194 unexploded WWII grenades delay Cambridge construction project

A construction project in Cambridge faced weeks of delays after 194 unexploded World War II grenades were uncovered at the site of the new Cambridge ice arena. Initially, 40 grenades were discovered, but as work continued, an additional 154 were unearthed – some still packed inside their original wooden crates.

Among the finds was a crate containing 24 “A.W. bombs”, marked with warnings stating they were “fragile,” “highly flammable,” and should be handled “with great care”. The presence of such a large quantity of unexploded ordnance (UXO) suggests that no prior UXO risk assessment had been carried out before site works commenced – an oversight that resulted in significant disruption.

Why was unexploded ordnance present at the Site?

During WWII, Britain produced vast quantities of grenades, bombs, and other munitions, many of which were stored in rural areas, repurposed military depots, or even buried and forgotten. Cambridge, like much of the UK, was affected by wartime bombing campaigns, military training activities, and munitions stockpiling, all of which contribute to lingering UXO risks today.

One of the key finds at this site was the Self Igniting Phosphorus (SIP) grenade, also known as the No.76 special incendiary grenade – a crude yet effective defensive weapon issued to the Home Guard in preparation for a German invasion.

Self Igniting Phosphorus (SIP) Grenades

The No.76 grenade was a glass bottle filled with white phosphorus, benzene, water, and rubber and sealed with a crown stopper – similar to a beer bottle. Upon impact, the bottle would shatter, exposing the chemicals to oxygen and triggering a fierce incendiary reaction.

By late 1941, over six million of these grenades had been manufactured in Britain. However, they were never used in combat, leaving thousands unaccounted for after the war. Today, they are one of the most commonly found UXO items on construction sites due to their mass production and the way they were stored or discarded post-war.

You can learn more about UXO contamination in the UK on our blog here.

Could this UXO delay have been prevented?

Had Brimstone UXO been involved in this project before construction began, a comprehensive UXO risk management plan could have been implemented. This would have included:

• UXO Risk Assessment: Identifying potential UXO hazards based on historical research.
• UXO Survey: Detecting buried munitions before breaking ground.
• On-Site UXO Supervision: Ensuring safe excavation and disposal processes.

By taking a proactive approach to UXO risk, project managers could have avoided costly delays and ensured a safer working environment for their teams.

Avoid UXO-related delays on your project

Unexploded ordnance remains a serious risk for construction and development projects across the UK. If your site has any potential UXO contamination, it’s essential to assess the risk early to prevent unexpected delays and safety hazards.

Contact our dedicated commercial team to discuss your site’s UXO risk assessment and mitigation needs.

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