Manufacture detonators

Priming charge. In detonator manufacture, the charge of initiating explosive. 

Fig. 63. Detonator manufacture—a line of compartments in which the filling and pressing of detonators is carried out automatically. Courtesy Imperial Chemical Industries Ltd., Nobel Division.

Essentially, the requirements have led to reliance on batch processes, because safety is greater the smaller the quantity in process at one time, specifications can be rigorously checked, and the minute quantities used in detonators imply that batches of just a few pounds are adequate for steady production. Apart from these considerations the detonator manufacturer and the explosive designer look for a product which is dense or readily densifiable, is safe subject to prescribed precautions (Chapter 3), has flow properties suitable for pouring and pressing in detonator cups, is reasonably priced, and is adequately storable (Chapter 3). 

Hill, S.G. Comercial detonators Manufacture of lead styphnate and lead azide. Can. Chem. Process Ind. 26(18), 43 (1942)... 

Electric detonators manufactured in North America are equipped with shunts that protect the detonator leg wires from contacting and transmitting stray or extraneous current to the internal detonator mechanism. In areas that are prone to exposure to extraneous current and/or radio frequencies, a blaster may prefer to use detonating cord or other nonelectric initiation system. It is important to understand, however, that even nonelectric sjstems are susceptible to premature detonation caused by lightning strikes, heat, and impact stresses. 

Plutonium (Pu) is an artificial element of atomic number 94 that has its main radioactive isotopes at 2 °Pu and Pu. The major sources of this element arise from the manufacture and detonation of nuclear weapons and from nuclear reactors. The fallout from detonations and discharges of nuclear waste are the major sources of plutonium contamination of the environment, where it is trapped in soils and plant or animal life. Since the contamination levels are generally very low, a sensitive technique is needed to estimate its concentration. However, not only the total amount can be estimated. Measurement of the isotope ratio provides information about its likely... 

Only relatively few compounds can act as primary explosives and still meet the restrictive military and industrial requirements for reflabiUty, ease of manufacture, low cost, compatibiUty, and long-term storage stabiUty under adverse environmental conditions. Most initiator explosives are dense, metaHoorganic compounds. In the United States, the most commonly used explosives for detonators include lead azide, PETN, and HMX. 2,4,6-Triamino-l,3,5-triuitrobenzene (TATB) is also used in electric detonators specially designed for use where stabiUty at elevated temperatures is essential. 

Lead Azide. The azides belong to a class of very few useflil explosive compounds that do not contain oxygen. Lead azide is the primary explosive used in military detonators in the United States, and has been intensively studied (see also Lead compounds). However, lead azide is being phased out as an ignition compound in commercial detonators by substances such as diazodinitrophenol (DDNP) or PETN-based mixtures because of health concerns over the lead content in the fumes and the explosion risks and environmental impact of the manufacturing process. 

Ammonium nitrate is normally classified as an oxidizing agent. The pure salt is not classed as an explosive because it is difficult to detonate. Spark, flame, or friction do not cause detonation, and ammonium nitrate is relatively insensitive to shock. However, a variety of substances, such as chloride and oil, are known to sensitize the material, so manufacturers strive to eliminate such substances from their processes. 

In the manufacture of explosives, sodium nitrate is used mainly in blasting agents. In slurries and emulsions, sodium nitrate improves stabiUty and sensitivity. It also improves the energy balance because sodium nitrate replaces water, so that more fuel can be added to the formulation. Sodium nitrate reduces crystal size of slurries, which in turn increases detonating speed. In dynamites sodium nitrate is used as an energy modifier. Typical content of sodium nitrate is 20—50 wt % in dynamites, 5—30 wt % in slurries, and 5—15 wt % in emulsions. Sodium nitrate is used also in permissible dynamites, a special type of dynamite for coal (qv) mining. 

Continuous Flame Test A test in which a flame arrester is subjected to flame of a continnonsly burning mixture (as specified in UL 525 for deflagration or detonation flame arresters) on the outlet face of the arrester for one hour (or longer at the manufacturer s request). 

Accidents have also occurred while NG was being transported around manufacturing facilities via gravity flow in gutters. To increase the safety of such transport, detonation breakers can be introduced along its flow path. An example of a detonation breaker is shown in Fig... 

Nitroglycerine can detonate in pipes of diameter down to approximately 5 mm. In nitroglycerine manufacture there is, therefore, an inherent danger of transmission of detonation from one manufacturing house to another in the series. Even a pipe which has been emptied of nitroglycerine can have on it a skin of the product sufficient to enable transmission of detonation from one end of the pipe to the other. To prevent the spread of an accident it is now usual to transfer nitroglycerine as a non-explosive emulsion in an excess of water. Such emulsion transfer is particularly convenient with the NAB process, as the emulsion transfer lines can also carry out the necessary process of washing and purification. 

In the manufacture of high explosives, the possibility of accidental detonation must always be borne in mind and buildings are constructed and arranged so as to minimise the possible effects of such an explosion. The buildings are placed sufficiently far apart so that an explosion in one building will not cause sympathetic detonation in the other. Practical distances do not make it completely impossible for detonation in one house to leave all other houses unaffected, for two reasons ... 

Lead azide is manufactured by reaction of sodium azide with either lead nitrate or lead acetate. It is a white crystalline solid, insoluble in cold water and stable on storage. It is very sensitive to friction and impact and has a velocity of detonation, when pressed to a density of 3-8, of4500 ms 1. 

Two crystallographic forms of lead azide are important, the ordinary alpha form which is orthorhombic and the beta form which is monoclinic. The densities of these forms are 4-71 and 4-93 respectively. It was for many years believed that the beta form is the more sensitive to friction and impact and accounted for detonations which have occurred in the manufacture and handling of the substance. It is now known that the beta form is in fact no more sensitive than the alpha. Even the alpha form, when present as large crystals, is very sensitive and conditions can arise (particularly when the formation of the lead azide is controlled by diffusion effects) where spontaneous detonation occurs. Although with modern knowledge these hazards can be avoided, pure lead azide is nevertheless a dangerous compound and is now made only for military purposes. 

Tetrazene is a light yellow crystalline substance, insoluble in water and most organic solvents. The density is low under normal conditions, but on pressing can reach approximately 1 g ml-1. Tetrazene is weak as an initiating explosive, and is therefore not used alone. It has no advantages to commend it for use in commercial detonators, but does find application in the manufacture of military and other percussion caps. Like diazodinitrophenol, tetrazene does not detonate when ignited in the open, but only when ignited under confinement. 

The original initiating explosive used by Nobel and all manufacturers for many years was mercury fulminate. This had the disadvantage of decomposing slowly in hot climates, particularly under moist conditions. For this reason mercury fulminate is no longer widely used. In most countries it has been replaced by a mixture of dextrinated lead azide and lead styphnate. In the U.S.A. some detonators are made containing diazodinitrophenol. 

Although the requirement for flame sensitiveness is the main consideration for initiating explosives for plain detonators, others are important in manufacture. The explosive must be capable of compression into a coherent mass and at the same time leave the equipment free from adhesions. Lead azide can be somewhat deficient in cohesion, and to improve this a small proportion of tetryl is sometimes added to the... 

Detonators of the first three types all employ bridgewires and therefore require low voltages for their initiation. The choice is one of manufacturing convenience, but as most makers prefer type 3, only this will be described in detail. 

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