The Gas Vents are a trigger object found in Lara Croft and the Temple of Osiris.
Lara first finds these gas burners in the Tomb of the Lamplighter. They can be lit with Lara's Torch, the Flamethrower, or even by using Sun Balls. When lit they can heat up water - in order to get it to boil - or set fire to other gas emitting vents that come near.
Gas Vents are mostly part of Puzzles that need to be solved to continue the game, unlike Braziers which can be lit, too, but are mainly decorative and for hiding gems.
Those vents bring the gas up from beneath the earth...
— Isis, Lara Croft and the Temple of Osiris in-game dialogue