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It seems that containing lava in solid glass, stone and iron blocks may not be sufficient to prevent wool from burning, even if the lava is completely encased.

ironironwool
ironiron
ironlavairon
ironironiron

After some delay, it seems that fire will jump onto the wool above the iron.

  1. Are solid blocks more effective than airspace, or not?
  2. If so, Does it matter whether the corner block is filled in?
  3. What are the exact rules on distance that I need, and how can I prevent flammable blocks from being eliminated by nearby lava?
  4. Bonus: Does a flowing lava block behave differently than a lava source block when it comes to fire creation?
musicwithoutpaper
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3 Answers3

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The wiki is a bit vague in describing where can fire be started from a lava block. The behavior is similar to fire spread, but it is not identical.

When you deal with fire mechanics there are three basic things that can help you understand it:

  1. Fire is a block! Although visually it looks like some block is burning, the fire is an independent block that is adjacent to the "burning" block. Try setting a wooden wall on fire and see how you can take damage as soon as you touch the adjacent to wall blocks, while visually you are still almost one block away from the fire.
  2. Fire blocks can only exist adjacent to flammable blocks.
  3. Fire needs air block to be able to spread with one exception: if a flammable block is adjacent to fire, it can burn out - in this case fire can take the place of the burned out block.

Having said that, fire can spread in a 3x3 column from 1 block below to 4 blocks above it. Fire can jump over gaps and blocks, so you cannot contain it by covering it. Any of the glass blocks here could be turned into fire block, if it was an air block and there were an adjacent flammable block:

Fire spread illustration

Fire can also be born from lava. Fire is always created above the lava position. Fire can be created in a 5x5x2 shape above it (see the example - fire can be created at any of the glass blocks, if it was an air block and there were an adjacent flammable block). To prevent lava from creating fire, cover it fully (3x3) with blocks that have a collision mask.

Lava spread illustration Lava spread illustration

Once a fire is created it behaves like a normal fire and can spread further according to fire spread rules.

In conclusion, this will never burn:

enter image description here

But if you place any flammable block inside this structure, it will catch fire eventually.

Kcats
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  • So it is safe to build flammable walls 3 blocks away from lava, above lava level, right? – Orc JMR May 28 '13 at 09:50
  • Yes, it should be, but I'd do some testing first. – Kcats May 28 '13 at 10:26
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    Please explain "blocks that have a collision mask". – musicwithoutpaper May 29 '13 at 16:43
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    @musicwithoutpaper Those are blocks that are considered 'solid' in game. Those are all full blocks, all slabs, stairs, even trapdoors should work. Blocks that are not considered 'solid' are liquids, redstrone-related stuff (levers, repeaters), torches, ladders, tall grass, vines, mob heads, flower pots etc. – Kcats May 30 '13 at 07:35
  • So Glass is solid, and Glass Panes are not, right? – musicwithoutpaper May 30 '13 at 12:37
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    @musicwithoutpaper Strangely enough, class panes, iron bars and fences/walls are considered 'solid' – Kcats May 31 '13 at 09:16
  • "eventually" -- this is the tricky part, as if you want to test if something is going to burn how long do you need to wait until a lack of fire means one will never start? As an example, I put a lava block surrounded by stone on all sides horizontally and one directly above, and put a bookshelf on top of that and diagonally up, and as it didn't catch fire even after several minutes. Yet when installing bookshelves underground I apparently have to be super-careful there is no lava behind rock as my library has caught fire on multiple occasions because of this. – Michael Aug 09 '19 at 16:25
6

Ok, so i did some test manually, seeing as though I could not find the answer to this on the Wiki. Let the redstone blocks represent where the fire can spread: enter image description here

So basically between these redstone blocks is the Iron. Underneath the iron is LAVA. It spreads adjacent to the blocks. On a 2D View:

b = Fire
L = Lava
I = iron
 B 
BIB
ILI
III

It would also seem that Airspace is quite useless when it comes to protecting blocks. Also, flowing lava is exactly the same as source lava when it comes to producing fires.

Brandyn
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-1

No, I did testing by putting a flire block then a solid block cand then wood... th wood never burned even if i gave it space below it (fire, solid block, air, wood). I am confused.

user220012
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