It is widely understood that fire and water are opposing forces, making the idea of fire existing underwater seem impossible. While a typical campfire cannot burn beneath the waves, certain chemical reactions and conditions can lead to combustion-like phenomena in an aquatic environment, revealing a more complex scientific reality.
The Essentials of Fire
Fire, at its core, is a rapid chemical process known as combustion, which releases heat and light. For this process to occur, three components are typically necessary: fuel, an oxidizer, and heat. These elements are often visualized as the “fire triangle.” Fuel refers to any combustible material that can burn, ranging from wood to gasoline. An oxidizer, usually oxygen from the surrounding air, reacts with the fuel to sustain the combustion. Heat provides the initial energy to ignite the fuel and continues to sustain the reaction, causing it to spread.
Why Water Typically Stops Fire
Water is a highly effective fire suppressant because it interferes with all three components of the fire triangle. Primarily, water cools the burning material, lowering its temperature below the ignition point. Water also turns into steam when heated, displacing oxygen around the fuel and smothering the flames. Additionally, water can create a physical barrier on the fuel’s surface, preventing oxygen from reaching it.
When Fire Can Exist Underwater
Despite water’s fire-extinguishing properties, specific scenarios allow for combustion or intense heat-generating reactions to occur underwater. One such instance involves certain alkali metals, like sodium and potassium, which react vigorously with water itself. This reaction generates hydrogen gas and significant heat, often igniting the hydrogen as it bubbles to the surface, creating a flame above or near the water. The reaction of heavier alkali metals, such as rubidium and cesium, is even more violent, potentially leading to explosions.
Some materials can burn underwater because they contain their own oxidizer, eliminating the need for external oxygen. Thermite, a mixture of metal powder (like aluminum) and a metal oxide (like iron oxide), is a prime example. When ignited, thermite undergoes an extremely exothermic reaction, producing intense heat and molten metal without relying on atmospheric oxygen. Magnesium is another substance that can burn underwater, as it reacts with the oxygen atoms in water molecules at very high temperatures, producing magnesium oxide and hydrogen gas.
Specialized equipment also allows for controlled combustion underwater by supplying oxygen directly to a fuel source. Underwater cutting and welding torches, for example, use a pressurized supply of oxygen along with a combustible gas, such as acetylene, to create a flame hot enough to cut or weld metals. These tools are used in marine construction and salvage operations.