Introduction to Fire Protection and Arson Investigation

Fire: a state, process, or instance of combustion in which fuel or other material is ignited and combined with oxygen, giving off light, heat and flame.
- Rapid oxidation with evolution of heat and light.
Cold Fire: fire that burns below a temperature of 400^\u00b0F. These are cooler-than-normal fires. Example: Alcohol produces a cooler flame than acetylene.

Elements of Fire

Classic Fire Triangle: HEAT, OXYGEN, FUEL.
- Fire occurs when fuel reaches its ignition point (via heat) and reacts with oxygen in surrounding air, causing combustion.
- The fire continues to burn until at least one of the three elements runs out.

FIRE TRIANGLE

Elements:
- FUEL
- HEAT
- OXYGEN
Notes on FUEL:
- Fuels can be solid, liquid, or gaseous.
- A fuel is anything that can burn; removing fuel or having too little fuel causes the fire to go out.
- Example: paper or wood.
Notes on HEAT:
- The flash point of the fuel determines how much heat is necessary for the chemical reaction.
- Heat can be generated by various means (e.g., friction, chemical reactions).
- Lowering the material temperature is a method of fire suppression (e.g., water or chemical extinguishing agents).
Notes on OXYGEN:
- Fire typically requires oxygen; air contains about 21\% oxygen.
- Extinguishers and blankets reduce or cut off oxygen to the fire.

WHY OXYGEN IS IMPORTANT TO FIRE

The chemical process when a fuel is ignited requires oxygen for the reactions that cause burning.
Oxidation generates heat and combustion byproducts (e.g., smoke, gases).
The fire continues as long as there is oxygen in the air.
Some extinguishing agents work by reducing oxygen concentration (e.g., CO₂ or inert gases).

FIRE TETRAHEDRON

Adds a fourth element to the Fire Triangle: chemical chain reaction.
This chemical chain reaction provides adequate heat to sustain the fire.
Fire grows and burns as long as the chain reaction is sustained.
Suppression occurs when at least one element of the fire tetrahedron is removed.

STAGES OF FIRE DEVELOPMENT

1) Ignition – when the four components combine and combustion starts.
2) Growth – a fire plume develops above the burning fuel; surrounding air is entrained into the plume.
3) Fully-Developed – all combustible materials in the compartment are involved.
4) Decay – heat release declines as fuel is consumed.

Note: Flashover is not a stage; it is a rapid transition between growth and fully developed stages.

COMBUSTION

Combustion: an exothermic sequence of chemical reactions between fuel and an oxidant, producing heat and changing chemical species; can present as heat with glowing or flame.
A complex reaction requiring: a fuel (gas/vapor), an oxidizer (oxygen), and heat to proceed.

TYPES OF COMBUSTION

A. Glowing Combustion

Occurs when solid fuels do not produce enough gases during pyrolysis to sustain a flame.
If access to oxidant is limited, glowing combustion may occur.

B. Flaming Combustion

Commonly recognized type; occurs with gaseous fuel sources.
Flame color can indicate fuel composition.

C. Spontaneous Combustion

Ignition of organic matter without apparent cause, typically via internally generated heat from rapid oxidation (self-heat).

D. Explosive Combustion

Occurs when vapors, dust, or gases are premixed with air in the right proportions and ignite.

PRODUCTS OF COMBUSTION

A. Fire Gases

Byproducts of combustion in gas phase (e.g., CO, CO₂, SO₂, soot).

B. Heat

The energy released by combustion that propagates the fire; causes burns and heat-related injuries.

C. Smoke

Visible product of incomplete combustion; typically a mixture of O₂, N₂, CO₂, CO, soot, and other products.

D. Flame

Incandescence of gases accompanying rapid oxidation; the luminous portion of a burning gas.

PROPERTIES OF FIRE

A. Physical Properties

Specific Gravity – ratio of the weight of a solid/substance to the weight of an equal volume of water.
Vapor Density – weight of a volume of pure gas compared to weight of a volume of dry air at the same temp/pressure.
Vapor Pressure – force exerted by molecules on the surface of the liquid at equilibrium.
Temperature – measure of thermal agitation of molecules in a substance.
Boiling Point – constant temperature at which a liquid's vapor pressure equals atmospheric pressure.
Fire Points – lowest temperature at which vapors evolve fast enough to sustain continuous combustion; higher than flash point.
Flash Point – temperature at which a liquid gives off enough vapor to form an ignitable mixture; e.g., gasoline around -50^\u00b0F; kerosene around 100^\u00b0F.
Auto-ignition Point / Kindling Temperature – temperature at which a flammable liquid forms a vapor–air mixture that ignites.

B. Chemical Properties

Endothermic Reaction – chemical change where energy/heat is absorbed before reaction proceeds.
Exothermic Reaction – release of energy/heat; products have less energy than reactants.
Oxidation – chemical change where a fuel reacts with an oxidizer (e.g., oxygen).
Pyrolysis – production of incandescent gases and heat; a combustion product when solid fuel thermally decomposes.

ELEMENTS AND THEIR USES

FUEL

Fuels can be solid, liquid, or gaseous; any material that can burn.
Example: paper or wood.

GENERAL CATEGORIES OF FUEL

Solid Combustible Materials

Includes organic/inorganic, natural or synthetic solids, including metals.
Common solids: wood, paper, cloth; dust can burn faster than bulky material.
Types of Flammable Solids:
a. Pyrolyzable Solid Fuels – burn readily; vapors released during chemical breakdown mix with air to form flames.
b. Non-Pyrolyzable Fuels – harder to ignite; e.g., charcoal; no pyrolyzable components; no fumes released; gas-to-solid flame interaction.

Liquid Combustible Materials

All flammable liquid fuels and chemicals.
Rate of vaporization is greater for liquids than for solids because of looser molecular packing.

Gaseous Substances

Examples: acetylene, propane, butanes.
Properties: compressibility, expandability, permeability, diffusion.

GROUPS OF SOLID FUELS

A. Biomass – replaceable organic matter (e.g., wood, garbage, animal manure) used for energy.

Factors affecting combustibility of wood/wood-based products:
- Physical Form (smaller pieces ignite more easily than large pieces)
- Moisture Content (dry wood ignites more easily than wet wood)
- Heat Conductivity (good heat conductor ignites more easily)
- Rate and Period of Heating (less-flammable materials require direct contact)
- Rate of Combustion (more oxygen increases burn rate)
- Ignition Temperature (higher temperature reaches ignition faster)

B. Fabrics and Textiles – most fibers are combustible; fabrics are twisted/woven; textiles may be machine-woven/knitted.

Classification of Fibers:
a. Natural Fibers – from plants, animals, minerals.
b. Synthetic/Artificial Fibers – organic/cellulose fibers, acetate; non-cellulose/inorganic fibers (e.g., fiberglass, steel).
Factors affecting combustibility of fibers: chemical composition, fiber finish/coating, fabric weight, weave tightness, flame retardant treatment.

LIQUID COMBUSTIBLE MATERIALS

Includes flammable liquids and chemicals.
Rate of vaporization is greater for liquids than solids; liquids release a wide range of vapors, making gasoline a major fire hazard due to flammable vapor at normal temperatures.
General characteristics of liquids: definite volume but no definite shape; assumes vessel shape; slightly compressible but not indefinitely expandable.

General Groups of Liquid Fuels

Flammable Liquids – flash point around 37.8^\u00b0F and vapor pressure around 40\;psia.
Combustible Liquids – flash point at or above 37.8^\u00b0F.
Factors affecting flame propagation and burning of liquids: wind velocity, temperature, heat of combustion, latent heat of evaporation, atmospheric pressure.
Latent heat – heat absorbed by a substance when changing phase (e.g., solid to liquid to gas); heat released during gas–to–liquid or liquid–to–solid transitions.

Gaseous Substances

Examples: acetylene, propane, butanes.
Gaseous properties: compressibility, expandability, permeability, diffusion.

CHARACTERISTICS OF GAS FUELS

Gas molecules are in rapid movement and random motion; no definite shape.
Molecular collisions occur with container walls.

1) Classification of Gases

Based on Source:
a. Natural Gas – mainly methane; odorized for leaks; often mixed with small amounts of butane/propane (LPG/LNG).
b. Manufacture Gas – synthetic fuels derived from coal, petroleum, or biomass.

2) According to Physical Properties

a. Compressed Gas – gas at normal temperature inside a container remains gaseous under pressure (e.g., oxygen tanks).
b. Liquefied Gas – gas exists partly as liquid and partly as gas under pressure.
c. Cryogenic Gas – gas at very low temperatures (far below ambient), typically near its boiling point with moderate pressure (e.g., nitrogen).

3) According to Usage

a. Fuel Gases – flammable gases used with air to produce heat, power, light, or process energy.
b. Industrial Gases – used in industrial processes (e.g., oxygen, acetylene for welding/cutting; refrigerants like Freon, ammonia, sulfur dioxide).
c. Medical Gases – used for treatment (e.g., anesthesia, respiratory therapy).

FLAMES

Flames are incandescent gases, bright and hot; a combustion product in gas-phase combustion.
Difference between Fire and Flame:
- Flame: a stream of hot, burning gas from something on fire.
- Fire: the state of burning that produces flames, heat, light, and might produce smoke.

TYPES OF FLAMES

A. Based on Color and Completeness of Combustibility of Fuel

Luminous Flame – orange-red; deposits soot; incomplete combustion; lower temperature (center part of a candle flame).
Non-Luminous Flame – blue; complete combustion; higher temperature (outer layer of candle flame).

B. Based on Fuel and Air Mixture

Premixed Flame – air thoroughly mixed with hydrocarbons before entering flame (e.g., Bunsen burner; low flame velocity).
Diffused Flame – gas confected into atmosphere, diffuses with air; examples: candle flame, oxyacetylene torch; diffusion controlled by molecular diffusion.

C. Based on Smoothness

Laminar Flame – particle follows a smooth path through flame.
Turbulent Flame – erratic, irregular flows; all laminar flows can become turbulent with increasing physical size, gas density, or velocity.

HEAT

Thermal Energy: energy possessed by a material due to molecular activity; energy in transit due to temperature difference.
Thermal Balance: natural condition created by fire or normal movement of fire, smoke, and gases within a structure.
Thermal Imbalance: turbulent circulation of steam and smoke that can mislead investigators about origin; hot spots may appear.
Heat transfer: moving heat from warmer to cooler objects.

TYPES OF ENERGY

1) CHEMICAL ENERGY

Primary heat source in combustion.
Subtypes:
- Heat of Combustion (calorific or fuel value): quantity of heat released during complete oxidation of a fuel to water and carbon dioxide.
- Spontaneous Heating: gradual heat buildup from slow oxidation leading to ignition.
- Heat of Solution: heat released when a substance dissolves.
- Heat of Decomposition: heat released during decomposition requiring heat input for formation.

2) ELECTRICAL ENERGY

Can generate high enough temperatures to ignite nearby combustibles.
Produced when current flows through a conductor or a spark jumps an air gap.
Types:
- Resistive heating: rate of heat generation proportional to resistance and square of current.
- Lighting: heat from lightning; static electricity (electrical discharge on contact and separation).
- Heat from Arcing: caused by interruption of circuit or loose connections.
- Inductive Heating: heating increases with frequency.

3) NUCLEAR ENERGY

Generated by fission or fusion; releases heat, radiation, pressure.
Nuclear Fusion – two light nuclei combine to form heavier nucleus with emission of particles or gamma rays.
Nuclear Fission – neutron bombardment causing nucleus split (e.g., uranium, thorium).

4) MECHANICAL ENERGY

Energy from friction and compression.
Heat of Friction: ignition from sliding contact between surfaces.
Heat of Compression: heating due to gas compression.

FIRE EXTINGUISHER

A fire extinguisher is a mechanical device usually made of metal containing chemicals, fluids, or gases to stop fires.
Portable device used to extinguish fires of limited size.

Four General Methods of Fire Extinguishment

a. Extinguishment by Temperature Reduction (Cooling)

Use water to cool the fuel, reducing temperature to below the point where vapors form enough to sustain ignition.

b. Extinguishment by Fuel Removal (Fuel Depletion)

Eliminate fuel source or supply; stop flow of liquid fuel; prevent production of flammable gas; remove solid fuel along path; allow burn to complete if fuel is consumed.

c. Extinguishment by Oxygen Dilution (Oxygen Exclusion)

Reduce oxygen concentration at the burning area; introduce inert gases; separate oxygen from fuel.

d. Extinguishment by Chemical Inhibition

Effective mainly for burning gas and liquid fuels; cannot stop smoldering combustion; disrupts the chemical chain reaction.

Extinguishing Fires Without Water or Standard Extinguishers

Clean agent fire suppression systems can stop fires with no cleanup and no risk to people or environment, protecting precision gear, data centers, electrical cabinets, etc.
Choice of agent depends on fire type; some agents more effective for specific classes.

How to Fight Fires: Key Considerations

Do not fight unless trained and confident of the extinguisher type; if unsure, evacuate and call fire department.

CLASSES OF FIRE AND APPROPRIATE EXTINGUISHERS

Class A: Ordinary combustibles (wood, paper, cloth).
Class B: Flammable liquids (paints, oils, greases).
Class C: Live electrical equipment.
Class D: Combustible metals.
Class K: Commercial cooking oils and oils in kitchen appliances.

EXTINGUISHER TYPES

Water Extinguisher – for Class A and B (not for Class C).
Liquefied Gas Extinguisher – CO2-based; for Class A, B, and C.
Dry Chemical Extinguisher – powder for all classes.
Foam Extinguisher – foam with sodium bicarbonate and aluminum sulfate to form CO₂ foam.
Soda-Acid Extinguisher – sodium bicarbonate with a sulfuric acid component activated by inversion.
Vaporizing Liquid Extinguisher – non-conducting liquid (e.g., chlorinated solvents) for liquids and electrical fires.
Carbon Dioxide Extinguisher – effective for liquids and live electrical fires; mainly for Class C.
Wet Chemical Extinguisher – specialized for commercial cooking fires.

EXTINGUISHER COMPARISON TABLE (summary)

Range: varies by class; effectiveness and safety considerations (e.g., CO₂ can cause breathing difficulties in enclosed spaces; powders may leave residue).

REMEMBER (SAFETY CHECKLIST)

Ensure proper training before using an extinguisher.
Know the material type and fire class.
Use the correct extinguisher type.
If the fire spreads beyond its origin, evacuate.
Do not fight if uncertain or unconfident.
Pull alarm, evacuate, and call the fire department when needed.

HYDRANTS AND SPRINKLER SYSTEM

Fire Hydrant (also called fireplug, firecock, or Johnny Pump): a connection point to access a water supply for firefighting; part of active fire protection.
Underground hydrants have existed since at least the 18th century; above-ground pillar hydrants were invented in the 19th century.
Main function: provide rapid access to water for firefighters; ensures high-pressure water delivery.
Water Hammer: a pressure surge when a fluid in motion is forced to stop or change direction suddenly.

MAIN PARTS OF A FIRE HYDRANT

Bonnet – top cap removable to access hydrant.
Nozzles – side openings for hoses.
Barrel – main body containing water.
Stem – internal mechanism controlling flow.
Flange – base connecting hydrant to the underground main.
Threads – threaded openings for hose connections.
Port – side opening where water exits.

TYPES OF FIRE HYDRANT

Dry Fire Hydrant – used where temperatures fall below freezing; primary valve is below the frost line; hydrant is kept dry when not in use to avoid freezing; supply must be activated.
Wet Fire Hydrant – used where temperatures do not fall below freezing; primary valve at the bottom; barrel remains full of water.

HOW TO PROPERLY USE A FIRE HYDRANT

Assess the situation: determine fire size/location/intensity; ensure safety; identify the nearest hydrant and coordinate with team and incident command.
Gather necessary equipment: hydrant wrench, hose, nozzle, etc.; ensure equipment is in good condition.
Remove obstructions from access to hydrant (snow, ice, vehicles, debris).
Open the hydrant: loosen and remove the cap with a hydrant wrench; stay clear of residual pressure; inspect threads/connections before attaching hose.
Attach the hose: connect one end to hydrant outlet; ensure threads match; tighten; inspect hose for kinks or damage.
Control water flow: slowly open hydrant valve; monitor pressure gauge; adjust as needed for required flow/pressure.
Direct water stream: gradually open valve; maintain stable pressure; adjust as needed.
Monitor water supply: assign a firefighter to monitor supply/pressure; report fluctuations to incident commander; adjust hydrant valve as needed.
Coordinate with firefighters: maintain communication to align with incident strategy.
Close the hydrant: when fire is out or under control, tighten the valve clockwise; replace cap; inspect hydrant area before ending.