Commercial aircraft air quality:

Airplane cabin IAQ, fresh air ventilation, and oxygen and carbon dioxide levels were examined by measuring CO₂ and O₂ levels during long flights.

This article reports the results of a limited study of the variation in oxygen levels and carbon dioxide levels during long commercial air flights in 2014. This study was made by performed by using safe, simple and accurate gas detection tube analysis to measure both oxygen and carbon dioxide levels at various points in fight.

Results suggest that the levels of these two gases in the aircraft cabin indeed varied, but not by much during these particular long commercial airline flights at typical high altitudes.

Levels of Carbon (CO₂₎ Dioxide & Oxygen (O₂) & Ozone During Flight

Waters et al (2002) reported "Carbon dioxide exposures were highest on shorter and high-occupancy flights, aircraft with greater recirculated-to-fresh-air ratio, and narrow-bodied aircraft. In general contaminant levels were low compared to standards.

Carbon dioxide levels indicated lower ventilation rates per occupant than most other indoor environments."

[Click to enlarge any image]

Those authors measured aircraft cabin CO₂ at 515 - 4902 ppm and reported that CO₂ levels were likely to be elevated in aircraft cabins on short flights in full or nearly-full aircraft.

They also provide a succinct description of how cabin air is supplied to airline passengers:

Engine compressor bleed air is pre-conditioned, sent to the air conditioning packs, and delivered to the cabin through a manifold that permits mixing with recirculated cabin air.

Outside air is not filtered but the recirculation system incorporates air filtration; types and efficiency of filters vary by aircraft.

Recirculation maintains air supply rate and minimizes use of more costly bleed air.  - Waters et al (2002)

I previously studied the rate of change of indoor CO₂ in a crowded synagogue that had no functional fresh air ventilation system. During the religious service the CO₂ level indoors increased significantly, possibly shifting an explanation of the apparent drowsiness of the congregants from Rabbi Arnold's sermon to the building's indoor air quality.

One might ask if similarly the CO₂ might increase in the cabin of a crowded airplane during a long flight - a different hypothesis than that offered by Waters et als and one that investigates the current (2014) ventilation rate on commercial aircraft.

I have received anecdotal reports of a air passengers experiencing dizziness and fainting during long air flights (Lukacher 2014) , typically transcontinental travel.

While altitude has been discussed regarding air passenger comfort anecdotal reports speculated on changes in either oxygen level or carbon dioxide level as possible contributors to the experiences of these passengers.

While altitude or other explanations for fainting and dizziness during long air flights may pertain, I wanted to investigate the cabin air quality, specifically oxygen and carbon dioxide, and to compare those results with air passenger speculations about oxygen and CO₂ levels in aircraft during long flights.

Previously I have collected airborne particle samples using an adhesive air sampling cassette in order to examine in-cabin airborne particulates in the air stream from the cabin's ovehead air supply. Particulate levels down to 1u were very low: I did not find much of interest. Particulate filtration on modem aircraft appears to be quite effective at least for larger particles such as common dust, pollen, and mold spores.

Very small particles such as bacteria and viruses were not studied by the author but were studied by some of the authors cited below.

In 2014, on a series of long commecial air flights including trips between Mexico and the U.S. and between the U.S. and New Zealand, the author used a simple air sampling pump made by Drager to collect periodic samples of the level of both carbon dioxide and oxygen in the passenger cabin of the commercial aircraft during those flights.

At left are the oxygen sampling tube (above) showing about 11.25% concentration of oxygen in the aircraft's cabin, and a carbon dioxide gas sampling tube after 20 pump strokes showing nearly 1500 ppm - a number that must be divided by two to obtain the actual concentration of about 750 ppm of CO₂ for this measurement.

The data recorded included the total flight time, altitude, aircraft model and number of passengers aboard, along with the point in the flight by time and distance at which various samples were collected. The results are reported in the airplane cabin IAQ table below.

Notes to the Table Above

Notes:

1. Time in minutes into the total flight time

2. Dates are given in international format dd/mm/yy

3. Second reading using same sampling tube by doubling number of pump strokes for increased precision.

4.Drager gas detection tubes used: colorimetric type. Selecting the proper detection device sensitivity range is important for obtaining accurate measurement of gases in air. I used:

• Carbon Dioxide level measurement: Drager Rohrchen Carbon Dioxide 100/1, certified manufacturer ISO 9001. This tube is designed for measuring CO₂ levels are between 100 - 3000 ppm. Ten Drager gas pump measurement strokes are used with this tube, or the operator can use 20 pump strokes and divide the resultant measurement by 2 for increased precision. Standard deviation is +/- 10-15%.
  
  The tube colour changes from white to violet on exposure to CO₂. and operates at temperature ranges from 15°C to 25°C and at humidity less than or equal to 23 mg/L (corresponding to 100% RH at 25C). An atmospheric correction factor to be applied is F=1013 / actual ATM pressure.
• Oxygen level measurement: Drager Rohrchen Oxygen 5%, certified manufacturer ISO 9001. This tube is designed for measuring the level of oxygen in air in the range of 5% to 23% by volume. One pump stroke is used to perform a measurement.
  
  Standard deviation is +/- 10-15%. The tube changes color from blue-black to white on exposure to oxygen and operates in the temperature range of 5°C to 50°C and at humidity from 0-40 mg/L. The literature includes a correction factor F = 1013hPa (14.692 psi) / actual atmospheric pressure - a factor that may be especially pertinent at high altitudes or in examining aircraft cabin conditions.
  
  The detector tube also has two reading scales, chosen based on which Drager sampling pump is used. Because this tube heats to as much as 100°C it should not be used where explosive gases may be present.
• The Dräger sampling pump was leak-tested prior to use of the detection tubes by using the manufacturer's recommendations. The pump was air-flushed between measurements.
• Draeger Safety Inc. 101 Technology Drive Pittsburgh, PA 15275-1057 USA, Tel: +1-800-858-1737 +1-412-787-2207, Website: http://www.draeger.com (their website was not functioning properly - Nov. 2014)
  Draeger Safety Inc. (Gas Detection Systems) 505 Julie Rivers Suite 150 Sugarland, TX 78478-2847 +1-800-230-5029 +1-800-375-3073. Drägerwerk AG & Co. KGaA

5. Other gas concentration in air conversions:

1 ppm CO₂ = 1.8 mg CO₂M³
1 mg CO₂ = 0.56 ppm CO₂ (at 20°C, 1013hPa)

Discussion

With additional measurement reports pending, I found in-flight cabin air quality measurements of oxygen to be relatively stable, ranging from 11.2% to 12.5%.

Typical outdoor CO₂ levels are between 350-400 ppm (0.035% - 0.04%) or up to 500 ppm by some sources.

Carbon dioxide levels measured in-flight in the aircraft cabin ranged between 0.04% or 400 ppm and 0.1% or 1000 ppm to date in our studies and were measured at close to 0.5% or 5,000 ppm in earlier studies.

As indicated at CO₂ HEALTH EFFECTS, occupants are unlikely to be affected or to notice CO₂ levels under 2% or 20,000 ppm - a far higher number than in-flight aircraft cabin carbon dioxide levels.

Conclusions

Opinion: Perhaps to investigate or reduce air traveler complaints of dizziness or fainting we should look more closely at altitude and cabin pressures as well as other factors such as passenger hydration (drink plenty of fluids), anxiety, physical stresses before the flight (rushing, carrying bags), passenger movement & stretching during flight (avoid blood clots), the increasingly cramped seat space limitations and cramping, and aircraft cabin ozone levels.

Note: my measurements of equivalent altitude indicate that typical cabin pressures during flight give an altitude of about 7,000 feet. As I have observed simply among visitors to San Miguel de Allende, Mexico, (altitude about 6500 feet), unaccustomed people are often physically stressed at that altitude, experiencing shortness of breath and on occasion dizziness.

Opinion: An increase in respiration rate by an "out-of-breath" passenger experiencing quite understandable anxiety can exacerbate those conditions.

Bagshaw et als (2002) point out that

Commercial air carriers train their flight attendants to recognize common symptoms of distress and to respond to medical emergencies with first - aid, basic resuscitation techniques, and the use of emergency medical oxygen. ... It cannot be overemphasized that these medical kits are only for emergency use and not for routine medical care.
...
In general, ... studies have consistently revealed levels of organic substances, carbon monoxide, carbon dioxide, and airborne particles in the cabin air well below regulatory standards and below those encountered in offices, the street, or subway.

One exception is ozone, a substance found naturally in the atmosphere at altitudes where most commercial aircraft fly. It enters the cabin with outside air that is used for cabin ventilation. Ozone is a respiratory system irritant and can cause chest tightness, coughing, and shortness of breath if exposure occurs at high enough concentrations.

In general, low levels have been found in aircraft cabins although, in several instances, levels were measured slightly exceeding regulatory standards. Most aircraft flying at altitudes and latitudes where high ozone concentrations are encountered now have ozone converters which break down the ozone before it reaches the cabin. - Bagshaw (2002)

Keep calm. Carry on.

In-Flight Air Quality-Particulate Test

In a rather amateur first effort we looked for airborne particles in aircraft supply air over a passenger seat.

After adjusting the air supply flow rate down to a rate slow enough to collect particles during a commercial air flight in 2000 this sampling cassette was used to test for and permit identification of particles in the conditioned air provided over a passenger seat.

There were several technical shortcomings that would prevent an accurate quantitative analysis of particles collected using this method, including a lack of accurate measurement of the air flow rate to be sure that it is within the CFM specified for the sampling cassette and its collection media.

With an inaccurately-calibrated particle collector there will be particle loss because some particles bounce off of the slide if the air flow rate is too great, or alternatively, particle loss because some particles, depending on their size and mass, may fail to adhere to the collection media on the slide if the air flow rate is too weak.

Nevertheless the near-total absence of particles in samples collected in this matter suggested that airborne particulates in the 1u and larger size range were not likely to be an issue in this environment.

Excluded from consideration were bacteria and viruses as the size of those particles were not within the detection range of this device.

In a second effort a calibrated, battery-operated vacuum pump was used with the same type of vacuum cassette to collect particles in the passenger seating area during the same flight.

This procedure also found that the particulate level was very low in the supply air over the passenger seat. It would appear that the aircraft's air conditioning system filtration was very effective at removing particles at 1u and larger.

Typical particles collected were fabric fibers and skin cells - the same as one would expect in any space occupied by humans.

Research on In-Flight Air Quality, Oxygen & Carbon Dioxide Levels & Other Factors

• AAIB, Claiden, P.T., UK, Air Accidents Investigation Branch REPORT on the incident to BAe 146, G-JEAK during the descent into Birmingham Airport on 5 November 2000" [PDF] (2004), Air Accidents Investigation Branch, UK, P T Claiden Inspector of Air Accidents Air Accidents Investigation Branch Department for Transport January 2004 retrieved 2018/08/16, original source: https://assets.publishing.service.gov.uk/media/5422f01ded915d13740002e3/1-2004_G-JEAK.pdf
  Excerpts:
  
  Fumes were evident in both the cabin and on the flight deck of G–JEAK, indicating contamination of at least the No 1 ECS pack, prior to and after the event, until the replacement of the APU on 14 Nov 2002.
  
  The APU on G-JEAK supplied air contaminated with oil to the ECS packs. ...
  
  The regulations JAR 25.831, JAR-APU-210, JAR-E-510 and JAR-E690, all deal with unacceptable levels of contamination of the bleed air, but do not provide details of toxic contamination that is deemed as unacceptable.
  
  Early conclusions by previous studies indicated that oil decomposition products are unlikely to be more toxic than the CO content in contaminated air.
  ...
  Boeing indicated that all airplane models occasionally experience some odours or fumes in the flight deck from a variety of sources, but a review of available data indicated that the Model 757-200 with Rolls Royce RB211-535C engines appear to have a higher incidence of events than expected. Most of the 757-200 airplanes with this engine type are operated by a UK operator.
  
  Boeing worked closely with Rolls Royce (the engine supplier), Honeywell (the auxiliary power unit supplier) and the UK engine overhaul company to resolve the issue.
• AEROTOXIC SYNDROME: A NEW OCCUPATIONAL DISEASE? [PDF] WHO, Susan Michaelis, Jonathan Burdon, C. Vyvyan Howard, Public Health Panorama, VOl. 3 No. 2, June 2017, pp. 141-356, retrieved 2018/08/16, original source: http://www.euro.who.int/__data/assets/pdf_file/0019/341533/5_OriginalResearch_AerotoxicSyndrom_ENG.pdf
  Excerpt:
  Concerns related to adverse health effects experienced by aircrew exposed to aircraft contaminated air have been ongoing for over 6 decades. Unfiltered breathing air is supplied to the cabin via the engine compressor.
  
  The likelihood that oil leaking over the engine oil seals may enter the cabin air supply has prompted continuing debate about the hazards associated with exposure to neurotoxic substances and to the thermally degraded or pyrolysed mixture.
• Aerotoxic Association, 27 Old Gloucester Street , London, London WC1N 3AX United Kingdom - Europe Website: https://www.aerotoxic.org/
• ASHRAE. 1999. ANSI/ASHRAE Standard 62-1 999. Ventilation for Acceptable Indoor Air Quality, Atlanta, GA: American Society of Heating, Refrigerating and Air-Conditioning Engineers, Inc.
• Australia, Parliament of the Commonwealth of Australia, AIR SAFETY and CABIN AIR QUALITYin the BAe 146 Aircraft: Report by the Senate Rural and Regional Affairs and Transport References Committee (PDF), (2000) Commonwealth of Australia, ISBN 0-642-71093-7, retrieved 2018/08/16 original source: http://ashsd.afacwa.org/docs/AustSen.pdf
• Backman, Howard, and Fariborz Haghighat. "Air quality and ocular discomfort aboard commercial aircraft." Optometry (St. Louis, Mo.) 71, no. 10 (2000): 653-656.
• Bagshaw, Michael (2008-11-29). The "AEROTOXIC SYNDROME" (PDF). European Society of Aerospace Medicine, retrieved 2018/08/16, original source: https://web.archive.org/web/20100827071537/http://www.esam.aero/main/docs/ecam08/No%207%20Bagshaw%20paper.pdf
  Excerpt:
  Conclusions:
  
  There has been an increase in reported incidents of in-flight smoke/fume events since 1999, with a small number of crew members reporting adverse health effects which they associate with the events.
  
  The source of oil contamination of engine bleed air was identified in early versions of the BAe 146 and the Boeing 757 and suitable modifications were implemented.
  
  A range of chronic health effects are reported by some crew members, although there have been no payments of damages to affected individuals. The reported symptoms are wide-ranging with insufficient consistency to justify the establishment of a medical syndrome.
  
  It has been noted that many of the acute symptoms are normal symptoms experienced by most people frequently; some 70% of the population experience one or more of them on any given day. Individuals can vary in their response to toxic insult because of age, health status, previous exposure or genetic differences. In addition, it can be difficult to disentangle the physical, psychological and emotional components of well-being, and ther
  
  e is no doubt that different people may respond in different ways on different occasions.
  
  Symptoms reported by some crew members who have been exposed to fumes in the cabin are similar to those seen in chronic hyperventilation.
• Bagshaw, Michael, DeVoll, James R., Jennings, Richard T., McCrary, Brian F., Northrup, Susan E., Rayman, Russel B. (Chair), Saenger, Arleen, Thibeault, Claude, MEDICAL GUIDELINES FOR AIRLINE PASSENGERS [PDF] Aerospace Medical Association, Alexandria VA (2002), retrieved 2018/08/14, original source https://www.asma.org/asma/media/asma/Travel-Publications/paxguidelines.pdf
  
  Excerpt: In general, these studies have consistently revealed levels of organic substances, carbon monoxide, carbon dioxide, and airborne particles in the cabin air well below regulatory standards and below those encountered in offices, the
  street, or subway.
• Bagshaw, Michael (July 2013). "Cabin Air Quality: A review of current aviation medical understanding" [PDF]. Aerospace Medical Association. Retrieved 2014-09-28.
  Excerpt from Conclusions:
  
  There has been an increase in reported incidents of in-flight smoke/fume events since 1999, with a small number of crew members reporting adverse health effects which they associate with the events.
  
  The source of oil contamination of engine bleed air was identified in early versions of the BAe 146 and the Boeing 757 and suitable modifications were implemented. A range of chronic health effects continue to be reported by some crew members.
• Brown, S. S., T. B. Ryerson, A. G. Wollny, C. A. Brock, R. Peltier, A. P. Sullivan, R. J. Weber et al. "Variability in nocturnal nitrogen oxide processing and its role in regional air quality." Science 311, no. 5757 (2006): 67-70.
• Coggon, David CABIN AIR QUALITY THE COT INVOLVEMENT AND FINDINGS (PDF) 2013). aerotoxic.org.
• Cottrell, Joseph J. "Altitude exposures during aircraft flight flying higher." CHEST Journal 93, no. 1 (1988): 81-84.
• Dechow, M., H. Sohn, and J. Steinhanses. "Concentrations of selected contaminants in cabin air of airbus aircrafts." Chemosphere 35, no. 1 (1997): 21-31.
• FAA, "Airliner Cabin Environment Research", ACER Federal Aviation Administration (US), retrieved 2018/08/14, original source: https://www.faa.gov/data_research/research/med_humanfacs/CER/
  
  The link given above provides links to PDF files of ACER-supported studies of air quality on commercial air flights.
  
  Excerpt:
  
  In 2004, the FAA's Office of Regulation and Certification established a National Center of Excellence (COE) for Airliner Cabin Environment Research, which in 2007 was broadened and renamed to the National Air Transportation COE for Research in the Intermodal Transport Environment (ACERite).
  
  The ACERite COE brought together airliner cabin environment expertise from academic, industry, and government organizations. Over the next decade, the FAA sponsored numerous cabin air environment research projects. Key research included:
  
  1) health and safety effects of the airline cabin environment on passengers and crewmembers,
  
  2) the efficiency and effectiveness of aircraft environmental control systems, and
  
  3) the study of emerging technologies with the potential to eliminate bleed air contaminants and purify aircraft air supplies. Should you have questions or like additional information, please contact the Civil Aerospace Medical Institute.
  
  Commercial air carriers train their flight attendants to recognize common symptoms of distress and to respond to medical emergencies with first - aid, basic resuscitation techniques, and the use of emergency medical oxygen. ... It cannot be overemphasized that these medical kits are only for emergency use and not for routine medical care.
  • Spengler, John D., Jose Vallarino, Eileen McNeely, Hanine Estephan, "In-Flight/Onboard Monitoring: ACER’s Component for ASHRAE 1262, Part 2" [PDF] (2012) Harvard School of Public Health, for National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) Airliner Cabin Environmental Research (ACER) Program, U.S. DOT, U.S. FAA, ACER.
    Excerpt:
    
    Carbon dioxide values ranged from 863 to 2,056 ppm during cruise and were highly correlated (r2 =0.7) with load factors.
    
    While still very much below the 5,000 ppm limit set by FARs (FAA 2011), recent studies show impaired cognitive function at CO2 exposures in the range of 1,000 ppm to 2,500 ppm, raising concerns about possible diminutions of flight crew performance that needs further evaluation.
    ...
    This onboard study of environmental conditions in the passenger cabin of commercial flights, along with evidence on health, irritation and discomfort of exposures to some of the environmental conditions that have emerged since many of the FARs related to cabin air quality were established, suggests that FAA ought to rigorously review the adequacy of current FARs.
  • McNeely, Eileen, John Spengler, Jean Watson, "Health Effects of Aircraft Cabin Pressure In Older and Vulnerable Passengers" [PDF] (2011), Harvard School of Public Health, Office of Aerospace Medicine, FAA, for Airliner Cabin Environment Research (ACER) Program National Air Transportation Center of Excellence for Research in the Intermodal Transport Environment (RITE) - Retrieved 2018/08/14, original source: https://www.faa.gov/data_research/research/med_humanfacs/cer/media/HealthEffectsVulnerablePassengers.pdf
    
    Excerpt from Conclusions:
    This study is the first single-blind investigation we know to include a broad accounting of physiological effects of cabin pressure in older and susceptible passengers. The results suggest that a significant portion of older passengers may be moderately hypoxic (≤ 90% oxygen saturation) at 7,000 feet equivalent cabin pressures, pressures still slightly above the regulated limit to 8,000 feet.
  • Overfelt, R.A. et als, "Sensors and Prognostics to Mitigate Bleed Air Contamination Events 2012 Progress Report" [PDF] (2012), sponsors as cited previously, retrieved 2018/08/14, original source: https://www.faa.gov/data_research/research/med_humanfacs/cer/media/SensorsPrognostics.pdf
• Federal Air Regulation (FAR). 1996. Title 14 Code of Federal Regulations, Chapter I– Federal Aviation Administration, Department of Transportation, Part 25–Airworthiness Standards: Transport Category Airplanes, Section 831: Ventilation, as amended June 5, 1996.
• Gavine, Adam, "'Care Pathway' for aerotoxic syndrome created in the UK", Aircraft Safety, 31 August 2017, retrieved 2018/08/16, original source: https://www.aircraftinteriorsinternational.com/news/safety/care-pathway-for-aerotoxic-syndrome-created-in-the-uk-2.html
  Excerpt:
  August 31, 2017 – With ‘aerotoxic syndrome’ being a talking point in the aerospace industry today (indeed it is the cover story of our September 2017 issue), the British Airline Pilots’ Association (BALPA) has worked with clinical toxicologists to create a ‘care pathway’ for patients exhibiting possible cabin fume-related symptoms, which could include itching or soreness of the eyes, nasal discharge, sore throat or coughing.
  
  BALPA has been liaising with Guy’s and St. Thomas’ NHS Foundation Trust, the Royal College of General Practitioners, the Civil Aviation Authority, easyJet and academia for the initiative.
• Hale MA, Al-Seffar JA (September 2009). "Preliminary report on aerotoxic syndrome (AS) and the need for diagnostic neurophysiological tests". Am J Electroneurodiagnostic Technol. 49 (3): 260–79. PMID 19891417.
• Harding, Richard. "Cabin air quality in aircraft." BMJ: British Medical Journal 308, no. 6926 (1994): 427.
• Hocking MB. 2002. Passenger aircraft cabin air quality: trends, effects, societal costs,proposals. Chemosphere . Vol. 41(4), pp 603-15.
  Abstract:
  
  The small air space available per person in a fully occupied aircraft passenger cabin accentuates the human bioeffluent factor in the maintenance of air quality. The accumulation of carbon dioxide and other contributions to poor air quality that can occur with inadequate ventilation, even under normal circumstances, is related to the volume of available air space per person and various ventilation rates.
  
  This information is compared with established air quality guidelines to make specific recommendations with reference to aircraft passenger cabins under both normal and abnormal operating conditions.
  
  The effects of respiration on the air quality of any enclosed space from the respiration of a resting adult are estimated using standard equations. Results are given for different volumes of space per person, for zero air exchange, and for various air change rates. The required ventilation rates estimated in this way compared closely with results calculated using a standard empirical formula.
  
  The results confirm that the outside air ventilation required to achieve a target carbon dioxide concentration in the air of an occupied enclosed space remains the same regardless of the volume of that space. The outside air ventilation capability of older and more recent aircraft is then reviewed and compared with the actual measurements of cabin air quality for these periods. The correlation between calculated and measured aircraft cabin carbon dioxide concentrations from other studies was very good.
  
  Respiratory benefits and costs of returning to the 30% higher outside air ventilation rates and 8% higher cabin pressures of the 1960s and 1970s are outlined. Consideration is given to the occasional occurrence of certain types of aircraft malfunction that can introduce more serious contaminants to the aircraft cabin.
  
  Recommendations and suggestions for aircraft builders and operators are made that will help improve aircraft cabin air quality and the partial pressure of oxygen that is available to passengers at minimal cost. Also suggested are some measures that passengers can take to help improve their comfort and decrease their risk of illness, particularly on long-haul flights.
• Hocking, Martin B. "Trends in cabin air quality of commercial aircraft: industry and passenger perspectives." Reviews on environmental health 17, no. 1 (2002): 1-50.
  Note: this appears to be essentially the same article as the Chemosphere version cited above - Ed.
• Hocking, Martin B. "Passenger aircraft cabin air quality: trends, effects, societal costs, proposals." Chemosphere 41, no. 4 (2000): 603-615.
• Hocking, M. B. "Indoor air quality: recommendations relevant to aircraft passenger cabins." American Industrial Hygiene Association 59, no. 7 (1998): 446-454.
• Hodgson, Michael. "Low relative humidity and aircraft cabin air quality." Indoor Air 11, no. 3 (2001): 200-214.
• Hunt, Elwood H., and David R. Space. "The airplane cabin environment, Issues Pertaining to Flight Attendant Comfort." [PDF] TSP 3, no. 2 (1994): 1-000.
  Excerpt from Conclusions:
  The symptoms experienced by flight attendants, such as fatigue, headaches, tiredness, nausea and illness—often attributed to cabin air quality—are more likely due to an interaction of factors that include cabin altitude, flight duration, jet lag, turbulence, noise, work levels, dehydration, an individual’s health and stress.
  
  Efforts to improve the working environment of flight attendants must be focused on these factors. As many recent air quality studies have shown, the cabin is a healthful environment, meeting all applicable safety and health regulations and standards.
  
  However, the cabin also is a unique environment. As average flight durations continue to increase, the combined effects of jet lag, low cabin humidity, cabin altitude, workload and other environmental stressors will continue to be compounding factors on the general comfort of flight attendants.
• James JT. Carbon dioxide. In: National Research Council, Spacecraft Maximum Allowable Concentrations for Selected Airborne Contaminants, Vol 5. Washington, DC: National Academy Press;2008:112-124.
• James JT. The headache of carbon dioxide exposures. Society of Automotive Engineers. Paper No. 07ICES-42, 2007.
• Law, Jennifer, Sharmi Watkins, and David Alexander. IN-FLIGHT CARBON DIOXIDE EXPOSURES AND RELATED SYMPTOMS: ASSOCIATION, SUSCEPTIBILITY, AND OPERATIONAL IMPLICATIONS. [PDF] NASA Technical Paper 216126 (2010).
  
  Abstract: The effects of ambient carbon dioxide and exposure limits have been well studied on Earth.
  
  However, informal crew reports on the International Space Station have suggested that astronauts are developing CO2-related symptoms such as headache and lethargy at lower than expected CO2 levels and that symptoms tend to resolve when CO2 level is decreased.
  
  In-flight data to date support an association between elevated ppCO2 and CO2-related symptoms, but more research is needed to conclude causality.
  
  What appears to be increased CO2 sensitivity in microgravity may be attributable to individual predisposition to CO2 retention, adaptation to microgravity, and local fluctuations in CO2 that are not measured by fixed sensors.
  
  A review of the current occupational exposure limits supports lowering of the permissible exposure limit for the ISS and beyond, although evidence-based limits for space flight have yet to be defined.
  
  Introduction Excerpts:
  
  Carbon dioxide is a natural product of metabolism. Each person exhales about 200 mL of CO2 per minute at rest and may produce over 4.0 L/min at maximal exercise (Williams 2009). Left unchecked, CO2 can accumulate quickly inside a closed environment. Other sources of CO2 include combustion, decay of organic matter, and fire suppression systems.
  
  On Earth, the ambient CO2 concentration is about 0.03% by volume (0.23 mm Hg).
  
  In spacecraft, it is not practical to control CO2 to such low levels. ... CO2 concentrations in spacecraft are typically about 0.5±0.2% (3.8±1.5 mm Hg, or 2.3 to 5.3 mm Hg), with large fluctuations occurring over hours to days (James 2007).
  
  The highest ppCO2 recorded in a U.S. spacecraft was 14.9 mm Hg on Apollo 13 (Michel 1975).
• Lee, Shun‐Cheng, Chi‐Sun Poon, Xiang‐Dong Li, and Fred Luk. "Indoor air quality investigation on commercial aircraft." [PDF] Indoor Air 9, no. 3 (1999): 180-187.
  Abstract:
  Abstract Sixteen flights had been investigated for indoor air quality (IAQ) on Cathay Pacific aircraft from June 1996 to August 1997.
  
  In general, the air quality on Cathay Pacific aircraft was within relevant air quality standards because the average age of aircraft was less than 2 years.
  
  Carbon dioxide (CO2) levels on all flights measured were below the Federal Aviation Administration (FAA) standard (30,000 ppm). The CO2 level was substantially higher during boarding and de-boarding than cruise due to low fresh air supply.
  
  Humidity on the aircraft was low, especially for long-haul flights. Minimum humidity during cruise was below the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) minimum humidity standard (20%). The average temperature was within a comfortable temperature range of 23∫2æC.
  
  The vertical temperature profile on aircraft was uniform and below the International Standard Organization (ISO) standard. Carbon monoxide levels were below the FAA standard (50 ppm). Trace amount of ozone detected ranged from undetectable to 90 ppb, which was below the FAA standard.
  
  Particulate level was low for most non-smoking flights, but peaks were observed during boarding and de-boarding. The average particulate level in smoking flights (138 mg/m3 ) was higher than non-smoking flights (7.6 mg/m3 ). The impact on IAQ by switching from low-mode to high-mode ventilation showed a reduction in CO2 levels, temperature, and relative humidity
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• Nagda NL, Rector HE, Zhidong L et al. 2000. Aircraft cabin air qua lity: A critical review of past studies. In Air Quality and Comfort in Airline Cabins , ASTM STP 1393, NL Nagda, ed. West Conshohocken PA: American So ciety of Testing Materials, pp 215-235.
• Nagda, Niren L., Harry E. Rector, Zhidong Li, and David R. Space. "Aircraft cabin air quality- A critical review of past monitoring studies." Air quality and comfort in airliner cabins (1999): 215-239.
• Nagda, Niren L., Michael D. Koontz, Arnold G. Konheim, and S. Katharine Hammond. "Measurement of cabin air quality aboard commercial airliners." Atmospheric Environment. Part A. General Topics 26, no. 12 (1992): 2203-2210.
• Nagda NL, Fortmann RC, Koontz MD, et al. 1989. Airliner Cabin Environment: Contaminant Measurements, Health Risks, and Mitigation Options . US Department of Transportation, Report No. DOT-P-15-89-5. Washington, DC: Govt Printing Office.
• National Research Council (U.S.), Committee on Air Quality in Passenger Cabins of Commercial Aircraft (6 December 2001). The Airliner Cabin Environment and the Health of Passengers and Crew. National Academies Press. p. 5. ISBN 0-309-08289-7.
• National Research Council (U.S.), Committee on Air Quality in Passenger Cabins of Commercial Aircraft (6 December 2001). The Airliner Cabin Environment and the Health of Passengers and Crew. National Academies Press. pp. 182–213. ISBN 0-309-08289-7.
• NCBI, The Airliner Cabin Environment and the Health of Passengers and Crew. 7 Air-Quality Measurement Techniques and Applications [PDF] National Center for Biotechnology Information, U.S. National Library of Medicine, 8600 Rockville Pike, Bethesda MD, 20894 USA (2002) retrieved 2018/08/14, original source: https://www.ncbi.nlm.nih.gov/books/NBK207475/
  Conclusions:
  
  Current air-quality measurement practices on commercial aircraft include only indicators of temperature and pressure. These practices are insufficient to determine all cases when the ECS is not working properly or when air-quality incidents occur, and they do not allow evaluation of the possible link between exposures and health effects.
  
  Although continuous air monitoring has not been implemented, it is technically feasible for a number of air-quality characteristics on commercial aircraft, including temperature, barometric pressure, O3, CO, CO2, relative humidity, and fine PM.
  
  Collecting filter samples of suspended PM that could be archived for analysis is also feasible.
  
  Although air-quality monitoring techniques for additional agents, such as pesticides, are available, their applicability to aircraft may require further research and development.
• NIOSH. 1998. Methods 500, 600, 1400, 1500, 1501, 2539, 2549, 2551. In NIOSH Manual of Analytical Methods (NMAM) , 4 th ed, Eller PM, Cassinelli ME, eds. Cincinnati OH, DHHS Publication 98-119.
• Pierce WM, Janczewski JN, Roethlisberger B, et al. 1999. Air quality on commercial aircraft. ASHRAE Journal . Vol. 41, pp 26-34.
• Proussaloglou, Kimon, and Frank S. Koppelman. "The choice of air carrier, flight, and fare class." Journal of Air Transport Management 5, no. 4 (1999): 193-201.
  [Do air travel passengers consider aircraft cabin air quality when choosing an airline?]
• Rankin WL, Space DR, and Nagda NL. 2000. Pa ssenger comfort and the effect of air quality. In Air Quality and Comfort in Airline Cabins , ASTM STP 1393, NL Nagda, ed. West Conshohocken PA: American Society of Testing Materials, pp 269-289.
• Rayman, Russell B. "Cabin air quality: an overview." Aviation, space, and environmental medicine 73, no. 3 (2002): 211-215.
• Ryan, P. Barry, John D. Spengler, and Paul F. Halfpenny. "Sequential box models for indoor air quality: Application to airliner cabin air quality." Atmospheric Environment (1967) 22, no. 6 (1988): 1031-1038.
• Spengler, J. D., and D. G. Wilson. "Air quality in aircraft." Proceedings of the Institution of Mechanical Engineers, Part E: Journal of Process Mechanical Engineering 217, no. 4 (2003): 323-335.
• Spengler J, Burge H, Dumyahn T, et al. 1997. Environmental Survey on Aircraft and Ground-based Commercial Transportation Vehicles. Report of May 31, 1997, Boston MA, Harvard School of Public Health.
• Thibeault, C. L. A. U. D. E. "Cabin air quality." Aviation Space and Environmental Medicine 68 (1997): 80-82.
  Abstract:
  
  Cabin Air Quality has generated considerable public and workers' concern and controversy in the last few years. To clarify the situation, AsMA requested the Passenger Health Subcommittee of the Air Transport Medicine Committee to review the situation and prepare a position statement.
  
  After identifying the various sources of confusion, we review the scientifically accepted facts in the different elements involved in Cabin Air Quality: pressurization, ventilation, contaminants, humidity and temperature. At the same time, we identify areas that need more research and make recommendations accordingly
• US NRC, The Airliner Cabin Environment: Air Quality and safety. National Academic Press United States National Research Council (1986). ISBN 0-309-03690-9.
• Wang, Jun, and Sundar A. Christopher. "Intercomparison between satellite‐derived aerosol optical thickness and PM2. 5 mass: Implications for air quality studies." Geophysical research letters 30, no. 21 (2003).
• Waters, M. A., T. F. Bloom, B. Grajewski, and J. Deddens. "Measurements of indoor air quality on commercial transport aircraft" [PDF] In Indoor air 2002: proceedings of the 9th international conference on indoor air quality and climate, Santa Cruz, California, pp. 782-787. 2002. Abstract:
  
  Exposures to cabin environmental contaminants were measured on 36 commercial transport aircraft. The objectives were to characteri ze levels of contaminants and evaluate the relationship between flig ht factors such as aircraft size , occupancy, ventilation, and flight length, and environmental parameters. Monito ring was conducted at two coach locations for the duration of the flight for VOCs, nitrogen oxides, CO, CO2 , O3 , temperature, relative humidity, total particulates, and barometric pressure.
  
  Five-minute average concentration ranges were: CO 2 515-4902 ppm; O 3 <0.05-0.24 ppm; CO <0.2- 2.9 ppm; nitrogen oxides <0.05-2.0 ppm; and total pa rticulates <0.028-0.197 mg/m 3 . Gate-to-gate average concentrations of VOCs we re: toluene <3-130 ppb, limonene <3-12 ppb, and ethanol <0.8-2.4 ppb.
  
  Carbon dioxide exposures were highest on shorter and high-occupancy flights, aircraft with greater recirculated-to-fresh-air ratio, and narrow-bodied aircraft. In general contaminant levels were low compared to standards. Carbon dioxide levels indicated lower ventilation rates per occupant than most other indoor environments.
• Zhang, Yuanhui, Yigang Sun, Aijun Wang, Jennifer L. Topmiller, James S. Bennett, and RW BESANT. "Experimental characterization of airflows in aircraft cabins, Part II: Results and research recommendations. Discussion." ASHRAE transactions (2005): 53-59.
• Zitter, Jessica Nutik, Peter D. Mazonson, Dave P. Miller, Stephen B. Hulley, and John R. Balmes. "Aircraft cabin air recirculation and symptoms of the common cold." Jama 288, no. 4 (2002): 483-486.

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On 2020-05-30 - by (mod) -

Thanks for the comment, FG.

Just to be clear: We measured CO2 not O2 - i.e. we measured Carbon Dioxide levels, we did NOT measure Oxygen levels in this test. Please take another look at the data tables above.

On 2020-05-30 by FG

There must be something wrong with your data because with 11% oxygen against a normal 25% every body would have died on your flight.

On 2018-08-14 - by (mod) -

IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-08-14 - by (mod) -

Similarly here is an example of cabin pressure control
IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-08-14 - by (mod) -

PS: the same pilot briefing slides given in the link I cited, include further details including a cockpit readout of the air BLEED system display that shows its status.

Here is a description of the system from p. 161 of that briefing
IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-08-14 - by (mod) -

Thank you for the comment, Carl.

I cannot speak with authority about aircraft design, disasters, nor the specific Flight 370 disappearance.

I agree that the disappearance of Malaysia Airlines Flight 370 on 8 March 2014 is widely recognized as mysterious; the flight appeared to continue (on radar) for an hour after last voice contact with the pilots.

I am not an expert on the operation of air quality equipment on aircraft to offer an authoritative opinion in reply to your speculation, but in my lay opinion it seems to me that for hypoxia or a similar event to incapacitate the pilots, both pilots would succumb to low oxygen or high CO2 at the same time. While that seems unlikely in general, it appears to have happened as I will cite below.

I infer therefore that for loss of cabin pressure or adequate oxygen and CO2 level maintenance to explain what happened to Malaysia Airlines Flight 370 a double fault would have to have occurred: a failure of the air recirculating system and a failure of any alarm system present in the cockpit.

My understanding is that commercial aircraft maintain and monitor cabin pressure but do not monitor oxygen and CO2 levels nor other IAQ indicators. In normal operation the aircraft's air conditioning system mixes outside air in with cabin air such that cabin air is being constantly refreshed. Yet as numerous studies report and our own measurements show that depending on the pressure being maintained in the cabin the air quality and its effects on passengers and crew can be significant.

Just what air quality and air safety alarms are standard parts of commercial aircraft is not yet clear to us lay people. That's a question I invite you to investigate and to report back here.

According to NASA Spinoff,

"Typical cruising altitudes for business and commercial aircraft are up to 50,000 feet or more. At such altitudes, the oxygen concentrations in the air are much lower than on the ground. Occupants could not survive in this environment without pressure inside the aircraft being controlled to maintain oxygen concentrations consistent with those at lower altitudes.

One startling tragedy that illustrated the importance of cabin-pressure regulation took place in 1999 when a Learjet was flying golf champion Payne Stewart from Orlando to Dallas. Six minutes after the Learjet pilots reported that all was well, the aircraft ceased communication with the air traffic controllers. Military aircraft in the vicinity were able to view the aircraft but reported that frost or condensation obscured most of the windshield and no movement could be seen inside the jet. Eventually, the plane ran out of fuel and crashed. There were no survivors.

"When the National Transportation Safety Board investigated the accident, it found that the plane had experienced a loss of cabin pressure, and all onboard were incapacitated due to hypoxia, an insufficient supply of oxygen to the body’s tissues and organs.

"If sudden cabin depressurization occurs in an aircraft like a Learjet flying at 40,000 feet, the pilots and passengers may initially experience a brief euphoria and then have as little as 5 to 12 seconds of useful consciousness to don their oxygen masks. Following this brief period, without supplemental oxygen, their cognitive and motor skills diminish, leading to incapacitation, often with fatal consequences.

"However, Stacy Pappas, founder and owner of Aviation Technology Inc. (AV Tech), based in San Diego, says an instance of depressurization is rarely so sudden or dramatic, making it all the more dangerous.

“Assuming that the cabin-pressure warning system installed on the aircraft is working properly, a warning light, and in some cases a warning tone, in the cockpit alerts crewmembers that their cabin pressurization is approaching a dangerous level,” Pappas says.

Usually, the pressurization system either has failed or was not turned on in the first place.

“When you combine a subtle malfunction with a failure of the aircraft warning system, which was likely the case in the Stewart accident, the crew becomes slowly incapacitated without any awareness of the situation,” says Pappas. - source: Cabin Pressure Monitors Notify Pilots to Save Lives, - retrieved 2018/08/14, original source: spinoff.nasa.gov/Spinoff2015/t_4.html

At AIRBUS A319/A320/A321 FLIGHT DECK and SYSTEMS BRIEFING for PILOTS (1998) we found this illustration explaining the environmental control system of a typical modern commercial aircraft - you can see that outdoor air is continually mixing. -original source: - https://www.slideshare.net/FernandoNobre1/a319-320-321-flight-deck-and-systems-briefing-for-pilots

This presentation contains 223 slides and as of 29 April 2021 was still available at the link given above. - Ed.

IMAGE LOST by older version of Clark Van Oyen’s Comments Box code - now fixed. Please re-post the image if you can. Sorry. Mod.

On 2018-08-14 by Carl Alexander

I found this article intriguing, after previous reading re: carbon dioxide informed me that it can cause loss of consciousness/death in higher does >even when there is adequate amounts of oxygen present.

i am wondering if there is any way that the malaysia airlines flight which vanished in 2014 could have had some sort of failure with its re-circulation system, eventually causing its loss with all on board?

...

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