Understanding Explosives: Types, Mechanisms, and Ignition
What is an Explosive?
An explosive is a material that undergoes rapid decomposition or oxidation when initiated by heat or electric shock. This process releases gaseous compounds that occupy a significantly larger volume than the original material. The rapid expansion displaces large volumes of air, creating a sonic boom due to the expansion rate exceeding the speed of sound.
Types of Explosives
High-Order Explosives
High-order explosives detonate. Detonation occurs only in high-order explosives and is typically triggered by a shock or electric shock passing through the material. This shock breaks the molecular bonds at a speed near or equal to the speed of sound within the material. In these explosives, the fuel and oxidizer are chemically linked. The shock breaks this link, causing the components to recombine and produce a large volume of gas. Examples of high-order explosives include TNT, ammonium nitrate, and RDX.
Low-Order Explosives
Low-order explosives do not detonate; they burn or undergo oxidation. When heated, the fuel and oxidizer combine to produce heat, light, and gaseous products. Some low-order materials, like black powder, burn at a similar speed under pressure and in the open. Others, such as nitrocellulose (gunpowder), burn rapidly in confined spaces like firearm barrels but generally slower than black powder in open areas. Black powder, nitrocellulose, and flash powder are examples of low-order explosives.
Primers
Primers, or detonating caps, are specialized explosives used to initiate other explosives. Some primers, like mercury fulminate, can function as both low- and high-order explosives. These are typically more sensitive to friction, heat, or electric shock than most high-order and some low-order explosives. Most primers detonate like high-order explosives but are more sensitive. Others burn rapidly, producing a large amount of gas and heat in confined spaces. Primers are commonly used to initiate high-order explosives and sometimes low-order explosives.
Improvised Explosives and Ignition Methods
Molotov Cocktails
Molotov cocktails are simple yet dangerous incendiary devices. They consist of a glass bottle filled with a flammable liquid (e.g., gasoline, kerosene, alcohol) and a piece of cloth soaked in the liquid acting as a fuse. Upon impact, the bottle breaks, spreading the flammable liquid, which is then ignited by the burning cloth. Mixtures like kerosene and motor oil may require the addition of a more volatile liquid for reliable ignition. Adding tar or grease to gasoline creates a sticky mixture that adheres to surfaces and is harder to extinguish.
Wicks
Wicks are a common and reliable ignition system. Modern waterproof fuses are highly reliable, burning at a consistent rate (e.g., 1 inch every 2.5 seconds). A simple wick ignition system can be made using waterproof fuse, matchbook striking paper, and electrical tape. The fuse length is calculated based on the desired delay time and the fuse’s burn rate.
Radio Detonators
Radio detonators allow for remote triggering of explosives. While commercially available radio detonators can be expensive, improvised versions can be created using radio-controlled toys. By modifying the toy’s solenoid or motor, the electrical signal can be used to trigger an explosive primer or igniter. Thorough testing is crucial for safety and reliability.
Paper Containers for Explosives
Paper, historically used for firecrackers, is a simple and inexpensive container for explosives. A basic example is a paper tube filled with black powder, Pyrodex, nitrocellulose, or other fast-burning oxidizing mixtures. More complex designs, like the Mexican “dove” rocket, involve folding a paper sheet to create a container for the explosive and a wick.
Disclaimer: This information is for educational purposes only. Building or using explosives is extremely dangerous and illegal in most jurisdictions. This information should not be used for any illegal or harmful purposes.