A small NeoForge mod for Minecraft 1.21.1 that fixes a bug in Create: Deep Seas (CDS) where players inside a hermetically sealed submarine still take fire and lava damage while the submarine is submerged in lava, even though CDS correctly empties the interior of lava. This mod is intended for players who use the Create: Deep Seas mod and have encountered this issue during gameplay.

The bug occurs because Minecraft's damage checks do not account for the sealed compartment created by CDS. When a submarine pumps out all fluid from its interior, players moving around inside are still treated as being in contact with lava, triggering fire ticks and damage. This mod detects when a player is inside or climbing out of a sealed compartment and suppresses the fire and lava damage, as well as the on-screen fire overlay, in those situations.

Fire/lava damage while standing inside a sealed, lava-submerged submarine is prevented.
Damage while in hatches or doorways at the lava surface (entry and exit points) is also fixed.
Damage while seated in Create seats, on ladders, or in doorways inside the sub is eliminated.
Endless fire ticks after leaving the submarine are no longer applied.

To use this mod, you need NeoForge for Minecraft 1.21.1 and the Create: Deep Seas mod installed. The fix is client-side and server-side compatible; if you play on a server, both client and server should install it. The mod is provided under the MIT license with full source available for study or integration. Note that this mod does not alter any other behavior of Create: Deep Seas – it only corrects the unintended damage logic.

Create: Deep Seas - Lava Fix