Deep Fat Fire Is Very Difficult to Extinguish! Is your kitchen safe?

Lately, i have been working on some specification on Fire Extinguisher specially designed to extinguish fires resulting from deep fat.  Most of our homes have kitchens and we also do frying using cooking oil.  Sometimes, so much oil is used, especially deep frying, which is the favourite of malaysian cooking. Do you know that, among all the types of fires, deep fat fire is the most difficult and messy to deal with?
Why??

Most people will think that cooking oil fire is relatively easy to extinguish, judging from the tameness, less radiant heat and colour of the fire.  Most people will think petrol fire is fierce.  Talking about fire fierceness, i recently had the oppurtunity to witness a fire testing using methanol.  For those F1 fan, i think you may know that methanol is used in F1 cars.  Apparently, methanol fire is almost invisible, at first i thought the fire has been extinguihsed, but later learned that the fire is still burning.

Back to our story of cooking fire.
Theoretically, to extinguish burning cooking oil fire, we have to first prevent the oil evaporation from happening.  In other words, stop the oil from boiling and releasing the oil into the air.  The oil vapor, in the air, when mixed with oxygen, with the heat still around, is like the combustion of the engine, ignites and burns, then generating further heat, in return releasing more heat and oil vapour.

Let's look at how hot is burning oil.
Example: Sun Flower oil starts to smoke at 232 Deg Celcius.
This is the condition we need to start frying, right?
Then, how much heat (or rather, energy) is already being supplied into the oil?
For a typical vege oil, it's heat capacity is something like : 1.67 kJoule/kg.K.
This figure means, to heat up 1kg of vege oil, for 1 degree C, we need 1.67 kJ.
In the case, if there is 10 liter of oil, heated up until smoking condition, the heat enegy it contain, will be:


0.9 x 10 x (232 - 30) x 1.67  kJ  =  3036 kJ


0.9 is applied to 10Liter, to convert into kg.


And we should remember, that water starts boiling at 100 degree Celcius.
So, using water to cool down the burning oil is out of the question.
Neither is trying to use any other method containing water, simply because, when water in in contact with the hot oil, it just boils and turns into steam, and boils violently, causing the oil to splash out everywhere violently.


Take a look at this video:
http://www.metacafe.com/watch/1082868/cooking_oil_dangerous/


How about the fire extinguisher that we normally have around us, the Powder or CO2 type?
I have personally tried using these types of extinguishers on burning cooking oil, yes, the fire is extinguished, but not long, it reignites again, something, we call, autoignition. 
Reason, simply because, the powder or CO2, when applied on the surface of the fire, is effective on the fire, killing the fire, but what it cannot do, is to cool down the oil, which is still hot, so hot, that it keeps on evaporating oil into the air, mixing with oxygen in the air, and ignites, because the temperature is well above the ignition point of the oil.


Then, how do we extinguisher burning cooking oil?