Fire

Fire is a block. It has an animated face on all four sides, and two faces on the inside at slants. Fire is never created naturally when chunks generate. It will only be created if the player or a Ghast causes it or Lava burns a flammable object. Fire produces 15 units of light.

Fire is only available for use in Indev, Infdev, Alpha, and Beta.Flint and Steel is used to place Fire. When placed, the fire will burn for a short, randomly determined period of time. If nothing flammable is next to it, the flames will die out. Wood, Logs, Leaves, Wool, and Bookcase blocks are all flammable, while TNT will detonate if exposed. Fire burns leaves slightly faster than the other flammable objects. Fire will spread over flammable surfaces, slowly causing all the blocks it can reach to burn away. Fire can climb up walls, across floors and ceilings and over small gaps of 2 blocks maximum.

As one would expect, any mob (including the player) will be lit on fire if exposed to it. The fire will obstruct the player's view slightly and they will slowly lose life. The fire will burn out after a while, but it is a good idea to try to jump into some Water as soon as possible. A water bucket functions as a portable fire extinguisher as a player who is on fire can dump the water at their feet to put out the fire instantly. With 'peaceful' mode enabled, the player won't die from fire.

Fire can be used as an attack against mobs. Lighting dropped items or blocks on fire will cause them to burn away. This trick can be used to dispose of materials quickly. Anything that touches Lava or Fire, whether it is a mob or a dropped object, will be lit on fire. Although lava can set off TNT, it takes several minutes and is easily fixable if the lava can be reached and cleared.

Punching or hitting the side the fire is on will extinguish the fire on the side that was hit. Water, sand, and gravel will also extinguish fire.

Eternal Fire
If Netherrack, found in The Nether, is lit on fire, it will burn forever.

It can therefore be used as a trap/defense, though it will burn dropped items that fall in the fire.

Lit Netherrack can also be used as an alternative to torches. If the player is running low on coal then they can use Netherrack and Flint and Steel instead. It is brighter than torches and be quickly extinguished.

Chainmail Armor
It is possible to craft Chainmail Armor out of fire blocks. It is only possible to get actual fire blocks in the players inventory by means of using the /give command or an Inventory editor. Chainmail can be crafted like any other armor and has the same durability as Gold.

History
In versions from Alpha to Beta 1.2_02, a non-netherrack flammable block, like wood, may burn continuously when its sides are surrounded by non-flammable blocks, like stone or dirt (the bottom is not necessary, though it is best not to have anything explicitly flammable underneath). A fire will only stay burning at the top of a flammable block, not on the sides or the bottom. Once the fire is burning - and has continued to do so for ten seconds or more without consuming the block beneath - you may remove all the adjacent blocks, and it will keep going forever. If the block burns away, simply replace and re-ignite until it works. Alternatively, you can punch out any adjacent fires that appear instead of surrounding the block. Eternally burning blocks was fixed in Beta 1.3.

It was also possible to make larger blocks of endless fire by putting flammable blocks diagonally adjacent to a block that is burning continuously. Since the already-burning block counts as non-flammable - it is already on fire - the adjacent blocks may also burn continuously. By igniting multiple blocks this way, you could make a grid of diagonally adjacent burning blocks.

Currently, Netherrack, found in The Nether, is the only way to obtain eternal fire.

Trivia

 * When smoke hits water, it hisses just as if water has hit a fire.
 * During Indev, you could use fire to mimic a furnace, by dropping items onto it.
 * Since Alpha version 1.2.6, forest fires may start spontaneously if an above-ground lava pool is generated amongst trees during a biome's creation. This is a rare side-effect of starting a new world or exploring.
 * Fire could be directly placed in Indev before flint and steel were added.
 * Fire is often used to make a fireplace in a house, by lighting netherrack. Before the eternal fire bug fix, logs were often used instead.
 * When playing on Peaceful mode, if you start burning, and get away from the fire source, you can't die from the burning; your health regenerates at the same speed that the fire damages it.
 * If you are on fire and use a bucket of water on the ground you're standing on, it will put your fire out. The same happens for jumping in any water.
 * It is possible for lightning to light a surface on fire during thunderstorms, but it will almost immediately be put out by rain. In rare cases in SMP, fire may not get extinguished,

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