GB556071A - Improvements in means for safeguarding electric igniters of blasting detonators against accidental firing - Google Patents

Abstract

556,071. Protective arrangements. ROLFES, Ltd., and ROLFES, H. J. Oct. 31, 1941, No: 14060. [Class 38 (iv)] [Also in Group XXI] Means for safeguarding an electric igniter of a blasting detonator from atmospheric electricity comprises the combination of (a) a mass which is in contact with each lead or with extensions thereof and which offers a high resistance to voltages of the magnitude used for intentionally firing the igniter and a low resistance at voltages substantially higher than said firing voltages and caused by atmospheric electricity, and (b) discharge points disposed on or opposed to the leads or extensions in such a position as to promote the discharge from either or both of the leads or extensions through the mass. The mass, which is earthed, may be the " coherer mass" described in Specification 555,969, or may be galena, yellow crystalline iron pyrites, or zincite. In Fig. 2, which shows a wax primer, the discharge points 23, 24 are formed on bare parts of conductors 1a, 1b which end in a bridge-wire 8 which, on firing, is heated to incandescence. The points are embedded in a discharge layer 21 which is in contact with rock or with the side of the borehole. The discharge mass may be in the form of a plug contained in an earthed metal casing, and the discharge points may be on the inside of the casing. Two plugs may safeguard one detonator. The plug may be disposed exteriorly of the detonator, as in Specification 555,969. The discharge points may be constituted by two strips of metal foil' adhesively secured to the opposite sides of a I-shaped piece of cardboard embedded'in a discharge mass contained in a casing connected to the detonator by a copper wire and a sleeve.