Issues of Oxygen Depletion in Enclosed Spaces

The time it takes for oxygen levels in a confined space to decrease to problematic levels can vary depending on several factors. The main variables include the size of the space, temperature, degree of enclosure, level of internal activity, and oxygen consumption rates. Below is a general explanation based on relevant research and calculations:

Time for Oxygen Level Decrease

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1. General Enclosed Space:

   • An oxygen concentration below 19.5% is considered hazardous. Experimental results indicate that the time taken for oxygen levels to drop to 19.5% varies with temperature and the degree of enclosure:
     • In a completely sealed space at 10°C: approximately 1.7 hours¹.
     • In a completely sealed space at 23°C: approximately 0.38 hours (23 minutes)¹.
   • As oxygen concentration decreases further, the time taken increases. For instance, it takes about 15.9 hours at 10°C to reduce to 10%, and about 25.3 hours to reach 6%¹.

2. Enclosed Room with People:

   • In a room with people, oxygen consumption occurs with each person’s breathing rate. On average, one person consumes about 300 cubic feet of air per day, roughly 6% of which is oxygen².
   • Based on this calculation, the time one person can survive in a completely sealed room due to oxygen depletion is estimated to be about 12 days³⁴. However, during this time, carbon dioxide levels may rise to dangerous levels, posing a risk before oxygen depletion becomes a critical issue.

Carbon Dioxide Issues

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In enclosed spaces, the accumulation of carbon dioxide can pose a threat more rapidly than oxygen depletion. The carbon dioxide exhaled by a person increases its concentration in the air, and reaching a certain level (about 3% or more) can have physiological effects². Therefore, in a sealed environment without carbon dioxide removal systems, the survival time may decrease due to carbon dioxide toxicity before oxygen depletion becomes critical.

Conclusion

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The time it takes for oxygen depletion in an enclosed space to become problematic varies depending on the size of the space, temperature, and level of internal activity. Generally, it can take several hours to days. However, the accumulation of carbon dioxide is more likely to pose a threat to life first, making non-ventilated enclosed spaces always dangerous.