The three ways a fire spreads!

[MondoMarcus]

So I'm taking FireTech 105: building construction for the fire service, and we were talking about the three ways a fire spreads. I wasn't clear on that, though I am sure radiation was one of them.
We were also discussing how fuel, oxygen, heat, and reaction in the right circumstances will create a fire, and by taking one of the four out of the equation you will have no more fire ;) (hence the use of foam or blankets to kill the oxygen, or water to kill the heat).
My question (aside from the one in the first paragraph) is, how is is possible to know wich of the four components of a fire to eliminate in a given situation? The instructor was giving us scenarios, most of the class was getting the right answers, and I was feeling pretty stupid and left out.
I'm assuming the answer to my first question will help me with the answer to my second.
I'm very sorry that this post is everywhere, and may be a bit confusing, but I'm not very clear on the subject myself :p
Thanks in advance!!!

[FFEMTMills]

The three ways a fire will spread are through conduction, convection and radiation.

[CaptainGonzo]

Fire spreads by conduction, convection and radiation.

The removal of any part of the fire triangle (heat, fuel and oxygen) will result in the extinguishment of the fire. The chemical chain reaction, which makes the fire triangle a fire tetrahedron only exists if there is a fire present.

A simple example... a pan of food burning on a stove. The food is the fuel, the stove is the heat, and the oxygen in the air is enabling the food to burn. The fire is being spread through conduction of heat via the impingement of heat on the surface of the pan.

When we take a lid and place it on the pan, the fire will extinguish itself once the usable oxygen trapped in the pan is exhausted.

Knowing what agent to apply to a fire mean knowing what is burning in the first place! Water on flammable liquids will sink right through the fuel, as water is heavier than most hydrocarbons. Foam must be applied to smother the vapors that are coming off of the fuel.

Water on ordinary combustible materials cools the fuel below it's ignition temperature, thereby extinguishing the fire.

Magnesium fires burn hot enough to separate water into it's two components... hydrogen, a flammable gas and oxygen, which supports combustion. Water on a magnesium fire will look like the grand finale on the 4th of July fireworks. Dry powder (not dry chemical) must be used to break up the chemical chain reaction.

For flammable gasses, the only thing that will extinguish the fire is shutting off the supply of gas and letting the product run out.

PS: The cost of this tutoring session is a pint of Guinness! :D

[doughesson]

Fire also travels upwards until it meets a surface that it cannot burn then spreads out like a mushroom on available fuel until it can move up again.

[Rossco]

That would be convection.

[MondoMarcus]

Ok, I think I'm getting this.
Radiation is the heat transfering from the actual fire to another surface (or fuel) wich in turn, because of extremely high temperatures will cause THAT to burn.
Convection is the fire traveling to the highest point possible until it has nowhere else to go.
And conduction? The one I'm still iffy on.
I don't understand how you can decide wich of the three parts of the triangle to eliminate? In some fires water will do nothing but spread the fire and make matters worse. But putting the 'wet stuff on the red stuff' would be taking out the heat part of the triangle, wouldn't it?

I really appreciate your help guys. It means alot.
I didn't grow up with any dads, brothers or uncles in the FD so this stuff is all new to me.

[FFTrainer]

I don't understand how you can decide wich of the three parts of the triangle to eliminate? In some fires water will do nothing but spread the fire and make matters worse. But putting the 'wet stuff on the red stuff' would be taking out the heat part of the triangle, wouldn't it?

Yes but putting wet stuff on red stuff that is a fueled by a flammable liquid will not be able to extingish because it will 'scatter' the fuel because the water will go right through it. In this case an application such as foam which blankets the top of the liquid rather than breaking it up would cut off its supply of oxygen.

How do you know which one??? You don't always know 100% and alot of times it gets mixed so you go with the largest fuel source. For example the contents of a home... mainly standard combustibles of wood, fabrics, etc. However you can have plastics that have liquified, fuels such as small gas cans in a garage all mixed in. In this case you are going with the volume of fire and reducing the temperature by applying water to eat BTU's. Same thing with a vehicle fire... yes the initial ignition may have been oil on a hot object, but a working vehicle fire is often the seats, the vinyl on the dash, the carpet, the fabric of the roof liner.

I guesss it comes down to STUDY. I give you credit for admitting you don't know something. Most guys these days are too macho to admit they might need help. God forbid we be embarrassed and have the guy sitting next to me think I'm dumb. I would rather have someone think I'm dumb then know I'm DEAD because I never found out the answer and it bit me in the a$$.

[Golzy12]

conduction, convection and radiation are the ways heat spread. The heat from the fire will spread those ways, the fire itself will spread up, like said earlier.

When trying to figure out what part of the tire tetrahedron (eat, fuel, oxygen, sulf sustaining chemical reaction) to remove, think of what class fire it is,

class A fire (ordinary combustables) remove the heat.

class B (flammable liquids) remove the fuel, by coverin the fuel with a foam blanket(if I remember right the liquid itself doesnt burn the vapors from the liquid do, covering the liquid with the foam stop the vapors.

class c (electrical) you can either disconnect the power and treat it as a class A fire, or use a class C fire extinguisher. a carbon dioxide fire extinguisher would cut the oxygen out from the fire.

class D (flammable metals) you need to use a chemical to stop the chain reaction in this progress dry powder.

[dmleblanc]

Ok, I think I'm getting this.
Radiation is the heat transfering from the actual fire to another surface (or fuel) wich in turn, because of extremely high temperatures will cause THAT to burn.
Convection is the fire traveling to the highest point possible until it has nowhere else to go.
And conduction? The one I'm still iffy on.
I don't understand how you can decide wich of the three parts of the triangle to eliminate? In some fires water will do nothing but spread the fire and make matters worse. But putting the 'wet stuff on the red stuff' would be taking out the heat part of the triangle, wouldn't it?

I really appreciate your help guys. It means alot.
I didn't grow up with any dads, brothers or uncles in the FD so this stuff is all new to me.

Heat rising is an example of convection. When the heat encounters an obstacle (like a ceiling), it then begins to flow outwards. This is also convection. Heat transferred by the movement of a fluid substance (like air) is convection.

The reason a thermos bottle keeps your food hot is because there is a vacuum space in the bottle between the food and the outer shell of the bottle. There is no air through which the heat can transfer...therfore the heat does not transfer, or travel, out of the food (or at least not as quickly).

Radiation is not dependant on having a fluid medium like air to transfer the heat. It is the transfer of heat energy across a space, independant of any fluid movement. The warmth we feel from the sun is an example of heat transfer via radiation.

Conduction is the transfer of heat energy through a solid medium. Hold a metal rod in your hand and hold the other end in a fire. Eventually your hand will get hot where you are holding the rod. The heat is travelling through the rod. This is conduction. Some materials conduct heat better than others, which has an effect on the speed of heat transfer.

As far as knowing what method to use to extinguish the fire, it depends on what's burning. As firefighters, the vast majority of the fires we respond to are fought by cooling...that is, applying a large enough volume of water to absorb the heat being generated by the fire. For ordinary combustible, or Class A, materials (you'll learn that too), such as paper, wood, or cardboard, applying water to cool the burning material is usually enough to extinguish the fire.

Class B materials, such as flammable liquids and gases, generate higher heat and are often resistant to water (like oil or gasoline). For many of these materials removing the oxygen by applying foam is the preferred solution.

Ever cooked on a gas stove? How do you shut it off? By turning off the gas. You have just extinguished the fire by removing the fuel, the third side of the fire triangle.

Hope this has been helpful..Just be sure to ask questions in class if you don't understand....to be an effective firefighter you MUST understand fire behavior!

[IACOJRev]

class B (flammable liquids) remove the fuel, by coverin the fuel with a foam blanket(if I remember right the liquid itself doesnt burn the vapors from the liquid do, covering the liquid with the foam stop the vapors.


I thought a foam blanket removed the oxygen...

[FFTrainer]

class B (flammable liquids) remove the fuel, by coverin the fuel with a foam blanket(if I remember right the liquid itself doesnt burn the vapors from the liquid do, covering the liquid with the foam stop the vapors.

Yes and no...

A foam blanket extinguishes the fire by cutting off the supply of oxygen.

Once extinguished or if never ignited, a foam blanket would suppress vapors and reduce the exposive hazard and potential for fire. Hence why you NEVER disrupt a foam blanket once applied.

[Rossco]

I have seen different instructors teach this both ways. It will take away oxygen, and it will suppress vapors, so is this the chicken and egg question?

[doughesson]

I know I am still in the learning as you earn stage of firefighting.That is why even if I know an answer and don't hear someone asking it,I'll pop up and get another part of the training addressed.
Sometimes people do ask me"You didn't know that?They do that in the Navy,don't they?"or simliar expression of thinking I didn't know something.It might make people think that I am as dumb as I look but I'd rather have that than someone,including me,not get a question put out because someone is afraid of being embarrassed.
I'd rather get embarrassed and learn something than see my Chief have to go to someone's house and tell his wife that her husband was taken to a hospital because no one asked.



I guess it comes down to STUDY. I give you credit for admitting you don't know something. Most guys these days are too macho to admit they might need help. God forbid we be embarrassed and have the guy sitting next to me think I'm dumb. I would rather have someone think I'm dumb then know I'm DEAD because I never found out the answer and it bit me in the a$$.

[Skwerl530]

class B (flammable liquids) remove the fuel, by coverin the fuel with a foam blanket(if I remember right the liquid itself doesnt burn the vapors from the liquid do, covering the liquid with the foam stop the vapors.


You remember correctly but the key is to know that solids and liquids will not burn. A material will only burn once it has reached a gaseous state. In the case of a liquid the "fumes" being thrown off by the liquid will burn. In the case of a solid the material has to be heated to the point that it will produce various flammable gases. Thus a thick heavy piece of wood is harder to ignite than a smaller one. The larger piece has more mass that can conduct the heat away, thus it takes longer to produce the required gasses.

Once the gasses have ignited they can re-heat the material via radiation and create a self sustaining reaction that lets the material burn until extinguished or the material has produced all the gasses it is capable of producing, leaving behind carbon and various other things depending on the material.

Excellent question BTW.

[Skwerl530]

I thought a foam blanket removed the oxygen...

Yeah it's a chicken and egg kind of thing. The foam cuts off the O2 from the fire but it mainly suppresses the ability of the liquid to evaporate. If the vapor can't be produced then vapor and O2 can't mix.

[BerwynFD]

The flammable liquid thing:

The liquid itself isn’t burning, the vapours above it are. The vapour mixes with the air until it reaches its combustible range. Then the heat of the fire ignites it and the process continues.

An application of class B AFFF foam slips a thin layer on the fluid between the fire and the liquid. The source of flammable gas is cut off., not really the oxygen source.

Putting a lid on a pot ABOVE the flames cuts off the oxygen.

The fire spread thing:

Convection
Hold a peace of paper above a fire, the fire heats the air, the air raises heats the paper, the paper PYROLISIZES, the gases reach their OUTO IGNITION temperature, the fire spreads.

Conduction

Put same peace of paper in a fry pan. Pan heat paper, paper gasses off, gas ignites.

Radiation

Hold paper below flame. RE the sun, standing beside the fire place…

Fire Tetrahedron:

Each and every element must be there for the fire to continue. Look for the easiest to remove

Take the fuel away
Take the heat away
Take the oxygen away
Disrupt the reaction

What’s handy, what will work?