From IFWiki

Fire is one of the Big Three objects - fire, liquids and rope - that have a reputation for being very difficult to implement realistically and fully. However, it is such a core component of human culture (and has so many practical uses) that it appears quite frequently in IF, although usually not in full simulationist glory.

Starting Fire

  • Matches. Usually there will be a matchbox object; sometimes there will be individual match objects inside this, or sometimes matches will be dynamically generated. As a rule, matches will burn out quickly, and you may have a limited supply; they are best-used to light something more permanent.
  • Cigarette lighter. If functional, this is the simplest fire source: just use LIGHT (object) or LIGHT (object) WITH (lighter).
  • Flint and tinder. This may be implemented as a single item (a tinderbox) or as its separate elements - metal, flint and easily-combustible fuel. You may have to improvise - hitting a sword against a rock, for instance.
  • Friction. This can come in many forms, from the archetypical two-sticks method to the fast movement of powders through pipes.
  • Electricity. A bolt of lightning, a severed power cable, an overloaded or damaged circuit; you may want to take precautions, and as a firelighter it's a bit extreme, but as a last resort it's worth considering.
  • Lava.
  • Chemical. Certain chemicals will burst into flame on contact with water; others will conflagrate if exposed to air, if combined with other chemicals, or if knocked about too much.
  • Flame-breathing monsters.

Dousing Fire

  • Cut off the fuel source.
  • Exhaust the supply of oxygen:
    • with a fire-extinguisher. These are implemented variously, and hence will often have instructions on.
    • with water.
    • by putting something non-flammable on top of it.
    • by containing it within an airtight area. If this works, wait for a while before unsealing again, or you may get an explosion.

Uses for Fire

  • Fire is a convenient, if unreliable light source.
  • Fire can be used to destroy objects that can burn, melt or evaporate.
  • Fire makes a good weapon, if it can be harnessed properly.
  • Fire can cauterise wounds, preventing further blood loss; it can also be used to sterilise equipment. Injuries from fire tend to become infected very easily, however.
  • Fire may often be a component of cooking puzzles.
  • If you or an NPC are suffering from the cold, fire is frequently the answer.
  • Heat dries things out faster.
  • The heat from fire can be used to make metals expand, and render them more pliable.
  • Hot gases and fluids rise. You may need fire to lift a balloon, or something of the kind.
  • Fire could be an energy source for various machines and engines.
  • Fire is often a component of alchemy or elemental puzzles.
  • You may need fire for cigarettes and their ilk.
  • Fire generates (or can be made to generate) smoke, which has its own uses:
    • concealment; it's hard to be seen in a room full of thick smoke.
    • getting rid of NPCs or animals
    • signalling
    • depending on what's being burned, the smoke may be poisonous, soporific or have other effects; this might be used to sedate bees, knock out a room-full of enemies, or get rid of an unpleasant smell.
  • Pain. Sticking a finger in a flame might bring a drowsy, asleep or drugged character to attention.
  • Meditation. Staring into a candle-flame is a traditional technique for this.