Detonator design

The transit time is mainly a function of the particular detonator design, that is, the type, density, and length of the explosives loaded into the detonator. The transit time is equal to the length of each explosive element or pressing, divided by the detonation velocity of that element, plus the excess transit time due to the buildup of run distance to steady-state detonation. Recall that the run distance, and hence excess transit time, is a function of the initiating shock pressure. Also, the initiating shock pressure from an EBW is a function of the burst current. Therefore, the transit time of an EBW detonator is not independent of the system. 

The use of lead azide in one-ampere, no-fire detonator designs is shown in Figure 5. In these designs, the high-temperature stability of lead azide is needed if the detonators are not to fire with a 1-A current flow. To keep the azide below its initiation temperature, heat conduction paths are provided from a thin-film, resistive-bridge element (Figure 5b) through the electrical connections and the... 

CP forms yellow monoclinic crystals with crystal density 1.97 g cm [11]. It is compatible with most metallic and ceramic materials used in typical detonator design and also epoxies cured by amines or anhydrides. This is interesting since many organic explosives and amine cured epoxy materials have compatibility problems. It is also compatible with PETN [12]. 

Fig. 9.3 Generalized CP detonator design [4, 20]. Reprinted by permission of fPSUSA Seminars, Inc.

A great deal of experimental work has also been done to identify and quantify the ha2ards of explosive operations (30—40). The vulnerabiUty of stmctures and people to shock waves and fragment impact has been well estabUshed. This effort has also led to the design of protective stmctures superior to the conventional barricades which permit considerable reduction ia allowable safety distances. In addition, a variety of techniques have been developed to mitigate catastrophic detonations of explosives exposed to fire. 

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. 

W. C. Davis, "Detonation Phenomena," ia / 2th A.nnual Symposium on Behaniour and Efiliation of Explosives in Engineering Design, University of New Mexico, Albuquerque, 1972. 

In designing faciUties for handling and processing nitromethane, it is recommended that nitromethane not be processed in high pressure equipment. AH vessels for nitromethane service should be protected to prevent adiabatic compression. Detonation traps should be installed at each end of transfer lines and in every 61 m (200 feet) of continuous line. Nitromethane lines should be located underground or in channels wherever possible. Pressure rehef devices (rated - 690 kPa = 100 psig) should be installed between closed valves (81). 

Installation End-of-line arresters should be protected using appropriate weather hoods or cowls. In-hne arresters (notably detonation arresters) must be designed to withstand the highest hue pressure... 

Deflagration Arresters The two types of deflagration arrester normally considered are the end-of-line arrester (Figs. 26-23 and 26-24) and the tank vent deflagration arrester Neither type of arrester is designed to stop detonations. If mounted sufficiently far from the atmospheric outlet of a piping system, which constitutes the unpro-tec tea side of the arrester, the flame can accelerate sufficiently to cause these arresters to fail. Failure can occur at high flame speeds even without a run-up to detonation. 

In certain exceptional cases, a specially designed deflagration arrester may be mounted in-line without regard to run-up distance. This can be done only where the system is known to be incapable of detonation. An example is the decomposition flames of ethylene, which are briefly discussed under Special Arrester Types and Alternatives. ... 

Decomposition Flame Arresters Above certain minimum pipe diameters, temperatures, and pressures, some gases may propagate decomposition flames in the absence of oxidant. Special in-line arresters have been developed (Fig. 26-27). Both deflagration and detonation flames of acetylene have been arrested by hydrauhc valve arresters, packed beds (which can be additionally water-wetted), and arrays of parallel sintered metal elements. Information on hydraulic and packed-bed arresters can be found in the Compressed Gas Association Pamphlet G1.3, Acetylene Transmission for Chemical Synthesis. Special arresters have also been used for ethylene in 1000- to 1500-psi transmission lines and for ethylene oxide in process units. Since ethylene is not known to detonate in the absence of oxidant, these arresters were designed for in-line deflagration application. 

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