Many years ago after we did our O levels at school we had a bunch of organisations come in to school doing talks and demonstrations. One such talk was by the Fire Brigade who demonstrated the dangers of chip pan fires. I remember the fireman extinguishing a chip pan fire and then shortly after, him pointing his finger near it, and the fire reigniting. I think I remember him saying it was the heat from his finger but recounting this story tonight, my friends don’t believe me, or at least would like to know how this can happen. Can anyone help explain please?
In: Chemistry
No way that the heat from his finger reignited it. Assuming that you remember his trick correctly, what he did was move enough air around the pan to introduce fresh air to the hot oil. Poof, instant fire.
Edit: the full trick is covering the pan with a metal lid which snuffs the fire because it runs out of oxygen. The oil is still hot enough to ignite, but it needs more oxygen to burn.
Now he removes the lid carefully which leaves a layer of smoke overtop of the oil. That smoke contains no free oxygen because it’s already all been burnt off. Then he waves his hand near the pan, that moves a bit of air that disturbs the blanket of smoke and allows the fire to start.
The fire was absolutely going to start again on its own as soon as the smoke started to dissipate. All he did was set the timing. This is why grease fires are so dangerous. You put them out by smothering them, but that doesn’t remove the heat
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