It is estimated that as many as one in ten bombs dropped on Britain, and one in six elsewhere did not explode, and of these, up to half are unrecovered. Unless the recovery of unexploded ordnance is carefully planned, they can cause significant project delays, as well as injuries and loss of life.

This webinar explored how to evaluate your construction project’s risk potential, who best to approach, the cartographic, image, and text data that must be consulted, and the appropriate methodologies to adopt.

Remnants of War (ROW)

In October 2020, the “Tallboy” bomb dropped by Britain during World War 2 exploded after being discovered in Poland. Similarly, in 2017, residents of a city in Frankfurt were forced to evacuate their homes while experts disposed of a World War 2 bomb found during the construction of a new kindergarten. With more than 54,000 people evacuated, it was the largest evacuation since the end of World War 2. Each year hundreds of unexploded devices are uncovered in Germany. As such, before any construction project begins, the ground has to be certified as cleared of unexploded ordnance.

Chris Going explains that since the development of modern warfare, building and infrastructure projects in Europe and Asia have had to contend with the legacy of war, i.e., remnants of war (ROW). A sub-category of ROW, is explosive ROW (EROW). The “Tallboy” bomb is an example of an EROW. EROW includes explosive devices left unused, weapons put in the ground, or weapons that failed to explode as intended (commonly referred to as unexploded ordnance). After landmines, unexploded ordnance (UXO) is the biggest challenge concerning construction.

A global problem

As Chris Going explains, the principal geographic regions where EROW poses a problem are those areas repeatedly fought over since the American civil war. Specifically continental Europe, North Africa, the Middle East, and Southeast Asia. In all these areas, airdropped weapons and landmines are an inherent development hazard causing delay and additional construction costs. According to Chris Going, approximately 15% of bombs failed to explode during the two World Wars, and a quarter of those bombs are still undiscovered. Consequently, there may be roughly 750,000 remaining unexploded bombs in continental Europe.

It is estimated that 1 in 10 bombs dropped did not explode as intended, and approximately 25% of those bombs remain undiscovered in the UK ( around 7,500 bombs). According to the Ministry of Defense, some 60 airdropped bombs are recovered every year in Britain. Assuming they continue to be retrieved at a constant rate, it will take well over a century until they are all cleared.

However, as time passes, some types of bombs are becoming more dangerous. These are bombs with time delay fuses designated to explode up to a week after striking the ground. In mainland Europe, one or two of these explode per year, usually in Germany. The reason is that components in these fuses are failing and leading to spontaneous explosions. The good news in the UK is that these types of time fuses are not known to be found.

Sources for locating Explosive Remnants of War 

Next, Dr. Seppe Cassettari explains how you can establish if you are likely to encounter an EROW. In the UK, one can use wartime records that log and map where wartime bombs were dropped. However, while wartime census maps and supportive textual records are of considerable significance, they are still limited. As Chris Going explains, air photography is an excellent complementary source for tracking EROW.

From 1942 onwards, allied reconnaissance aircraft usually returned with imagery of bomb sites. The imagery has been used to identify the impacts of bombs that did not explode. For example, Dr. Cassettari provides a wartime reconnaissance photograph near Venice where the detail is so clear that the impacts of two unexploded bombs can be seen. Cumulatively, textual records and aerial photography permit detailed mapping over time of many bombed areas.

Moreover, in the UK, the past two decades has seen numerous companies carrying out ROW survey work with archival specialists. They investigate the risk potential of a site and, when necessary, pinpoint suspected bombs. Once ordnance is confirmed, responsibility passes on to the relevant military unit. However, despite this, when a bomb is found, it is still often accidentally discovered.

 Mapping possible EROW sites

To conclude, Chris Going describes how to map possible EROW sites. Such an approach would be most useful in infrastructure projects involving linear and multiple points such as strategic roads and railways. Linear sites such as railways were often attacked by fighter bombers as well as medium and heavy bombers. Chris provides a map showing a section of line between Innsbruck and Kufstein in Austria depicting all known bomb strike locations.

In addition, Dr. Cassettari outlines that your approach to EROW should be dictated by where your project is located. In the UK, your first step is to examine the CIRIA Report, which is the first construction industry guide to be produced on the subject of unexploded ordnance. This publication provides the UK construction industry with a set and defined process for managing risks associated with unexploded ordnance and aerial bombardment. Dr. Cassettari emphasizes that if your site is in a historic urban area, it is prudent to bear in mind that unexpected ground conditions may well include unexploded ordnance. Currently, there are on-going projects to collate information on where bombs were dropped, including GeoHistoric’s Bomber Command Database (BCD).