Most of the time, ventilation solves your CO2 problem — you simply exchange stale air for fresh. But in the scenario where you must button up completely and cannot vent to the surface, carbon dioxide becomes the limiting factor on how long you can stay sealed. That is where monitoring and scrubbing come in.
Why CO2 is the silent clock
People exhale CO2 constantly. In a sealed space it accumulates long before oxygen runs low, and rising CO2 causes headaches, drowsiness, confusion, and eventually death — often before anyone realizes what is happening. It is invisible, odorless, and gradual, which makes measuring it essential.
Monitor first — always
Before you think about scrubbing, you need to *see* the number. A Aranet4 CO2 Monitor is the gold standard: accurate, low-power, and easy to read at a glance. For a second location or a budget option, the INKBIRD CO2 Monitor adds configurable alarms so you get warned automatically.
When and how to scrub
If ventilation is impossible for an extended sealed period, a CO2 scrubber uses a chemical sorbent (such as soda lime) to chemically absorb CO2 from the air, buying you time. Scrubbing capacity must match your occupancy, and sorbent is a consumable you resupply.
Purpose-built scrubbing systems and bulk sorbent are specialty items rather than general retail products, so we don't list product cards here — source sorbent from a reputable supplier and size the system to your headcount and sealed duration.
The realistic plan
For nearly every shelter, the right answer is: ventilate whenever you safely can, monitor CO2 continuously so you know your margins, and treat full scrubbing as a specialized capability for the rare fully-sealed scenario. Get the ventilation basics right first — a scrubber is a backup, not a substitute for fresh air.