Let’s start by understanding the basics.

Any object that occupies Space with weight is called matter. One can find matter in various forms, such as solid, liquid, gas, and semi-solid. In general, solid substances are measured in kilograms, while liquids are measured in litres, and gases are measured in cubic meters. Liquid, gases and vapours are calculated based on their volume (Volume is the space occupied by a substance)

Properties of Matter

There are three states of matter

• Solid
• Liquid
• Gas

But some substances, like water, are also known as Universal Solvents.

However, most of the substance can be found in two states at normal temperatures. Example – steel has a melting point of 1400°C & a boiling point at which it starts to turn into vapour is 3000°C.

All substances are made up of small particles. These particles are called atoms; every atom has a central point known as the nucleus. An atom consists of Protons as positive, Electrons as negative and Neutrons as neutral particles.

The number of these protons and electrons and the electric charge of the atom remain in such a way that they remain balanced. The chemical behaviour of an atom is based on the number and arrangement of electrons present in it.

Now, we will move on to some basic terminology.

Elements – An element is a substance which is made up of many atoms, and all the atoms in it are similar.

Energy – Energy is consumed in doing any work and can be found in different forms, such as heat, light & electrical energy.

There are two forms of Energy.

• Kinetic Energy – It is obtained from the movement of the object
• Potential Energy – It is obtained from the position of the object

Firefighting is primarily related to a form of energy known as heat. A chemical reaction produces heat, that is, combustion. In fact, chemical energy itself gets converted into heat energy.

Weight: All objects have a different weight. Due to this difference, wood floats on water & stone sinks in water. This difference in substance is expressed as density or specific density.

Density: It is very important for a firefighter to know about Density. In a large building, when a fire breaks out, the density of the burning gas determines whether more gas & vapour will be found in the upper part of the building or in the lower part of the building.

If we consider two pieces of solid material that are exactly equal in length, width & height, let’s say one is made of iron and the other of wood. Despite being identical in size and shape, iron would weigh more than wood—the reason behind the density. The density of iron compared to wood is greater; in other words, the mass of one unit volume of iron is greater than the mass of one unit volume of wood, or one can say iron is denser than wood.

Density =     Mass
_________
Volume

Relative Density is sometimes used to measure density. Relative density is the ratio of the mass (weight) of a unit volume of a substance to the mass of a unit volume of water.

Relative Density =  Mass of Volume of a Substance
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Mass of the same Volume of Water

The ratio of the density of any substance & the density of water is the expected density of that substance.

Solubility: The property of whether a liquid is soluble in water or not is called Solubility. If the density of a substance is less than that of water, then it cannot be dissolved in water; that is, the substance floats on the surface of water. That is the reason why wood floats on water & iron sinks in water.

Difference in density of liquids.

The density of liquids helps us to some extent in determining whether we should use water, foam, or another fire extinguishing medium to extinguish the fire.

Note – A substance whose specific gravity is less than one will float on water

One might think that using water on fire is the easiest solution for a firefighter. Still, in actuality, it is a difficult task for a firefighter (Fireman) when water is used as a medium to extinguish a fire, especially when there is burning liquid present.

Due to their density, petrol & many other main burning liquids float on the surface of water; they cannot be submerged in water. Therefore, if water is used on these, it will not only fail to extinguish the fire but also spread it further.

In firefighting services, it is crucial to compare the density of gas or vapour with the density of air to determine which gas or vapour can mix with air and which is heavier or lighter than air.

All gases and vapours are mixable, but the difference in the densities of gases and vapours can prevent their mixing to some extent. Methane is a light gas with a vapour density of about 0.5. If this gas is leaked into a room, being lighter than air, it will move towards the ceiling. However, if a propane gas, whose vapour density is 1.5, is leaked, it will get deposited as a layer on the floor of the room due to being heavier than air.

Fire produces heat, which mainly has a destructive effect. Firefighters should be fully aware of the impact of heat on substances. Heat & temperature are closely related to each other. The change in temperature has an effect on how any solid, gas & liquid will behave.

Heat is a form of energy and can be produced by chemical reactions. For example, mechanical energy can be converted into heat through the burning of coal or oil. Heat can also be produced by resistance to the flow of electric current through friction.

Heat always flows from higher temperature to lower temperature, for example, when a hot object is placed next to a cold object, the hot object loses its heat and the cold object absorbs it. It is essential to distinguish between heat and temperature. This can be understood through a simple experiment. For example, keeping a piece of good-quality copper wire in a fire for some time & after a few seconds, we can see that the wire heats up & starts turning a shining red colour. This gives us a temperature of 800-900°C. Now, if you place a kettle containing one litre of water in the same flame for the same time, there is not much difference in the temperature of the water, after heating it for that long, even though the amount of heat given to both the wire & the water is equal.

When heat is applied to a substance, its temperature depends on three main factors: –

• The amount of heat given to the substance
• Mass of the substance
• The specific heat capacity of the substance

Temperature indicates that heat levels of an object, just as a leveller indicates the water level in a water tank above ground level. Just as water moves from the higher level to a lower level, heat also moves from a higher temperature object to a lower temperature object. The law of motion in both is independent of the amount of water & temperature.

Temperature is a number that indicates the level of heat in a body according to a specific value. The most familiar instrument for measuring temperature is a thermometer. Its action depends on the expansion of a liquid, such as mercury or alcohol. Temperature determines the hotness or coldness of the object.