Initiation, explosives

Initiators. Explosives such as mercury fulminate and certain metallic azides which are extremely sensitive to mechanical shock, and are accordingly used in small quantities in detonators to initiate the explosion of larger masses of less sensitive material. 

Explosives are commonly categorized as primary, secondary, or high explosives. Primary or initiator explosives are the most sensitive to heat, friction, impact, shock, and electrostatic energy. These have been studied in considerable detail because of the almost unique capabiUty, even when present in small quantities, to rapidly transform a low energy stimulus into a high intensity shock wave. 

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. 

Flammability and Explosivity. Ozone is endothermic, thus it can bum or detonate by itself and represents the simplest combustible and explosive system. The concentration threshold for spark-initiated explosion ofHquid ozone in oxygen at —183° is 18.6 mol % O the concentration limit... 

About three minutes after the initial explosion or hie, the tank failed and produced fragments and a hreball. Blast effects were far heavier in the upward and windward directions than otherwise. About 75 m (250 ft) from the explosion center. 

An initial explosion occurred on the production deck of the Piper Alpha Offshore Platform in the North Sea at about 1 00 PM on July 6,1988. The incident escalated into a tragedy that cost the lives of 165 of the 225 persons on the platform. Two additional fatalities occurred on a rescue boat. The Piper Alpha Platform was totally devastated. 

Ref. [40] points out that the effects of a Bleve depends on whether the liquid in the vessel is flammable. The initial explosion may generate a blast wave and fragments from the vessel. For a flammable material, the conditions described in Ref. [34] above may result, and even a vapor cloud explosion may result. 

If, however, the material is concentrated in a small area or when it is in a confined space, explosion may occur. Burning Picric Acid containing metal picrates may result in explosion. Similarly a potential danger exists when burning Picric Acid is in contact i ith metals, since in the molten state it forms picrates which may initiate explosion. This depends largely on the metal lead, iron, copper should be considered particularly dangerous ... 

System Initial Explosive Density, g/cc Foam Density, g/cc CJ Pressure, kbars... 

Primary Explosives. See under Initiating Explosives in Vol 7,1105-L to I106-L... 

Synonym(s) Lead metal plumbum olow (Polish) pigment metal Lead(2+) acetic acid plumbous acetate Initiating explosive (lead azide, dextrinated type only) Lead (II) bromide d... 

Synonym(s) Initiating explosive lead styphnate lead trinitroresorcinate styphnate of lead Sulfuric acid lead(2+) salt lead (II) sulfate Lead monosulfide lead(2+) sulfide Lead (II) sulfide plumbous sulfide natural galena Lead tetraethide TEL tetraethyllead tetraethylplumbane... 

Nitroglycerine and other high explosives of this type are difficult to initiate into detonation simply by the use of a flame. Mercury fulminate, discovered by Howard, is an explosive of relatively low power which can, however, always be relied on to detonate when ignited by a flame. Explosives like mercury fulminate are known as initiating explosives. 

Initiating explosives (sometimes called primary explosives). 

Tetryl is a pale yellow solid, melting at 129°C. It is moderately sensitive to initiation by friction or percussion. Tetryl is most used in the form of pressed pellets as primers for other less easily initiated explosives. 

Commercially, lead azide is usually manufactured by precipitation in the presence of dextrine, which considerably modifies the crystalline nature of the product. The procedure adopted is to add a solution of dextrine to the reaction vessel, often with a proportion of the lead nitrate or lead acetate required in the reaction. The bulk solutions of lead nitrate and of sodium azide are, for safety reasons, usually in vessels on the opposite sides of a blast barrier. They are run into the reaction vessel at a controlled rate, the whole process being conducted remotely under conditions of safety for the operator. When precipitation is complete, the stirring is stopped and the precipitate allowed to settle the mother liquor is then decanted. The precipitate is washed several times with water until pure. The product contains about 95% lead azide and consists of rounded granules composed of small lead azide crystals it is as safe as most initiating explosives and can readily be handled with due care. 

Lead styphnate is a poor initiating explosive which when dry is very sensitive to friction and impact, to electrostatic discharge, and to flame. Its main use is as an additive to lead azide to improve flame sensitiveness (see p. 101). When pressed to a density of 2-6 g ml-1 it has a velocity of detonation of4900 m s l. 

Diazodinitrophenol is a yellow powder, almost insoluble in cold water. It does not detonate when unconfined, but when confined has a velocity of 6900 m s-1 and a density of 1-58 g ml-1. For an initiating explosive it is relatively insensitive to friction and impact, but still is powerful when confined. DDNP has good properties of storage and has found application in detonators, particularly in the U.S.A. 

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. 

The initiating explosive used must ignite with certainty from the spit of a safety fuse. It must be remembered that the intensity of the spit can be reduced if the safety fuse is not cut squarely and also that the fuse may in practice not always be fully inserted into the detonator. Lead azide by itself is not sufficiently easily ignited to give a satisfactory plain detonator and it is therefore used in admixture with lead styphnate, which is very readily ignited by flame. The proportions of such mixtures vary from 25 to 50% of lead styphnate. Mercury fulminate and diazodinitrophenol are sufficiently sensitive to flame not to require such additives. 

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... 

A bridge of resistance wire is connected across the ends of two leading wires and surrounded by a loose charge of flashing composition or of initiating explosive. 

The second dip, or series of dips, is intended to provide a suitable flame which can ignite the initiating explosive in the detonator. These dips are commonly based on potassium chlorate and charcoal, again suspended in... 

Assembly commences with a plain detonator containing its base charge and initiating explosive. These detonators are held in plates and the processes are insertion of suitable delay elements, followed by pressing in the normal way. They are then checked by X-ray examination to ensure... 

Gunpowder was first employed as a propellent explosive in guns, although later it was also employed for blasting. In neither case, however, does it detonate in the same way as the blasting explosives described in Part I, or the initiating explosives described in Part II of this book. 

Initiating explosive. An explosive which when lit by a flame immediately detonates. 

Primary explosive. An alternative name for an initiating explosive. A flame causes the explosive to detonate immediately. 

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

Lithium is stable in contact with dry bromine, but heavy impact will initiate explosion, while sodium in contact with bromine needs only moderate impact for initiation [1], Potassium ignites in bromine vapour and explodes violently in contact with liquid bromine, and rubidium ignites in bromine vapour [2], Aluminium,... 

The peroxy compound initiated explosive polymerisation of tetrafluoroethylene... 

Silver acetylide is a more powerful detonator than the copper derivative, but both will initiate explosive acetylene-containing gas mixtures [1]. It decomposes violently when heated to 120-140°C [2], Formation of a deposit of this explosive material was observed when silver-containing solutions were aspirated into an acetylene-fuelled atomic absorption spectrometer. Precautions to prevent formation are discussed [3], The effect of ageing for 16 months on the explosive properties of silver and copper acetylides has been studied. Both retain their hazardous properties for many months, and the former is the more effective in initiating acetylene explosions [4],... 

At the end of a generation run, maximum temperature and high moisture content of acetylene may cause the finely-divided acetylide to overheat and initiate explosion of pressurised gas [1]. During analysis of technical carbide by addition of water, the explosive mixture formed in the unpurged reaction vessel exploded, ignited either by excessive local temperature or possibly by formation of crude phosphine from the phosphide present as impurity in the carbide [2],... 

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