Heat and Oxygen

Heat

Heat is energy in motion.

Without any form of activity, there is no heat. In other words, heat is the flow of kinetic energy from one body to another.

Heat always flows from a hotter body to a cooler one. It never moves in the other direction unless another form of energy is present during the transfer. The transfer will continue until thermal equilibrium is achieved.

This "hotness" or "coldness" is expressed as temperature. Technically speaking, the temperature of an object is the average kinetic energy of the movement of its molecules. Thermometers are used to measure temperature.

Ignition Temperature or Ignition Energy

As mentioned in Lesson 1.1, ignition temperature is the minimum temperature at which a substance can burn. A given material must be heated up to this temperature before ignition can begin. At this temperature, the material starts to release vapors which enables the combustion process to commence.

Sources of Heat

Heat is an essential part of fires. Without heat, no fire can start. Heat must also be continually present in the fire for it to keep burning and spreading. There are four general types of heat sources: mechanical, chemical, electrical, and nuclear. Under each type are various sources that range from daily objects to unusual ones.

Investigators must be familiar with all of these heat sources to be able to understand fires. If your knowledge in this area is weak, you will be faced with more fire incidents than you can properly resolve.

Mechanical

Mechanical heat comes from friction which is a type of force that resists motion. Commonly, we observe this in two objects rubbing against each other. Friction by itself does not automatically cause a fire. Different factors, including the properties of the materials and the nature of the motion generating the heat, should be considered.

Chemical

This is heat that comes from exothermic chemical reactions. As discussed in a previous lesson, exothermic reactions are those that include heat as one of its reactions products. Under the right circumstances, the heat released during an exothermic reaction can be sufficient to start a fire.

Spontaneous heating, or heating that occurs without an external source, can also occur biologically. Decaying matter gives off heat as they break down. If the heat is contained, the temperature of the material can keep rising to its ignition temperature. If a sufficient amount of oxygen is available, it can result in spontaneous ignition.

Electrical

Electrical sources of heat are, as the name implies, electrical devices. Under normal circumstances, appliances will only produce heat according to the constraints of their design. For instance, heat may be generated as a by-product of normal operation or an electrical appliance may be specifically made to provide heat, such as in the case of heaters. These are generally of no concern.

However, these devices can sometimes malfunction due to the poor quality of materials and/or construction. When this happens, the device produces an unexpected amount of heat that could be responsible for fires.

Electricity can come from the smallest sources, like a tiny watch battery, to the largest, such as a lightning bolt. An investigator would be remiss for not being familiar with the materials included in this wide variety.

Nuclear

As mentioned in the previous lesson, we have a special category of fuels called nuclear fuels. Initially, they were mainly utilized for their devastating potential, such as when the atom bomb was first manufactured. Today, however, nuclear fuels are being used for their energy production capabilities. Of course, the planet still has enough stores of nuclear weapons that could destroy the Earth many times over.

Heat Transfer

In sum:

Conduction: transfer of heat via direct contact between two bodies or through a heat-conducting medium

Convection: heat transfer through a circulating medium, usually air or liquids

Radiation: movement of heat via waves

Temperature Scales

Other notable temperature scales:

• Rankine °R: Another temperature scale that has an absolute zero at its lowest point. Unlike Kelvin, which scales with the Celsius measure, Rankine scales with the Fahrenheit measure.

• International Temperature Scale (ITS): This measure is based on the electrical resistivity, with platinum wire being used as the standard for temperature between –190°C and 660°C

Oxygen

As previously discussed, oxygen is a chemical element with the chemical symbol O. As a gas, it exists as a colorless, odorless, tasteless substance in the form of O₂. It occurs freely in the air and combines easily with other elements.