Logotype Logotype
Logotype

CO₂ symptoms on the International Space Station

 CO₂ on the International Space Station: An Operations Update

 

PROBLEM STATEMENT: We describe CO symptoms that have recently been reported by crew members on the International Space Station, and our continuing efforts to control CO to levels lower than historically accepted. 

 

Background

Throughout the International Space Station (ISS) program, anecdotal reports have suggested that crew members develop CO-related symptoms at lower CO levels than would be expected terrestrially. Since 2010, operational limits have controlled the 24-hour average CO to 5,300 ppm or below, as driven by crew symptomatology. In recent years, largely due to increasing awareness by crew and ground team, there have been increased reports of crew symptoms. The aim of this presentation is to discuss recent observations and operational impacts to lower CO levels on the ISS.

 

Case presentation

Crew members are routinely asked about CO symptoms in their weekly private medical conferences with their crew surgeons. In recent ISS expeditions, crew members have noted symptoms attributable to CO starting at 3,000 ppm. Between 3,000–3,500 ppm, fatigue and full-headedness have been reported. Between 3,500–4,000 ppm, there have been self-reports of procedure missed steps or procedures going long. Above 4,000–4,500 ppm, headaches have been reported. A wide range of inter- and intra-individual variability in sensitivity to CO has been noted.

 

Operational / Clinic relevance

These preliminary data provide semiquantitative ranges that have been used to inform a new operational limit of 3,500 ppm as a compromise between systems capabilities and the recognition that there are human health and performance impacts at recent ISS CO levels. Current evidence would suggest that an operational limit between 650 and 2,600 ppm may maintain health and performance. Future work is needed to establish long-term ISS and future vehicle operational limits. 

 

References:

https://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20150019624.pdf