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Aircraft cabin CO2 and Oxygen measurements (C) InspectApedia.comIn-Flight Carbon Dioxide CO2 & Oxygen Levels on Commercial Aircraft

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.

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

Airborne debris indoors (C) InspectApedia.com

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)

Aircraft cabin air quality (C) InspectAPedia.com

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.

Airborne debris indoors (C) InspectApedia.com

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.

Oxygen & carbon dioxide sampling results inside a commercial aircraft, in-flight (C) Daniel Friedman

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.

Table of Carbon Dioxide CO2 and Oxygen Levels Measured in Commercial Aircraft Cabins During Flight

Flight / Row / Date Carbon
Dioxide
ppm
Oxygen
%
Sample
Time
[1]
Total
Flight
Time
Altitude Aircraft / Capacity Passen-
gers + crew
% Capac. Comments
UA 1063 / r10 04.07.14[2] 400ppm   1 hr
09:30 A
4 hr 35,000 ft B737-800/900 / 145 144 100% EWR->MEX, est. Cabin Temp 70F,Tube 100/a, 10 pump strokes
400   1 hr
5 min
35,000 ft Control. Cabin air samples collected @ lap height
630   3 hr
12:30 P
35,000 ft 20 pump strokes for precision
 
UA 718 / r8 /
03.09.14
600
750[3]
11.5%
13%
0.00
02:55 P
2 h 40m Ground A320 / 120-150 90 66% MEX->SFO Control, prior to takeoff
600
625[3]
11.2%
12.5%
05:50 P 34,000 ft 66% MEX->SFO
 
NZ 7 / r14 /
03.09.14
600
700[3]
12.8% 16:00 NZT 12 h 32,000 ft
9753 m
B747 400 / 416-524
332 79% SFO->AKL dep , climbing, 20 min. into flight. Total distance 10,618 Km
650
900[3]
12.25% 20:34 NZT 33,999 ft
10,363m
8 hrs from destination, outside temp -42C
600
700[3]
12%
11.75%[3]
01:00 NZT 35,997 ft
10,972m
over PagoPago, outside temp -46C
 
NZ 531 /r10/
05.10.14
                AKL->CCH
 
NZ 548 / r13/
23.10.14
  12%
11.5%[3]
20:40 NZT 1h 5m 35,000 ft
10,668m
A320   100% CCH->AKL
 
NZ 2 / r45/
23.10.14
      11h 25m 30,997 ft
9448m
B777-300 250 + crew 83%

Traveled: 5054 Km
Total distance 10,373 Km
Skycouch
Outside -46C

600
750[3]
12.25%
12.25%[3]
03:53 NZT
07:53 LAT
32,998 ft
10,058m

Over the Equator Lat 0.09S
Long: 154.10W
Outside -38C
Speed 946 KmH

800
1000[3]
12.25%

06:45 NZT
10:45 LAT

35,000 ft 10,668m Lat 17.47N
Long: 1.39.12W Outside -45C
Speed
901 KmH
Traveled:
7819 Km
Remaining
2757 Km
 
UA 274 /r22/
23.10.14
                LA->MEX
 
Further studies pending                  

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:

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

Particle collection cassette on a commercial airline flight in 2000 (C) InspectApedia.comIn 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.

Cassett sampler for airborne particulates on a commercial airline flight in the U.S. in 2000 (C) InspectApedia.com

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

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Reader Comments, Questions & Answers About The Article Above

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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
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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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