Explosive Trains

An explosive composition is initiated or detonated via an explosive train. The explosive train is an arrangement of explosive components by which the initial force from the primer is transmitted and intensified until it reaches and sets off the main explosive composition. Some components of explosive trains are summarized in Table 4.5. 

Almost all explosive trains contain a primary explosive as the first component. The second component in the train will depend upon the type of initiation process required for the main explosive composition. If this main explosive composition is to be detonated then the second component of the train will burn to detonation so that it imparts a shockwave to the main composition. This type of explosive train is 

Primer Initiating device Initiated by percussion, stabbing, electrical current, heat, etc. 

Detonating Detonate base Ignited by primer. Small quantity of 

Flash Ignite base charge Ignited by primer. Burn explosively but will not detonate 

---

Explosive Trains , AMCP 706-279 (March 1965) 3) Encycl 4 (1969), D879-931. ... 

Anon, Engineering Design Handbook, Explosives Series, Explosive Trains , AMCP 706-179 (1974), 4-11 4-12... 

Statistical Methods Appropriate for Evaluation of Fuze Explosive Train Safety and Reliability , NAVORD 2101 (1953), AD 066 428 3) A. 

Explosive train Arrangement of explosive components in which the initial force from the primer is transmitted and intensified until it reaches and sets off the main explosive composition. 

Primers are used for the ignition of propellants and pyrotechnics. They are categorized as percussion primers, used mainly for the ignition of propellants, and stab primers, used in explosive trains of fuses and electric primers. 

Detonators are used to detonate high explosives. Stab detonators are initiated by sharp firing pins and are used in explosive trains of different types of fuses. Flash detonators are initiated by flames produced by safety fuses, primers, or delay elements. A special type of flash detonator ignited by the flame of a safety fuse is called a blasting cap. Detonators are primarily composed of three types of explosives including sinoxid mixtures, lead azide-based mixtures, and mercury fulminate-based mixtures. 

If an explosive train is only required to ignite a main composition, an igniter that produces a flash instead of a detonation is used. Explosives of this kind are known as deflagrating explosives. Similar to detonators, igniters can be initiated by electrical means, friction, flash, or percussion. An example of an igniter is a squib, a small explosive device loaded with an explosive that deflagrates. Its output is primarily heat.8... 

Explosives are classed as primary or secondary. Typically, a small quantity of a primary explosive would be used in a detonator (known colloquially as a cap ), whereas larger quantities of secondary explosives are used in the booster and the main charge of a device. This collection of explosives is known as an explosive train in which a signal (mechanical, thermal, or electrical) from the control system is converted first into a small explosive shock from the detonator, which in turn initiates a more powerful explosion in the booster, which amplifies the shock into the main charge. 

The requirement for an explosive train, that is, a primary explosive to initiate the secondary explosive, is a safety feature. In the past, people wishing to illegally use explosives usually had to steal the detonators (e.g., Timothy McVey). Consequently, the effective control of access to detonators has been widely regarded as a key pubhc safety measure by many governments and law enforcement agencies. However, recently, triacetone triperoxide (TATP) has been used as the primary explosive (e.g., Richard Reid s shoe bomb) and TATP is readily, although hazardously, synthesized from acetone, hydrogen peroxide, and acid. 

INITIATOR The first component in a pyrotechnic or explosive train. 

NOLR ini (1952) Collective, "Ordnance Explosive Train, Designers Handbook , NOLR (Naval Ordnance Laboratory. Report) 1111, USGovtPtgOff, Washington, DC (1952)... 

Bursting Charge Explosive Train. Same as Explosive Train or High-Explosive Train... 

Ordnance Explosive Train Designers Handbook , NOLR 1111 (1952), p G1 2a) C.G. Dunkle, "Introduction to Theory of Detonation of Explosives , Lecture delivered at PicArsn on 13 Dec 1955, pp 1-14 (Definitions of detonation, detonation process and other terms) 3) Clark Hawley (1957), pp 293-95 ("Detonation , by W.H. Rtnkenbach) 370-71 (Explosives and Detonation, by M.A. Cook)... 

Detonation (and Explosion) by Priming and Boostering. These are means of building up a detonation from an initiating shock (Ref 2, p 294). The detonator, the first element in an explosive train or "explosive chain , may have three parts. 

High-Explosive Train. See Explosive Train in this Glossary... 

Initiating Agent. An explosive material which has the necessary sensitivity to heat, friction, or percussion to make it suitable for use as an initial element in dn explosive train (Ref 40a, p 92)... 

Pistol (British). A mechanical device used since WWI, which is designed to initiate an explosive train by either freeing or functioning a striker but which contains no explosive itself. It is comparable in its mechanical function with US fuzes... 

Propellent (or Low-Explosive) Train. Combination of primer, igniter and propellant used for propelling artillery ammun ition. See Section 3, Part D... 

Relay. A component of a high-explosive train that provides the required energy to reliably initiate the next element in the train. Specifically applied to small charges that are initiated by a delay element and, in turn cause the functioning of a detonator (Ref 40a, p 120)(See slso in this Volume, Section 4, Part F (Compare with Lead)... 

See Section 4, Part F, of this write-up) can be included in the 2nd part of an explosive train... 

Since in the anvil-type of primer the cup is not pierced, obturation (sealing) is obtd after the primer is fired, because the entire cup is pressed into cartridge cavity. Such primers are also known as obturated type, to distinguish them from the unobturated type, which is usually employed as an "explosive-train element" in fuzes. This type and some obturated types employed in fuzes are described in Ref 4, Part F... 

According to definition given by Ohart (Ref 17, p 55), such a detonator is "an explosive component for initiation of detonation in an explosive train or transmitting a primer im-... 

---