Cache of WWII phosphorus grenades found on agricultural land

A significant cache of 24 World War II-era phosphorus incendiary grenades was unearthed in a field near Halesworth Road, Sibton, Suffolk. Emergency services, including the Police, Fire and Rescue Service, and a British Army bomb disposal team, swiftly responded to the discovery.

Safe disposal of the phosphorus grenades

Army engineers relocated the Self-Igniting Phosphorus (SIP) grenades to a trench where they were safely destroyed in a controlled burn. Due to the presence of incendiary chemicals, the grenades burned intensely for an extended period, highlighting the dangerous nature of this type of unexploded ordnance (UXO).

The history behind phosphorus grenades

During 1940, Britain was urgently fortifying its coastline in anticipation of a potential German invasion. Coastal defence units were established, and many areas inland from the coast were used for military storage, training, and tactical defence. The field where the grenades were found is located just 10km from the Suffolk coastline, making it highly likely that these grenades were originally stockpiled or discarded by coastal defence soldiers.

Home Guard and unregulated ordnance storage

The Home Guard, a wartime volunteer force tasked with defending Britain, was known for its poorly managed ammunition storage and unauthorised disposal of explosives. This has resulted in numerous UXO discoveries across England, particularly in rural and coastal areas where defensive preparations were concentrated.

What were SIP grenades?

The British Army designated the SIP grenade as the No.76 Special Incendiary Grenade. Over six million units were produced and distributed to Home Guard battalions across the UK. Designed as an improvised anti-tank and incendiary weapon, the grenade was a simple but highly dangerous device.

Composition of a SIP Grenade:

• Container – A glass bottle with a crown stopper.
• Chemical Mixture – White phosphorus, benzene, water, and a strip of rubber.

How it worked:

Upon impact, the glass bottle shattered, causing the chemical mixture to oxidize, resulting in a violent incendiary reaction. The flames generated extreme heat, posing a severe burn hazard and producing toxic smoke. Due to their unpredictable nature, SIP grenades posed significant dangers not only to enemy forces but also to those handling or storing them.

Mitigating the risk of UXO on your site

The discovery of WWII-era ordnance on agricultural and development land highlights the ongoing risk posed by historic military activity. If you are planning construction, excavation, or land development, a UXO Risk Assessment is essential to ensure safety and prevent delays.

Brimstone UXO’s Risk Mitigation Services:

• UXO Risk Assessments – Identifying potential UXO risks based on historical records and military activity.
• Non-Intrusive & Intrusive UXO Surveys – Advanced detection methods to locate buried UXO before ground disturbance.
• UXO Disposal & Clearance – Safe removal and disposal of discovered ordnance to protect people and property.

Unlike many traditional UXO threats, phosphorus grenades do not contain ferrous metals, making them difficult to detect using conventional metal detection equipment. This makes UXO risk assessments even more critical for sites with known military history.

For more updates on UXO safety and risk mitigation, follow Brimstone UXO on Facebook, Instagram, Twitter, LinkedIn and YouTube.