Just watched Crawl (2019) and got me thinking.
Edit: i should clarify, why do they not extinguish like a normal flame.
In: Technology
Anything which can sustain combustion underwater is able to do so because the three requirements for fire, namely a fuel, and oxidizer, and adequate heat, are present. For many fires, water is a good choice to extinguish the fire because it disrupts both the oxidizer and heat production. However, it is possible to create mixtures of substances which have adequate contact between fuel and oxidizer despite the presence of water and generate enough heat to continue the combustion reaction even though much of the heat is going towards boiling water.
A typical flare that works underwater will have a finely powdered metal like calcium, aluminum or magnesium mixed with an oxidizer like a sulfate or nitrate compound, all bound together with some glue-type mixture. These reactions release a lot of heat and the flare has the oxidizer and fuel in physical contact and therefore the flare can burn underwater.
There are also underwater cutting torches which work through a different mechanism, namely that they release high pressure shielding gas around the oxidizer and fuel gases to prevent the water from coming in direct contact with the flame so that the flame is not extinguished.
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Simpler:
Although the fires you’re used to generally consume air, you can create fires that don’t need air because they use a solid mixture of fuel and oxidizer. Those fires can burn underwater if they can produce enough heat to not be extinguished by the cold water.
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