Questions and Answers
What are the four components to the Fire Tetrahedron?
Fuel, Oxygen (or oxidizers), Heat, Chemical Reaction
What are oxidizers?
Substances that can release oxygen during combustion
Provide examples of oxidizers.
H2O2, Cl2, H2SO4
The richer the oxygen, the higher the ignition temperature.
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Define Class A Fire.
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Define Class B Fire.
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Define Class C Fire.
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Define Class D Fire.
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Define Class K Fire.
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What is pyrolysis?
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The ease of ignition is affected by _____
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What are the two fuel-related factors involved in combustion?
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Liquids burn, not vapours.
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Fuel in a gaseous state must be mixed with a(n) _____ in the proper ratio for combustion to occur.
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What is the lower flammable limit (LFL)?
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What is an explosive range?
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Explain spontaneous heating.
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Combustion cannot occur when concentrations are above or below the _____ or _____.
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What is flashover?
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What causes backdraft?
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What is the main difference between a fire and an explosion?
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What is exothermic?
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How does heat flow?
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Study Notes
Fire Tetrahedron Components
- Four essential elements: Fuel, Oxygen (or oxidizers), Heat, and Chemical Reaction.
Oxidizers
- Substances, such as H2O2, Cl2, and H2SO4, that release oxygen during combustion, facilitating fire.
Classifications of Fires
- Class A Fire: Involves combustible materials like wood and paper.
- Class B Fire: Pertains to flammable gases and liquids.
- Class C Fire: Involves fires where electricity is present.
- Class D Fire: Combustible metals like aluminum and magnesium are involved.
- Class K Fire: Relates to fires involving cooking oils and fats.
Combustion Dynamics
- Ease of ignition increases with a higher surface-to-mass ratio and larger surface area, lowering ignition temperatures.
- Fuels exist in multiple states: solid, liquid, or gas, but must typically be in gaseous form or vapor to combust.
Gas Characteristics
- Combustion occurs when a gaseous fuel is mixed with an oxidizer in the appropriate ratio.
- Flammable range is defined as the percentage of gas in the air necessary for combustion.
- LFL (Lower Flammable Limit) and UFL (Upper Flammable Limit) indicate concentrations at which combustion cannot occur.
Vapor Behavior
- Vapour density compares the density of gases with air; lighter gases (density less than 1) rise, while heavier gases sink.
- Specific gravity measures the density of liquids in relation to water, influencing whether a substance sinks or floats.
Heat and Energy
- Heat affects combustion; the conservation of mass and energy principles define that these cannot be created or destroyed, only transformed.
- Chemical reactions during combustion produce heat and light alongside byproducts like smoke and fire gases, which can be lethal.
Fire Behavior in Spaces
- Thermal Layering: Gases stratify by temperature, with the hottest gases at the ceiling.
- Mushrooming: Heat and smoke rise until they encounter obstructions and spread laterally before descending.
Fire Dynamics
- Ignition temperature is the threshold at which a substance ignites, while flashpoint is the minimum temperature for vaporization sufficient for burning.
- Different stages of a fire: beginning phase, free burning (growth phase), and smoldering (decay phase).
Explosions and Combustion Types
- Flashover: Rapid transition from localized fire to widespread burning.
- Backdraft: Explosive growth when oxygen enters a confined space post-smoldering phase.
- Distinction between deflagration (slow combustion wave) and detonation (shockwave faster than sound).
Chemical Reactions
- Combustion is an exothermic reaction, releasing heat. Both heat and friction can serve as ignition sources.
- Spontaneous Heating: Occurs when heat accumulates without escaping, often seen with certain organic materials.
Unique Mixtures
- Hypergolic Mixtures: Fuels and oxidizers that ignite on contact without external ignition sources.
- Anergols: Fuels and oxidizers that do not react when combined.
Effects of Fire Products
- Heat leads to increased heart rates, dehydration, and burns; smoke causes reduced visibility and respiratory issues.
- Primary cause of fatalities in fires is typically smoke and fire gases.
Energy and Heat Transfer
- Heat flows from warmer to cooler substances; the transfer rate is influenced by temperature differences.
- Molecular action within substances generates heat, allowing for combustion and contributing to fire dynamics.
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Test your knowledge on fire prevention concepts with these flashcards. Explore key components like the Fire Tetrahedron and the role of oxidizers in combustion. Perfect for anyone studying fire safety or preparing for related certifications.