It's not that hard. What if a propane or liquid nitrogen tanker lost containment in one of the underground/underwater tunnels? (Lincoln tunnel into New York, either of the Baltimore tunnels, etc.)
Well done, that's perfect.
(Of course, you do realize that the protagonist in your plan needs some way to keep breathing, right? They can maybe gain a little time by turning off the HVAC, but they probably need an oxygen tank and either masks or a way to isolate/pressurize the cabin.)
Walter
Yes, I did note that up front though I didn't propose a solution. If they happened to have a scuba tank in the back seat they could crack the valve and that would probably do the trick. But if the cabin is moderately air tight, it looks like the trapped air will be enough.
Per some random page on the Internet (
Friday Fiction Facts: Trapped in an airtight room! | Endless Forms Most Beautiful) the equation we want is
Time Our Hero can survive = (volume of air in cu ft) * 0.03 / (number of people * hourly production of CO2 per person).
Let's suppose Our Hero is alone. A Tesla Model S (why not) has a volume of 93 cubic feet and a person under stress produces CO2 at a rate of 1.7 cu ft per hour (same reference). So:
T = (93 * 0.03) / (1 * 1.7) = 1.64 hours!
Come to think of it, this is consistent with the intuition we might take from considering that a typical scuba tank (a so-called "aluminum 80") holds a nominal 80 cubic feet of air at STP. Of course, with scuba you don't have to worry about accumulating CO2, but the similarity of the numbers is still comforting. So we can even chuck a sidekick in, derate all our numbers by 50% because it's not really air tight, and still have 25 minutes to get out of the tunnel, all without adding a scuba tank. With a smaller car (that Smart ForTwo) we have to get them out of the tunnel quicker, but we weren't going to leave them in there for 25 minutes anyway. In the mean time, I am pretty sure the ICE car engine is going to stop working within seconds of entering the tunnel. (Not sure about a FCEV, but it seems likely that it would choke just about as fast.)