Safety fuses

36.03 - Safety fuses; detonating fuses; percussion or detonating caps; igniters; electric detonators. These products, which are generally called blasting accessories, are required to ignite powders and explosives. The heading covers : (A) Safety fuses and detonating fuses r Safety fuses (slow fuses or Bickford fuses are devices desi ed to transmit a flame towards an ordinary igniter or detonator. T ey consist genera ly of a thin envelope of textile material, tarred or impregnated with rubber or plasttcs, containing a linear charge of black powder. Detonating fuses serve to transmit one or more detonations, and generally comprise a core of pentrite or other explosive in a waterproofed covering of textile material or plastics (flexible fuses) or in a sheath of lead or tin (leaded or tinned hses). In certain cases the explosive charge is placed, in a thin layer only, on the inner surface of a tube of pIastics. They are most frequently used in mines and quarries and on civil engineering sites. (E3) Percussion or detonating caps. (1) Percussion caps (percussion primers) consist of a small container, general1 metallic, usually containing a mixture based on lead ainitroresorcinate (styphnatef with the addition of tetrazene and various oxidising and reducin agents; charges of this explosive mixture usually weigh between 10 and 200 mg. 7%ese caps are intended for fixing in the bases of cartridge cases and are used to ignite propellent powder. a (2) Friction ercussion caps or firing tubes consist generally of two concentric metal or cardboar tubes contaimng different charges. The ex losive charge in the inner tube is ignited by the tearing out of a saw-toothed wire an thus fires the charge of owder between the two tubes which transmits the ignition. Like the caps describe in (1) above, firing tubes are used for frring propellent powders. X (3) Detonating caps (detonators) consist charge of, e.g., pentrite, hexogen or protective ca sule. They are used for i powders an are generally fired by them. a 'I' of a small charge of primary explosive plus a tetryl, in a tube of metal or plastics under a iting pre ared explosives other than ro ellent e flame om the safety fuse which ea s into R Pf (C) Igniters This group includes : (1) Electric igniters consisting of an electric fuse head and a small charge of igniting powder, generally black powder. An electric fuse head consists of two insulated conductors to the ends of which a conducting metal filament is soldered to form an electrically resistant bridge; this filament is embedded in an igniter bead. It is used to ignite a powder charge or to initiate a primary explosive. (2) Chemical igniters such as those consisting of a cylinder containing a glass ampoule filled with a chemical product (e.g., sulphurrc acid) and a charge of potassium chlorate, the two being separated by a metal diaphragm. When the ampoule is broken the acid eats away the metal diaphragm (which serves as a dela .element) and reacts with the potassium chlorate, producing intense heat capable o Igniting a powder charge or safety fuse. (D) Electric detonators Electric detonators consist of an electric fuse head, as described in Item a tube of metal (or possibly lastics), a small char e of primary explosive a composition based usual y on lead azide) an a somewhat larger explosive (e.g., pentrite, hexogen or tetryl). P % This group also includes certain electric detonators known as electric primers. These are often miniaturised, and the fuse head may be replaced b the incorporation, in the rimary composition, of additives to make the cornposibon con uctive and enable it to be L e d by induction. dY This heading does not include : (a) The paraffined amorce strips or rolls used in miners' lamps, nor caps for toy pistols (heading 36.04). (b) Articles not containin any explosive or inflammable charge (small caps, tubes, electrical apparatus, etc.) which are clsssifkd according to their nature under their respective headings. (c) Shell fuses and cartridge cases with or without caps (heading 93.06).