Fire
Fire is the rapid oxidation of a material in the exothermic chemical process of combustion, releasing heat, light, and various reaction products. 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 across the globe. The positive effects of fire include stimulating growth and maintaining various ecological systems. Fire has been used by humans for cooking, generating heat, signaling, and propulsion purposes. The negative effects of fire include water contamination, soil erosion, atmospheric pollution and hazard to human and animal life.
PHASES OF A FIRE
First Phase – Incipient
Oxygen content 20% - 21% with ceiling temperatures of approximately 37˚ C°. At this stage the produces of combustion are water vapour, carbon dioxide and sulphur dioxiode, and hot gases rising. Smoldering fires my last for a few seconds to several hours before breaking into flames. A large volume of smoke will be present until flaming starts and then progress is rapid.
Second Phase – free burning, flame producing or steady state
At this stage the oxygen content is 15% - 19% and the ceiling temperatures are above 537°C and the products of combustion are water vapour, carbon dixiode, carbon monoxide and sulphur dioxide. There large quantities of dark grey smoke and rapid destruction of combustible materials. It is at this point that flash over occurs. Flash over is when room and all its contents reach their ignition temperature and the area becomes fully involved in fire. Flame is now rapid.
Third Phase – smoldering
Oxygen content is less than 15% - 16% and ceiling temperature is above 815° C and soot is now added to the produce of combustion. Dense, dark flammable smoke and toxic flammable gases are being emoted and a black draft or smoke explosion is now possible.

Some typical indications of a back draft are:
a. little flame
b. high temperature
c. the smoke under pressure will “puff or breathe”
d. smoke colour is very dark and dirty or yellow grey just prior to back draft
e. smoked stained windows
f. muffled sounds
g. rapid inward movement or air when an opening is made
Classes of Fires
Fire classes
From Wikipedia, the free encyclopedia
Comparison of fire classes
American European Australian/Asian Fuel/Heat source
Class A Class A Class A Ordinary combustibles
Class B Class B Class B Flammable liquids Class C Class C Flammable gases
Class C Class F/D Class E Electrical equipment
Class D Class D Class D Combustible metals
Class K Class F Class F Cooking oil or fat
In firefighting, fires are identified according to one or more fire classes. Each class designates the fuel involved in the fire, and thus the most appropriate extinguishing agent. The classifications allow selection of extinguishing agents along lines of effectiveness at putting the type of fire out, as well as avoiding unwanted side-effects. For example, non-conductive extinguishing agents are rated for electrical fires, so to avoid electrocuting the firefighter.
Multiple classification systems exist, with different designations for the various classes of fire. The United States uses the NFPA system.Europe use the European Standard "Classification of fires" (EN 2:1992, incorporating amendment A1:2004). Australasia uses yet another.

Class A fires are those which involve ordinary combustible materials such as wood, paper or cloth. These fires should be extinguished by using a dry chemical extinguisher. Water is effective in extinguishing these type fires, however, water extinguishers are rarely found in the
Medical Center.
Ordinary combustibles "Ordinary combustible" fires are the most common type of fire, and are designated Class A under both systems. These occur when a solid, organic material such as wood, cloth, rubber, or some plastics[1] become heated to their ignition point. 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.
This class of fire is commonly used in controlled circumstances, such as a campfire, match or wood-burning stove. To use the campfire as an example, it has a fire tetrahedron—the heat is provided by another fire (such as a match or lighter), the fuel is the wood, the oxygen is naturally available in the open-air environment of a forest, and the chemical reaction links the three other facets. This fire is not dangerous, because the fire is contained to the wood alone and is usually isolated from other flammable materials, for example by bare ground and rocks. However, when a class-A fire burns in a less-restricted environment the fire can quickly grow out of control and become a wildfire. This is the case when firefighting and fire control techniques are required.
This class of fire is fairly simple to fight and contain—by simply removing the heat, oxygen, or fuel, or by suppressing the underlying chemical reaction, the fire tetrahedron collapses and the fire dies out. The most common way to do this is by removing heat by spraying the burning material with water; oxygen can be removed by smothering the fire with foam from a fire extinguisher; forest fires are often fought by removing fuel by backburning; and an ammonium phosphate dry chemical powder fire extinguisher (but not sodium bicarbonate or potassium bicarbonate both of which are rated for B-class[2] fires) breaks the fire's underlying chemical reaction.
As these fires are the most commonly encountered, most fire departments have equipment to handle them specifically. While this is acceptable for most ordinary conditions, most firefighters find themselves having to call for special equipment such as foam in the case of other fire.

Class B fires are those which involve flammable liquids, gases, oil, paint and greases. Either dry chemical or carbon dioxide extinguishers should be used to extinguish these type fires. Note: flammable liquids may re‐ignite after being extinguished. DO NOT USE WATER!
Flammable liquid and gas A CO2 fire extinguisher rated for flammable liquids and gasses
These are fires whose fuel is flammable or combustible liquid or gas. The US system designates all such fires "Class B". In the European/Australian system, flammable liquids are designated "Class B", while burning gases are separately designated "Class C". These fires follow the same basic fire tetrahedron (heat, fuel, oxygen, chemical reaction) as ordinary combustible fires, except that the fuel in question is a flammable liquid such as gasoline, or gas such as natural gas. A solid stream of water should never be used to extinguish this type because it can cause the fuel to scatter, spreading the flames. The most effective way to extinguish a liquid or gas fueled fire is by inhibiting the chemical chain reaction of the fire, which is done by dry chemical andHalon extinguishing agents, although smothering with CO2 or, for liquids, foam is also effective. Halon has fallen out of favor in recent times because it is an ozone-depleting material; the Montreal Protocol declares that Halon should no longer be used. Chemicals such as FM-200 are now the recommended halogenated suppressant.

Class C fires are those which involve electricity. Either dry chemical or carbon dioxide extinguishers should be used to extinguish these type fires. DO NOT USE WATER!
Electrical

Electrical fires are fires involving potentially energized electrical equipment. The US system designates these "Class C"; the Australian system designates them "Class E". This sort of fire may be caused by short-circuiting machinery or overloaded electrical cables. These fires can be a severe hazard to firefighters using water or other conductive agents: Electricity may be conducted from the fire, through water, the firefighter's body, and then earth. Electrical shocks have caused many firefighter deaths.
Electrical fire may be fought in the same way as an ordinary combustible fire, but water, foam, and other conductive agents are not to be used. While the fire is or possibly could be electrically energized, it can be fought with any extinguishing agent rated for electrical fire. Carbon dioxide CO2, FM-200 and dry chemical powder extinguishers such as PKP and even baking soda are especially suited to extinguishing this sort of fire. PKP should be a last resort solution to extinguishing the fire due to its corrosive tendencies. Once electricity is shut off to the equipment involved, it will generally become an ordinary combustible fire.We don't know what colour this fire goes.

Class D fires are those which involve combustible metals such as magnesium or sodium. Water can react with sodium and other alkali metals explosively, therefore DO NOT USE WATER! Also understand that CO2 extinguishers are unlikely to be able to contain a Class D fire.
Metal

Certain metals are flammable or combustible. Fires involving such are designated "Class D" in both systems. Examples of such metals include sodium, titanium, magnesium, potassium, uranium, lithium, plutonium, and calcium. Magnesium and titanium fires are common. When one of these combustible metals ignites, it can easily and rapidly spread to surrounding ordinary combustible materials.
With the exception of the metals that burn in contact with air or water (for example, sodium), masses of combustible metals do not represent unusual fire risks because they have the ability to conduct heat away from hot spots so efficiently that the heat of combustion cannot be maintained—this means that it will require a lot of heat to ignite a mass of combustible metal. Generally, metal fire risks exist when sawdust, machine shavings and other metal 'fines' are present. Generally, these fires can be ignited by the same types of ignition sources that would start other common fires.
Water and other common firefighting materials can excite metal fires and make them worse. The NFPA recommends that metal fires be fought with "dry powder" extinguishing agents. Dry powder agents work by smothering and heat absorption. The most common of these agents are sodium chloride granules and graphite powder. In recent years powdered copper has also come into use.
Some extinguishers are labeled as containing dry chemical extinguishing agents. This may be confused with dry powder. The two are not the same. Using one of these extinguishers in error, in place of dry powder, can be ineffective or actually increase the intensity of a metal fire.
Metal fires represent a unique hazard because people are often not aware of the characteristics of these fires and are not properly prepared to fight them. Therefore, even a small metal fire can spread and become a larger fire in the surrounding ordinary combustible materials.
Cooking oils and fats (kitchen fires)

Laboratory simulation of a chip panfire: a beaker containing wax is heated until it catches fire. A small amount of water is then poured into the beaker. The water sinks to the bottom and vaporizes instantly, ejecting a plume of burning liquid wax into the air.
Fires that involve cooking oils or fats are designated "Class K" under the American system, and "Class F" under the European/Australasian systems. Though such fires are technically a subclass of the flammable liquid/gas class, the special characteristics of these types of fires are considered important enough to recognize separately. Saponification can be used to extinguish such fires. Appropriate fire extinguishers may also have hoods over them that help extinguish the fire.

Types
Fire

There are four different types, or classes, of fire: Class A fires involve solid materials of an organic nature such as wood, paper, cloth, rubber and plastics that do not melt. Class B fires involves liquids. They include petrol, diesel, thinners, oils, paints, wax, cooking fat and plastics that melt. Class C fires involve electricity. Class D fires involve flammable metals such as magnesium, aluminium, titanium, sodium and potassium.

UNIT I PHYSICS AND CHEMISTRY OF FIRE 9

Fire properties of solid, liquid and gases fire spread toxicity of products of combustion theory of combustion and explosion vapour clouds flash fire jet fires pool fires unconfined vapour cloud explosion shock waves auto-ignition Physical properties
Combustion
Main article: Combustion

The fire tetrahedron
Fires start when a flammable and/or a combustible material, in combination with a sufficient quantity of an oxidizer such as oxygen gas or another oxygen-rich compound (though non-oxygen oxidizers exist that can replace oxygen), is exposed to a source of heat or ambient temperature above the flash point for the fuel/oxidizer mix, and is able to sustain a rate of rapid oxidation that produces a chain reaction. This is commonly called the fire tetrahedron. Fire cannot exist without all of these elements in place and in the right proportions. For example, a flammable liquid will start burning only if the fuel and oxygen are in the right proportions. Some fuel-oxygen mixes may require a catalyst, a substance that is not directly involved in any chemical reaction during combustion, but which enables the reactants to 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.
Fire can be extinguished by removing any one of the elements of the fire tetrahedron. Consider a natural gas flame, such as from a stovetop burner. The fire can be extinguished by any of the following:
• turning off the gas supply, which removes the fuel source;
• 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;
• 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), or
• application of a retardant chemical such as Halon to the flame, which retards the chemical reaction itself until the rate of combustion is too slow to maintain the chain reaction.
In contrast, fire is intensified by increasing the overall rate of combustion. Methods to do this include balancing the input of fuel and oxidizer to stoichiometric proportions, increasing fuel and oxidizer input in this balanced mix, increasing the ambient temperature so the fire's own heat is better able to sustain combustion, or providing a catalyst; a non-reactant medium in which the fuel and oxidizer can more readily react.
Flame
Main article: Flame

A candle's flame

Photo of a fire taken with a 1/4000th of a second exposure
A flame is a mixture of reacting gases and solids emitting visible, infrared, and sometimes ultraviolet light, the frequency spectrum of which depends on the chemical composition of the burning material and intermediate reaction products. In many cases, such as the burning of organic matter, for example wood, or the incomplete combustion of gas, incandescent solid particles called soot produce the familiar red-orange glow of 'fire'. This light has acontinuous spectrum. Complete combustion of gas has a dim blue color due to the emission of single-wavelength radiation from various electron transitions in the excited molecules formed in the flame. Usually oxygen is involved, but hydrogen burning in chlorine also produces a flame, producinghydrogen chloride (HCl). Other possible combinations producing flames, amongst many, are fluorine and hydrogen, and hydrazine and nitrogen tetroxide.
The glow of a flame is complex. Black-body radiation is emitted from soot, gas, and fuel particles, though the soot particles are too small to behave like perfect blackbodies. There is also photon emission by de-excited atoms and molecules in the gases. Much of the radiation is emitted in the visible and infrared bands. The color depends on temperature for the black-body radiation, and on chemical makeup for the emission spectra. The dominant color in a flame changes with temperature. The photo of the forest fire is an excellent example of this variation. Near the ground, where most burning is occurring, the fire is white, the hottest color possible for organic material in general, or yellow. Above the yellow region, the color changes to orange, which is cooler, then red, which is cooler still. Above the red region, combustion no longer occurs, and the uncombusted carbon particles are visible as black smoke.
The common distribution of a flame under normal gravity conditions depends on convection, as soot tends to rise to the top of a general flame, as in acandle in normal gravity conditions, making it yellow. In micro gravity or zero gravity,[4] such as an environment in outer space, convection no longer occurs, and the flame becomes spherical, with a tendency to become more blue and more efficient (although it may go out if not moved steadily, as the CO2 from combustion does not disperse as readily in micro gravity, and tends to smother the flame). There are several possible explanations for this difference, of which the most likely is that the temperature is sufficiently evenly distributed that soot is not formed and complete combustion occurs.[5]Experiments by NASA reveal that diffusion flames in micro gravity allow more soot to be completely oxidized after they are produced than diffusion flames on Earth, because of a series of mechanisms that behave differently in micro gravity when compared to normal gravity conditions.[6] These discoveries have potential applications in applied science and industry, especially concerning fuel efficiency.
In combustion engines, various steps are taken to eliminate a flame. The method depends mainly on whether the fuel is oil, wood, or a high-energy fuel such as jet fuel.
Heat
Main article: Heat
Fires give off heat, or the process of energy transfer from one body or system due to thermal contact.
Typical temperatures of fires and flames
• Oxyhydrogen flame: 2000 °C or above (3600 °F)[7]
• Bunsen burner flame: 1,300 to 1,600 °C (2,400 to 2,900 °F)[8]
• Blowtorch flame: 1,300 °C (2,400 °F)[9]
• Candle flame: 1,000 °C (1,800 °F)
• Smoldering cigarette:
• Temperature without drawing: side of the lit portion; 400 °C (750 °F); middle of the lit portion: 585 °C (1,100 °F)
• Temperature during drawing: middle of the lit portion: 700 °C (1,300 °F)
• Always hotter in the middle.
Temperatures of flames by appearance
The temperature of flames with carbon particles emitting light can be assessed by their color:[10]
• Red
• Just visible: 525 °C (980 °F)
• Dull: 700 °C (1,300 °F)
• Cherry, dull: 800 °C (1,500 °F)
• Cherry, full: 900 °C (1,700 °F)
• Cherry, clear: 1,000 °C (1,800 °F)
• Orange
• Deep: 1,100 °C (2,000 °F)
• Clear: 1,200 °C (2,200 °F)
• White
• Whitish: 1,300 °C (2,400 °F)
• Bright: 1,400 °C (2,600 °F)
• Dazzling: 1,500 °C (2,700 °F)
UNIT II FIRE PREVENTION AND PROTECTION 10
Sources of ignition – fire triangle – principles of fire extinguishing – active and passive fire protection systems – various classes of fires – A, B, C, D, E – types of fire extinguishers – fire stoppers – hydrant pipes – hoses – monitors – fire watchers – lay out of stand pipes – fire station-fire alarms and sirens – maintenance of fire trucks – foam generators – escape from fire rescue operations – fire drills – notice-first aid for burns.
“must classified: house, school, building,
Protection and prevention
Main articles: Wildfire and Fire protection

This visualization shows fires detected in the United States from July 2002 through July 2011. Look for fires that reliably burn each year in western states and across the Southeast.
Wildfire prevention programs around the world may employ techniques such as wildland fire use and prescribed or controlled burns.[23][24][25]Wildland fire use refers to any fire of natural causes that is monitored but allowed to burn. Controlled burns are fires ignited by government agencies under less dangerous weather conditions.[26]
Fire fighting services are provided in most developed areas to extinguish or contain uncontrolled fires. Trained firefighters use fire apparatus, water supply resources such as water mains and fire hydrants or they might use A and B class foam depending on what is feeding the fire.
Fire prevention is intended to reduce sources of ignition. Fire prevention also includes education to teach people how to avoid causing fires.[27]Buildings, especially schools and tall buildings, often conduct fire drills to inform and prepare citizens on how to react to a building fire. Purposely starting destructive fires constitutes arson and is a crime in most jurisdictions.
Model building codes require passive fire protection and active fire protection systems to minimize damage resulting from a fire. The most common form of active fire protection is fire sprinklers. To maximize passive fire protection of buildings, building materials and furnishings in mostdeveloped countries are tested for fire-resistance, combustibility and flammability. Upholstery, carpeting and plastics used in vehicles andvessels are also tested.
Where fire prevention and fire protection have failed to prevent damage, fire insurance can mitigate the financial impact.