That is a very useful table, GasMonkey. Thanks.
May I ask what are the sources for the data? We all need to be as sure as possible that the data is reliable, since failure and waking up with brain damage would be very unpleasant.
Has anyone researched using pure propane? Why, for example, use a propane heater in a closed space like a closet, thus risking a fire? Why not just open the valve of a tank of propane and breath it in?
One advantage of propane over CO2 is that CO2 is "toxic": it does serious damage to organs and tissues. Propane is an "asphyxiant", and simply replaces oxygen in the lungs. At lower exposures to propane, waking up after a failure would result in a headache. Of course, waking up after a higher exposure could result in brain damage, just as with CO2.
One aspect of suicide that I don't see discussed much is how to make death look accidental, to reduce trauma for the family. Using a propane heater or pure propane in a closet spells suicide. But what about creating the impression that you were working on a project in a garage, and the propane heater malfunctioned, releasing pure propane into the garage?
How to create the false impression? Have a partially-completed project on a work table. Have the heater with empty tank attached, valve open. To observers, it will seem that the heater malfunctioned while you were working on the project, and released pure propane into the garage. Open the valves of the other tanks when you're ready to "exit this vale of tears", or CTB, or (insert favourite euphemism), to make sure you reach a lethal level of propane. It will look to observers as if you had used the empty tanks one by one, over time, to heat the garage.
The question for me is, how to ensure a lethal level of propane ? Assuming that GasMonkey's table is correct, then we need 10,000 ppm of propane in the garage. Buy how can I know that 3-4 BBQ tanks of propane opened simultaneously will create this level of ppm? It's a big garage. Should I use a shower curtain to enclose my space, to concentrate the propane, and hope the curtain doesn't make the scene look like it was set up for suicide?