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The Fire Triangle

Part 1 - Heat & Fuel

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The Fire Triangle

Conceptual Model

Simplified representation of a concept or of concepts related to a phenomenon
Show processes or describe the relationships between concepts or factors essential to a phenomenon
Often depicted as diagrams

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The Fire Triangle

Conceptual Model
Fire has three components

Heat
Fuel
Oxygen

Heat

Fuel

Oxygen

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The Fire Triangle - Heat

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The Fire Triangle - Fuel

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The Fire Triangle - Oxygen

Atmosphere’s Composition

N₂ ~ 78.084%
O₂ ~ 20.940%
Argon ~ 0.934%
Other ~ 0.042%

CO₂ ~ 0.0407%
CO₂ ~ 407 ppm

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Cellulose (C₆H₁₀O₅)_n as a Fuel

Most abundant organic polymer on Earth (“skeleton” of plants)
A straight-chain, insoluble polysaccharide that is composed of glucose from photosynthesis

Glucose molecules linked (glycosidic bonds)
Hydrogen bonding between chains results in microfibrils
Wood can ignite between 150 ^oC and 260 ^oC (300 ^oF - 500 ^oF)

Chemical equation similar to cellular respiration

PhET Balancing Equations Investigation

When talking about vegetation as a fuel source, what’s providing most of the energy released by combustion is cellulose. Very simply, cellulose is a chain of glucose molecules. Not only is glucose an important molecule for storing energy but it is also a molecule essential to the structure of plants. An example of a fuel composed primarily of cellulose is wood. The exact ignition temperature of wood is difficult to determine because even trees of the same species can vary in tissue composition and surrounding environmental conditions. When discussing combustion, the Law of Conservation of Matter can be quickly reviewed using the “PhET” link in this slide. Can anyone tell me what the The Law of Conservation of Matter is? Matter can neither be created nor destroyed. Matter can’t disappear from a chemical reaction, and it can’t appear from nowhere. Whatever is present “before” must also be present “after.” Let’s review this law by balancing one of the simplest combustion reactions, the combustion of methane. After clicking on the PhET link, go to “Introduction,” and, then, “Combust Methane.” This reviews the balancing of a chemical equation to reflect conservation of matter. Using the “tools” will help students visualize the balancing of reactant and product atoms. Click

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Cellular Respiration and Combustion

Cellular Respiration Reactants - Glucose and Oxygen
Cellular Respiration Products - Carbon dioxide and Water
Cellular Respiration also releases energy
C₆H₁₂O₂ + O₂ → CO₂ + H₂O + Energy
C₆H₁₂O₂ + 6O₂ → 6CO₂ + 6H₂O + Energy

+ HEAT + HEAT & LIGHT

Now I would like for you to balance the classic chemical equation for cellular respiration next to the fire triangle you drew earlier. To make sure we’re all starting correctly, does anyone remember what the reactants are for cellular respiration? Click The products? Click Besides the products, what else is released as a result of this reaction? Click Okay, write out and balance the chemical equation for cellular respiration. Give students a few moments. I’m now going to reveal the unbalanced chemical equation for cellular respiration in case you can’t recall the chemical formulas for the reactants and the products. Click Give students more time to balance the equation. Here is the balanced chemical equation for cellular respiration. Click Does the number of carbon atoms in the reactants equal the number of carbon atoms in the products? The number of hydrogen atoms? The number of oxygen atoms? Where did the energy come from? The release of energy came from the potential energy stored in the chemical bonds found in glucose. How is the chemical reaction for cellular respiration similar to the one for combustion? Molecules containing carbon and hydrogen are combined with oxygen to produce carbon dioxide and water. Heat and light are given off. Click How are cellular respiration and combustion different? Combustion needs some heat energy to get the process going and energy is released in the form of heat and light. Click Convert your cellular respiration equation to the combustion equation by adding “Heat” to the left-hand side of the equation. Now, draw arrows from the three sides of your fire triangle to the corresponding “reactant” in your combustion equation. Click

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Chemical & Physical Changes

A physical change occurs when a specific molecule/substance/material undergoes a change or changes form without the molecule/substance/material having its unique chemical identity changing. Phase changes are a great example.
For a transformation to be a chemical change, the original unique chemical identity of a material/substance must change to a different chemical identity as a result of a chemical reaction. Examples include burning, rusting, cooking, digestion, and photosynthesis.

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Activity

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Safety Checklist for Fire Activities

Wear appropriate Personal Protective Equipment [PPE].

100% cotton clothing; safety goggles; closed-toed shoes

Tie back loose sleeves and long hair.
Make sure a charged fire extinguisher is close. Know how to use it.
Make sure each station has a spray bottle that is filled with water.
Always be aware of the fire’s location. Never lean over the fire!
Extinguish burned materials with water before putting them in the trash. Fire is not out if there is any smoke or heat coming from the fuels.
If a fire starts on you … Stop! Drop! and Roll!

An instructor must be present for fire to be used.

(Adapted from the USFS “FireWorks Safety Poster”)