I just did a calculation of my own (using dimensions of boat and some biophysics), and understand where they are coming from w.r.t 3 days and 72 hours.
Numbers/assumptions I used and the results:
Pressure hull (using diameter of 6m and an approx 50+m length of cylinder and minimum packing factor)
Volume = 1500 m^3 (somewhere between 1400 and 1600, but this is small +/- sensitivity in the end)
CO2 starting concentration = 400 ppm
CO2 Toxic range assumed around 40,000+ ppm
*
CO2 density = 2 kg/m^3
Air density = 1.2 kg/m^3
Total air = 1800 kg
Humans convert/displace O2 and exhale about 1kg/day of CO2 (but could be less
**)
In the end it boils down to time it takes for 60 m^3 CO2 (4% i.e 40,000 ppm) or about 120 kg to occur.
120 kg of CO2 at 1kg/day times 53 crew comes to around 3 days (the starting air volume could indeed be larger like 1700 m^3 etc and there can be give with some of the other numbers like CO2 exhale per day).
However
* and
** can buy some more time, in fact a lot more time given it is observed (in couple MSDS and OSHA I looked up), many healthy adult humans can tolerate/survive up to 80,000 ppm CO2 or even a bit more than that.....and by breathing exercise/training, the metabolism can be slowed sufficiently for producing as little CO2 (even compared to regular sedentary) quite drastically.
The 80,000 ppm tolerance by itself buys twice the time for example. I am unsure how low CO2 production can be reduced with training (it would buy further time as well), maybe someone can find out.
Thus it is not surprising
@anmdt referred to latter already a number of times.
There might be a few other factors I am missing, but just to give ballpark of where the 3 day number comes from...and also why it shouldn't be applied so prematurely.
These two (
*/
**) factors will be crucial in the end if the submarine is intact.
Let us continue to hope and pray for the best.
.
