CO2 Pocket at the Sleep Station

Sleep Station Controls

Breathing rate 15 br/min

Ventilation fan 0%

Vent duct distance 0.60 m

Time acceleration 6×

Head-Level Readouts

Safe

CO2 near face

400 ppm

Sleep elapsed

0.0 min

Net removal rate

0.15 /min

Equilibrium level

9300 ppm

How it works

On the ground, warm exhaled CO2 rises away from a sleeper's face — a buoyancy-driven convection current. In orbital free-fall there is no "up", so that current does not exist: molecular diffusion is far too slow to clear the roughly 300 mL of CO2 exhaled every minute, and it collects in a stagnant pocket right around the head. Real ISS crews have reported waking with headaches when a sleep-station fan failed — flight rules now mandate airflow at every crew quarter.

This model tracks the local CO2 concentration C (ppm) inside the ~0.15 m³ hood volume of a sleep restraint with a simple mass balance:

dC/dt = P/V − (k_diff + k_fan)·(C − C_ambient)
P  = CO2 production rate (∝ breathing rate)
V  = local pocket volume
k_diff = weak baseline mixing (diffusion + cabin leakage)
k_fan  = fan_power × (ref_distance / vent_distance)²

Breathing rate — scales CO2 production P; faster breathing (restless sleep, exertion before bed) raises the source term.
Ventilation fan — the only real removal mechanism in microgravity; 0% reproduces the historical "fan-off headache" reports.
Vent duct distance — airflow strength falls off with the square of distance from the duct to the sleeper's head.
Equilibrium level — the steady-state concentration C = C_ambient + P·V⁻¹ / (k_diff + k_fan) the pocket is heading toward; watch it fall as you turn the fan up.

Risk bands loosely follow NIOSH/OSHA CO2 exposure guidance: under 1,000 ppm is unremarkable indoor air, 1,000–5,000 ppm brings drowsiness and headache risk over a sleep shift, and above 5,000 ppm is treated as an occupational exposure limit exceedance.

Vent duct CO2 concentration

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