UK Mandates Low-Noise Deflagration as Default Method for Marine UXO Clearance

Technical Summary

The United Kingdom government has formalised a significant shift in marine Explosive Ordnance Disposal (EOD) doctrine through a Joint Position Statement (JPS) published by the Department for Environment, Food & Rural Affairs (Defra), the Marine Management Organisation (MMO), the Scottish Government Marine Directorate, the Welsh Government, Natural Resources Wales, the Department of Agriculture, Environment and Rural Affairs (Northern Ireland), Natural England, NatureScot, and the Joint Nature Conservation Committee (JNCC). The JPS replaces the November 2021 interim statement and establishes low-noise clearance methods—principally low-order deflagration—as the mandatory default for all marine UXO disposal across UK waters.

This policy applies primarily to Unexploded Ordnance encountered during offshore energy development, particularly the construction of wind farm foundations, cable routes, and associated infrastructure. UK waters retain an estimated 100,000 items of legacy ordnance from both World Wars, predominantly German and British aerial bombs ranging from 50 kg to 1,000 kg General Purpose (GP) class, along with sea mines, depth charges, and artillery projectiles. Offshore wind developers routinely encounter UXO during pre-construction geophysical surveys and seabed preparation activities.

Deflagration Versus Detonation: The Technical Distinction

The regulatory shift codifies a technical distinction between two fundamentally different explosive disposal outcomes. High-order detonation involves complete and near-instantaneous conversion of the explosive fill to gaseous products via a supersonic detonation wave (Velocity of Detonation/VoD typically 6,000–8,000 m/s for TNT-based fills). This produces the characteristic blast overpressure wave, underwater shock, and acoustic signature that causes lethal and sub-lethal injury to marine mammals within several kilometres of the detonation point. A 250 kg GP bomb containing approximately 80–120 kg of Amatol or TNT explosive fill generates peak underwater overpressure exceeding 200 kPa at 100 m range—well above the threshold for permanent auditory injury to cetaceans.

Low-order deflagration uses a small shaped charge or specialist tool to penetrate the bomb casing and initiate combustion (deflagration) of the explosive fill rather than detonation. The explosive content burns at subsonic rates, causing the casing to crack and fragment at low velocity without generating the supersonic shock wave characteristic of detonation. The resulting underwater noise signature is typically 100 to 1,000 times lower than high-order detonation, bringing acoustic levels below the threshold for marine mammal injury at much shorter ranges. The UXO is rendered permanently safe through consumption of the explosive fill, though the process may leave residual energetic material that requires assessment.

Regulatory Framework: The Four-Category Hierarchy

The JPS establishes a four-tier classification system for marine licence applications involving UXO clearance. Category A (preferred) requires applicants to demonstrate a low-noise tool with both controlled environment testing evidence and operational at-sea validation. Category B permits low-noise tools with controlled testing evidence only. Category C allows high-order clearance only under “extraordinary circumstances”—defined as situations where the UXO type, condition, or location “far exceed the expected or demonstrated capabilities of any known low-noise clearance tool,” and only after a minimum of three failed low-noise attempts with prior licensing authority agreement. Category D applications proposing high-order clearance without adequate justification are assessed as unlikely to receive marine licence approval.

For EOD practitioners, this regulatory structure introduces operational constraints. The three-attempt minimum before escalation to high-order clearance requires multiple diver or remotely operated vehicle (ROV) deployments to each UXO location, increasing subsea operational time, vessel costs, and weather-window dependency. Operators must maintain both low-order and high-order capability on-site throughout clearance campaigns, with appropriate mitigation measures (marine mammal observers, acoustic deterrent devices, bubble curtains) pre-positioned for potential Category C escalation.

Personnel and Safety Considerations

The policy shift raises several practitioner-relevant considerations. Low-order deflagration tools require precise placement against or adjacent to the UXO, which in turn demands accurate identification of ordnance type, orientation, fuze condition, and casing integrity before tool deployment. Corroded World War II ordnance with deteriorated fuzing mechanisms presents particular challenges: sensitised explosive fills (particularly Amatol that has absorbed seawater, or Torpex with degraded aluminium component) may exhibit reduced deflagration-to-detonation transition (DDT) thresholds, increasing the risk of unintended high-order detonation during low-order procedures.

The JPS acknowledges this risk implicitly through the Category C extraordinary circumstances provision, recognising that certain ordnance conditions may exceed low-order tool capabilities. EOD operators must maintain current competence in both low-order and high-order techniques, and risk assessments must account for DDT probability as a function of explosive fill condition, fuze state, and degree of casing corrosion. JNCC’s updated marine mammal mitigation guidelines (JNCC Guidelines for Minimising the Risk of Injury to Marine Mammals, 2025 edition) now include specific mitigation requirements for low-order clearance operations in addition to the established protocols for high-order detonation.

Data Gaps & Confidence Assessment

The JPS framework is well-documented and sourced from primary government publications (A1 reliability/accuracy). Operational data on low-order deflagration success rates across different ordnance types remains limited in open-source literature. Failure rates for low-order tools against specific WWII ordnance configurations (particularly large GP bombs with deteriorated Torpex fills or armed time-delay fuzes) represent a significant data gap. The acoustic noise reduction claims (100–1,000x) are based on controlled testing; at-sea performance data across varied seabed conditions remains sparse. Residual energetic material quantities following deflagration events are not consistently reported.