Explosives Study Guide

Compare and contrast an accelerant vs. an explosive

Similarities

1. Chemical Energy Release – Both accelerants and explosives release energy through exothermic chemical reactions.

2. Combustion Process – Both involve oxidation reactions that generate heat, flames, or gas expansion.

3. Forensic Detection Methods – Techniques like gas chromatography-mass spectrometry (GC-MS) and infrared spectroscopy (FTIR) are used to analyze residues from both.

4. Potential for Criminal Use – Both are commonly used in arson and bombing cases, making them central to forensic investigations.

5. Residue Analysis – Both leave behind chemical signatures that can be traced for investigation.

6. Reaction Speed Variability – While their reaction rates differ (more below), both can result in dangerous, rapid combustion under the right conditions.

7. Volatility – Many accelerants (like gasoline) and some explosives (like nitroglycerin) are volatile, meaning they easily evaporate and pose a risk of accidental ignition.

Differences

What is an explosion?

An explosion is a rapid and violent release of energy, typically accompanied by heat, light, sound, and a shockwave. This release of energy results from a sudden chemical or physical reaction, often leading to the expansion of gases and causing damage to surrounding structures. Key characteristics; rapid energy release, gas expansion, shockwave generation, heat and light emission, sound/blast wave. 

Difference between Deflagration and Detonation

 Deflagration; produce a shockwave that travels slower than sound (<330 m/s or <720 mph), caused in low explosives, subsonic 

Detonation; produces a shock wave that travels faster than sound, caused in high explosions. 

Compare/contrast low explosives vs. high explosives + examples

 Low explosives

• slow rate of reaction

• deflagrates, subsonic

• utilizes propellants 

• low activation energy (Ea) 

• confined in a container to produce an explosion

• black powder/ gunpowder (C + S + KNO3) 

High Explosives

• rapid rate of detonation

• detonates, blasting/shattering effect

• higher Ea than low explosives 

Primary High 1

• sensitive to heat and shock

• lower Ea than 2, less stable

• nitroglycerin, lead aside, lead styphnate, silver cyanate, mercury fulminate

• used in primer and blasting caps

• triggers 2 explosives

Secondary High 2

• more stable 

• higher Ea

• most powerful

• TNT, ANFO, RDX, PETN, Dynamite

Components of black powder &  combustion products

C, S, and KNO3. CO2 and H2O

Compare/contrast Primary High Explosives vs. Secondary High Explosives and give examples

Above

Difference between TNT and Dynamite

Key Takeaways

• TNT is a pure chemical compound, while dynamite is a mixture of nitroglycerin and stabilizing substances.

• TNT is more stable and widely used in military applications.

• Dynamite is more powerful but less stable, making it historically popular in construction and mining.

Types of Bombs-

Plastic Bombs; high explosives mixed into a plastic binder. Moldable, less sensitive to shock, harder to detect. Add compounds with high vapor pressures to make them easier to detect. 

Improvised explosives (IED device) ; chemicals that aren’t explosive on their own, but form explosive mixtures when combined. KClO3 + sugar, glycerin +KMnO4, acetone (TATP) +H2O2. 

By How They Detonate

• Contact Bombs – Go off when touched.

• Time Bombs – Go off after a set time.

• Pressure Bombs – Go off when pressure is applied (like stepping on it).

• Remote-Controlled Bombs – Set off by a remote.

• Magnetic Bombs – Stick to metal and detonate when triggered.

2. By Purpose

• Conventional Bombs – Regular bombs (like TNT).

• Nuclear Bombs – Use nuclear reactions to explode (atomic bombs).

• Chemical Bombs – Release harmful chemicals.

• Biological Bombs – Spread diseases with bacteria or viruses.

• Incendiary Bombs – Set things on fire (like napalm).

• Cluster Bombs – Release smaller bombs over a big area.

3. By Delivery Method

• Aerial Bombs – Dropped from airplanes.

• Hand Grenades – Small bombs thrown by hand.

• Car Bombs – Explosives in a car.

• Suicide Bombs – Carried by a person and detonated by them.

4. By Explosive Material

• TNT Bombs – Made with TNT.

• Dynamite Bombs – Made with dynamite (contains nitroglycerin).

• Gas Bombs – Release harmful gases.

• Plastic Explosives – Soft explosives like C-4, which can be shaped.

5. By Impact

• Shaped Charges – Focus the explosion in one direction.

• Fragmentation Bombs – Break into pieces that spread out when they explode.

Main Parts of a Bomb- timer/switch, detonator(blasting cap), detonating cords, eboosters, main charge, electronic circuitry, batteries/wires

1. Explosive Material

This is the core substance that causes the explosion. It can be things like TNT, dynamite, or C-4. It’s the part that generates the energy and destructive force when detonated.

2. Detonator (or Initiator)

This is the component that triggers the explosion. It can be set off by heat, pressure, electrical charge, or a timer. Common types include:

• Fuse – A timed fuse that burns until it reaches the detonator.

• Electric Detonator – Triggered by an electrical signal.

• Impact Detonator – Set off by shock or pressure.

3. Casing

The outer shell of the bomb. It holds everything together and can be made of metal, plastic, or another material. In some bombs, the casing is designed to break into shrapnel to cause additional damage upon explosion.

4. Power Source

If the bomb uses an electric detonator or timer, it requires a power source like a battery or capacitor to function.

5. Timer or Triggering Mechanism

This is used to set when the bomb will explode (a timer) or to detect certain conditions (like movement or pressure). Examples include:

• Timer – Bomb explodes after a certain amount of time.

• Pressure Switch – Explodes when pressure is applied (e.g., a vehicle drives over it).

6. Booster

Some bombs have a secondary explosive (called a booster) that helps detonate the main charge. It's often used in bombs with less sensitive primary explosives.

What are plastic explosives? Examples?

Plastic explosives are a type of explosive material that is soft, malleable, and can be easily molded into different shapes. They are often preferred because of their versatility, allowing them to be shaped to fit specific targets or packed into small spaces for maximum impact. Plastic explosives are typically more stable and safer to handle than other high explosives like dynamite, but they are still very dangerous.

Key Characteristics of Plastic Explosives:

• Malleable – Can be molded into any shape to suit the target.

• Stable – Less sensitive to shock, friction, or temperature changes compared to other explosives.

• High Explosive Power – They can produce significant explosive force when detonated.

Common Examples of Plastic Explosives:

1. C-4 – The most well-known plastic explosive, consisting of RDX (a powerful explosive compound) combined with a plastic binder. It's stable, can be molded into any shape, and is widely used by military forces.

2. Semtex – Another popular plastic explosive, similar to C-4 but often used in civilian applications like demolition. It’s also used by military forces.

3. PE4 – A type of plastic explosive made from RDX, commonly used by NATO forces.

4. TNT-based Plastics – Some plastic explosives use a mixture of TNT with other ingredients to make them more malleable.

Plastic explosives are often used for military, demolition, or covert operations because they can be hidden or shaped to avoid detection and cause controlled destruction.

What are taggants? How are they useful in forensic investigations/what kind of information can they provide? Arguments against requiring taggants?

A taggant is a micron sized polymer chip that is layered with multiple colors of plastics. It's like a barcode and can identify the manufacturer, date of manufacture, lot number, and intended distribution sites. A method is being developed that relies on the trace components. They can tell you the identification of the manufacturer and source, tracing supply chains, reconstructing crime scenes, and deterring illegal use. Arguments against taggants include increased costs to industry, possible contamination with other taggants at the bomb site, homemade bombs wouldn’t have them, and reduced performance of explosives with taggants. 

What is oxygen balance? How is it determined? Examples of explosives with neutral, positive and negative oxygen balance

Oxygen balance (OB) is a measure of whether an explosive compound has the right amount of oxygen to fully oxidize all of its carbon, hydrogen, and metal content into carbon dioxide (CO₂), water (H₂O), and metal oxides. It is expressed as a percentage and helps determine how efficiently an explosive will burn or detonate.

• Positive oxygen balance (+OB): The explosive has excess oxygen, which can help burn surrounding materials.

• Negative oxygen balance (-OB): The explosive lacks enough oxygen, leading to incomplete combustion and the production of toxic gases like carbon monoxide (CO) or unburned carbon (soot).

• Zero oxygen balance (0% OB): The explosive has exactly enough oxygen to fully react with all fuel components.

ex. TNT 

1. Find chemical formula (count elements) C7H5O6N3

2. Amount of oxygen and carbon? C7 + 14O -> CO2

• Only 6 oxygen in TNT, so not enough to form 7CO2, negative OB

Nitroglycerin    

C3H5O9N3 -> 3CO2 and 2H2O -> 2O + 6O = needs 8 oxygen. 

Has 9 oxygen, needs 8 for complete decomposition, 1 oxygen left over, positive OB

Why are isomers useful in forensic investigations? Be able to draw the structure of TNT and at least 2 isomers

Isomers are chemicals with the same formula but different structures. In forensic science, they help identify drugs, explosives, and other substances.

How Are They Useful?

1. Identifying Explosives & Drugs

   • Some chemicals have harmless and dangerous isomers.

   • Example: TNT has different forms, but only one is highly explosive.

   • This helps investigators confirm if a substance is dangerous.

2. Tracing Where Chemicals Come From

   • Some factories make different isomer mixes.

   • Scientists can check these mixes to find where a drug or explosive was made.

   • Example: Different methods of making methamphetamine create different isomer ratios, which help track illegal drug labs.

3. Catching Athletes Using Illegal Drugs

   • Some steroids and stimulants have natural and synthetic isomers.

   • Example: Your body makes natural testosterone, but synthetic versions have different isomers, helping drug tests catch cheats.

4. Telling Legal & Illegal Substances Apart

   • Some legal medicines have isomers that can be turned into illegal drugs.

   • Example: Pseudoephedrine (cold medicine) and methamphetamine have the same formula but different structures. This helps forensic labs tell the difference.

5. Finding Out How Fires & Explosions Start

   • Different fuels and explosives have unique isomer patterns.

   • Example: Gasoline used to start a fire has specific isomers, helping investigators prove arson.

In Short:

Isomers help forensic scientists identify, trace, and differentiate chemicals, making them important in solving crimes involving drugs, explosives, arson, and illegal substances.

How does an electronic ‘sniffer’ work?(pg 326 of Explosives 101 packet). Other methods for detecting explosives? 

A sample of air taken from an area near the explosive material will contain molecules of the material, which can be detected by an electronic instrument designed for such analysis or by the nose of a trained bomb-sniffing dog. 

1. Chemical Tests

🔹 Colorimetric Tests: Chemicals react with explosives and change color.

• Example: Diphenylamine test for nitrates (common in explosives).
  🔹 Ion Mobility Spectrometry (IMS): Detects explosive particles in the air by analyzing ion movement.

• Used in: Airport security scanners.

2. Spectroscopy Methods

🔹 Raman Spectroscopy & Infrared (IR) Spectroscopy: Identify explosive materials based on how they absorb or scatter light.
🔹 Mass Spectrometry (MS): Breaks chemicals into pieces and identifies them based on mass.

3. Chromatography Methods

🔹 Gas Chromatography (GC): Separates chemicals in an explosive sample to identify each one.
🔹 Liquid Chromatography (LC): Works like GC but for non-gaseous explosives.

4. X-ray Scanning & Imaging

🔹 X-ray Diffraction (XRD): Identifies explosives based on crystal structure.
🔹 Computed Tomography (CT) Scans: Used in airport luggage screening.

5. Canine Detection (Bomb-Sniffing Dogs)

🔹 Trained dogs detect explosives based on scent, even in tiny amounts.
🔹 Often used in military and airport security.

6. Biosensors & Electronic Noses

🔹 Electronic "noses" detect explosive vapors using sensors that mimic a dog's ability to smell.
🔹 Biosensors use bacteria or proteins that glow when they come into contact with explosives.

7. Neutron Activation Analysis (NAA)

🔹 Bombards a sample with neutrons to detect elements like nitrogen, which is common in explosives.

8. Thermal & Vapor Detection

🔹 Explosive Vapor Detectors: Sniff out trace amounts of explosive gases.
🔹 Thermal Analysis: Heats samples to see if they react like an explosive.

In Short:

Explosives are detected using chemical tests, spectroscopy, chromatography, X-rays, dogs, electronic sensors, neutron scans, and vapor analysis. Each method helps in different situations, from airport security to forensic labs.

What are ‘marker compounds’ and why are they added to plastic explosives? (pg 328-329 Explosives 101)

Explosive compounds that have large vapor pressures that ease the detection of plastic explosives are added for the purpose of detection. 

Information from Chemmatters article- Vision for Airport Security

- how x-ray scanners work 

They interact with atoms rather than molecules and the way these atoms absorb x-rays depends on their atomic number - the higher the atomic number, the stronger the absorption. 

- complications/challenges with x-ray screening

Human error (Things may be awkwardly placed),  not all things are in baggage, also cannot detect substances

-Methods for detecting non-metallic explosives & how they work- 

-Explosive Detection System (EDS) ; collects a sample of the air or the object being sampled, sample is taken from vapor or dust the explosive gives off. The system uses special sensors that can detect the unique chemicals or particles in explosives (some look for specific gases or vapors, others look for physical particles). The sensors send the sample to a computer that analyzes the chemical makeup of the sample. The system looks for signatures or patterns that match known explosives. If it matches an explosive, it sends an alert. 

- Explosives Trace Detection machine (ETD); collects a sample through air sampling or swabbing to gather residue. Some systems may use a vacuum nozzle or a sticky pad to capture particles. The sample’s analyzed mostly with Ion Mobility Spectrometry, and are heated or exposed to charged particles, explosive particles react to the ions and release a unique signature. The machine measures how long it takes for the particles to travel through a chamber and it compares it to known explosives signatures. If it's a match, it alerts security. It can also detect very small (trace) amounts

- Airline passenger screening methods & how they work- 

Pulse Induction Technology (PI); used in metal detectors, especially for buried objects like bombs or landmines. It sends a short pulse of electricity through a coil, creating a magnetic field and happens very quickly. If there's metal underground, the magnetic field interacts, the metal reflects or induces its own magnetic field in response to the pulse. The detector has a cold that listens for the magnetic signal from metal. After the pulse is sent, the machine detects how long it takes for the metal’s  magnetic field to decay, different metals take different times. If something is metal, it sends an alert. 

 Microwave devices; send out microwaves, measure how they interact with materials, and use this information to identify substances like explosives. It’s a non-invasive way to analyze materials. 

X-ray backscatter detection; sends x-rays at an object, then measures how it bounces back. This helps identify hidden items like explosives or weapons by creating a detailed image or what's inside or beneath surfaces. 

Information from Forensic Chemists Chemmatters article-

-     Types of crimes investigated by the ATF; unlawful manufacture, use and possession of firearms and explosives, acts of arson and bombings, and the illegal trafficking of alcohol and tobacco products. 

-     Types of evidence analyzed by an explosives analyst ; fragments from a pipe bomb, or debris from a blast scene. 

• Procedure for analyzing evidence from an explosion; The evidence is packaged based on the materials it's made of and sealed with special tape to show it hasn't been tampered with. The evidence is then documented, and the forensic scientist tries to identify the chemicals in the sample by looking for residues that didn't burn. They use a scanning electron microscope to analyze the x-rays emitted by the material, which helps identify the elements in it. Throughout this process, the scientist takes detailed notes. Once the analysis is complete, the notes and data from the machines are added to the case file. The forensic scientist writes a report on their findings, which is reviewed by a colleague or supervisor before being returned to the original investigator.

• Determining the chemical composition of residues and what can be determined from that information; 

• Collecting Residues: Scientists collect the leftover material after something burns or explodes.

• Analyzing the Chemicals: They use special tools to identify the chemicals in the residue.

• Finding Clues: By knowing what chemicals are present, they can figure out:

  • What caused the explosion or fire (like what kind of explosive was used).

  • Where it came from (if certain chemicals are linked to specific places or people).

  • How it happened (for example, matching residues to specific bombs or devices).

What can be determined:

• The type of explosive or substance used.

• If the residue matches known criminal activities.

• Information about how the event occurred (like if it was an accident or deliberate).

• Types of instruments used for examining explosive residue; 

Gas Chromatograph Mass Spectrometer (GC-MS)

• Gas Chromatograph: Turns a sample into gas and then separates its parts by how fast they move through a special tube.

• Mass Spectrometer: Identifies the parts based on their size.

• How it's helpful for explosives: It can detect small traces of chemicals in explosive residues, both before and after something explodes.

2. Scanning Electron Microscope with Energy-Dispersive X-ray Spectrometer (SEM-EDX)

• How it works: The microscope uses charged particles to make the atoms in a sample give off X-rays, and it looks at the X-rays to figure out what elements are in the sample.

• How it's helpful for explosives: It helps identify the elements that make up the explosive, so you can know exactly what materials were used.

3. Thin-Layer Chromatography (TLC)

• How it works: A small drop of a sample (like ink) is placed on a special plate, then dipped in a liquid. The liquid moves up the plate, spreading out the ink into different colors.

• How it's helpful for explosives: It shows the different chemicals in explosive residues, helping to identify things like accelerants or parts of a bomb.