A recent (Sept. 2017) news item on the company website of Gas Sensing Solutions Innovative sensor technology assists NASA with vital wearable CO2 monitoring equipment caught my eye. A section of the article is quoted below, with the accompanying photo of Expedition 49 crewmember Kate Rubins of NASA working "...with the airlock inside of Kibo, the Japanese Experiment Module. Rubins was installing the Robotics External Leak Locator (RELL), a technology demonstration designed to locate external ISS ammonia (NH3) leaks." (quoted caption from the copy of this image found in Wikimedia Commons and in NASA Johnson's Flikr where it is dated 27-Sep-2016).

See also SST Sensing's Innovative Sensor Technology Assists NASA with Vital Wearable CO2 Monitoring Equipment and CO2Meter.com's NASA Wearable CO2 Monitor uses CozIR Sensor.

I know that CO2 buildup is an issue in confined spaces in microgravity, but the article suggests that even the baseline levels experienced by ISS astronauts might be a problem.

Question: Do ISS astronauts notice, or experience symptoms of elevated CO2 levels? Do they wear monitors regularly? I wonder if some confided sections, like end modules or the Bigelow Expandable Activity Module might be more at risk, and astronauts are more likely to use personal monitors there for safety, or if they are used strictly for data collection and archiving.

These are commercial websites selling or advocating products. I'm wondering if there are NASA or other non-commercial, authoritative sources that address this question.

Though extensive terrestrial studies have shown that this increased level will have no effect on the continued good health of those exposed to it, there must be some acknowledgement of the fact that crew members onboard the ISS still regularly experience symptoms of acute CO2 toxicity – such as headaches or lethargy.

Per this answer, the image is that of astronaut and molecular biologist Dr. Kathleen "Kate" Rubins (Ph.D.), the first person to sequence DNA in space.

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It is generally accepted that human adaptations to microgravity conditions will cause astronauts in space to become more sensitive to elevated CO2 levels. This can result not only in physical discomfort, but also impinge on their cognitive skills and reaction times – thereby potentially leading to safety risks. On average crew members stay on the ISS for a period of around 6 months, so having a good grasp of the ongoing implications is clearly of great value.

With operational practicalities meaning that it is not possible (either technically or financially speaking) to remove enough CO2 to replicate normal conditions here on Earth, the ISS has to function with relatively high ambient CO2 concentrations present in the air. Yet its occupants have to live and work in an acceptable environment.

NASA scientists have, for many years, wanted to embark on a thorough investigation of how elevated CO2 levels impact on ISS crew members’ ability to carry out their allotted tasks, but it has taken a long time for them to be in a position to employ a method for acquiring data to a high enough degree of precision. Given that, as already mentioned, air does not mix well without the influence of gravity, wall-mounted sensors had proved themselves to be an unsuitable means by which to get an accurate reflection of a crew member’s exposure to CO2. What was needed instead were wearable CO2 sensors.


I don't have anything public I can point to, but yes, they do notice. The CO2 target is a frequent topic of conversation between the crew and ground personnel, and the crew haven't been shy about pointing out when CO2 concentrations are too high for their liking.

  • $\begingroup$ Thanks! In this particular case I can understand why there might not be public supporting links. $\endgroup$ – uhoh Jan 25 '18 at 1:27
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    $\begingroup$ Tristan, do not feel I have a full answer but possible reference for yours is Scott Kelly in 'Endurance: A year in space' who has a great deal to say about CO2 Levels and the discomfort they caused, to the point it is almost a theme of the book. $\endgroup$ – GremlinWranger Nov 6 '18 at 9:52
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    $\begingroup$ @GremlinWranger if you have a copy handy, a quote or two in a short supplementary answer would be really interesting to read. $\endgroup$ – uhoh Aug 12 '19 at 17:46

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