Air

In short

Breathing toxic air increases your exposure.
A mask with a filter slows it, a backtank stops it, a sealed room brings it down.
Deeper means a darker filter.

Beyond Wall Sina, hydrogen sulphide from underground and gas fires makes the air toxic. A roof alone does not keep the gas out. Use a respirator outside and a sealed room with an air scrubber at your base.

The dose

The dose and what holds it back

No maskThe dose rises: faster deeper, faster still in flight
Mask with a filterRises more slowly; the filter burns out
Create backtank and diving helmetHolds while the air lasts
Sealed room with a scrubberThe dose falls

Poisoning point

Filters: the deeper, the darker

White
Yellow
Black

Tainted food is a dose of its own, at home too

Toxic exposure increases while you breathe the outside air. Once it reaches the poisoning threshold, you take damage. More exposure causes stronger poisoning.

The indicator to the right of the hotbar changes with your equipment. Without a respirator, it shows your exposure. With a respirator, it shows time until severe poisoning; with a backtank, remaining air. From the Ash onward, its small marks show how many thirds of your starting air have been used.

The mask and filters

A respirator consumes filters as you breathe. Carry spares. Deeper layers need better filters; JEI shows their recipes:

Filter	Made from	The bloom ripens
White	White Sulphur Flower, charcoal, wool or string	Near the wall
Yellow	Yellow Sulphur Flower, Activated Carbon (pressed from bitumen), wool or string	In the Ash
Black	Black Sulphur Flower, Activated Carbon, a Plastic Sheet (pressed from naphtha)	From Talmora on

An Anthralite Respirator takes white or yellow filters. Upgrade it to a Netherite Respirator at a smithing table to use black filters.

Tainted food

Food obtained from fishing or killing animals beyond the wall, outside a sealed room, is tainted. Cooking it does not remove the contamination. Eating it adds exposure even in the Safe Zone.

The sealed room and the scrubber

Keep an Air Scrubber running inside a sealed room to maintain clean air:

Close the room on every side. Put the Air Scrubber inside it, rather than in a wall. An open door lets outside air in.
Connect a Create shaft and add filters suitable for the layer. More rotation speed increases capacity, but the room still has size limits. Deeper layers also require fuel; see the layer table.
Wear Engineer's Goggles and look at the scrubber. Its messages show leaks, capacity, filters and fuel problems.
In deeper layers, unsuitable wall materials consume filters faster. Cold can reduce the scrubber's output; supply heat when its goggles message asks for it.

A scrubber on a turning shaft serves a room closed on every side. An open door is a leak. — A sealed room

Air Scrubbers work in stationary rooms. A comparator on the scrubber shows whole hours of air remaining. Place a Room Monitor nearby to check the room's air, burner fuel, backtank reserves and shaft load.

If the room develops a leak, its air reserve lasts for a while. Once it runs out, you breathe the outside air. Repair the leak before the reserve is exhausted.

Inside clean air, your exposure decreases and the Dark Zone's undead do not spawn. Place a bed there as your return point.

An airlock

Build a small room between two doors. Set an Air Reserve Gauge in it and wire a comparator to the inner door.

The gauge feeds a comparator, and the comparator keeps the inner door shut until the air is back. — An airlock

What grows past the wall

The sulphur flower cycle

Grows only past the wall, outside clean air

The deeper it ripens, the darker it is

Becomes a filter: white, yellow, black

A filter goes into a mask or a scrubber — the scrubber gives a room clean air

In clean air the flower wilts but never dies

Carried back out, it ripens again

back to the first step

Grow sulphur flower outside clean air, then use it to make filters

Outside clean air, crops stop growing and animals cannot breed. Animals also breathe the toxic air. Keep your greenhouse and animals in a sealed room with a running Air Scrubber.

Sulphur Flower grows only beyond Wall Sina, outside clean air. Find its seeds at vents, in caches or as drops from some undead. Grow it outside the sealed room; use harvested flowers for respirator and scrubber filters.