Fire, Explosions, and Forensic Chemistry – Lecture Review

A comprehensive set of key vocabulary terms covering combustion, fire suppression, arson investigation, explosives, reaction kinetics, post-mortem chemistry, and weapon forensics.

Fire Triangle

The three essential components for fire: oxygen, heat, and fuel.

Combustion

A high-temperature, exothermic redox reaction between a fuel and an oxidant that produces heat, light, gases, and smoke.

Hydrocarbon

An organic compound composed solely of carbon and hydrogen; its combustion yields CO₂ and H₂O.

Activation Energy

The minimum energy required to start a chemical reaction.

Exothermic Reaction

A reaction that releases heat to its surroundings.

Endothermic Reaction

A reaction that absorbs heat from its surroundings.

Smothering

Fire-extinguishing method that removes oxygen from the combustion zone.

Starvation

Fire-extinguishing technique that eliminates the fuel source.

Cooling

Fire-suppression method that lowers temperature below activation energy, often using water.

Breaking the Chain Reaction

Fire-fighting strategy that uses chemicals to interrupt the combustion reaction sequence.

Arson

The criminal act of deliberately setting fire to property.

Accelerant

A flammable substance (e.g., gasoline) used to speed up fire spread in arson.

Vapor Pressure

The pressure exerted by a liquid’s vapor at a given temperature; higher values mean easier vaporization.

Flash Point

The lowest temperature at which a liquid produces enough vapor to ignite.

Explosive

A substance that undergoes rapid oxidation to produce large volumes of gas, causing an explosion.

Low Explosive

Explosive that burns on its surface and must be confined to detonate (e.g., gunpowder).

Primary High Explosive

Highly sensitive explosive used in primers or blasting caps; detonates readily (e.g., nitroglycerin).

Secondary High Explosive

Stable high explosive requiring a strong initiation (e.g., TNT, dynamite).

Gas Chromatography (GC)

Analytical technique that separates volatile compounds to identify accelerants or residues.

Gas Chromatography–Mass Spectrometry (GC-MS)

Combined GC and mass-spectrometric method for precise identification of chemical components.

Ion Mobility Spectrometer (IMS)

Instrument that identifies chemicals by measuring ion drift speeds in a gas phase; detects explosives and drugs.

Reaction Rate

The speed at which reactants are converted to products, expressed as change in concentration over time.

Catalyst

A substance that increases reaction rate by lowering activation energy without being consumed.

Inhibitor

A substance that decreases the rate of a chemical reaction.

Surface Area Effect

Phenomenon where increased solid surface area leads to faster reaction rates.

Rigor Mortis

Post-mortem stiffening of muscles occurring 2–48 hours after death due to ATP depletion.

Livor Mortis

Pooling of blood in the lowest parts of the body after death, causing skin discoloration.

Algor Mortis

Post-mortem cooling of the body as it equilibrates with ambient temperature.

Autolysis

Self-digestion of cells by their own enzymes after death.

Putrefaction

Decomposition stage where bacteria break down tissues, producing gases and odors.

Ballistic Trauma

Tissue damage caused by projectiles such as bullets.

Blunt Force Trauma

Injury produced by impact with a non-sharp object, leading to bruises, lacerations, or fractures.

Ligature Strangulation

Homicidal or suicidal asphyxiation caused by tightening a cord or wire around the neck.

Gunshot Residue (GSR)

Soot and particulate matter from burning gunpowder deposited on shooter, victim, or surroundings.

Cartridge

The spent shell casing left behind after a bullet is fired from a firearm.

Rifling

Spiral grooves inside a gun barrel that impart spin to a bullet, leaving unique marks.

IBIS / NIBIN

Imaging systems that store and compare ballistic markings on cartridges and bullets to link firearms to crimes.

Yaw

The wobbling or tumbling motion of a bullet that affects wound severity.

Fragmentation (Ballistics)

Breaking apart of a bullet upon impact, increasing tissue damage.

Coup–Contrecoup Injury

Brain injury pattern from blunt force: coup at impact site, contrecoup on the opposite side due to rebound.

Muzzle Velocity

The speed of a bullet as it exits a firearm barrel.

Primer (Ammunition)

Sensitive explosive compound that ignites the propellant in a cartridge.

Formalin

A 37–40 % aqueous formaldehyde solution used to preserve biological tissues by cross-linking proteins.

Cryopreservation

Long-term preservation technique that slows decomposition by freezing tissue or bodies.

Metallic Bonding

Attractive force between metal cations and a sea of delocalized electrons, giving metals strength and conductivity.

Grain (Metallurgy)

Region within a metal where atoms share the same crystal orientation; smaller grains increase hardness.

Plastic Explosive

Moldable secondary high explosive (e.g., Semtex) that detonates with a blasting cap.

Glaister Equation

Formula estimating time since death from body temperature: (98.4 °F – rectal temp) / 1.5 = hours.

Vitreous Potassium Method

Time-of-death estimate using K⁺ concentration rise in eye fluid after death.

Forensic Entomology

Study of insect activity on decomposing bodies to estimate post-mortem interval.