2.1: Scientific Concepts and Terminology

Matter

Matter is any substance that has mass and takes up space.¹

While there are numerous states of matter in the physical sciences, for the purposes of this course, we will focus on three: solid, liquid, and gas.

• Gas – Matter that has no definitive size or shape
• Liquid – Matter that has a definite volume but no definite shape
• Solid – Matter that has a definite shape and volume

These definitions are simple enough, and it is easy to understand the difference between air, water and a block of wood. However, when examining fire dynamics, the state of matter significantly influences the process of burning depending on a fuel's state of matter. The process of burning in each of these states will be discussed in subsequent units.

Heat

Heat is a form of energy characterized by vibration of molecules and capable of initiating and supporting chemical changes and changes of state.²

Heat is a key aspect of modern fire behavior. A large amount of time will be spent on heat release rate in Unit 6. Heat and temperature are often thought of as the same thing, however it is important to understand that temperature is a measurement of heat.

Temperature

Temperature is a measurement of the amount or degree of heat (vibration of molecules) in an object or substance.³

There are three typical temperature scales that are utilized in this course and in the scientific information that you will see as you continue to learn fire behavior throughout your career in the fire service. You will primarily see Fahrenheit and Celsius used in fire behavior research; Kelvin is also cited occasionally. Each of these scales are defined by their association with both the freezing point and the boiling point of water.

• Fahrenheit – A temperature scale that has freezing set at 32 degrees and the boiling point set at 212 degrees.
• Celsius – A temperature scale that has freezing set at 0 degrees and the boiling point set at 100 degrees.
• Kelvin – A temperature scale that starts at absolute zero.

Figure \(\PageIndex{1}\): Fahrenheit, Celsius, and Kelvin Temperatures
Copyright: “Fahrenheit, Celsius, and Kelvin Temperatures” by David W. Ball, licensed CC BY-NC-SA 4.0

Heat Capacity

Heat capacity describes the amount of energy required to increase (or decrease) the temperature of a certain mass of material by a certain amount.⁴ Heat capacity is an important aspect in creating fuel, igniting fuel and cooling fires. For instance, wood will begin to produce flammable vapors at around 400°F, which means the surface of a chunk of firewood needs to be heated to that temperature in order to burn. This means that to start a campfire, enough of the wood needs to be heated to produce vapors, but also enough excess energy needs to be available (heat feedback loop) to heat more wood to continue the sustained reaction. Heat capacity also works in the opposite direction, where water absorbs a certain amount of heat when applied to a fire. Water's high heat capacity is what makes it a preferred extinguishing agent.

Expansion of Matter

Substances tend to expand when they are heated. In fact, this property was utilized to create analog thermometers. Because the molecules within the object have more motion as they heat up, it makes sense that most substances will expand when heated.⁵

This property has some significant implications for firefighters. For instance, steel beams can expand, causing them to buckle or push over supporting walls. Water expands 1700 times as it turns to steam, which can force superheated steam and gases into the normally cooler lower layers that firefighters operate in.

Figure \(\PageIndex{2}\): Building with fire damage.
Copyright: Image cropped from "Fire Damage at U.S. Bank in Minneapolis" by Tony Webster, licensed CC BY 2.0.

Heat Transfer

Heat, or the vibration of molecules, is transferred from high heat to low heat. Firefighters must understand this phenomenon, as they typically are the coolest part of a room that is on fire, which means heat from nearly everything in the room will be transferring to them. Heat is transferred in three different ways: conduction, convection, and radiation.

Conduction is “heat transfer to another body or within a body by direct contact.”⁶

Figure \(\PageIndex{3}\): Conduction Animation.
Copyright: "Heat Transfer: Conduction" by UL Research Institutes’ Fire Safety Research Institute. Used with Permission; see Terms of Use.

Convection is “heat transfer by circulation within a medium such as gas or a liquid.”⁷

Figure \(\PageIndex{4}\): Convection Animation.
Copyright: "Heat Transfer: Convection" by UL Research Institutes’ Fire Safety Research Institute. Used with Permission; see Terms of Use.

Radiation is heat transfer by way of electromagnetic waves.⁸

Figure \(\PageIndex{5}\): Radiation Animation.
Copyright: "Heat Transfer: Radiation" by UL Research Institutes’ Fire Safety Research Institute. Used with Permission, see Terms of Use.

As mentioned earlier, heat transfer can have significant impacts on firefighters. The animation below illustrates the three ways these heat transfer impacts firefighters.

Figure \(\PageIndex{6}\): Heat Transfer to Firefighter.
Copyright: "Heat Transfer for Firefighter Animation" by UL Research Institutes’ Fire Safety Research Institute. Used with Permission; see Terms of Use.

Energy

Energy can be defined as the ability to do work.⁹ Energy comes in many forms such as mechanical, thermal, chemical, and electrical. Most energy can be divided into two categories: potential and kinetic. Kinetic energy is the energy of moving matter, while potential energy refers to objects with stored energy. A swinging axe would be described as kinetic mechanical energy, however if a firefighter held the axe in the air waiting to swing it down, this would represent potential mechanical energy. Another example would be a can of gasoline, which would be chemical and thermal potential energy when stored and kinetic chemical and thermal energy once ignited.

Work is done whenever a force is used to move matter.¹⁰ When work is done, energy is transferred from one object to another. For example, when a firefighter uses energy to swing an axe, he transfers energy to the axe. The moving axe, in turn, transfers energy to door.

Like work, energy is measured in the joule (J), or newton·meter (N·m)

Measurements

• BTUs
• Calories
• Newtons

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References

^1. Flowers, P., Theopold, K., Langley, R., & Robinson, W. R. (2019). 1.2 Phases and classification of matter. In Chemistry 2e. OpenStax. https://openstax.org/books/chemistry-2e/pages/1-2-phases-and-classification-of-matter. Licensed CC BY-NC-SA 4.0.

^2. National Fire Protection Association. (2024). NFPA 921: Guide for fire and explosion investigations. https://link.nfpa.org/free-access/publications/921/2024

^3. Flowers, P., Theopold, K., Langley, R., & Robinson, W. R. (2019). 1.4 Measurements. In Chemistry 2e. OpenStax. https://openstax.org/books/chemistry-2e/pages/1-4-measurements. Licensed CC BY-NC-SA 4.0

^4. Pasquale, A. J., Fazzini, D. R., & Bennett, C. (2024). Temperature and heat. In Conceptual Physics. College of DuPage. https://cod.pressbooks.pub/physics1100/chapter/temperature-and-heat. Licensed CC BY-NC 4.0.

^5. Pasquale, A. J., Fazzini, D. R., & Bennett, C. (2024). Phase change. In Conceptual Physics. College of DuPage. https://cod.pressbooks.pub/physics1100/chapter/phase-change. Licensed CC BY-NC 4.0.

^6. National Fire Protection Association. (2024). NFPA 921: Guide for fire and explosion investigations. https://link.nfpa.org/free-access/publications/921/2024

^7. National Fire Protection Association. (2024). NFPA 921: Guide for fire and explosion investigations. https://link.nfpa.org/free-access/publications/921/2024

^8. National Fire Protection Association. (2024). NFPA 921: Guide for fire and explosion investigations. https://link.nfpa.org/free-access/publications/921/2024

^9. Ball, D. W., Hill, J. W., & Scott, R. J. (2011). 7.1 Energy and its units. In Introduction to Chemistry: General, Organic, and Biological. https://2012books.lardbucket.org/books/introduction-to-chemistry-general-organic-and-biological/s10-01-energy-and-its-units.html. Licensed CC BY-NC-SA 3.0.

^10. Adapted from Brainard, J. (2014). 16.1 Work. In CK-12 Physical Science For Middle School. https://www.ck12.org/book/ck-12-physical-science-for-middle-school/r2/section/16.1/. Licensed CC BY-NC.