The safety fuse is a type of fuse invented and patented by English inventor William Bickford in 1831. Originally it consisted of a "tube" of gunpowder surrounded by a waterproofed varnished jute "rope." It replaced earlier and less reliable methods of igniting gunpowder blasting charges which had caused many injuries and deaths in the mining industry. The safety fuse burns at a rate of typically about 30 seconds per foot (1 second per cm).
History
Documented evidence suggests that the earliest fuses were first used by the Chinese between the 10th and 12th centuries. After the Chinese had invented gunpowder, they began adapting its explosive properties for use in military technology. By 1044 they were using gunpowder in simple grenades, bombs, and flamethrowers. Gunpowder did not reach Europe until the early 13th century, carried over from China by Middle Eastern traders and merchants along the old Silk Road.
For three centuries gunpowder was primarily used for military warfare. It was not until 1574 that gunpowder was first introduced to the mining industry, and it took until 1617 before it was first used in a large-scale mining operation—at Thillot in France.
Sensitivity of gunpowder
One of the problems miners faced when introducing gunpowder into their operations was that it was relatively easy to ignite when exposed to sparks, intense heat, or flames. The method used by miners to blast away rock involved drilling several holes across a rock face which would be filled with charges of gunpowder. In order to confine the gases produced on ignition, the gunpowder was confined within each shot hole by inserting a pointed rod known as a "needle" in the gunpowder-charged hole and then packing in soft clay and tamping it down to form a plug. The "needle" was then removed and replaced by a fuse made of straws or quills filled with black powder. To prevent sparking, a copper needle and a non-metallic ramming rod, typically made from hickory, were used.
If a spark was created, the results could be disastrous to the work force, and this was a common occurrence. Miners and mine owners were aware of the dangers of the use of gunpowder in mining, as is evident in their instructions for handling the material. A mill in England preparing the material wrote in its instructions, "Whosoever is at Labour within or without the powder magazines should execute his commission in such a respectful and revered silence as is seemly in such a place where (unless the Almighty in his Grace keeps a protective hand over the Labour) the least lack of care may not alone cause the loss of life of all present, but may even in a moment transform this place as well as its surroundings into a heap of stone."
The other major problem concerned the intentional ignition of the gunpowder charges. To provide some protection from the blast and the fumes, a nominated miner ignited the far end of the fuse which was intended to burn at a known rate. The miners, therefore, knowing the length of the fuse, could estimate the delay between ignition of the fuse and the ignition of the main charges. However, early fuses, known as filled "quills", had a tendency to either burn irregularly, "flash off", or break—either by separation or by "pinching" in the shot hole due to the tamping process. They could also be damaged allowing moisture in, which could cause them to smoulder instead of burn and introduce a long delay. If the main charge failed to ignite, this was known as a misfire or "hang fire", and the miners would need to wait before returning to the work face to set new fuses. Increasingly, miners in Cornwall in the late 18th and early 19th centuries were becoming badly injured as a result of suspecting that there had been a misfire and returning to the work face just as a smouldering damp quill ignited the gunpowder charges.
William Bickford
In 1831 English merchant William Bickford moved to the heart of the Cornish mining district near Camborne; where at Tuckingmill he developed the first practical and reliable means for igniting gunpowder when mining, the "Safety Fuze". After earlier attempts at developing a safer way had failed, Bickford had an insight while visiting his friend who was a ropemaker. While observing his friend winding cord together to generate a rope, Bickford believed he could adapt the same method towards developing a fuse. This was done with the help of his son-in-law George Smith and a working miner named Thomas Davey.