The M-451 Firestorm flamethrower is a product of human ingenuity, ruthlessness, and industrial espionage. Its origin dates back to the 2160s, when human colonists to new planets used flamethrowers to clear vegetation or ice. The fuels performed erratically on planets with extremely cold temperatures and differing air compositions from Earth. Realizing this could be a problem for military units, Systems Alliance intelligence operatives stole the turian design for the "Hieras" flamethrower, a battle-tested workhorse that functioned in nearly every environment.
The result was the Firestorm, an anti-personnel and anti-armor flame unit that can accept a variety of liquid fuels. The turian design used low-octane hydrocarbons thickened with dentra oil, which is taken from large marine animals similar to Earth's whales. Humans then reverse-engineered a synthetic composite with almost identical properties that could be fabricated from heavy weapon fuel cells using an omni-tool.
The result is a sticky spray that burns at approximately 1,600 degrees Celsius, a less intense fire than plasma weapons but covering a significantly wider target area. Adding to the trauma is the choking smoke produced by the spray, and if the target's armor is breached, the fires quickly consume the oxygen within. The Firestorm may not be the most efficient weapon in the Systems Alliance arsenal, but the sheer ugliness of how it kills ensures it is the most feared.