These tools that hurl plumes of fire through the air were originally weapons of war
Different forms of flamethrowers have existed for thousands of years, but the first handheld flamethrowers emerged during World War I. A creation of the German army, early handheld flamethrowers consisted of backpack-style fuel tanks with gun-like nozzles that, when ignited, released a torrent of flame towards their enemies. Used again in World War II and the Vietnam War as incendiary weapons, it wasn’t until 1980 that their use was restricted under Protocol III of the Geneva Convention. Today the main role of flamethrowers lies in land management, such as eradicating invasive plant species, clearing croplands and burning land to recycle nutrients.
For a flamethrower to work, it needs to supply two of the three basic ingredients that cause the reaction that leads to fire: heat and a fuel source. The third ingredient, oxygen, comes straight from the atmosphere. To supply the heat, flamethrowers supply an initial spark when the trigger is pulled and the fuel released.
Once the spark ignites the fuel, the heat generated by the fire becomes enough to sustain the reaction. As long as the trigger is held down, gasoline or diesel continues to feed the reaction with atmospheric oxygen.
With all the ingredients needed to create fire, flamethrowers need a way to prevent the flames from travelling back up the device into the tank – with explosive results – when the trigger is pulled. This is achieved by adding a tank of pressurised gas. When the trigger is pulled, the gas forces the fuel through the nozzle, creating a continuous stream of fire in one direction. When the trigger is released, a valve cuts the fuel and oxygen supply off, preventing fire from forming within the flamethrower. This pressurisation also means that flamethrowers can shoot fire over impressive distances. For example, flamethrowers used in World War I could spray fire over 40 metres.
