Understanding fire
Of the many thousands of offices, shops and factories that were gutted by fire last year, more than half probably had fire extinguishers installed. Clearly, possessing fire safety equipment isn’t enough; understanding fire is just as essential. |
The Fire Tetrahedron
This is a model used by the fire fighting and protection industry to identify the four major components required to start a fire. |
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| Heat: Fire cannot begin or continue without a sufficient amount of heat. It is necessary therefore, to reduce the amount of heat in case of a fire. This can be done with the application of extinguishants like water and certain types of powder and gas. |
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| Fuel: Without fuel, a fire will stop. When fire consumes all the burnable fuel, it will extinguish itself without external aid. Unfortunately it is neither safe, nor practical to rely on this in case of a potentially large fire. Fuel can be rendered harmless by using chemical means. |
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| Oxidising agent (usually oxygen): Without oxygen, fire can neither begin nor sustain itself. A decrease in oxygen levels slows the combustion process. |
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| Chemical reaction: A chemical reaction is essential to both start a fire and keep it burning. E.g.: combustion is the chemical reaction that feeds a fire more heat and allows it to continue. |
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Heat spreads through three methods
Heat transfer (also known as heat flow, heat exchange, or transfer of thermal energy) is the movement of heat from one place to another. When an object is at a different temperature from its surroundings, heat transfer occurs so that the body and the surroundings reach the same temperature.
The three most fundamental modes of transfer are:
Conduction
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It is the transfer and distribution of heat energy from atom to atom within a substance. For example, a spoon in a cup of hot tea becomes warmer because the heat from the tea is conducted along the spoon. Conduction is most effective in solids, but it can happen in fluids.
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Convection
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Convection is the transfer of heat energy in a gas or liquid by movement of currents (it can also happen is some solids, like sand). For instance, heat leaves the coffee cup as the currents of steam and air rise.
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Radiation
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This refers to the transfer of energy from or to a body by the emission or absorption of electromagnetic radiation. Electromagnetic waves directly transport energy through space. Sunlight is a form of radiation that is radiated through space to our planet without the aid of fluids or solids.
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From a spark to an inferno in 6 minutes flat
What adds to the large-scale destructiveness of fire is the incredible speed at which it grows. A flame unchecked can amount to a furnace that even a fire brigade would find impossible to put out, in barely six minutes. So clearly, the sooner you act, the easier it is to put out a fire. |
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The Speed Power Equation
For every few minutes that pass, the fire’s intensity multiplies. And depending on when you attack the fire, the quantity of extinguishant required escalates as well. This graph illustrates just how quickly a fire can spread and the amount of extinguishing agent you’ll require to fight it. |
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| FIRE EXTINGUISHING CAPACITY REQUIRED TO FIGHT FIRE OVER TIME (IN KGS.). |
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| In addition to this, as the time-probability graph (below) illustrates; the time taken to fight a fire is inversely proportionate to your chances of fighting it successfully. To put it in another way, the sooner you attempt to fight a fire, the easier it is to put it out. |
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The stages of fire
Stage 1: Ignition
This is the only stage at which a fire extinguisher can be used safely, when the flame is relatively small.
Stage 2: Critical
Fire begins to engulf large areas and a huge amount of extinguishing agent is required to put it out. Only sophisticated sprinkler systems will prove useful at this point.
Stage 3: Blaze
By now the fire is out of control. It can only be put out with thousands of litres of extinguishing agent. Only a fire brigade might be able to tackle it. Not so much to put out the fire, but to prevent it from spreading to neighbouring properties. |
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STAGE 1 |
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STAGE 2 |
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STAGE 3 |
Classes of fire
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| Based on the cause, characteristics and the means required to fight it, fires have been classified into six different categories. |
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| A CLASS |
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Class A fires are the most common kind. These occur when a solid, organic material such as wood, cloth, rubber, or some plastics become heated and ignite. At this point the material undergoes combustion and will continue burning as long as the four components of the fire tetrahedron (heat, fuel, oxygen, and the sustaining chemical reaction) are available. |
Fires involving
solids like wood,
cloth and plastic. |
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| B CLASS |
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Class B fires involve flammable or combustible liquids. A solid stream of water should never be used to extinguish this type because it can cause the fuel to spread, causing the fire to increase. |
Fires involving
liquids like petrol, paint
and chemicals. |
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| C CLASS |
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This sort of fire is caused by combustible or flammable gasses. E.g.: L.P.G., butane, acetylene, hydrogen, natural gas, methane etc.; |
Fires involving
flammable gases. |
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| D CLASS |
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Certain metals like titanium, magnesium, potassium, steel and uranium are flammable. Fires involving these materials are called Class D fires. Generally, metal fire risks exist when machine shavings and other metal fines are present. |
Fires involving metals
such as magnesium
and titanium. |
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| Electrically Started Fire (ESF) |
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Class E fires are those that involve potentially energised electrical equipment. This fire is caused by short-circuiting machinery, overloaded electrical cables and other such instances. Since water is a good conductor of electricity, attempting to put out an electrical fire with it could be fatal. |
Fires involving
electrically energised
equipment. |
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| F CLASS |
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Class F refers to those fires that involve cooking oils or fats. Though commonly mistaken as a Class B fire, its characteristics are different. This kind occurs when cooking oil or fats are heated at a temperature high enough for it to burst into flame. |
Fires involving high
temperature deep
fats over 360
degrees Celsius. |
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As the data above attests, different kinds of fire require different extinguishants.
E.g.: Electrical fires and fires caused by fuels must not be put out with water.
To determine the type of extinguishing agent required you need to understand the nature of the fire and the components that caused it.
We have extinguishers for every kind of fire
At Ceasefire, our experts will determine the kind of extinguisher you need. E.g.: At kitchens, where fire is most commonly caused by high temperature fats, our sputtering watermist extinguisher is best suited. By studying your environment, we’ll ensure that you are equipped by the most scientific means to put out any fire that might break out. |