Elsewhere we briefly touched on the oddity of many shirtsleeve worlds all having O2 concentrations within comfortable range for humans.
Comfortable range, by the way, is somewhere between about 19.5 and 22 percent, as far as OSHA is concerned. Lower than that, you fatigue easily - you can adapt given enough weeks, but it's a bit of a problem for people coming in from higher O2 regimes. Humans can actually adapt to quite a bit: Sherpas were documented to be functioning fairly normally on one Himalayas climb with O2 concentrations in the 70's at the 18,000 foot mark (about half an atmosphere pressure), levels that would put the rest of us in a hospital with an O2 cannula in our nose. Humans have settled regions as high as 15,000 feet, with air pressure 56-57% of sea level. However, us travelling types are likely to find such altitudes quite uncomfortable.
(Higher O2 concentrations, things are more combustible and burn brighter, not extremely so at 23 percent but enough to be problematic in a work environment, apparently.)
At any rate, the idea that the various planets might actually vary in O2 concentrations brought to mind an item of modern tech: the O2 concentrator.
The O2 concentrator is a machine whose job is to take normal air and concentrate the oxygen in of it - in the modern world, so that some poor soul with a respiratory problem can breathe it. It does this by compressing air into a container that holds a mineral that traps nitrogen - a zeolite. The nitrogen gets trapped, the compressed air becomes almost pure oxygen. The machine then vents the oxygen into a reservoir, from which the patient can breathe it. In the process pressure drops, and the zeolite starts releasing the nitrogen. At that point, the machine closes the valve to the reservoir and opens up another, the zeolite releases the last of the nitrogen, the depleted air mix is released into the surrounding air, and a new air charge drawn in and pressurized to start the process again. Reservoir ends up delivering a 90% pure O2 mix to the patient. Unlike O2 bottles, which carry a limited charge and can break, releasing their O2 (and going all frosty in the process, which is actually rather neat to see), the concentrator can keep delivering O2 as long as there's air around it and power to run it.
Standard O2 concentrators draw about 300 watts to deliver 5 liters per minute and weigh 20 to 40 pounds; the newer ones can deliver 10 liters per minute and draw a bit under 600 watts. Battery-powered shoulder-carry models exist in the 10-pound range, delivering 2 liters per minute for about 40-45 minutes continuous or 3.5 hours in "pulsed" doses (the idea being to deliver the O2 only when you're actually inhaling).
A shoulder-carried battery-powered O2 concentrator - especially with Imperial battery tech to back it - opens up the possibility of creating worlds that don't all have to be carbon copies of Earth's atmosphere, worlds with standard-pressure atmospheres but sub-par O2 concentrations where the human population runs around wearing concentrators with cannulae under their noses. That assumes of course the atmosphere is otherwise dominated by nitrogen. There are strategies for bleeding out other gases, even CO2, but I'm not real familiar with them.
Comfortable range, by the way, is somewhere between about 19.5 and 22 percent, as far as OSHA is concerned. Lower than that, you fatigue easily - you can adapt given enough weeks, but it's a bit of a problem for people coming in from higher O2 regimes. Humans can actually adapt to quite a bit: Sherpas were documented to be functioning fairly normally on one Himalayas climb with O2 concentrations in the 70's at the 18,000 foot mark (about half an atmosphere pressure), levels that would put the rest of us in a hospital with an O2 cannula in our nose. Humans have settled regions as high as 15,000 feet, with air pressure 56-57% of sea level. However, us travelling types are likely to find such altitudes quite uncomfortable.
(Higher O2 concentrations, things are more combustible and burn brighter, not extremely so at 23 percent but enough to be problematic in a work environment, apparently.)
At any rate, the idea that the various planets might actually vary in O2 concentrations brought to mind an item of modern tech: the O2 concentrator.
The O2 concentrator is a machine whose job is to take normal air and concentrate the oxygen in of it - in the modern world, so that some poor soul with a respiratory problem can breathe it. It does this by compressing air into a container that holds a mineral that traps nitrogen - a zeolite. The nitrogen gets trapped, the compressed air becomes almost pure oxygen. The machine then vents the oxygen into a reservoir, from which the patient can breathe it. In the process pressure drops, and the zeolite starts releasing the nitrogen. At that point, the machine closes the valve to the reservoir and opens up another, the zeolite releases the last of the nitrogen, the depleted air mix is released into the surrounding air, and a new air charge drawn in and pressurized to start the process again. Reservoir ends up delivering a 90% pure O2 mix to the patient. Unlike O2 bottles, which carry a limited charge and can break, releasing their O2 (and going all frosty in the process, which is actually rather neat to see), the concentrator can keep delivering O2 as long as there's air around it and power to run it.
Standard O2 concentrators draw about 300 watts to deliver 5 liters per minute and weigh 20 to 40 pounds; the newer ones can deliver 10 liters per minute and draw a bit under 600 watts. Battery-powered shoulder-carry models exist in the 10-pound range, delivering 2 liters per minute for about 40-45 minutes continuous or 3.5 hours in "pulsed" doses (the idea being to deliver the O2 only when you're actually inhaling).
A shoulder-carried battery-powered O2 concentrator - especially with Imperial battery tech to back it - opens up the possibility of creating worlds that don't all have to be carbon copies of Earth's atmosphere, worlds with standard-pressure atmospheres but sub-par O2 concentrations where the human population runs around wearing concentrators with cannulae under their noses. That assumes of course the atmosphere is otherwise dominated by nitrogen. There are strategies for bleeding out other gases, even CO2, but I'm not real familiar with them.
