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Basics of Fire Physics and Chemistry


Basic of Fire Physics and Chemistry: Physics and Chemistry are branches of science that studies the behavior of matter. Chemistry focuses on describing matter by its intrinsic behavior within itself as an entity or the systems that compose matter. It focuses on describing matter by its extrinsic behavior in systems with other entities of matter or the systems that matter behaves in. Physics is involved with the fundamental principles of physical phenomena and the basic forces of nature, and also gives insight into the aspects of space and time. It also deals with the basic principles that explain matter and energy, and may study aspects of atomic matter by following concepts derived from the most fundamental principles.

Chemistry focuses on how substances interact with each other and with energy (for example heat and light). The study of change of matter of chemical reactions and synthesis lies at the heart of chemistry, and gives rise to concepts such as organic functional groups and rate laws for chemical reactions.

Basics of fire Physics & Chemistry:

Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light and various reaction products. Slower oxidative processes like rusting digestion are not included by this definition. Fire is hot because of conversion of the weak double bond in molecular oxygen o2 stronger bonds in the combustion products carbon dioxide and water releases energy (418 k ie 32 g of 02); the bond energies of the fuel play only a minor role here.

The flame is the visihle per of the fire. Flames consist primarily of carbon dioxide, water vapour, oxygen and nitrogen. If the flame is hot enough, the gases may become ionized to produce plasma. Depending on the substances ,the colour of the flame and the fire’s intensity will be different. Fire in its most common form can result in conflagration, which has the potential to cause physical damage through burning. Fire is an important process that affects ecological systems around the globe.

The positive effects of fire

The positive effects of fireinclude stimulating growth and maintaining various ecological systems. Fire has been used by humans for cooking, generating heat, light, signalling and propulsion purposes. The negative effects of fire include hazard to life and property, atmospheric pollution, and water contamination. If fire removes protective vegetation, heavy rainfall may lead to an increase in soil erosion by water. Fire cannot exist without all of these elements in place and in the right proportiolis.

For example, a flammable liquid will start burning only if the fuel and oxygen are in the proportions. Some fuel-oxygen mixes may require a catalyst, a substance that is not consumed, when added, in any chemical reaction during combustion, but which enables the reactants combust more readily.
Once ignited, a chain reaction must take place whereby fires can sustain their own heat by the further release of heat energy in the process of combustion and may propagate, provided there is a continuous supply of an oxidizer and fuel. If the oxidizer is oxygen from the surrounding air, the presence of a force of gravity, or of some similar force caused by acceleration, is necessary to produce convection, which removes combustion products and brings a supply of oxygen to the fire.

The fire can be extinguish by any of the following:-

  1. Turning off the gas supply, which removes the fuel source.
  2. Covering the flame completely, which smothers the flame as the combustion both uses the available oxidizer (the oxygen in the air) and displaces it from the area around the flame with CO2.
  3. Application of water, which removes heat from the fire faster than the fire can produce it (similarly, blowing hard on a flame will displace the heat of the currently burning gas from its fuel source, to the same end).


Application of a retardant chemical such as Holon to the flame, which retards the chemical reaction itself until the rate of combustion is too slow to maintain the chain reaction. Contrast, fire is intensified by increasing the overall rate of combustion.

Physical properties of Matter:

Matter is anything that has mass and takes up space. It includes all the physical “stuff around, houses, water, air, people, ants, trees, etc. All matter can exist as a solid, a liquid, or a gas. Matter includes all the things we can weigh to find the mass and measure to find the volume (because they take up space) Different substances or matter have various properties that can be used to distinguish them from each other. These properties are things that you can observe or measure about the substance. For example, water and isopropyl alcohol (rubbing alcohol) are both clear, colour less liquids at room temperature. However, they can be told apart because they have other properties that are different.

Water is odourless while the isopropyl alcohol has a strong smell. The alcohol evaporates very quickly while the water evaporates slowly.  An example is odour. When you smell water or isopropyl alcohol, neither of these substances changes into something else. They remain water and isopropyl alcohol. Similarly, when water and isopropyl alcohol evaporate, they do not change into something else. They move from liquid into gases, because, these substances do not change into different substances, the properties of odour and speed of evaporation are physical properties.


Density is a measurement of how solid something is. Specifically it is the mass per unit volume of a substance. If you have two objects of the exact same size volume, the more dense object will weigh more than the less dense object.

So there are two things contributing to density:

  1. The mass of the atoms or molecules that makes up the material.
  2. The volume or amount of space the material takes up. If the molecules or atoms are “pack” in more closely, they will be denser.

For example, Styrofoam is a low density material. Even a large Styrofoam container does not weigh much. The molecules in the Styrofoam do not have much mass and there is a lot of space between them. A brick, on the other hand, is much more dense. Even a moderate sized brick can be pretty heavy.  Density and buoyancy are closely related. A less dense substance will float on a more dense substance.

Density of fire:

  • In artillery, the number of shells fire per minute per 100 m of target-length.
  • In small-arms fire, the number of bullets fire per minute per meter on a given-line by all types of weapons. The density of fire depends on the-number of weapons, their type.

Relative Density:

Relative density or specific gravity is the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity usually means relative density with respect to water. The term “relative density” is often prefer in modern scientific usage. Defined as a ratio of density of particular substance with that of water.

If a substance’s relative density is less than one then it is less dense than the reference; if greater than 1 then it is denser than the reference. The relative density is exactly 1 then the densities are equal; that is, equal volumes of the two substances have the same mass. And if the reference material is water then a substance with a relative density (or specific gravity) less than 1 will float in water.

For example, an ice cube, with a relative density of about 0. 91, will float. A substance with a relative density greater than I will sink.

Temperature and pressure must be specified for both the sample and the reference. Pressure is nearly always 1 atm (101. 325 kPa). Where it is not, it is more usual to specify the density directly. Temperatures for both sample and reference vary from industry to industry.

Liquids may change to a vapour at temperatures below their boiling points through the process of evaporation. Evaporation is a surface phenomenon in which molecules located near the liquid’s edge, not contained by enough liquid pressure on that side, escape into the surroundings as vapor. On the other hand, boiling is a process in which molecules anywhere in the liquid escape, resulting in the formation of vapour bubbles within the liquid.

Vapour Density:

Weight of a unit volume of gas or vapour compared or (divided by) the weight of an equal Volume of air or sometimes, hydrogen. Substances lighter than air such as acetylene, methane, oxygen are said to have vapour densities less than 1. 0 and substances heavier than air such as butane, chlorine, ethane are said to have vapour densities higher than 1. 0. Whereas all gases and vapors mix with air, the lighter substances tend to rise and dissipate, and the heavier substances tend to concentrate in low places along floors, sewers, trenches and may create fire and health hazards.

Melting Point:

The melting point of a solid is the temperature at which it changes state from solid to liquid at atmospheric pressure. At the melting point the solid and liquid phases exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard pressure. When considered temperature of the reverse change from liquid to solid, it is refers to as the freezing point or crystallization point. Because of the ability of some substances to super cool, the freezing point is not considered as a characteristic property of a substance. When the “characteristic substance is determined, in fact the actual methodology is almost always “the principle of observing the disappearance rather than the formation of ice”, that is the melting point.

Boiling Point:-

The boiling point of a substance is the temperature at which the vapor pressure of the liquid equals the pressure surrounding the liquid and the liquid changes into a vapour. The boiling point of a liquid varies depending upon the surrounding environmental pressure. A liquid in a partial vacuum has a lower boiling point than when that liquid is at atmospheric pressure. A liquid at high pressure has a higher boiling point than when that liquid is at atmospheric pressure.