[kristeen]

I lit a candle then blew it out. Then I put a piece of aluminum foil over the wick and tried to relight the candle but it wouldn't light up. what's going on?

[Yggdrasil]

Fire needs two things to burn.  One is fuel, what is the other?

[Borek]

Fire needs two things to burn.  One is fuel, what is the other?

Always thought there are three things needed to start a fire. One is fuel.

[Yggdrasil]

Ah yes, I forgot the ignition source.

[DrCMS]

It's actually four things. Think how halogen or powder fire extinguishers work.

[P-man]

No it's only three things. Think of the fire triangle... heat, fuel and...

[DrCMS]

The fire triangle is out of date. 

Combustion is a radical reaction and if you introduce a radical trap such as a halon or powder fire extinguisher it stops the fire without removing the fuel, oxygen or the ignition source.

[constant thinker]

For simplicity reasons, and in the vernacular of every day people (non chemists), you can think of the fire triangle. DrCMS is right since he is getting more technical than most people do or really need to.

Heat, fuel, and the 3^rd thing is what the aluminum foil is depriving. The 3^rd part has already been mentioned once in this thread.

Think of the combustion of methane (this isn't what the candle is burning, but it's simple).

CH₄ + x --> CO₂ + H₂O

x is the thing that aluminum is depriving. Can you figure out what it is from the equation?

[DrCMS]

This is however a CHEMISTRY forum, surely we can talk technically about it. 

Yggdrasil made a mistake to say fire only needs two things.  Borek said it needs three and i corrected that to say it needs four.
P man then tried to to back up Borek and made a statement that is inaccurate that needed to be corrected.

The Fire Triangle is out of date and WE should give the correct info.

[mir]

The fire triangle is out of date. 

Combustion is a radical reaction and if you introduce a radical trap such as a halon or powder fire extinguisher it stops the fire without removing the fuel, oxygen or the ignition source.

Wow, interesting! A radical reaction you say? That makes some sense. But...

In my physic lessons my teacher did an experiment with a lighted candle under to vertical copper rods, 3 cm apart. Between the rods 5000 V made a "lightning" of some sort that began over the flame, and it moved with the hot air. The teacher told us that the candle ionized gases, and so could the electricity jump through space, without help from ordinary conductors.

Radicals are usually neutral species. But in redox reactions, anions and cations is formed.

Could you give me some references?

[Borek]

The Fire Triangle is out of date and WE should give the correct info.

I have a feeling that it is a nitpicking. Fire triangle is kind of simplification, but a very usefull one.

95% of chemistry we teach are simplifications, more or less usefull, that can't survive detailed analysis. Changes are either chemical or physical, salts are either soluble or insoluble, oxidation numbers, pV=nRT - all can be easily proved wrong. But at some moment during chemistry education they can serve their purpose. Fire triangle surely does and throwing it away doesn't make sense.

[DrCMS]

No its not nitpicking the fire triangle does not explain how halon or powder fire extinguishers work.
Powder fire extinguishers are one of the best and most widely used modern fire extingiushers. 

The last time I had a fire in the lab I grabbed a powder extinguisher even though it was further away than the CO2 one and the fire alarm point.  I did that beacuse i knew it would work well.  The reason it did work so well is that it stopped the fire chemistry without needing to remove the oxygen, fuel or ignition source.

Yes the fire triangle was a handy reminder but it does not give the full picture and we should not blindly stick to it beacuse it is simple.