Toxic Warfare Secrets: Melt Raiders With Gas Traps Before They Reach Your Walls
Gas and Shell-Based Traps in RimWorld
1.4 Biotech & Beyond - Updated 2025
Traps in RimWorld can significantly bolster your base defenses when used wisely. Recent updates (v1.4 Biotech DLC era) introduced new gas-based traps alongside the classic shell-based IEDs, expanding the toolbox for dealing with raids. This guide covers how these traps work in vanilla, effective configurations, and insights from the community.
📋 Contents
🔧 Understanding Trap Mechanics in Vanilla
RimWorld's vanilla traps fall into two broad categories: reusable spike traps and one-time explosive traps (IEDs). This guide focuses on IED-type traps that consume shells or release gas.
💡 How Traps Trigger
An IED (Improvised Explosive Device) is essentially a shell rigged to explode on contact. By default, any hostile pawn stepping directly on the trap will set it off (100% trigger chance for enemies). Non-hostile animals have a smaller chance to set off traps (e.g. 25% for wild animals) to reduce random wildlife detonations. IEDs can also be triggered by damage – if a trap is shot or caught in an explosion, it will detonate after a short fuse (usually 0.5–1 second).
⚠️ AI and Pathing
Enemies generally do not recognize hidden traps and won't deliberately avoid a properly concealed IED. However, they will avoid obvious trap corridors if an alternate path exists. In practice, this means you should funnel enemies so that going over your trap is the path of least resistance. For example, lay faster floor tiles on the trap route and rough terrain elsewhere to "entice" raiders onto the mines.
📏 Placement Rules
IED traps occupy a 1x1 cell and cannot be placed adjacent to each other (they need spacing just like spike traps). The blueprint preview will show a radius – that is the blast radius (damage area), not a proximity sensor. Keep your own colonists away from trap-laden halls to avoid accidents – pawns generally path around known traps, but if there's no other route they can blunder into them just like enemies.
💣 Shell-Based IED Traps and Variants
"Shell-based traps" in RimWorld refer to IEDs constructed from mortar shells. Each trap consumes one or more shells of a specific type during construction and is a one-use device. As of the Biotech (1.4) era, there are several IED variants in vanilla:
📊 Trap Comparison Table
| Trap Type | Shell Required | Effect Radius | Primary Effects | Best Uses |
|---|---|---|---|---|
| High-Explosive IED | 1× HE mortar shell | ~5-6 tiles | High damage explosion (~50 dmg) | Hitting clustered enemies; breaching sappers |
| Incendiary IED | 1× Incendiary shell | ~5 tiles | Fire spread; minor blast damage | Fire walls; insect control; area denial |
| EMP IED | 1× EMP shell | ~11 tiles | EMP pulse (50 EMP damage) | Mechanoid defense; breaking shields |
| Tox Gas IED | 2× Tox shells | ~7 tiles | Tox gas cloud with debuffs | Non-lethal takedowns; debuffing raids |
☁️ Gas-Based Mechanics: Tox Gas, Pollution, and "Gas Chambers"
The addition of tox gas in the Biotech expansion introduced new gameplay involving poisonous gas – essentially RimWorld's take on chemical warfare. Unlike a conventional explosion, gas doesn't deal immediate damage to limbs; instead it creates an environmental hazard that lingers and debilitates.
☣️ Tox Gas Effects
When pawns are in tox gas, they suffer tiered effects depending on gas concentration (mild, moderate, severe):
- At severe density (which a tox trap produces): -40% sight, -60% breathing, +25% pain almost immediately
- This effectively halves combat abilities
- Prolonged exposure adds toxic buildup
- ~30+ seconds in 100% density = extreme toxic buildup
- Likely collapse after ~37 seconds
- Potential death after ~45+ seconds at maximum exposure
Important Gas Mechanics to Remember
Tox gas does not ignite and does not harm structures or items directly. It can be cleared by ventilation over time; open areas dissipate faster, enclosed areas hold the gas longer. Waster pirates and certain factions have 100% toxic immunity - they'll wade through your tox traps unaffected!
🧪 Pollution and "Passive" Gas
Biotech's pollution system is another way toxic gas can play a role. Polluted terrain causes a constant low-level toxic buildup to anyone walking on it (about 40% toxic severity per day of exposure). Some players use pollution as a strategic defense by intentionally dumping Toxic Wastepacks around approaches to their base, creating "toxic mire" fields.
💀 Rot Stink
Corpses now rot and produce a gas called rot stink if left to decay, which can cause diseases like gut worms or lung rot. While rot stink isn't as acutely lethal as tox gas, some players have incorporated it into defenses – essentially creating a corpse gas chamber by packing a tunnel with rotting corpses and then luring raiders through to weaken them before a fight.
🔫 Deploying Gas Offensively
Aside from traps, you have Tox grenades and Toxbomb launchers as weapons (Biotech content) to manually throw poison gas at enemies. Mortars can fire tox shells across the map. These are more "offensive" uses of gas – for example, shelling a sieging enemy with tox shells to force them to attack in a weakened state. The key is saturation: a single grenade or shell will slow a few enemies; a barrage can blanket an area.
🏗️ Killbox Designs and Defensive Setups with Traps
A well-designed killbox or trap hallway can leverage gas and shell traps to devastating effect. Here are some popular designs:
🏠 Base Interior Traps
For drop pod raids or unexpected breaches, have some interior traps as backup:
- Place incendiary IEDs in crucial hallways inside your base
- Set up "panic rooms" with traps that you can lure intruders into
- For mountain bases, rig vulnerable areas with incendiary IEDs to counter infestations
- Keep some IEDs in storage - they're minifiable so you can quickly deploy them where needed
📝 Recent Changes, Balance, and Mods
⚖️ Official Balance Tweaks
The Biotech patch (1.4) introduced the IED tox trap with its new mechanics. Subsequent updates addressed a few balance issues: for example, Update 1.4.3580 in Dec 2022 reduced the explosive radius of tox shells when detonated by damage. There haven't been major nerfs to trap damage - shell traps are still as potent as ever.
👥 Community Consensus
There's a bit of debate on whether traps are overpowered or underpowered. Some high-difficulty players claim traps are essential for extreme raids. The community widely agrees that killboxes with traps trivialize many raids (becoming a meta strategy), which is why some choose not to use them for a greater challenge. In short: traps are extremely strong if set up optimally, but consume resources and time to rebuild.
⚙️ Performance Considerations
Each active gas cloud, fire, or explosion can add CPU load, especially if dozens go off at once. A few traps won't cause issues, but rigging an entire map with 100 IEDs and setting them off simultaneously might cause a momentary freeze. Gas clouds dissipating are fairly lightweight, so having a tox box full of gas shouldn't lag the game significantly – just don't also ignite 1000 tiles of fire at the same time.