Unexploded ordnance is found quite frequently during dredging.
Most common; ammunition is found in the dragheads of trailer dredgers. Specials grids are fitted, with small openings, to stop explosives entering the suction pipes and dredgepumps inboard, where their impact may be much larger.
The dangerous ammo frequently dates back to WW-II, but is still highly dangerous and instable.
Some dredging areas are notorious well known to contain large amounts of ammunition: certain area's in Singapore (Jodoh Bay), Hong kong, Germany (especially Jade and Weser rivers...), some parts of France (Dunkerque, ...), etc...
During the Chep Lap Kok project in Hong Kong, trailer dredger "HAM308" hit a large bomb or mine, which exploded in the draghead, with sufficient force to dislocate the vessel's main drive gear. The ship was subsequently declared constructive total-loss and scrapped.
Common sense is best for dealing with high explosives onboard.
Whenever a bomb is discovered onboard, leave it be, get a professional bomb squad onboard and let them handle the job.
Most self-declared "specialist" macho crewmembers will get away with handling a bomb or two. But there is a limit to luck...
Seal the area, make sure no crewmembers go near the unexploded ordnance, until the bomb squad arrives.
The following is based on Marine Guidance Note MGN 323 (download pdf 248 kB) from the Maritime and Coastguard Agency, UK.
Explosive weapons are dangerous even if they have been in the water many years, and the following guidance is given in dealing with them:
(a) A suspected explosive weapon should not be landed on deck if it has been observed while the dredge equipment is still outboard.
(b) Suspect items should not be subjected to any form of impact.
You may fabricate a makeshift cushion under the explosive, to soften its fall, and rig a net to prevent its fall.
(c) If an item is inadvertently brought onto a vessel, it should be secured on deck and kept wet. Attempting to lift and swing the item outboard to return the item to the sea will significantly increase the risk to the vessel and her crew.
The following procedures should be followed:
(i) Great care should be taken to avoid bumping the weapon. If retained onboard it should be stowed on deck, away from heat and vibration, firmly chocked and lashed to prevent movement.
(ii) IT SHOULD BE KEPT COVERED UP AND DAMPED DOWN. (This isimportant because any explosive which may have become exposed to the atmosphere is liable to become very sensitive to shock if allowed to dry out.)
(iii) The weapon should be kept on board for as short a time as possible.
(iv) Under no circumstances should crew tamper or open a weapon in any way. Phosphor bombs require special care. Phosphorous is an extremely hazardous chemical with ability to cause serious injury and under no account should non-qualified personnel touch or handle a phosphorous device. Phosphorous devices may be leaking with toxic smoke and whilst considerable leakage runs a significant fire risk, massive and sudden exposure of dry phosphorous may cause an explosion.
Phosphor bombs require special care. Phosphorous is an extremely hazardous chemical with ability to cause serious injury and under no account should non-qualified personnel touch or handle a phosphorous device. Phosphorous devices may be leaking with toxic smoke and whilst considerable leakage runs a significant fire risk, massive and sudden exposure of dry phosphorous may cause an explosion.
Additionally, there is a risk of chemical poisoning and burns if handled and the formation of phosphoric and phosphine gasses if stored.
Marc Van de Velde