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| A water column rises during underwater blasting operations |
Underwater blasting equipment has been used for a variety of purposes during the development of diving techniques. As long ago as 150 years , divers were using explosives underwater to remove submerged rocks and debris for construction work. The condition upon which the work had to be carried was so varied that no hard and fast rules were laid down save those of safety. When blasting rock , use was always made of the natural fault lines or fissures in the stone . If the rock was smooth and had no natural weak points a process called mud capping was used . This was done by placing the charge flat against the surface of the rock and covering it with a thick layer of clay.
An artist's impression of the Removal of Pilgrim Rock during the construction of a lighthouse. The tender on the right can be seen holding a 10 foot long Nitro-glycerine can for blasting The diver at the top of the picture is E Hickman one of the divers on the Pilgrim Rock project.
Blasting was also used in the dispersion and salvage of sunken ships. Rivets could be easily fractured and the integrity of the sunken vessel destroyed by placing charges at the junctions of beams and frames. It was quickly discovered that a single charge on a beam did little more than bend it whilst two charges on opposite sides but at staggered intervals produced a shearing effect . Teams of two divers were normally used to minimise the time the charge was left in the water. Explosives were developed to be used underwater and had special properties and great pressure upon detonation, in some cases up to 2 tons per square inch.
Detonating fuse was used in many underwater blasting operations. The fuse had a velocity of thousands of meters per second and was waterproof to 20 meters though certain precautions were taken to prevent the ingress of water to the fuse cover.. In extremely cold condition the charge became sold and lost its pliability . In those cases it could be gently warmed by applying indirect heat . Direct heat had catastrophic results and instant detonation could occur . After preparation of the charge the electric detonator having been previously tested could now be inserted into the charge . A cable was then connected to the detonator and run to the exploder . As soon as the exploder has been operated the cable was disconnected from the exploder. The exploder was essentially a high voltage electrical generator activated by a plunger mechanism operating a dynamo enclosed in a wooden box
A large submerged ship with a displacement of say 1000 tons could be dispersed by using 1000 lbs of explosive charge strategically placed throughout the vessel.
