NASA-STD-3001 Technical Brief

Relevant Technical 

Requirements

Carbon Dioxide (CO2)

OCHMO-TB-004

Rev C

NASA-STD-3001 Volume 1, Rev C

[V1 3003] In-Mission Preventive Health Care 

[V1 3004] In-Mission Medical Care

[V1 5002] Crewmember Training

[V1 5009] Physiological Exposure Mission 

Training

NASA-STD-3001 Volume 2, Rev D

[V2 4015] Aerobic Capacity

[V2 6001] Trend Analysis of Environmental and 

Suit Data

[V2 6004] Nominal Vehicle/Habitat Carbon 

Dioxide Levels

[V2 6006] Total Pressure Tolerance Range for 

Indefinite Crew Exposure

[V2 7041] Environmental Control During 

Exercise

[V2 6020] Atmospheric Data Recording 

[V2 6021] Atmospheric Data Displaying

[V2 6022] Atmospheric Monitoring and 

Alerting Parameters 

[V2 6107] Nominal Vehicle/Habitat 

Atmospheric Ventilation

[V2 6108] Off-Nominal Vehicle/Habitat 

Atmospheric Ventilation

[V2 11034] Suited Atmospheric Data Recording

[V2 11035] Suited Atmospheric Data Displaying

[V2 11036] Suited Atmospheric Monitoring and 

Alerting

[V2 11037] EVA Suited Metabolic Rate 

Measurement

[V2 11038] EVA Suited Metabolic Rate Display

[V2 11039] Nominal Spacesuit Carbon Dioxide 

Levels

Executive Summary

On Earth, physiological Carbon Dioxide (CO2) 

levels are managed by our lungs and 

environment. Our lungs collect vital oxygen 

(O2) through inhalation, circulate O2 

throughout our body and to vital organs via 

the bloodstream, and then upon exhale, 

release CO2 into the environment. When our 

respiratory system does not function 

nominally, either from physical or 

environmental limits, CO2 can build-up in our 

bodies (hypercapnia) and cause symptoms 

such as headache, dyspnea, fatigue, and in 

extreme cases, death. Our environment 

naturally eliminates CO2 through 

photosynthesis of plants and trees, 

weathering, and other experimental CO2

removal processes. Humans in space face 

hostile, enclosed environments (including 

vehicles and suits) that do not have the benefit 

of natural CO2 removal, relying on CO2 removal 

equipment (e.g., the Carbon Dioxide Removal 

Assembly (CDRA), lithium hydroxide, and 

amine systems) to help regulate CO2 levels in 

the environment and help decrease risk of 

negative consequences of elevated CO2

exposure. 
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

Main Symptoms of CO2 Toxicity (Hypercapnia)

11/13/2023

Rev C 2

These symptoms represent potential 

side-effects of hypercapnia, however it 

is important to note that most of these 

symptoms have never been observed 

during spaceflight.

• The most common symptoms experienced during spaceflight are headaches and vision changes 

(Spaceflight Associated Neuro-ocular Syndrome [SANS]).

• These two symptoms are commonly linked to fluid shifts and potential increase in intra-cranial pressure 

(ICP) due to the microgravity environment in spaceflight.
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Effects of CO2 on Cognitive Functioning

Prior research offers conflicting data on CO2 exposure and the effects on cognitive functioning, including 

memory, concentration, decision-making, and task performance. However, several recent terrestrial studies have 

shown the CO2 exposure at levels currently maintained onboard spacecraft and submarines does not reduce 

cognition and performance in astronaut-like subjects or submarine officers.

• Effects of acute exposures to carbon dioxide on decision-making and cognition in astronaut-like subjects (Scully 

et al., 2019). Findings state “There were no clear dose-response patterns for performance on either Strategic 

Management Simulation or Cognition”. 

• Acute Exposure to Low-to-Moderate Carbon Dioxide Levels and Submariner Decision Making (Rodehe et al., 

2018). Findings state “There were no significant differences for any of the nine Strategic Management 

Simulation measures of decision making between CO2 exposure conditions”.

• Effects of -12°head-down tilt with and without elevated levels of CO2 on cognitive performance: the SPACECOT 

study (Basner et al., 2017). Findings state “There were no statistically significant time-in-CO2 effects for any 

cognitive outcome”. 

Effects of −12°head-down tilt (HDT) with and without elevated CO2 on cognitive performance

Background

11/13/2023

Rev C 3

1=0.1 hours 

2= 5.2 hours

3= 21 hours

into HDT

The chart represents a summary of 

results from a subset of tests from 

a widely used and validated 

neurocognitive battery, the Penn 

Computerized Neurocognitive 

Battery, as well as a number of 

additional tests that have either 

been used extensively in 

spaceflight or that assess cognitive 

domains of particular interest in 

spaceflight (including spatial 

orientation, emotion recognition, 

and risk decision making).

Displayed data reflect Standard Deviation (SD) units. Error bars reflect 95% 

confidence intervals. A confidence interval that does not include 0 indicates a 

statistically significant difference relative to baseline data collection (BDC) at P < 

0.05. The only outcomes with a significant time-in-HDT main effect in both the 

discrete and the continuous exposure duration models were physical exhaustion 

(P = 0.0012 and P = 0.0043, respectively) and mental fatigue (P = 0.0328 and P = 

0.0205, respectively). The severity of these symptoms increased with increasing 

exposure duration. 0.5% CO2 = 3.8 mmHg CO2. Source: Basner et al., 2017. 
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Key Historical CO2 Concentrations

Background

11/13/2023

Rev C 4

Anecdotal evidence from previous spaceflight missions 

have found the following associations between CO2 levels 

and symptomology:

• Headaches at levels between 2.8-4.5 mmHg; worsening 

with increasing levels of CO2 accompanied by fatigue 

and malaise flushing. 

• Fatigue malaise, decreased sleep, and nausea reported 

at levels above 4.5 mmHg.

• 5th cranial nerve dysesthesia at 4.5-5.0 mmHg.

• Chronic cough, poor sleep, blurred vision, and frontal 

headaches reported at 3.5 mmHg.

Current NASA-STD-3001 Volume 2 

Rev D [V2 6004] limits the average 

1-hour CO2 partial pressure (ppCO2) 

in the habitable volume to no 

more than 3 mmHg. Previous 

requirements accepted a larger 

range (3.8 to 7.5 mmHg) that has 

been lowered to 3 mmHg due to 

evidence from observed 

operational and research data. 

*Referenced New NIOSH 

Recommended Exposure Limit 

dated 2005. See source (NASA/TP–2010– 216126) for listed references
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Background

CO2-Induced Headaches

Research and past historical data has revealed an association between reported headaches and CO2 levels 

among crewmembers.

• A study of data collected from Expeditions 2 to 31 (N=49) found that CO2 level, age at launch, time in-flight, 

and data source were significantly associated with reported headaches on the ISS.

• 19 of the 49 astronauts reported experiencing headaches (~38.7%).

• To keep the risk of headache below 1%, average 7-day CO2 needs to be maintained below 2.5 mmHg (current 

ISS range: 1 to 9 mmHg; 3001 standard requires <3 mmHg).

• Most experienced headaches were moderate intensity, requiring the use of analgesics in many cases.

• A retrospective analysis of the case reports found a total of 46 days with reported headaches and 1,670 days 

of non-reports (no headaches observed). 

• Based on this data, the current NASA-STD-3001 Volume 2 Rev D [V2 6004] limits the average 1-hour CO2

partial pressure (ppCO2) in the habitat volume to no more than 3 mmHg to keep incidence of headaches 

below 1.4%. 

Figure: Predicted probability of headache on the basis of average 7-day CO2 levels

11/13/2023

Rev C 5

Some observations suggest that what appears to be increased CO2 sensitivity during spaceflight may 

actually be attributed to individual predisposition to CO2 retention, adaption to microgravity, and 

local fluctuations of CO2 that are not measured by fixed sensors (Law, Watkins, & Alexander, 2010). 

Fluid shift due to decreased venous and lymphatic drainage in microgravity largely contributes to 

symptoms similar to CO2 over-exposure, including headaches.
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Reference Information

Contributors to CO2 Levels During Spaceflight

• On earth, average indoor air contains CO2 concentrations between 0.08% to 0.1% (0.608 to 0.76 mmHg).

• NASA-STD-3001 Volume 2 Rev D [V2 6004]: The system shall limit the average one-hour CO2 partial pressure 

(ppCO2) in the habitable volume to no more than 3 mmHg. 

Crew-Induced Metabolic Loads for a Standard Mission Day with Exercise

11/13/2023

Rev C 6

Crewmember Activity Description Duration of 

Activity (hr)

O2 Consumption

kg/min 10-4

(lbm/min 10-4)

CO2 Output

kg/min 10-4

(lbm/min 10-4)

Sleep 8 3.60 (7.94) 4.55 (10.03)

Nominal 0.25 5.68 (12.55) 7.2 (15.87)

Exercise 0-15 min at 75% VO2max 0.25 39.40 (86.86) 49.85 (109.90)

Exercise 15-30 min at 75% VO2max 0.25 39.40 (86.86) 49.85 (109.90)

Recovery 0-15 min post 75% VO2max 0.25 5.68 (12.55) 7.2 (15.86)

Recovery 15-30 min post 75% VO2max 0.25 5.68 (12.55) 7.2 (15.86)

Recovery 30-45 min post 75% VO2max 0.25 5.68 (12.55) 7.2 (15.86)

Recovery 45-60 min post 75% VO2max 0.25 5.68 (12.55) 7.2 (15.86)

Total Per Day 24 0.82 (1.80) 1.04 (2.29)

Total Per Day (no exercise) 24 0.72 (1.59) 0.91 (2.00)

Source: Human Integration Design Handbook (HIDH) NASA (2014)

• Respiratory quotient (RQ) is used in calculations of 

basal metabolic rate when estimated from CO2

production. It is calculated from the ratio of CO2

produced to O2 consumed by the body 

(RQ = CO2 eliminated / O2 consumed). The RQ value is 

linked to intake of macronutrients (carbohydrates and 

fats). An RQ of 0.92 is assumed for the 

O2 consumption and CO2 output determinations in 

the table above. Modifying crew diet can help 

lower the environmental CO2 output levels 

(example: consuming more fats and less 

carbohydrates). See Da Poian, et al. (2010). Nutrient 

Utilization in Humans: Metabolism Pathways.
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

Existing Technology

Carbon Dioxide Removal Assembly (CDRA) on the ISS 

(International Space Station):

• CDRA continuously removes six person-equivalent 

of CO2, when operating with both CO2 removal beds 

(dual beds functioning).

• Minimum ISS CO2 removal rate is based on the 

equation for human equivalent unit (HEU) with the 

CO2 partial pressure ranging from 2.0 to 3.9 mmHg.

• The CDRA houses a four-bed molecular sieve 

(4BMS) that utilize zeolite crystals composed of 

silicon, aluminum, and oxygen to remove excess 

carbon dioxide exhaled by the crew.

Process:

• Air enters CDRA, it passes through 1st bed where 

water is removed via desiccant portion of Bed 1.

• The Dry air is then routed to the zeolite portion of 

Bed 2 for CO2 removal. 

• The Scrubbed air flows over the previously 

saturated desiccant portion of Bed 2 absorbing 

previously removed moisture and returning it to 

cabin.

• Simultaneously, the isolated Adsorbent portion of 

Bed 1 is exposed to space vacuum and heated, 

causing the adsorbed CO2 to be released and vented 

to space. 

• When the adsorbent portion of Bed 2 becomes 

saturated the valves are reconfigured and the beds 

switch roles allowing the saturated Bed 2 to replace 

Bed 1 and vent CO2 into space. 

Advantages/Disadvantages:

• Pros – Closed loop (does not require consumables 

other than power); conserves water while removing 

CO2.

• Cons – Significant volume, replacement parts, and 

maintenance required. Risk of zeolite dust 

potentially affecting seals and mechanical 

parts/function. 

11/13/2023

Rev C 7

ISS CO2 Removal Assembly (CDRA)

Crewmember performing maintenance on ISS CDRA
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

Existing Technology

Vozdukh Russian CO2 Removal System:

• Primary Russian segment CO2 removal system aboard ISS 

(located in Service Module).

• Has two desiccant beds and three adsorbent beds.

• Cabin air is drawn into Vozdukh, passed through the desiccant 

beds, moisture is removed, and CO2 is absorbed.

• As one bed becomes saturated, second bed is placed in line. 

The saturated bed is heated, and captured CO2 is released to 

space. 

• If necessary, two beds can be used simultaneously and a third 

bed acts in CO2 regeneration mode. 

• ISS utilizes both Vozdukh and CDRA in CO2 removal capacity.

Lithium Hydroxide (LiOH):

• Primary CO2 removal system aboard Apollo and the Space 

Shuttle, and currently used as backup CO2 removal system on 

ISS (CDRA is primary CO2 removal system on ISS).

• Currently used as one option for CO2 removal during space 

walks (regenerative Metal Oxide – METOX is the other method).

• The removal of carbon dioxide is accomplished by a chemical 

reaction using lithium hydroxide (LiOH) adsorbent. This method 

relies on the exothermic reaction of lithium hydroxide with 

carbon dioxide gas to create more innocuous compound 

lithium carbonate (Li2CO3) solid, and water (H2O). 

• LiOH material arranged in air-permeable canisters such that 

cabin air flowing through canisters facilitates removal of CO2.

Advantages/Disadvantages:

• Pros – Simple and effective; highly reliable.

• Cons – Canisters are not regenerated so may only be used once 

(mass, stowage volume).

11/13/2023

Rev C 8

Vozdukh

LiOH cartridge

Lithium Hydroxide cartridge exchange

CO2+LiOH 

= 

Li2CO3+H2O

CO2

CO2 and LiOH Chemical Reaction
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

11/13/2023

Rev C 9

Emerging Technology

Thermal Amine Scrubber (TAS):

CO2 removal system based on thermally regenerated solid amine adsorbent. TAS cycles between one 

adsorbing bed and one desorbing bed to remove CO2 and regenerate bed simultaneously. Desorbing bed 

is isolated from the process air and exposed to vacuum during thermal regeneration.

• Water locker has passive water save desiccant canister and can recover 90% of incoming humidity in 

process air stream, secondary desiccant wheel increases humidity recovery to 97%.

• CO2 locker receives dry air and splits flow between 2 CO2 removal beds.

• CO2 is removed from one bed containing solid amine while the other bed is regenerated. 

• During regeneration cycle the non-adsorbing bed is exposed to vacuum to purge CO2. 

• 96% of ullage air from adsorbing bed is evacuated using scroll compressor; removal rate of CO2 is 3.7 

kg/day at 2 mmHg partial pressure.

Carbon Dioxide & Moisture Removal Amine Swing-bed (CAMRAS):

• Pair of interleaved-layer beds filled with SA9T, a sorbent system, 

of highly porous plastic beads coated with an amine. SA9T is an 

effective CO2 sorbent and has an affinity for water vapor. 

• A linear multi ball valve rotates 270 degrees back and forth to 

control flow of air and vacuum to adsorbing and desorbing beds.

• Air flows into the Amine Swing bed, a regenerable desiccant 

wheel dries and heats the air; air is later re-cooled by noncondensing heat exchangers.

• Scrubbed air comes out of the CAMRAS and flows back into the double locker; flows through a blower, 

through an electric heater, and through the opposite side of the desiccant wheel for cooling and 

rehydration. 

• Air is returned to cabin through another filter and long hose that routes return air away from supply air 

inlet to prevent short circuiting of process air.

• CAMRAS sorbent beds are regenerated by exposure to space vacuum via direct connection to the ISS 

vacuum system. 

Amine based filter beads

Thermal Amine Scrubber
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

11/13/2023

Rev C 10

Existing Technology

Extravehicular Mobility Unit (EMU) CO2 Removal:

• When astronauts go on a Spacewalk/EVA 

(extravehicular activity), they build up CO2 levels from 

breathing into a small closed space. 

• The spacesuit has a backpack system aboard called the 

Portable Life Support System (PLSS), which controls the 

environment of the spacesuit.

• One of the key functions of the PLSS is to remove and 

control CO2 delivered to the crewmember. 

CO2 washout is a method in which CO2 levels are 

controlled within the spacesuit helmet to limit the 

amount inhaled by a crewmember.

• The PLSS utilizes LiOH or METOX cartridges to absorb 

and eventually disperse the excess CO2. 

• The lithium hydroxide cells are not regenerable and are 

exchanged after each EVA. 

• The METOX cells are regenerable. They contain CO2

absorbent material. After each EVA they are placed into 

a vehicle oven that heats off the CO2 from adsorbent 

beds and vents it to the vehicle. 

• The CDRA then absorbs the CO2 from the vehicle and 

vents into space.

• The spacesuit helmet also has an emergency purge 

valve to vent CO2 in emergency situations. This can 

adversely affect the O2/CO2 balance.

Portable Life Support System (PLSS)

Portable Life Support System (PLSS)

EMU Helmet Assembly

• Consists of: Transparent shell, Neck Ring, Vent 

Pad, Purge Valve and adjustable Valsalva 

Device.

• The Vent assembly diffuses incoming gas over 

the astronaut's face.

• Under the EMU helmet, astronauts wear the 

communications carrier assembly, A.K.A. 

Snoopy Cap. 
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Application

11/13/2023

Rev C 11

CO2 Washout System

• Carbon Dioxide washout describes the process of removing CO2 in an enclosed space. For the purpose 

of this brief, we are discussing CO2 washout in a spacesuit and space helmet. 

• CO2 is a significant concern as the consequence of inadequate CO2 removal can result in hypercapnia 

and related symptoms ranging from headache and fatigue to impaired cognitive function and death.

• CO2 removal in a space helmet is challenging as it is difficult to ensure the quantity of CO2 that is 

removed from the suit and not forming pockets in any area of the suit or helmet. It is also important to 

ensure when CO2 is purged, it does not disrupt the critical breathable oxygen balance.

• Fresh air outlet from the PLSS is located at the rear base of the helmet. Air flow is directed from the 

back of the crewmember’s head over their head and face into the suit where it exits the suit and flows 

into the PLSS for filtration. This provides a continuous airflow, so the exhaled CO2 is entrained with the 

fresh air loop from the PLSS. This mixed air then flows down into the suit to where it exits the suit and 

flows back into the PLSS. 

• Exhaled air including CO2 is flowed through an adsorbent charcoal bed and contamination control 

cartridges composed or either LiOH or METOX. This removes CO2, trace gases, and odors. The LiOH

cartridges are stored on the vehicle and replaced on the ground, the METOX cartridges can be 

regenerated on orbit. Either of these are installed in the PLSS prior to EVA. 

• To address the life support challenges, especially when considering future, longer space missions, NASA 

is developing an advanced portable life support system (APLSS) spacesuit for exploration. The 

ventilation loop of the APLSS is designed to assist with CO2

washout using a regenerable rapid cycle amine (RCA) removal 

system, efficient fan and heat exchange systems, and trace 

contaminant control (TCC) unit placed inside the suit hatch 

that allows for easy filter exchange. 

• NASA has also developed a new system called the Integrated 

Ventilation Test System (IVTS) designed to study CO2 washout. 

• The IVTS has a ventilation test loop as found in APLSS and 

suited manikin test apparatus (SMTA). The purpose is to 

supplement human testing, optimize CO2 removal efficiently, 

validate CO2 washout, evaluate spacesuit nitrogen efficiencies, 

and optimize the rapid cycle amine (RCA) performance for 

scrubbing CO2. 

Integrated 

Ventilation Test 

System
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Mishaps

11/13/2023

Rev C 12

Apollo 13 – April 11-17, 1970

• Apollo 13 began their mission to land on and discover 

new information about the moon on April 11, 1970.

• Two days into their mission, a stir of the Service 

Module (SM) oxygen tank resulted in an electrical 

short causing the tank to explode, leaving the crew 

without adequate life support.

• The Lunar Module (LM), originally supplied for 2 of 

the crew to use for 2 days on the lunar surface, 

became a lifeboat supporting 3 crew for 4 days due to 

the SM’s inability to power the CM.

• CO2 levels quickly rose (14.9 mmHg) and it became 

apparent the LM did not have enough LiOH cylinders 

to support the crew for 4 days.

• Ground support identified that the CM had usable 

remaining LiOH cartridges, but they were not the 

same type/shape as the LM filters.

• The astronauts were instructed to use plastic bags, 

duct tape, and a suit hose to modify the filters, 

enabling them to absorb CO2 and support the 3-

person crew. The CO2 levels dropped to 1 mmHg.

• The crew rationed supplies and water and used the 

minimum amount of power possible, allowing them 

to survive in the cold, dark LM for 4 days during their 

return to Earth.

• The objective of visiting the moon was aborted, but 

with significant ground support planning, the crew 

was able to transfer back to the CM and safely land.

Apollo 13 re-designed CO2 filter 

Damaged Apollo 13 Service Module

Apollo 13 safe landing!

Relevant Technical Requirements

[V2 6004] Nominal Vehicle/Habitat Carbon Dioxide Levels The 

system shall limit the average 1-hour CO2 partial pressure 

(ppCO2) in the habitable volume to no more than 3 mmHg.

[V2 9001] Crew Interface Commonality Hardware and 

equipment performing similar functions shall have commonality 

of crew interfaces.

[V2 10005] Crew Interface Consistency The system shall provide 

crew interfaces that are consistent in appearance, arrangement, 

location, and operation throughout systems.

From: NASA-STD-3001 Volume 2, Rev D
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Mishaps

11/13/2023

Rev C 13

Soyuz 23 – October 14, 1976

• The Soyuz 23 had an automatic docking system malfunction during the final approach to Salyut 5 due 

to an electronics failure. 

• Cosmonauts had less than two days of battery power remaining and missed the landing opportunity for 

the day, so they powered down systems to conserve power.

• A blizzard was active in the landing zone forcing a lake rather than land landing. 

• The descent module lowered in the dark on a single parachute which rocked as it entered the high 

winds of the landing area.

• They splashed down into the freezing water of Lake Tengiz, making recovery efforts extremely difficult.

• The cosmonauts stayed in the capsule with systems shut off to save power.

• As the capsule floated, the pressure equalization valve above the waterline provided air. 

• The salt water from the lake caused the secondary chutes to deploy by shorting out the sensors, the 

parachute filled with water and dragged the capsule below the surface. 

• The ventilation had to be closed to prevent water entering the vehicle.

• Finally, a helicopter, which could not lift the capsule due to water weight, was able to drag Soyuz 23 to 

the lake edge.

• The crew was found alive but incapacitated due to high CO2 levels inside the capsule.

Relevant Technical Requirements

[V2 6004] Nominal Vehicle/Habitat Carbon Dioxide Levels The system shall limit the average 

1-hour CO2 partial pressure (ppCO2) in the habitable volume to no more than 3 mmHg.

[V2 6006] Total Pressure Tolerance Range for Indefinite Crew Exposure The system shall 

maintain the pressure to which the crew is exposed to between 34.5 kPa < pressure ≤ 103 

kPa (5 psia < pressure ≤ 15.0 psia) for indefinite human exposure without measurable 

impairments to health or performance.

From: NASA-STD-3001 Volume 2, Rev D
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Back-Up

11/13/2023

Rev C 14
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Rev B  Rev C

• Updated information to be consistent with NASA-STD-3001 

Volume 1 Rev C and Volume 2 Rev D.

Rev A  Rev B

• Updated to new template format.

• Added additional information on Standard background and 

application.

Original  Rev A

• Updated information to be consistent with NASA-STD-3001 

Volume 1 Rev B and Volume 2 Rev C.

Major Changes Between Revisions

11/13/2023

Rev C 15
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

NASA-STD-3001 Volume 1 Revision C

[V1 3003] In-Mission Preventive Health Care All programs shall provide training, in-mission capabilities, 

and resources to monitor physiological and psychosocial well-being and enable delivery of in-mission 

preventive health care, based on epidemiological evidence-based probabilistic risk assessment (PRA),

individual crewmember needs, clinical practice guidelines, flight surgeon expertise, historical review, 

mission parameters, and vehicle derived limitations. These analyses consider the needs and limitations

of each specific vehicle and design reference mission (DRM) with particular attention to parameters such 

as mission duration, expected return time to Earth, mission route and destination, expected radiation

profile, concept of operations, and more. In-mission preventive care includes, but is not limited to: (see 

NASA-STD-3001 Volume 1 Rev C for full technical requirement).

[V1 3004] In-Mission Medical Care All programs shall provide training, in-mission medical capabilities,

and resources to diagnose and treat potential medical conditions based on epidemiological evidencebased PRA, individual crewmember needs, clinical practice guidelines, flight surgeon expertise, historical

review, mission parameters, and vehicle-derived limitations. These analyses consider the needs and 

limitations of each specific vehicle and design reference mission (DRM) with particular attention to 

parameters such as mission duration, expected return time to Earth, mission route and destination, 

expected radiation profile, concept of operations, and more. In-mission capabilities (including hardware 

and software), resources (including consumables), and training to enable in-mission medical care, and 

behavioral care, are to include, but are not limited to: (see NASA-STD-3001 Volume 1 Rev C for full 

technical requirement).

[V1 5002] Crewmember Training Beginning with the astronaut candidate year, general medical training, 

including, but not limited to, first aid, cardiopulmonary resuscitation (CPR), altitude physiological training, 

carbon dioxide exposure training, familiarization with medical issues, procedures of space flight, 

psychological training, and supervised physical conditioning training shall be provided to the astronaut 

corps.

[V1 5009] Physiological Exposure Mission Training Physiological training shall be provided to assist 

crewmembers with pre-mission familiarization to in-flight exposures including but not limited to: carbon 

dioxide [CO2] exposure training, hypoxia training/instruction, centrifuge, and high-performance aircraft 

microgravity adaptation training in preparation for each mission.

NASA-STD-3001 Volume 2 Revision D

[V2 4015] Aerobic Capacity The system shall be operable by crewmembers with the aerobic capacity as 

defined in NASA-STD-3001, Volume 1.

[V2 6001] Trend Analysis of Environmental and Suit Data The system shall provide environmental and 

suit monitoring data in formats compatible with performing temporal trend analyses.

[V2 6004] Nominal Vehicle/Habitat Carbon Dioxide Levels The system shall limit the average one-hour 

CO2 partial pressure (ppCO2) in the habitable volume to no more than 3 mmHg.

[V2 6006] Total Pressure Tolerance Range for Indefinite Crew Exposure The system shall maintain the 

pressure to which the crew is exposed to between 34.5 kPa < pressure ≤ 103 kPa (5 psia < pressure ≤ 15.0 

psia) for indefinite human exposure without measurable impairments to health or performance. 

Referenced Technical Requirements

11/13/2023

Rev C 16

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

NASA-STD-3001 Volume 2 Revision D

[V2 7041] Environmental Control During Exercise The system environmental control shall 

accommodate the increased O2 consumption and additional output of heat, CO2, perspiration droplets, 

odor, and particulates generated by the crew in an exercise area.

[V2 6020] Atmospheric Data Recording For each isolatable, habitable compartment, the system shall 

automatically record pressure, humidity, temperature, ppO2, and ppCO2 data continuously. 

[V2 6021] Atmospheric Data Displaying The system shall display real-time values for pressure, humidity, 

temperature, ppO2, and ppCO2 data to the crew locally and remotely.

[V2 6022] Atmospheric Monitoring and Alerting Parameters The system shall alert the crew locally and 

remotely when atmospheric parameters, including atmospheric pressure, humidity, temperature, ppO2, 

and ppCO2 are outside safe limits.

[V2 6107] Nominal Vehicle/Habitat Atmospheric Ventilation The system shall maintain a ventilation 

rate within the internal atmosphere that is sufficient to provide circulation that prevents CO2 and 

thermal pockets from forming, except during suited operations, toxic cabin events, or when the crew is 

not inhabiting the vehicle.

[V2 6108] Off-Nominal Vehicle/Habitat Atmospheric Ventilation The system shall control for ppO2, 

ppCO2, and relative humidity during off-nominal operations, such as temporary maintenance activities in 

areas not in the normal habitable volume.

[V2 11034] Suited Atmospheric Data Recording Systems shall automatically record suit pressure, ppO2, 

and ppCO2.

[V2 11035] Suited Atmospheric Data Displaying Suits shall display suit pressure, ppO2, and ppCO2 data 

to the suited crewmember.

[V2 11036] Suited Atmospheric Monitoring and Alerting Suits shall monitor suit pressure, ppO2, and 

ppCO2 and alert the crewmember when they are outside safe limits.

[V2 11037] EVA Suited Metabolic Rate Measurement The system shall measure or calculate metabolic 

rates of suited EVA crewmembers.

[V2 11038] EVA Suited Metabolic Rate Display The system shall display metabolic data of suited EVA 

crewmembers to the crew.

[V2 11039] Nominal Spacesuit Carbon Dioxide Levels The spacesuit shall limit the inspired CO2 partial 

pressure (PI

CO2) in accordance with Table 11.3-1—Spacesuit Inspired Partial Pressure of CO2 (PICO2) 

Limits.

Referenced Technical Requirements

11/13/2023

Rev C 17

View the current versions of NASA-STD3001 Volume 1 & Volume 2 on the 

OCHMO Standards website
NASA-STD-3001 Technical Brief

OCHMO-TB-004 Carbon Dioxide (CO2)

NASA Office of the Chief Health & Medical Officer (OCHMO)

This Technical Brief is derived from NASA-STD-3001 and is for reference only.

It does not supersede or waive existing Agency, Program, or Contract requirements.

Reference List

1. NASA-STD-3001 Volume 2, Revision B. (2009). 

https://www.NASA.gov/sites/default/files/atoms/files/NASA-std-3001_vol_2_rev_b.pdf

2. Law J, Watkins S, Alexander D. (2010). In-Flight Carbon Dioxide Exposures and Related Symptoms: 

Association, Susceptibility, and Operational Implications. NASA Scientific and Technical Information 

(STI) Program Office. NASA Internal Document NASA/TP–2010– 216126.

3. Lee AG, Mader TH, Gibson CR, Tarver W, Rabiei P, Riascos RF, Galdamez LA, Brunstetter T. (2020). 

Spaceflight associated neuro-ocular syndrome (SANS) and the neuro-ophthalmologic effects of 

microgravity: a review and an update. NPJ Microgravity, 6(7): 3771.

4. Evidence Report: Risk of Spaceflight Associated Neuro-ocular Syndrome (SANS). (2017). Human 

Research Program – Human Health Countermeasures Element. NASA Internal Document.

5. Basner M, Nasrini J, Hermosillo E, McGuire S, Dinges DF, Moore TM...& Bershad EM. (1985). Effects of -

12° head-down tilt with and without elevated levels of CO 2 on cognitive performance: the SPACECOT 

study. Journal of Applied Physiology, 124(3): 750-760.

6. Scully RR, Basner M, Nasrini J, Lam CW, Hermosillo E, Gur RC...& Ryder VE. (2019). Effects of acute 

exposures to carbon dioxide on decision making and cognition in astronaut-like subjects. NPJ 

Microgravity, 5(127).

7. Rodeheffer CD, Chabal S, Clarke JM, Fothergill DM. (2018). Acute Exposure to Low-to-Moderate 

Carbon Dioxide Levels and Submariner Decision Making. Aerospace Medicine and Human 

Performance, 89(6): 520-525.

8. Demontis GC, Germani MM, Caiani EG, Barravecchia I, Passino C, Angeloni D. (2017). Human 

Pathophysiological Adaptations to the Space Environment. Frontiers in Physiology, 8: 547.

9. James JT. Chapter 7: Carbon Dioxide. In: Spacecraft Maximum Allowable Concentrations for Selected 

Airborne Contaminants. Volume 5 (2008), National Research Council of the National Academies.

10. Astronaut Health and Performance. https://www.NASA.gov/centers/johnson/pdf/584739main_Wingsch5d-pgs370-407.pdf

11. Law J, Van Baalen M, Foy M, Mason SS, Mendez C, Wear ML, Meyers VE, Alexander D. (2014). 

Relationship between carbon dioxide levels and reported headaches on the International Space 

Station. Journal of Occupational and Environmental Medicine, 56(5): 477-483.

12. Widmaier EP, Hershel R, Strang KT. (2016). Vander's Human Physiology: The Mechanisms of Body 

Function (14th ed.). New York: McGraw Hill. ISBN 9781259294099.

13. Chullen,C, Conger,B Korona,A, Kanne,B Mcmillin,S, Paul,T, Norcross,J, Alonso,J, Swickrath,M, Utilizing a 

Suited Manikin Test Apparatus and spacesuit Ventilation Loop to Evaluate Carbon Dioxide Washout. 

JSC-CN-33276, Report Paper International Conference on Environmental Systems. July 12,2015

14. NASA Extravehicular Mobility Unit (EMU) LSS/SSA Data Book. September 2017 UTC Aerospace 

Systems. 

15. Da Poian, A. T., El-Bacha, T. & Luz, M. R.M.P. (2010) Nutrient Utilization in Humans: Metabolism 

Pathways. Nature Education, 3(9):11.

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