Fire and Explosions: Introduction

[Music] [Music] [Applause] welcome to this fire and exclusion module and in this particular module we are going to discuss about the fire and exclusion what are the basic definition of fire and exclusion and what is the difference between the fire and exclusion what kind of and conditions required to produce any kind of fire what how the heat being generated in fire or explosion being transmitted to some other places that is modes of heat transfer we will discuss about the fire triangle what are the necessary ingredients and what are their necessary arms of this fire triangle

we will discuss about the various kind of a flammability characteristics now we know that fire is extremely dangerous not only for our domestic affairs but for the various industrial establishment now sometimes this fire may lead to explosion because explosion is the rapid generation of shockwaves maybe because of fire may or may not be because of some other reasons so in this particular module we will discuss that what are the different conditions required for the fire how the fire may lead to the explosion what kind of explosion and are dangerous for the industrial establishments because ultimately

whenever there is a fire then definitely there is a law loss of not only to the human being but also for the vegetation animal and above all the property and sometimes explosion may lead to the hidden danger to the nearby buildings to the vegetation to the human being etcetera now question arises what is fire now fire is very common we cannot imagine our sustainability without fire we cannot cook food we cannot have several other aspects we cannot reduce is three etcetera so what is fire the wrath this is the rapid chemical process that produces heat

and usually light now fire is a visible effect of the process of combustion now for combustion what kind of different conditions required we will discuss in this particular module now it occurs between oxygen in the air and some sort of fuel this is known as fire triangle now before we go into detail of this fire triangle let us have a thing that what is fuel now fuel is that what is actually being burned because everything is not having the probability of fire generation ability now this fuel is available in three physically stated States solid liquid

and the gas was best example of solid is cool liquid your gasoline diesel gas was natural gas etc so combustion usually occurs when fuel presents in gas was state now let us have a discussion about the chemistry of combustion now usually oxygen and fuel they are having the affinity in three aspects one is oxidation another one is a combustion now if oxygen is not present then pyrolysis and usually whenever we discuss about fire then there are two three major issues related to the sustainability of the fire so if there is a net release of heat

then only the fire will sustain now when there is a combustion then we can expect a variety of products for of combustion usually the combustion produces smoke and other substances now this is smoke sometimes carry some dangerous or toxic materials so specific products whatever product being generated during the combustion they are dependent on what kind of fuel being used and what is the temperature and how much quantity of oxygen is available for that particular process suppose there are unsaturated hydrocarbon then they may lead to the generation of co2 Cu etcetera and how much fuel is

being consumed during during the process of fire so these all the product of combustion they all depend on these three criteria or these three three three systems sometimes you may experience that a few fires may consume all available fuels now let us have a look of smoke because usually when there is a fire then definitely you can expect a certain quantity of smoke being generated now usually the smoke U is airborne product of combustion usually consists of ashes some gases some unburned hydrocarbons or some unburned fuel different aerosols and usually these sometimes these ashes gases

or aerosols they causes severe health hazards so inhalation of smoke they may cause severe illness sometimes heaving it may lead to the dead and usually the dangerous part is that the generation of this type of smoke cloud it may propagate to the to the nearby population we are these ashes the people may inhale the ashes gases aero solar set at may create the health hazard now the smoke contents they are usually particles solid metal consisting of some unburned partially or completely burnt substances it can be very hot or toxic in nature sometimes certain vapors may

be generated they are the small droplets of liquid suspended in air oils from fuel or water from suppression efforts etcetera again this this type of effect is extremely dangerous there there may be a generation of certain gases certain of gases and usually these gases produced by fire they are toxic in nature see you co2 and unburned hydrocarbons in sometimes if a polymer or a plastic products on catches fire then some sort of dioxins etcetera and these all gases are extremely dangerous or extremely hazardous to the human being as well as they are the heat carriers

so carbon sorry common gases these usually includes the carbon monoxide carbon dioxide sometimes hydrogen cyanides sometimes Foss genes so so there are so many accidents in past in the chemical industries they took place and they generated these off or dangerous gases and they become the part and parcel of human being and causes a severe death and a fatality to the human being so practically one must know that what kind of fuel what kind of source of fuel is there and how the combustion took place so that the necessary action towards the safeguard of mankind or

towards the safeguard of environment can taking place now once we know that that the this chemistry of fire then question arises if this is an exothermic reaction and if the net heat being liberated during the course of fire then how it can be transmitted to some other place in the japonic student one particular storage tank cache the fire caught fire and then the heat was transmitted to some other tanks and through the auto ignition temperature all these tank the temperature of those tank rose very rapidly the vapor vapors were formed and they took the temperature

they acquired a temperature of auto-ignition and then they catch the fire so he must know that what kind of different modes of heat transfer be there so heat energy usually we know that this is a basic phenomena that heat energy always flows from hotter to colder part so combustion gives off heat that can ignite other nearby fuel sometimes maybe because of auto ignition and sometimes because of the conduction because of the convection or because of radiative heat transfer so three methods of heat transfer use conduction convection and radiation now let us have a brief look

about these modes of heat transfer conduction now heat transfer from one molecule to another they are the direct in contact and the conduct conductors usually transfer heat very well and you can experience that if you have a metal plate and if you try to heat one one end of that particular metal plate and automatically it goes to the other part of the metal plate now usually to overcome such type of problem in a positive manner we usually adopt the concept of insulation and usually insulator do not transfer heat very well so in case if you

wish to inhibit the heat transfer so that it cannot go from one place to another then you must use the insulators the convective heat transfer the convection movement of heat through a fluid medium such as air or liquid and usually they form the convective currents you can see in this particular figure they usually form the convective current and sometimes the heat may transfer from one place to another place through this convective layers now let us have an example suppose these two are the tanks where say petrol or a gasoline is filled and by any means

this particular tank catches fire and because of the temperature rise because of the other availability of oxygen in the near in the atmosphere the fire propagates and by this way a lot of heat being generated in due course of time to this particular area the generation of heat may led to the formation of more and more vapors that because oxygen is available in abundance because it is surrounded by air then the fire catches rapidly and if it even if it is having the heat value is substantially high then the heat may transfer to this particular

tank number two this is tank number one this is tank number two now through this convective heat transfer the content of this this particular tank is eaten up and it may it may produce enough vapor and if this particular tank is not equipped with safety devices or sometimes it may get with the safety of all so so enough vapors may generated and there are two possibility one possibility is that this the fire which is here it may come to this place and the the vapors being generated may catch the fire another possibility is that the

content of this particular tank may approach to the auto ignition temperature so that it may ignite and you can imagine the scenario that both of the tanks may be in a position of burning and the quantum of heat being generated in due course of time so you need to think about that what should be the how we can eliminate the formation of convective convective heat transfer how we can card on it off if once it is this particular tank catches fire and if it is not possible then how we can control the fire because if

there there is another tank then because the heat is propagated in such a way or heat is being liberated in such a way that both the tank they they they catches they catch fire then the excess amount of heat may may may propagate the fire to this tank number three so one must know that how to control this particular aspect sometimes when in our domestic affair there is a fire and that is unwanted fire then sometimes they it may create like suppose you are sleeping and you are having a room heater or somebody somebody ignited

the the cigarette and by any means the quilt or anything catches the fire and sometimes the convective convective layers may form within this room and these and the reason of the formation of these convective layers is that hot gases they are having the the density difference with cold gases so there may be a chance of formation of this type of convective layers and these hot gases usually they travel horizontally so gas then banked down a wall or move outside and sometimes horizontally or vertically etcetera and whatever toxic gas is being generated the somebody who is

within this this room the toxic gases those were generated in due course of time the the particular person may inhale this thing and it may create a future problem or it may create the immediate problem radiation the radiation is again a very good source of heat transfer and sometimes in past so many accidents attributed to the radiative heat transfer so the transfer of heat in the form of an invisible wave is clubbed under the head of radiation so heat radiated to nearby structure even it can ignite it radiated heat passing through a window can ignite

an object so in combination of radiative heat transfer and convective heat transfer sometimes major accident they took place and passed now how we can prevent the accident there those who are attributed to fire so a prime of AC the engineers must know or must be familiar with that the fire and explosion properties of the material it is quite obvious that if you are handling the petrol and if you are going to a petrol pump or petrol station petrol filling station then always you took a proper attention or you have to take the proper attention not

to ignite any kind of cigarette or sometimes there are so many advisories be written on those petrol pumps that not to do do and don'ts etc because we all know that what are the flammable properties of petrol similarly if you are working in a kitchen then you are familiar with with flammable properties of LPG so you cannot treat the petrol with simple potable water or simple water so because we all know that it catches fire immediately and it produces off gases and the fire may propagate and fire may destroy each and everything so so we

we usually take some precautionary measures so when in general perspective coming from the picture then ingenious must be familiar with the fire and explosion properties of the material that what is the boiling point what is the flash point what is the flame point etcetera the nature of fire and explosion process how it can catch as the fire what what kind of things may lead to fire then procedure to reduce fire and explosion hazard ha if once it is ignited then how can reduce the fire sometimes you may use the sprinkler system sometimes if you may

you use to garden of air sometimes you may use to to cut the fuel supply to the source etc so you must know and all three things which we have covered in this particular aspect they are particularly the engineered things and how we can engineer all those things we will discuss in next couple of slides now to be more precise and to be more in scientific matter the three essential elements are required for combustion or you can say fire fuel oxygen heat or source of ignition so all three combined to form a fire triangle now

if any one of the arm is missing then there would be no fire and if all the arms of this particular triangle are combined then there would be fire and suppose if you wish to extinguish the fire you need to eliminate any one of the arm so usually whenever we remove oxygen or net release of heat or fuel supply then fire is distinguished so usually in in other aspect this is the chemical chain reaction which keeps the fire burning now how we can assess that what are the necessary conditions for the formation of fire triangle

so a prime of AC first thing comes into our mind is the fuel because usually when we used to go to the petrol pump or when you used to go to the kitchen our subconscious mind says that there is a presence of LPG we don't bother about the source of ignition we don't bother about the availability of oxygen at the source so fuel let us have a brief discussion about fuel fuel must be present in certain concentration now remember there is a nice takeo metric demand of fuel let us have a basic equation of methane

burning this is the basic equation ch4 plus twice o2 co2 plus twice H 2 plus Delta H now for one mole of methane the two moles of oxygen is required so if the few the oxygen is available suppose in a two mood and if there is a half mole then this is takeo metric demand will not fulfill so fuel must be present in a certain concentration we will discuss about the lower flammability limit upper flammability limit in due course of time now typical cases we are fire occur or if there is a leak during the

filling operation transfer operation or excessive dust we will take up as a Jaipur accident as one of the case study and all aspects like filling operation transfer operation they took place in the Jaipur accident often cannot always eliminate these sources sometimes it is very impractical to eliminate all things like all arms of anyone off of fire triangle like if you have if you wish to cook something in your kitchen how can you imagine the scenario that your fire triangle is not fulfilled you you require the presence of fuel you require the presence of oxygen you

require the presence of source of ignition and above all you require that net chemical chain reaction be there so we cannot always eliminate these sources we can help by having the good ventilation or we can have help of good housekeeping to keep the vapors from building up now there are certain examples of liquid solid and a gas was fuels like gasoline acetone ether pentane they are clubbed under the head of liquid solid plastic wood dust wood dust fiber metal particles etcetera gas was acetylene propane carbon monoxide hydrogen etcetera so you can list it you can

enlist n number of a source of fuels so once you characterize the few then the oxidizers oxygen is the most common oxidizer especially that found in ambient air so now why the oxygen or oxidizers are important the reason is that suppose if we wish to extinguish the fire and sometimes it is not possible to Cardon of oxygen then we should aleut the fuel concentration in such a way that the essential amount of oxygen whatever required as per the requirement of stoichiometric nature then the concentration should be on the lower side so for oxygen we often

use in erting with the nitrogen or helium blankets over the flammability material to reduce the oxygen content or to to Cardon it off from the fire so the oxygen content should be below the required amount of a combustion go back to the previous example of ch4 plus twice o to co2 plus twice H 2o Delta H now if for one mole of ch4 if the oxygen is suppose oxygen the availability of oxygen is say for one mole then definitely there would be no fire because the mixture is too lean to combust so it is essential

that the oxygen must represent in sufficient quantity whether you are taking the fire in a positive manner all you are taking the fire in a negative manner so a different type of oxidizers available as on date the liquid hydrogen peroxide nitric acid perchloric acid there are certain solid oxidizes like metal peroxides ammonium nitrite etcetera they are certain gas was obviously oxygen is most common source of oxidizer than fluorine chlorine etcetera then the last thing in the fire triangle is this ignition source now usually heat is the common ignition source and remember one thing that all

the ignition sources are free even the static charge being developed or accumulated on your here may be dangerous and if you are wearing some silk cloths etc sometimes you may observe that the static electricity being generated and sometimes you may also that there is a generation of spark be dangerous the spar been produced by the shoe nails of your nails of your shoes again it's easily or it's the free available source of ignition now one can eliminate ignition sources it is almost inevitable that the ignition source it will be available if there is a large

release of filament material that cannot be diluted quickly one more thing is that whatever source of ignition you are using it must have a sufficient quantity of energy or Delta H within it so that it can ignite that combustion mixture so once it is ignite then there is a formation of chemical chain reaction and the net release based on its Delta H it is sufficient to sustain that particular file so the the various example of ignition sources like a spark flame static electricity heat etc so you can modify the fire triangle with respect to this

chemical chain reaction because if you wish to sustain the fire then definitely you must have a chemical change reaction within it now once we go into deeper in the fire and explosion we must know the various definition because we will use different type of terminology in due course of time in all more deals of this fire in explosion so we have divided the things into a couple of aspect so first we will discuss about the various definition the first scientific definition of combustion is the chemical reaction in which a substance combined with an oxidant and

releases energy remember that particular release of energy is required for the sustainability of the fire so if you you remove this particular energy being liberated during the course of fire you can extinguish the fire explosion the rapid expansion of gases resulting in rapidly moving pressure or shockwaves the mechanical explosion this is due to the sudden failure of vessel containing high-pressure non reactive gases there may be certain physical explosion this results from the sudden failure of a vessel containing high pressure of non reactive gases then detonation the explosion we will discuss this detonation and deflagration in

the subsequent modules the detonation explosion chemical reaction with a shockwave greater than speed of sound this is extremely dangerous because sometimes the shockwave whatever being generated due to the explosion and may match with the natural frequency of any object and a couple of times and that particular object may destroy or may collapse so this is the detonation is extremely important then deflagration the explosion or the chemical reaction with the shockwave less than the speed of sound then bleve the boiling liquid expanding vapor explosion when liquid is at a temperature above its atmospheric boiling point sometimes

vessel ruptures and flammable liquid flashes and results in fire or explosion we will discuss because this levy in detail in the subsequent modules the confined explosions then explosion occurring within a vessel or building usually results in injury to building inhabitants and extensively damaged the unconfined explosion and explosion occurring in open usually result from a spill of a flammable gases spill these explosions are rarer than confined since dilution occurs now you usually these unconfined explosions are extremely dangerous because you don't have any control and confined explosions suppose you are sitting in a particular room and sometimes

was vessel rupture ruptures and the vapor cloud of the flammable vapor forms and it moves here and there in that particular room then you are having the liberty or you are having some equipment or safety devices through which you can control that particular vapor cloud which is not this facility is not available for the vapor cloud explosion sorry unconfined explosion and in past of the flexible extrusion and and Jaipur accident they took place because of this unconfined explosive just explosion now this explosion results from the rapid combustion of fine solid particles and many solid material

become very flammable when it reduces to a fine powder another aspect is that since we we learn about the detonation and deflagration we must know that what is shockwave because we utilize the term shockwave over there so shockwave and a blood pressure wave moving through a gas and in open air a shockwave is followed by a strong wind the combination of a shockwave and winds can result in a blast pressure wave so you can see there is a combined effect of all factors overpressure the pressure of an explosion above atmospheric pressure and more specifically the

pressure on an object resulting from the shockwave we should know about the ignition usually a flammable material which may be ignited by the combination of a fuel and oxidant in contact with an ignition source or if a flammable gas is sufficiently heated the gas can ignite so must' where the the practical definition of ignition the minimum ignition energy the smallest energy input needed to start the combustion so usually the typical minimum ignition energy of hydrocarbon is around 0.25 mega Joule now to place this in perspective the static charge from walking a Krauss carpet is 22

milli Joule an automobile a spark plus plug is 25 lead you now you can imagine that this much amount of minimum ignition energy is required for combustion of hydrocarbon and walking across a carpet generates this much quantum of energy so how dangerous it is auto ignition temperature the temperature threshold above which enough energy is available to act as an ignition source so in this to a particular chapter we have discussed a particular module we have discussed about the various definition what is the chemistry of fire what is the concept of a fire triangle because the

knowledge of this fire triangle is extremely important to extinguish the fire in the subsequent modules we will discuss about the flammability characteristics what kind of definitions required what are the flammability limits how we can deal the mixtures etcetera thank you very much [Music] [Applause] [Music]