First Fires and Igniters

The theory of initiation has mainly been expounded in the field of solid-propellant ignition. A recent effort for pyrotechnics has been published by Johnson.The calculations are difficult since they involve calories transferred to the surface of the initiated column at certain temperatures and over a time interval heat absorption and flow in the main item, heat developed in the main item from the incipient final reaction, and, of course, heat losses. Johnson advocates on the basis of theoretical considerations a small area on which lire transfer is concentrated low thermal conductivity, density, and specific heat of the first fire and use of high-energy, flare-type first fire mixtures in such a way that radiant heat transfer is optimal. 

The need for first fires arises from the fact that many fuel-oxidizer combinations are difficult to initiate and that if there is a choice the least sensitive main item is the most desirable one from the viewpoint of safety in manufacturing and handling. The first fire, on the other hand, is often a much more hazardous mixture. However, only a small fraction of the weight of the main item has to be processed, and 

Since initiation may take place at high altitude, fire transfer may be impeded by the changes in burning rate or flame temperature caused by diminished atmospheric pressure. This can be counteracted if the fire transfer takes place in full confinement or under adequately obturated conditions. Also, certain first fire mixtures, as shown below, are less influenced by pressure changes than others. 

Transfer lines between prime ignition and first fire must be regarded as a part of the secondary ignition system. Quickmatch, a type of black powder fuse that has a more-or-less well-defined burning time and thus acts as a delaying element, will be described in the next chapter. It becomes a nearly-instantaneous transfer line if enclosed in a narrow paper tube and is thus used as piped match in fireworks for simultaneous initiation of several effects.  

First fires without metallic fuel are nowadays mainly found in fireworks items. The most important one of this class is black powder. It is fairly safe to handle, often serves as a combined ejection and ignition material, and is itself easily ignited over a wide range of temperatures and at diminished atmospheric pressure down to about 0.1 atm. Its property of fouling metal parts because of the corrosiveness of its reaction products need rarely be considered since pyrotechnic devices are one-shot items and if ejected from reusable dispensers their own expendable case is the actual gun barrel. Black powdo has been discussed in some detail in Chapter 20. 

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The specific functions that fall into this category are first fires and igniters for pyrotechnic mixtures and solid propellants fire transfer... 

Chlorate-sugar is one of the best of the first fire or igniter mixes. It bums very rapidly, with a yellow-white flame, and generates sufficient heat to ignite all homemade incendiaries mentioned in this handbook. 

Accdg to Ellern (Ref 57, p 189), the terms "first fire" and "starter" refer in pyrotechnics not to the "prime ignition" but to the "intermediate ignition" source which is located between "primary initiation "and the "main pyrotechnic item , such as flares, signals, etc. 

The compositions of typical igniter, first fire, and starter mixtures are also given in Table 5-29, p 5-48 of Ref 54. This Table is reproduced here as Table I ... 

Anon, "Engineering Design Handbook. Military Pyrotechnics Series. Part One. Theory and Application , US Army Materiel Command Pamphlet AMCP 706-185 (1967), pp 5-29 to 5-37 (Pyrotechnic delays) 5-37 to 5-40 (Ignition compns for gasless delay elements) 5-45 (Initiators, first fires, and star ter s) 5-45 to 5-46 (Pr ime ignition) ... 

Heat-transferring powder trains, surface coatings, and discrete subassemblies—used as fuses for fire transfer, delay timing, first fires, and rocket igniters. 

The combinations of boron with oxidizers other than lead compounds seem to be less subject to accidental ignition than comparable mixtures of sensitive metals and oxidizers. Boron is used extensively in first fires and delay compositions and may be useful as a specialty heat source. Because of the small amount of boron required in combination with heavy metal oxides, certain mixtures can be used... 

Fire test methods attempt to provide correct information on the fire contribution of a product by exposing a small sample to conditions expected in a fire scenario. Methods can be viewed in two ways the first entails the strategy of the fire test, ignition resistance or low flammabiUty once ignited the second addresses the test specimen, a sample representative of the product or a sample of a material that might be used in the product. Fire science has progressed markedly since the older test methods were developed and it is known that the basis for many of these tests is doubthil. Results from older tests must be used with great care. 

Napalm will keep well if stored in a tightly sealed container. It can be ignited with a match or any of the first fire mixtures described previously. The ignition packet should be placed adjacent to or just over the napalm, otherwise the petroleum may soak it and prevent its burning. 

Ignition compositions Hot solid or liquid particles are desirable in igniter and first-fire compositions to insure the transfer of sufficient heat to ignite the main composition. Fuels producing mainly gaseous products are not commonly used. 

Potassium nitrate is frequently used in igniters and first fires. Compositions made with this oxidizer tend to have low ignition temperatures (typically below 500 C), and yet the mixtures are reasonably safe to prepare, use in production, and store. Potassium chlorate formulations also tend to have low ignition temperatures, but they are considerably more sensitive (and hazardous). ... 

Pyrocore, manufd by DuPont Co. It consists of metal tubing 1/8 inch or less in diam filled with combined explosive and ignition mixture, 4-40 grains per foot. It is claimed that even coarse commercial Thermite can be initiated from Pyrocore if Alclo Pellets (A1 35, K perchlorate 64 vegetable oil 1%) are used as a starter or as a first fire (Ref 57, p 191 and "Explosives Specialty Manual" E.I. duPont de Nemours, Wilmington, Delaware. ( Not listed in alphabetical Index of Ref 50)... 

The rule should be to keep the more hazardous mixts at minimum size. Transfer lines (such as fuses, quickmatch, etc) between prime ignition and first fire are regarded as a part of the secondary ignition system... 

When used with highly compacted main pyrotechnic items, such as flare candles the "first fire" is either pressed (in dry form), or painted (in paste or slurry form) on top of item. For initiation of solid proplnts, a "first fire " mixt can be ignited if confined in a tube or capsule so that the hot gases will be spread over a larger surface area (Ref 57, pp 189 91) Table F lists various formulations for "starter mixtures" Table G for "ignition mixtures" and Table H for "first fire mixtures". -These formulations are given in Ref 57, pp 377-83. Some mixtures are taken from Ref 44a,... 

Formula 168, designated as "First Fire for Illuminating Flares" contains binder Laminae 4110 or 4116 with 1.4% catalyst Lupersol DDM. Used in pressed-on form as the final igniting mixt in many illuminating flares and illuminating candles... 

When the bomb strikes the target, inertia causes the firing pin to move forward striking the primer. The primer ignites the "first fire mixture" which ignites the filler (1) (0.63-lb of Thermate, TH3) and the Mg alloy body (2)... 

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