Design ventilation and air supply for an occupied room
People in a closed room breathe out carbon dioxide. Without fresh air it builds up quickly, so a safe room must never be fully sealed while occupied.
How
- Include ventilation openings in the design. US guidance gives minimum natural ventilation areas per occupant: a manufacturer summary of ICC 500 gives 2 square inches per person for residential shelters (up to 16 people), and BASC lists 4 for hurricane rooms. Use the calculator in this module for a first estimate and let the engineer confirm.
- ICC 500 requires at least natural ventilation for tornado shelters and asks for upper and lower openings on opposite walls or the roof to cross-ventilate.
- Vent openings must be protected against wind-borne debris to the same level as the walls (tested louvers or baffled ducts).
- If you add mechanical ventilation, its power supply must be protected to the same level as the shelter (ICC 500). Plan a battery or protected circuit from the power design.
- Fit a battery CO2 monitor inside. Properly ventilated rooms aim to stay below 1,000 ppm CO2; US workplace limits set 5,000 ppm as an 8 to 10 hour average.
- Do not rely on sealing the room against outside air for long periods. If you want protection from smoke or outside contamination, get specialist engineering advice.
Safety: Never seal an occupied room without a tested fresh air supply. In a small room CO2 can pass the 5,000 ppm long-exposure workplace limit within hours. The NIOSH short-term limit is 30,000 ppm.
Do these first
Sources
- Safe Rooms and Storm Shelters (Building America Solution Center). US DOE / Pacific Northwest National Laboratory, accessed 2026-11
- ICC 500: Standard for the Design and Construction of Storm Shelters (summary of the 2014 edition). Ready.gov / FEMA, accessed 2026-11
- Carbon Dioxide (CO2). Minnesota Department of Health (USA), accessed 2026-11
- NIOSH Pocket Guide to Chemical Hazards: Carbon dioxide. CDC / NIOSH, accessed 2026-11
- Carbon Dioxide Generation Rates from Building Occupants (Persily and de Jonge, Healthy Buildings 2017). US National Institute of Standards and Technology (NIST), accessed 2026-11
- Protecting ventilation openings for storm shelters and tornado safe rooms: FEMA louver requirements. Greenheck (manufacturer), accessed 2026-11