Fundamentals of Military Ordinance and Explosives

1. Primary Fragmentation: Resulting from the bursting of the explosive container itself.
2. Secondary Fragmentation: Resulting from the impact of primary fragments and pressure on surrounding objects.

The blast pressure itself consists of two distinct phases:

• Positive Pressure: A fast, short-duration wave that pushes objects away from the blast.
• Negative Pressure: A slower, longer-duration phase that pulls objects back toward the site of the blast.

Low vs. High Explosives

The arbitrary threshold used to separate low and high explosives is the speed of sound, approximately $3300 \text{ fps}$:

• Low Explosives: These burn at a rate less than $3300 \text{ fps}$ (deflagration). They require confinement (like a container) to build up enough pressure to cause an explosion.
• High Explosives: These detonate at rates exceeding $3300 \text{ fps}$. They do not require confinement to function.

Explosive Sensitivity and the Explosive Train

Explosives are categorized by how much energy is required to initiate them. This hierarchy is organized into an explosive train, which consists of components arranged in decreasing order of sensitivity to ensure controlled and predictable initiation:

1. Primary Explosives: Highly sensitive to heat, shock, friction, or flame. They are used as initiators (e.g., Lead Azide, Mercury Fulminate, or Lead Styphnate).
2. Secondary Explosives: Less sensitive; they require a primary explosive or a booster to initiate. Examples include TNT, RDX, and PETN.
3. Blasting Agents: These are not cap-sensitive and require a booster to function. A common example is ANFO (Ammonium Nitrate/Fuel Oil), which is a mixture of 94% AN and 6% fuel oil.

Exam Tip: Remember that military explosives are generally designed to be less sensitive than commercial explosives to minimize the risk of accidental detonation during handling by soldiers.

Shaped Charges and the Monroe Effect

Certain high explosives are used to create a shaped charge. This mechanism uses a focused jet of hot gas to penetrate targets, a phenomenon known as the Monroe effect. The efficiency of these charges depends on composition, angles, standoff distance, and the initiator.

Improvised Explosive Devices (IEDs)

Improvised explosives are highly unpredictable and dangerous because they are often constructed from non-standard materials. They are fundamentally based on the FOX acronym: Fuel and Oxidizer.

Chemical Hazards and Hypergolic Reactions

A major danger in IED construction is the hypergolic reaction, where two substances ignite spontaneously upon contact without the need for a spark or flame. Examples include:

• Mixing Calcium Hypochlorite with brake fluid.
• Mixing Potassium Permanganate with glycerin or sulfuric acid.

Common improvised primary explosives include TATP (Triacetone Triperoxide), HMTD (Hexamethylen Triperoxide Diamine), and the Armstrong Mixture (a 50/50 mix of potassium chlorate and red phosphorus).

Safety Protocols

To mitigate the risk of accidental initiation, safety protocols require that fuels and oxidizers be stored separately, horizontally, by at least 25 feet.

Summary of Chemical Characteristics

When analyzing explosive materials, it is important to distinguish between how substances are combined:

• Explosive Mixture: Two or more substances are physically combined but retain their independent physical properties (e.g., ANFO).
• Explosive Compound: Two or more substances are molecularly bonded to become a new substance.