Pyrotechnics sensitivity

Rat, R., and Isler, J. (1995) The static electricity hazards method for assessing pyrotechnics sensitivity and approach for hazard reduction. Proc. 26th Inti. Ann. 

J, Cherville, Relation Between the Electronic Structure and the Pyrotechnical Sensitivity of Secondary Nitrogen Explosives , ProcSymp-ChemProblConnectedStabExplos (1976) 4,179— 99 (1977) CA 87, 120025 (1977) 54)V.I. 

CAUTION When using this approach, serious consideration must be given to the possibility that dangerous chemicai combinations might be created by such mixing. (Discussed in Pyrotechnic Sensitivity, Module.)... 

Pyrotechnic sensitivity is often given as the level of stimulus that results in ignition in some percentage of triais. Often the 50% value is reported, but sometimes it is the 10% value or even the 1% value may be reported. In comparing data, it is essentiai to know which levei is being reported. 

As for the pyrotechnics sensitive to temperature, the quantitative relationship between reliability and storage life can be established. This paper presented the method and demonstrated it by a specific example. 

Pyrotechnic mixtures may also contain additional components that are added to modify the bum rate, enhance the pyrotechnic effect, or serve as a binder to maintain the homogeneity of the blended mixture and provide mechanical strength when the composition is pressed or consoHdated into a tube or other container. These additional components may also function as oxidizers or fuels in the composition, and it can be anticipated that the heat output, bum rate, and ignition sensitivity may all be affected by the addition of another component to a pyrotechnic composition. An example of an additional component is the use of a catalyst, such as iron oxide, to enhance the decomposition rate of ammonium perchlorate. Diatomaceous earth or coarse sawdust may be used to slow up the bum rate of a composition, or magnesium carbonate (an acid neutralizer) may be added to help stabilize mixtures that contain an acid-sensitive component such as potassium chlorate. Binders include such materials as dextrin (partially hydrolyzed starch), various gums, and assorted polymers such as poly(vinyl alcohol), epoxies, and polyesters. Polybutadiene mbber binders are widely used as fuels and binders in the soHd propellant industry. The production of colored flames is enhanced by the presence of chlorine atoms in the pyrotechnic flame, so chlorine donors such as poly(vinyl chloride) or chlorinated mbber are often added to color-producing compositions, where they also serve as fuels. 

The importance of frictional heating in the initiation of expls is a subject of considerable importance. The frictional sensitivity is directly involved in the handling hazards of all high-energy materials and considerable attention has been directed toward gathering of frictional sensitivity data on almost all mil expls, in addi- tion to an entire host of pyrotechnic mixts and certain propints (Refs 6 17)... 

The pyrotechnic literature does not contain a critical evaluation of the ignition response time. of primary initiators in terms of their compn, temp tolerance and shock sensitivity. In general, primary expls such as Pb Azide or styphnate are selected whenever a brief (microsecond) response is desired, while, for instance, Pb thiocyanate-chlorate mixts are selected when high temps and high radiation environments are encountered, and presumably a longer ignition delay is the price which is paid for the extra margin of safety... 

In devices which can tolerate moderate ignition delay, further development of non-primary initiators (Refs 31, 77, 97 112) will extend the storability, the manufacturing safety, the electromagnetic Held and spark sensitivity and the high temp compatibility of pyrotechnic devices... 

Whereas currently most studies deal with azides, a similar effort devoted to other metal salts such as nitrates and chlorates would be an important step toward understanding electrical initiation of pyrotechnics, and conversely to making possible safe, non-expl igniters. For instance, a study by Maycock (Ref 4) shows that those azides, perchlorates, and nitrates in which the solid state shows absorption on the long wavelength side of the anionic excitation band in soln, are the most unstable members of the respective series. Consequently, there is a direct relationship between the absorption spectra of pyrotechnic oxidizers and their respective sensitivities... 

New process technologies (Ref 53) such as jet mills (Fig 2) and co-precipitation (Ref 97) may allow safe compounding of sensitive or toxic formulations. New analytical tools such as neutron radiography (Ref 92) afford improved non-destructive testing of devices. X-ray fluorescence (Ref 93) and neutron activation (Ref 94) provide quantitative analysis of pyrotechnic compns and their trace contaminants... 

In one Instance, a pyrotechnic preparation, which contained aluminium, water traces, potassium chlorate and potassium and barium nitrates detonated violently twenty four hours after teing prepared. A mixture of barium nitrate, aluminium and magnesium proves very sensitive to friction or impact (risk of ignition or spontaneous detonation). 

Durgapal, U. C. et al., Propellants, Explosives, Pyrotechnics, 1995, 20, 64 This compound, made by mild nitration of polyvinyl alcohol, is an explosive as shock sensitive as tetryl. 

A pyrotechnic mixture containing the powdered ingredients was found dangerously sensitive to frictional initiation and highly explosive. 

Anon., Lab. Accid. Higher Educ., item 7, Barking, HSE, 1987 A pyrotechnic device was being prepared by loading 16 g of a mixture of 73% potassium chlorate, 24% gallic acid and 3% gum tragacanth into a 9 mm copper tube 280 mm long, when it exploded violently and caused shrapnel injuries. Such mixtures are very friction-sensitive. 

This combination has, in the past, been the base of various impact sensitive pyrotechnics, described by Haarmann [1] and more recently on the Internet, including reference to a report [2] of a mere 60-70 kg, dispersed in children s toy caps, demolishing a building in an accidental explosion. Red phosphorus is a material of variable composition and reactivity, so unreliability is to be anticipated. There have been passivating components in most of these mixtures, it is suggested that the pure dry powders will often react on contact. For the more reactive white allotrope ... 

Mixtures of sulfur and potassium perchlorate, used in pyrotechnic devices, can be exploded by moderate impact. All other inorganic perchlorates form such impact-sensitive mixtures. 

Survey of Sensitivity Characteristics of Typical Delay Ignitor Flash and Signal-Type Pyrotechnic Compounds Joseph Kristal and Seymour M. Kaye Picatinny Arsenal, Dover New Jersey 439383 111... 

Electric detonators are also used for detonation of high explosive charges. They are similar in design to other types of detonators except for the presence of an electric fusehead consisting of a bridgewire made of chromium and nickel. The bridgewire is covered by a heat-sensitive pyrotechnic mixture protected by varnish insulation. Standard fuseheads have electrical resistance of 1.2 to 1.4 ohms and... 

Polynitropolyphenylene (PNP) (159), which is a polymeric explosive, exhibits high thermal stability and possesses a low sensitivity to friction and impact. This polymeric mixture, synthesized from the reaction of styphnyl chloride (106) with copper powder in nitrobenzene, has found use as a thermally stable binder in pyrotechnic compositions. ... 

Tetranitrohexahydropyrimidine (DNNC) (94) has been synthesized from the nitrolysis of the A(iV -di-fert-butylpyrimidine (93). Levins and co-workers reported the synthesis of DNNC (94) from the nitrolysis of the analogous A. V -di-wo-propylpyrimidine (92). DNNC is a high performance explosive with a detonation velocity of 8730 m/s, impact sensitivity lower than RDX and a very favourable oxygen balance. DNNC has been suggested " for use as an oxidizer in propellant compositions. This is also considered as an excellent oxidant for pyrotechnic compositions. ... 

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