Flame weapons have been part of the human armoury since hallowed antiquity and continue to see use on the battlefield. Improvised fire weapons – usually thrown firebombs – are also used by insurgents and rioters.

Chemical flamers: Chemical flamers spray promethium or another highly flammable substance at high pressure using a pressurized container/nozzle assembly. The promethium is ignited by a burner as it leaves the nozzle, creating a spray of chemical fire that is almost impossible to put out (promethium burns even if submerged in water) and that can cause flammable targets to catch fire.

Promethium-based flamers are commonly used by the Imperial Guard to clear out enemy emplacements and such. These flamers come in pistol, rifle, and heavy support variants. Some rifle patterns have external tanks (carried on the trooper's back) that provide extra fuel and greater range (because of the higher fuel pressure inside the tank).

Because of the limited range of flamers and the danger presented by the pressurized fuel, many consider the role of the flamer-trooper to be an unlucky one. Flamer-equipped troopers should preferable wear sealed and fire-proofed armour because of the hazards created by the proximity to heat/fire and secondary smoke/noxious fuels.

Plasmatic flamers: Plasmatic flamers utilize the same basic principle that plasma guns do – hydrogen fuel is turned into high-energy plasma by a focused las-beam. The plasma is then accelerated out of the containment chamber and released from the weapon – creating a spray of super-hot plasma they will burn anything it touches (similar in effect to chemical flamers, but with increased damage potential).

Plasmatic flamers are quite bulky and because of the extremely hot payload they can only be used by troops in sealed armour. As a result plasmatic flamers are primarily found in the armouries of the Adeptus Astartes and the Sisters of Battle (both forces use power armour, which is fully sealed).