FRSC Fire and Explosion Investigations

Fire Def

Transformation process by which O2 is united with another substance to produce heat and light

Oxidation def

Combustion of O2 with other substances to produce new products

Fast oxidation example + equation

Methane and O2

Slow oxidation example + equation

Rust

Why is the oxidation of iron//rust a slow reaction?

The electrons can’t vibrate as fast because iron is solid. When something like methane is oxidizing the reaction is faster because the electrons in gas vibrate more quickly

Energy def + examples

The ability/potential of a system or materia to do work

• radiant

• Thermal

• Light

• Mechanical

• Nuclear

• Electrical

• Chemical

U get the idea

Where does the quantity of heat from a chemical reaction come from?

The breaking and formation of chemical bonds

Endothermic reaction + examples

Breaking of chemical bonds by absorption of energy

• photosynthesis

• Dissolving salt in water

Exothermic reactions + examples

Release of energy, typically as heat or light into the surroundings causing the temperature to increase

• rusting

• Campfire

• Water and acid reaction

• Freezing water into ice

When chemical bonds are formed, energy is____. This is an ____ reaction.

1. Released/liberated

2. Exothermic reaction

Combustion is a combination of what 3 things?

Oxygen, heat, and fuel

Energy barrier def

All reactions require an input of energy to start them

The _____ the energy barrier, the ____ energy is required to initiate the reaction

1. Higher

2. More

If iron + O2 has a low energy barrier and gasoline + O2 has a high energy barrier what is needed to cause a fast oxidation reaction

High temperature ! Must be applied to start the oxidation of the fuel

Ignition temperature

The temperature that the fuel must be raised to in order to exceed the energy barrier

Chain Reaction

Once combustion starts, enough heat is liberated to keep the reaction going by itself. The fire absorbs part of its own liberated heat to generate even more heat

Factors of influence for the rate of collision

1. Physical state of fuel → must be gaseous to support a flaming fire so that the molecules can collide frequently enough → high rates of collision

2. Temperature

Flashpoint def

The lowest temperature at which a liquid gives off sufficient vapor to form a mixture with air that will support combustion

3 requirements to initiate and sustain combustion

1. A fuel must be present

2. O2 must be available in sufficient quantities to combine with the fuel

3. Heat must be applied to initiate the combustion and sufficient heat must be generated to sustain the reaction

Heat transfer is critical in fire investigations as it explains how fire spreads. What 3 modes are there?

1. Conduction

2. Convection

3. Radiation

Conduction def

Heat travels through direct contact of solids to spread the fire or damage structures

The heat travels from HOT areas to COLD areas

Convection def

Heat transfer in fluids where the heated fluid rises and cooler fluid sinks, creating a continuous circulation loop

Ex. Boiling water

Radiation def

Transfer of heat energy from a heated surface to a cooler surface by electromagnetic radiation

Ex. Space heaters

Where do searches of fire investigations begin

Finding the origin

Pour patterns

V patterns

• points to the origin

• Can be unusually pointed with accelerants

U pattern

• “pour pattern”

• Suggests a pool of accelerant like gasoline

Fires tend to move upward, so the probable origin point will be at the lowest point with the mose intense characteristics of burning

Hydrocarbon detection

Good screening tool for checking suspect samples

Where are samples of fire evidence kept

Airtight containers to prevent loss of evidence

Headspace vapor