# Science Questions

## Surviving in a Sealed Car

Sun, 13th Apr 2008

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### Question

Paul, Hong Kong asked:

I tend to drive with all the windows closed and the recirculation function engaged. This way I keep out the fumes and dust. The flip side is I知 breathing in re-circulated and progressively stale air. My question is, if the car were a perfectly sealed container, how big would it have to be for me to survive in it for a day? I知 trying to figure out how long I can drive in a compact car without running the risk of passing out.

### Answer

Dr Gisli Jenkins, University of Nottingham:

The easy answer to this question is that you will never run out of air.  You will just exchange the breath that you breathe in with the breath that you breathe out.  I guess what the question alludes to is how long you have to survive in that box before you die. What you are doing is you池e exchanging ambient air with exhaled air and the gaseous composition of the two airs is quite different. Ambient air has a CO2 concentration of about 0.5% and oxygen concentration of about 21%. Exhaled air has a CO2 concentration of about 5% and an oxygen concentration of about 13% so what you値l do over time is you値l reduce the oxygen level. The problem is not so much the reduction of oxygen but the increase in carbon dioxide. By the time that the carbon dioxide levels in the air that you breathe reach 15% you値l effectively die. Assuming the box is about 4 cubic metres it would take about 16 hours or so. But you would actually start to feel ill and probably die a lot sooner than that. Actually it could be down to, sort of, five hours.

#### Make a comment

hmmm...
ok, here goes....
After some google searching I found that on average a male will breathe approximately 11 litres of air per minute while driving a car ( http://www.arb.ca.gov/research/resnotes/notes/94-11.htm )
And on wikipedia I found this page with some info about interior volumes of cars http://en.wikipedia.org/wiki/Vehicle_size_class
Assuming the above data is roughly accurate, (although its from american standards and they have HUGE cars) the volume of a compact car is about 2831.6 litres.
So, at 11 litres per minute of consumption you could last about 4 hours 20 minutes while breathing reasonably fresh air. Even though there would still be plenty of oxygen left in the air after this (only a fraction of the oxygen in each breath you take is actually absorbed) and you could probably last longer I would not advise doing so since you will suffer from the effects of excess carbon dioxide in the air before you run out of oxygen. Best open the window for a minute :P Madidus_Scientia, Thu, 10th Apr 2008

Interesting question. I offer the following for consideration: 1) What if the driver were able to induce the mammalian diving reflex - which should theoretically reduce oxygen demand extending the duration of occupancy ? 2) What impact would pressure and elevation have on the duration of occupancy ?

To the author of the question I would suggest a car with a cabin air filter. I am aware that Volvo, Subaru, BMW and others offer this option. emer_med, Wed, 23rd Apr 2008

I believe you missed one of the points, it is the toxic effect of the carbon dioxide that you would be worried about, not the lack of oxygen. Madidus_Scientia, Fri, 25th Apr 2008

It's unlikely that these filters remove anything but 'personal' smells. They would soon wear out if they absorbed CO2 - it's always in the air. lyner, Tue, 29th Apr 2008

Thank you for the reply. I should have been more specific re the cabin filter. I was thinking that by using the filter he would filter the outside air, thereby eliminating his need to use the recirculator. emer_med, Tue, 13th May 2008

We (2 people) sometimes carcamp in winter, sleeping on the thick futon in the back of the Jeep Cherokee with down converters.  One very cold night (-20 F) we closed all the windows completely.  I awoke more or less 4 hours later and quickly realized from diving lessons that it was the CO2 effect.  One whiff of a high concentration of CO2 and you never forget it.  Don't worry, you will definitely want fresh air long before you will die!  Few land animal species would last long without experiencing revulsion at high concentrations of CO2.

A few years ago, some staff at Mammoth ski area were fixing fencing around a volcanic vent when one fell through snow into the hole.  He and a couple of rescuers died from the CO2, certainly screaming. itisus, Tue, 3rd Feb 2009

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