Uncontrolled explosion during explosive ordnance disposal operations

While undertaking unexploded ordnance (UXO) disposal works, a remotely operated vehicle (ROV) was being used to deploy an explosive charge onto the target on the seabed and then detonate the charge remotely.

This was the 7th charge deployed using the ROV. In the previous two weeks no issues were encountered.

A standard charge carrier, containing the following, was fitted to the manipulator arms of the ROV:

• Charge carrier metal frame
• Blowfish transducer (LAT) with unique code
• 5kg Semtex explosive
• 1 x electrical detonator
• 0.5m detonating cord
• Rubber hose protector for detonating cord
• Swiss Shield radio frequency shield
• Various tie wraps and fixings

The ROV had been lifted outboard and was about to be lowered into the sea when an uncontrolled explosion occurred, causing considerable damage to the ROV.

There was no serious injury to personnel. However, 5 people were transferred to the local hospital once the vessel had docked, and were treated for temporary hearing loss and shock.

Prior to the explosion, the ROV had activated its thrusters and the sonar system in preparation of deployment subsea.

The cause of the explosion was likely due to:

• Generation of interference via either the detonator or the Swiss Shield
• The Swiss Shield introducing an unconsidered risk (e.g. introduction of an earthing arrangement)
• Electrical/acoustic interaction between the ROV and the charge (via normal or abnormal conditions)

ROV thrusters and sonar should not be powered up until the ROV is below the surface of the water.

The charge carrier should be made of a non-metallic material.

All leads and wires to be straight and not coiled.

Further investigation into shields used to protect from interference is recommended.

Greater assurance is required surrounding explosive ordnance disposal methodology and competency.

How can something like this happen here?

What precautions have we put in place to reduce the risk of uncontrolled explosions?

If this event was to occur here, what proactive measures do we have to minimise harm?