records, bomb census maps, and contemporary construction data to assess the likelihood of UXO contamination. The assessment factors in variables such as bomb penetration depth, post-war land use changes, and the potential for UXO disturbance by modern construction activity.
The goal is to provide a granular assessment of the specific UXO threat, enabling clients to make informed decisions about risk mitigation strategies.
3. Mitigation
If a site is confirmed to have a moderate or high UXO risk, the next step is to implement mitigation measures. The UXO specialists will work with you to find a solution to the problem. If a viable solution can’t be found, then you may have to make changes to your development plan. Fortunately, Brimstone are usually able to find workable solutions that take your project budget and site characteristics into account.
This mitigation plan may involve:
- UXO Surveys: specialised site-based services designed to explore beneath the surface and detect buried ferrous objects. These surveys come in two key forms: Intrusive and Non-Intrusive.
- On-Site Support: deploying a UXO engineer to site to support ground investigations. This could be in the form of a Watching Brief, Borehole Support or a Search and Clear.
- UXO Safety Awareness Briefings: Ahead of any work starting, a UXO engineer can brief your team on general UXO risks and hazards, basic UXO identification, and action to take in the event of a UXO encounter.
4. Implementation
The final stage is the onsite implementation of the UXO risk management plan. This is where we deploy our team to site, carry out the necessary services and then provide the results back to you.
Once the UXO risk is mitigated, construction can continue with confidence and you’ll be provided with an ALARP (as low as reasonably practicable) certificate.
Why choose Brimstone UXO?
As the UK’s only government-assured UXO company, Brimstone provides industry-leading risk management services. Our team consists of former military EOD specialists with expertise in UXO survey, investigation, and disposal.
We support clients across the construction, infrastructure, and marine sectors, delivering comprehensive UXO risk assessments, bespoke mitigation strategies, and safe, efficient disposal operations.
By partnering with Brimstone, you can be confident that your project complies with CIRIA C681 guidelines and meets the highest safety standards.
If you’re planning a construction or development project in a UXO-affected area, contact Brimstone UXO for expert guidance. Our commercial team can provide tailored advice and support at every stage, helping you mitigate risks, avoid delays, and keep your project running safely.
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