What is fire? Answer : Fire is a phenomena that occurs when a substance combines with oxygen from the air and typically gives out heat, smoke and bright light. But it is not all that simple!
What is fire? For fire to start, a combustible substance must be present, the temperature must be high enough to cause combustion, and enough oxygen must be present to sustain rapid combustion. It gets more complicated!
Chemistry of Fire Oxygen combines with other substances to produce new products – this is called “oxidation” When it is real slow it can be called “rusting”
Chemistry of Fire Stored chemical energy is converted to energy in the form of heat and light. The energy in these chemical reactions comes from the breaking and formation of chemical bonds.
Chemistry of Fire Once a fire starts it will continue to burn until the supply of oxygen is exhausted or until the fuel is removed or consumed or Someone extinguishes it
How Hot is Hot? The heat of combustion is an exothermic reaction – it gives off heat.
Activation energy –the minimum energy necessary for a specific chemical reaction to occur i.e. matches, electrical discharges, sparks, and chemicals.
How Hot is Hot? Ignition Temperature: Minimum temperature at which a fuel will spontaneously ignite.
Definitions of Terms for Solid Fuels Ignition Temperature- The temperature to which a fuel must be heated to initiate combustion Sometimes called the “autoignition” temperature. Every fuel has an ignition temperature!
Heat and Fuel Fuel needs to be in gaseous state to ignite – temperature must be high enough to vaporize the fuel.
Spontaneous Combustion Is a type of combustion which occurs without an external ignition source. Heat builds up to the point of ignition Uses chemicals to supply oxygen – such as oxidizing agents
Requirements for Combustion A fuel must be present Oxygen must be available in sufficient quantity Heat must be applied to initiate combustion, and sufficient heat must be generated to sustain the reaction.
Requirements for Combustion Rate of oxidation (reaction): Rate of oxidation of a fuel must be capable of sustaining a flaming fire.
Pyrolysis The chemical decomposition of a substance through the action of heat
Definition of Terms Flammable Liquids and Gases Flash Point: Minimum temperature at which a liquid fuel will produce enough vapor to burn. Flammable Range: The (range of) composition of fuel-air mixture required for combustion. Flammable range of gasoline is 1.3- 6%.
What is the difference between and Fire and a Explosion? Detonation The speed at which explosives decompose (detonation) varies greatly and permits the classification of explosives as high and low explosives.
What is the difference between and Fire and a Explosion? Deflagration Low Order Explosives: Low explosives have velocities of detonation less than 1,000 m/s. Less than the speed of sound
What is the difference between and Fire and a Explosion? Detonation High Order Explosives: High explosives have velocities of detonation more than 1,000 m/s. More than the speed of sound
Production of Smoke Carbon monoxide Carbon particles Carcinogens
Fire is not an accident- It is the presence of two behaviors Acts by individuals to allow the right combination of components to be present Or Omissions by individuals that allows the right combination of components to be present All Fire have “causes”
The Fire Triangle This combination is sometimes called the fire triangle because it has three sides.
What three components are required to have a fire start? Fuel Heat Air
Fuel can be solid, liquid or gas The more finely divided the fuel is the more likely it can be easily ignited.
Specific Solid Fuel Conditions On the basis of specific surface and fire susceptibility, all combustible solids can be classified into three categories: »Tinder »Kindling »Bulk fuel
Specific Solid Fuel Conditions Surface Area Volume Density TINDER : Solids with specific surface of Tinder can be ignited by very small heat sources
Specific Solid Fuel Conditions Surface Area Volume Density KINDLING : Solids with specific surface That can be ignited fairly easily Kindling requires a burning tinder for ignition.
Specific Solid Fuel Conditions Surface Area Volume Density BULK FUEL : Solids with specific Bulk Fuel requires burning Kindling for ignition.
Specific Solid Fuel Conditions Surface Area Volume Density Combustion
Liquid or Gaseous Fuels Liquid fuels have physical properties that increase the difficulty of extinguishment and hazard to personnel. Specific Gravity is important
Liquid or Gaseous Fuels Gases tend to assume the shape of their container but have no specific volume.
Heat is the Enemy Heat Now let’s go back and review the concept of how heat plays a part in the starting of fires.
Sources of Heat 4 General Categories Chemical Heat Energy Electrical Heat Energy Mechanical Heat Energy Nuclear Heat Energy
Sources of Heat Heat of Combustion Spontaneous Heating Heat of Decomposition Heat of Solution
How does a Fire Spread? A rate of combustion or the spread of fire depends on several variables:
How Does a Fire Spread? The area of solid/liquid in contact with air. The amount of heat generated to raise the temperature of un-burnt portion. The ability of materials to conduct heat away.
How Does a Fire Spread? Atmospheric humidity. Wind velocity. Air Temperature. Atmospheric pressure.
What are the methods of Heat Transfer? Conduction - Heat may be conducted from one body to another by direct contact of the two bodies or by an intervening heat-conducting medium.
What are the methods of Heat Transfer? Radiation Although air is a poor conductor, it is obvious that heat can travel where matter does not exist. This method of heat transmission is known as radiation of heat waves.
What are the methods of Heat Transfer? Convection - Convection is the transfer of heat by the movement of air or liquid.
Phases that a fire goes through Incipient Stage Low challenge High Challenge
How can a small fire become a big one in such a short time? Incipient Phase
How can a small fire become a big one in such a short time? Incipient Phase Smoldering Phase
How can a small fire become a big one in such a short time? Incipient Phase Smoldering Phase Low Challenge Open Flame
How can a small fire become a big one in such a short time? Incipient Phase Smoldering Phase Low Challenge Open Flame High Challenge Open Flame
Point of Origin The location where a fire begins
Area of Origin The area of a fire site where the combination of heat and fuel has resulted in damage or destruction
How are Fires Classified? Class A Fires involving ordinary combustible materials, such as wood, cloth, paper, rubber and many plastics. Water is used in a cooling or quenching effect to reduce the temperature of the burning Class A material below its ignition temperature.
How are Fires Classified? Class B - Fires involving flammable liquids, greases and gases. The smothering or blanketing effect of oxygen exclusion is most effective. Other extinguishing methods include removal of fuel and temperature reduction.
How are Fires Classified? Class C - Fires involving energized electrical equipment.
How are Fires Classified? Class D - Fires involving combustible metals, such as magnesium, titanium, zirconium, sodium and potassium.
How are Fires Classified? Class D - The extremely high temperature of some burning metals makes water and other common extinguishing agents ineffective..
How are Fires Classified? Class K - a new classification of fire as of 1998 and involves fires in combustible cooking fuels such as vegetable or animal fats.
How are Fires Classified? Class K - Its fuels are similar to Class B fuels but involve high temperature cooking oils and therefore have special characteristics.
Use the right type of extinguisher for the right class of fire
Products of Combustion Fire gases Flame Heat Smoke
Fire is never “An Accident” Keeping Heat away from Fuel Or Keeping Fuel away from Heat Is What Fire Prevention is all about
The Importance of Time Delay of Alarm is Deadly.