How Long Does Toxic Fallout Last in RimWorld (1.6)? | Timer + Survival Toolkit
How Long Toxic Fallout Lasts in RimWorld and How to Survive It
Ordinary toxic fallout lasts 2.5 to 10.5 in-game days. Anything alive under the open sky slowly builds up toxins, while anything under a roof is safe from it. Roof your routes, move food and animals inside, plan meals for the full 10.5 days, and if the green sky outlasts that, look for whatever is causing it.
RimWorld 1.6.4871Includes DLC-specific protection and hazards.
Face mask: 50% less buildup
Gas mask: 80% less (Biotech)
Indoor crops keep growing
Feed inside the barn
2.5 to 10.5 days, and the game picks the number when it starts
When the letter arrives, the game rolls a random duration between 2.5 and 10.5 days (150,000 to 630,000 ticks) and keeps it hidden. The middle of that range is 6.5 days, but that is only a planning average. Your colony could get a short 3-day dusting or the full week and a half, so plan for the long end.
| Rule | Value | What it means for you |
|---|---|---|
| Duration | 2.5–10.5 days | Hidden random roll; the mean is 6.5 days |
| Earliest day | Day 60 | Counted from when you settled, so a new colony is spared for its whole first year (four quadrums) |
| Cooldown | 90 days | Counted from when the last one fired, not from when it ended. It is a minimum gap, not a schedule |
| Where | Player home maps | Any biome, any temperature, any colony size |
| Turn it off | Storyteller setting | Disabling extreme weather events removes it from the random pool |
Fallout timer
Enter how many days ago the letter arrived. You get the window in which ordinary fallout can end.
What a roof stops, and what it does not
About every 1.4 in-game hours, the game checks every pawn on the map: colonists, guests, raiders and animals. If the cell they stand on has no roof, they gain toxic buildup. If it has any roof at all, they gain nothing from the fallout. Walls do not matter for this check; a roofed porch, a roofed walkway between two buildings or a roof over a pen counts the same as a sealed room.
Roof stops
- New toxic buildup from the fallout itself
- Crops and trees dying from fallout
- Extra rot on food lying on that cell
- Faster deterioration of items left outside
Roof does not stop
- Polluted ground under the roof (Biotech)
- Toxic water (Odyssey)
- A crop dying from darkness if it has no light
- Buildup a pawn already has; that has to fade on its own
Rain can fall during fallout and does not wash it away or shorten it. If you use the compact hub layout, most daily trips already stay under one roof.
How fast toxic buildup grows, and how fast it fades
An unprotected colonist standing outside all day gains about 40% toxic buildup per day. Each pawn has a fixed personal factor between 0.85 and 1.15, so the same exposure gives one colonist about 34% a day and another about 46%. Buildup fades by 8% per day once the pawn is out of the fallout.
| Buildup | Stage | Consciousness | Vomiting | Dementia | Carcinoma |
|---|---|---|---|---|---|
| 4–19% | Initial | −5% | — | — | — |
| 20–39% | Minor | −10% | — | — | — |
| 40–59% | Moderate | −15% | about every 5 days | ~0.7% a day | ~0.2% a day |
| 60–79% | Serious | −25% | about daily | ~2.7% a day | ~0.9% a day |
| 80–99% | Extreme | −25%, capped at 10% | about twice a day | ~7.4% a day | ~2.5% a day |
| 100% | Death | Toxic buildup is lethal at 100% | |||
The daily chances are averages for a pawn who stays in that stage the whole day. Dementia and carcinoma do not go away when the buildup does, so the real goal is to keep everyone under 40%. A pawn at 40% needs about 5 clean days to reach zero.
Exposure calculator
Average pawn, ordinary fallout, no polluted ground. Resistances come from the pawn's stats in the info card.
Masks, genes and implants that cut fallout buildup
Two stats protect a pawn. Toxic environment resistance protects against toxins in the air and on polluted ground. Toxic resistance is the general stat that also works against direct toxic damage. Fallout checks both, and the leftovers multiply: 80% environment resistance plus 50% toxic resistance lets through only 10% of the normal dose, about 4% buildup a day outdoors.
| Source | Protection | Notes |
|---|---|---|
| Face mask | +50% environment | Core. Cheap cloth headgear, the first thing to make |
| Veil | +35% environment | Core |
| Prestige robe | +20% environment | Royalty |
| Gas mask | +80% environment | Biotech |
| Vacsuit helmet | +80% environment | Odyssey |
| Detoxifier lung | +60% environment each | Biotech. Two lungs reach 100% |
| Detoxifier kidney | +50% toxic each | Biotech. Two kidneys reach 100% |
| Fleshmass lung | +30% environment | Anomaly |
| Partial / total antitoxic lungs gene | +50% / +100% environment | Biotech |
| Tox resistance / tox immunity gene | +50% / +100% toxic | Biotech |
| Breathless gene | +100% environment | Odyssey |
Bonuses inside one stat add up to a 100% cap, so a face mask plus one detoxifier lung already blocks all fallout buildup. Mechanoids have 100% in both stats and can do outdoor work for the whole event. Most animals have 50% toxic resistance, so they build up about half as fast as people; insects have more.
What happens to crops, trees and stored food
Fallout kills plants under the open sky at random. Each time the game checks a plant's cell, there is a 0.65% chance it dies on the spot, which works out to roughly a 1 in 5 chance per day for every outdoor crop and tree. After 2.5 days a little under half of an open field is gone; after 10.5 days almost all of it (around 90%). Growth itself is not slowed, so a crop that is close to ready is worth harvesting now.
Grow indoors
A roofed room with a sun lamp keeps crops alive. Soil works; hydroponics basins (280% fertility, 70 W each) grow faster but kill their plants if the power fails. A sun lamp draws 2,900 W while it is on. Plants left in the dark start to die after about 7.5 days without light.
Protect what you have
Food left outside under fallout rots much faster, and items outdoors deteriorate three times as fast. Haul meals, raw food and fresh carcasses under a roof, ideally into the freezer. Nutrient paste stretches raw food further than fine meals.
Some special plants ignore fallout entirely: the anima tree and anima grass, the Gauranlen tree and its pods, the polux tree, the harbinger tree and the archean tree.
Keeping animals alive through fallout
- Penned animals look for roofed cells inside their own pen during fallout. That only works if the pen has a roofed section they can reach, so build a barn roof over one end.
- Food inside the shelter. Grazing grass outside will die and animals walking out to eat take the full dose. Stack hay or kibble under the barn roof. The animal feeding planner shows how much each species eats.
- Trained and free-roaming animals follow allowed areas, so add them to the same roofed area as your colonists.
- Wild animals stay out in it. Their numbers do not refill while fallout lasts.
- Poisoned corpses. When anything dies with toxic buildup, the chance its body rots instantly equals its buildup. A muffalo at 40% has a 40% chance to leave a rotten carcass, so butcher or cull sick animals before they reach that point.
Toxic fallout still going after 10.5 days?
Ordinary fallout never runs longer than 10.5 days. If yours does, something else is holding the condition in place, and waiting will not help.
| Cause | How to tell | How it ends |
|---|---|---|
 Toxic spewer (Royalty) | A quest or mech cluster mentions it; a 6×5 machine sits on a map within 3 world tiles | Destroy it (1,500 HP, does not burn). The fallout fades within a couple of in-game hours. See beating a mech cluster |
| Quest or scenario | The condition was set up by a quest or your starting scenario | May have its own duration or be permanent; read the quest or scenario text |
| Ancient toxic vent (Odyssey) | A vent on your map switches fallout on and off | Cycles at random, averaging about 12 days on and 4 days off. Pawns close to an active vent take buildup even under a roof, far faster than from fallout |
| Ancient reactor (Odyssey) | An ancient reactor structure on the map | Hack it successfully to shut the fallout off |
| A mod | None of the above | Check the mod's settings or description |
Things that look like fallout but are not
| Hazard | Difference | Does a roof help? |
|---|---|---|
| Polluted ground (Biotech) | Builds up about 40% a day for an unprotected pawn standing on it. Wastepacks and toxifier generators spread it | No |
| Acidic smog (Biotech) | Lasts 1–2 days, halves plant growth, −5 mood outside. No toxic buildup. Triggered by world pollution nearby | Only in rooms that count as indoors |
| Tox rain (Odyssey) | A weather type with toxic buildup and no fixed fallout timer | Yes |
| Toxic water (Odyssey) | Three times the fallout rate while standing in it | No |
Fallout and polluted ground stack: an unprotected pawn outside on polluted soil gains about 80% a day. If colonists keep gaining buildup indoors, look for roof gaps, polluted floor tiles or a toxic water tile on their path. The Scarlands survival page covers polluted maps in depth.
Caravans
Ordinary fallout only poisons pawns on the affected map. A caravan that leaves is out of it, though it still takes buildup on moderately or heavily polluted world tiles and when it is less than 3 tiles from a toxic spewer. Evacuating is a real option when food runs out, as long as the route avoids those.
Toxic fallout survival checklist
- Pause and read the condition. If it came from a quest, a spewer or a vent, skip to the source table.
- Draw a roofed allowed area over bedrooms, kitchen, freezer, hospital and the routes between them. Fill any roof gaps.
- Give the pawns who must go outside face masks or gas masks, and keep their trips short.
- Harvest crops that are close to ready. Haul food and fresh carcasses under a roof.
- Roof one end of each pen and move feed into it.
- Count food against 10.5 days. Start a sun lamp or hydroponics room if you are short.
- Check toxic buildup in the Health tab every day. Anyone near 40% stays inside until it drops.
- After the sky clears, replant. Wild plants and animals return over time.