Air & Ventilation Guide
Estimate the airflow moving through a passage, and a rough CO₂ build-up if your group sits in a poorly ventilated chamber for a while — a planning aid, not a real-time air-quality reading.
Airflow & air-quality estimate
Modelled: low build-up from your group's own CO₂ at these numbers. This is not a reading of the actual air, and not a clearance to stay.
Whatever this says: if anyone has a headache, dizziness, nausea, confusion or breathing harder than the effort explains, the whole party leaves for fresh air now, and you call emergency services from the surface (ask for cave rescue) if anyone stays unwell. Never run a stove, heater, generator or any flame in a chamber or other enclosed space: it uses oxygen and gives off carbon monoxide, which this model does not count.
Two linked estimates
The first half of this tool is straightforward volumetric flow: cross-section times air speed gives a volume of air moving per minute, converted to an hourly rate and to air changes per hour for a reference chamber. Faster air, or a bigger passage, means more air turning over.
The second half models what happens if that airflow stops — a still pocket where a group's own breathing is the only thing changing the air's composition. Combining a standard CO₂ production rate with group size and sit time gives a rough estimated concentration, labelled low, caution, or poor against widely used indoor air-quality reference points. The lowest label is never a clearance: the model counts only your group’s breathing, from surface air unless you enter a meter reading.
Frequently Asked Questions
How is airflow through a passage calculated?
Airflow is the passage's cross-sectional area (its width times its height) multiplied by the air's speed through that section. The result is a volume of air per minute, which this tool also converts to an hourly rate and, given a reference chamber volume, to air changes per hour — a common way to describe how thoroughly a space's air turns over.
Where does the CO2 build-up estimate come from?
It uses a standard per-person CO2 production rate — higher for harder exertion — multiplied by the group size and how long they sit in the space, then spread across the chamber's volume as if the air were completely still. Adding that to a starting level gives a rough estimated concentration. The starting level is surface air (400 ppm) unless you enter a meter reading, and surface air is the best case: cave air often starts higher, because most bad air underground comes from the rock and from decay, not from the people in it.
Why does the tool assume a 'still' chamber for the CO2 estimate?
It's a worst-case planning assumption: if there's genuinely no effective air movement through a chamber, CO2 from breathing has nowhere to go and simply accumulates. Air movement can disperse CO2, but this tool cannot confirm that it does in your chamber on your day, and it cannot see CO2 or low oxygen coming from the cave itself. Treat a 'caution' result as a reason to shorten the stay and a 'poor' result as a reason to move to better-ventilated passage or leave; no result is a clearance to stay.
Should I carry a real gas meter instead of trusting this estimate?
Yes, for any trip into a known or suspected poor-air area — a personal CO2 or O2 meter gives you an actual reading on the day, which this planning tool cannot. Use this calculator to think through a trip in advance, and a real meter to make the actual go/no-go call underground.
What should we do if someone feels unwell underground?
Leave. Headache, dizziness, nausea, confusion, or breathing harder than the effort explains can all mean bad air, and confusion is the symptom that makes leaving harder the longer you wait. The whole party heads back toward fresh air together, and if anyone stays unwell, call emergency services from the surface and ask for cave rescue. Do not stop to work out a number first.
Can a stove or heater be used in a sheltered chamber?
No. Never run a stove, heater, generator, or any other fuel-burning device in a chamber, a tent, a vehicle, or any enclosed space. A flame uses oxygen and gives off carbon monoxide, which can kill without warning, and this tool's estimate does not count either. Stay warm with layers, an emergency shelter, and the group's own body heat.
Planning estimate only, not a safety certification. Carry a real gas meter for any trip into a known or suspected poor-air area, and turn back if conditions feel wrong regardless of what any calculator says. Cave with an experienced group, and leave your plan and expected exit time with someone on the surface.