The clearance of unexploded ordnance (UXO) poses special problems underwater. When UXO is determined to be too hazardous for removal, it must be blown-in-place (BIP). The potential for acute environmental damage to marine life from underwater explosions is proportional to the explosive weight of the UXO and can extend for thousands of feet in the case of larger UXO. Regulatory agencies may require special monitoring and mitigation efforts if endangered species are at risk from an underwater detonation. The objective of this study was to demonstrate a statistical reduction in explosive yield by causing underwater UXO to undergo a low-order detonation.

France, Germany, and the United States have recently developed small explosive tools to reliably render UXO safe. These tools shoot a high velocity projectile or moderated shape charge into the UXO to create a low-velocity detonation reaction that can result in a significant reduction in explosive yield. The success of the technique is dependent upon the specific UXO and its explosive fill. ESTCP leveraged these efforts to demonstrate the effectiveness of a tool underwater on a limited class of UXO.

The demonstration investigated the effectiveness and reliability of the German HL-21 shaped charge as a low-order underwater detonation tool. Tests were conducted on TNT-filled 155-mm projectiles and tritonal-filled Mk 82 bombs in a controlled underwater pond at the Aberdeen Test Center in Maryland. All twenty-one 155-mm projectiles tested resulted in low-order events, and 8 of the 11 Mk 82s resulted in low-order events, with one high order detonation and two instances with no reaction.

Effectiveness was measured by a reduction in the net explosive yield. The low-order detonation procedures were very effective in reducing blast effects while causing a complete disruption of the ordnance. The HL-21 reduced explosive yields over conventional BIP procedures based on both peak pressure and impulse in excess of 97 percent for the Mk 82 and by 67 to 99 percent for the 155-mm. Significant amounts of unreacted explosive fill were recovered from the low-order reactions.

Reliable reductions in explosive yield would provide Navy explosive ordnance disposal (EOD) divisions and civilian UXO companies with a method for ordnance disposal. The most significant benefit will be the reduction in acute hazards to marine life and public safety caused by underwater detonation procedures. (Project Completed - 2002)