Flamers are portable gas torches that produce heat intense enough to boil the water in plant cells. Killing a weed requires heat for only 1/10 of a second. Flamers are usually used to kill young weeds in prepared rows, just before seeds or seedlings are planted, as an alternative to pre-emergent herbicides. Flamers become trickier to use later, when the plants are actively growing, and they cannot be used where mulches are present. Flamers also are quite costly compared to a hoe, but may be a worthwhile investment if you have a number of straight rows to weed. They also are useful for killing weeds in between walkway pavers. The smallest models consist of a backpack that holds propane fuel, a hose, and a hooded nozzle at the end of a handle that resembles a carpet sweeper.