Air Quality

Aircraft Air Quality – Protecting Against Contaminates

See also: Friends Don’t Let Friends Breathe Oil Fumes

What is the Problem?

The Association of Flight Attendants-CWA has received reports from our flight attendant members, pilots and the traveling public related to health problems that they attribute to breathing poor quality air in the aircraft cabin. Maybe the air doesn’t have enough oxygen and maybe it is contaminated with oil, cleaning products, de-icing fluid, oil, or pesticides. Exposure to viruses (like the common cold) and bacteria (like tuberculosis) are also reported.

Basically, there can be four major types of problems with the air quality in the aircraft cabin:

  • not enough oxygen;
  • not enough outside air to dilute whatever is in the cabin air;
  • a contaminated air supply; and
  • exposure to high concentrations of pesticides on selected routes.

Here’s a quick course on the first three. Information on pesticides and more details on all these hazards is posted on our web site (, under “health”).

Problem 1: Not enough oxygen?

The aircraft cabin must be pressurized because there is not enough oxygen in the air above 25,000 feet for you to survive for more than a minute or two. It is important to remember that the amount of oxygen in the air is pretty much independent of the ventilation rate, namely, how many air packs are operating or on what setting. The amount of oxygen available to your body will depend on the altitude to which the cabin is pressurized. For example, the aircraft might be flying at 40,000 feet but the cabin may be pressurized to 8000 feet.

Aircraft cabins are not always pressurized to 8000 feet – that is the highest allowable. If a pilot is flying at a lower altitude, then the cabin will likely be pressurized to a lower altitude as well. Flying at a lower altitude likely means that you get more oxygen but it also means that the aircraft uses more fuel.

When it comes to oxygen, you might be told all about partial pressures and percentages, but the bottom line is this: all other things being equal, there is less oxygen in the air when the cabin is pressurized to 8000 feet (for example) than on the ground – about three-quarters as much (74%).

If your body is in good working order, you should use that smaller supply of oxygen more efficiently than you would on the ground. For example, a group of rated airline pilots whose blood absorbed about 97% (95-99%) of the maximum possible oxygen on the ground, absorbed about 89% (80-91%) at altitude. Smoking, being overweight, being old(er), not being fit, and taking certain medications will mean that your body will use that smaller amount of oxygen less efficiently.

There are mixed reviews as to whether or not the amount of oxygen you get when the cabin is pressurized to 8000 feet is enough. The Federal Aviation Administration (FAA) set a rule in 1957 that the airlines cannot pressurize the cabin to an altitude higher than 8000 feet. At the time, they did not explain their reasons for choosing 8000 feet as the limit, and the issue has not been revisited since.

Some articles suggest that the 8000-foot limit was developed for the needs of fit, young soldiers and that a 6000-foot limit would be more appropriate for the rest of us. Still, other people say that aircraft could be safely pressurized to an even higher altitude, meaning less oxygen for you.

It is true that people who live at 8000 feet (like in Buena Vista, Colorado) breathe air with this smaller amount of oxygen all the time, but their bodies have had time to adjust (or “acclimate”). Apparently, it takes the average person about six weeks of living at that altitude to properly adjust. Certainly, all other things being equal, you need more oxygen than the passengers do because you are moving and lifting and pushing and carrying, while they are watching a movie or sipping a drink.

In summary, there is less oxygen in the cabin air at altitude than on the ground. It is not clear if this reduced amount of oxygen is appropriate for people with certain physical conditions.

Problem 2: Not enough outside air.

The air inside the aircraft can be contaminated from a variety of sources. Maybe some deicing fluid vapors leaked into the cabin before take off, or the cabin wasn’t ventilated for long enough after pesticides were applied. Upholstery and carpet can emit low-level gases, and can be contaminated with allergens from pet hair that people bring in on their clothes. Damp insulation behind the walls can be a breeding ground for mold, and the insides of the ventilation ducts can be coated with oils.

On top of this, you (and everybody else) are a source of “bioeffluents.” For example, when you breathe out, your breath contains all kinds of gases and vapors (such as carbon dioxide, ethanol, and aldehydes). Water droplets in your breath (or in a sneeze or cough) can transport bacteria or viruses into the air. Meanwhile, you are busy shedding skin particles (that also serve to transport bacteria and viruses) and your digestive system is busy generating gases.

Typically, half of the air in the passenger cabin is recirculated. You might be told that if that recirculated air is first passed through a high-efficiency filter, then it will be clean. You might also hear that by cleaning the recirculated air and reducing the supply of dry outside air, your airline is doing you a favor. After all, you are getting “clean” air that isn’t as dry as usual. This is partly true, but not quite right.

Not all aircraft are equipped with HEPA (high-efficiency particulate air) filters because filters are not required. Also, filters are only effective if they are regularly inspected and changed. There are no such regulations in place.   Keep in mind also that even HEPA filters can only trap solid particles; they don’t remove gases (like carbon monoxide and ozone, for example) from the recirculated air.

Finally, even if the filter is installed properly and changed regularly, you ideally need a ventilation system that is designed so that the flow of the “supply air” will draw contaminants away from your face and towards the filter (“smart air flow”). Also, the outside air needs to be clean, and you need enough of it to dilute or remove contaminants in the cabin air. Some of these contaminants can be a nuisance, but others can be toxic.

It is true is that the outside air at altitude is very dry. The airlines choose not to humidify the air because moisture can cause problems of its own, such as mold growth and ice build-up in the space between the fuselage and the liner panels in the cabin, depending on the temperature. Mold can cause air quality problems and ice can put stress on the aircraft structure and components.

So given all of these contaminants, what about the amount of outside air that is brought into the cabin? Providing an adequate supply of clean, outside air has long been recognized as necessary to maintaining the quality of indoor air and reducing reports of occupant symptoms such as headache and fatigue.

But how much air is enough? You want enough to dilute or remove contaminants. Is there a minimum required air supply to ventilate the passenger cabin? No. The FAA just says that the passenger cabin must be “suitably ventilated” (14 CFR 121.219).

How much air is supplied in the economy section? Probably between 6 and 10 cubic feet per minute of outside air to each person which is about half what is recommended in buildings and transportation vehicles.   We have been told that the cockpit gets between 50 and 100 cubic feet per minute per person of outside air, or sometimes a mix of outside and recirculated air depending on the aircraft type. That is up to 20 times more than in the passenger cabin.

Some people say that an aircraft is a “unique environment”, so you don’t need as much outside air as in other vehicles or office buildings. We agree that the aircraft is “unique” but if anything, you need more air.

  • First, if you don’t feel well on a bus, you can open the window or get off at the next stop.
  • Second, people are more likely to travel on an aircraft when sick than on a bus because it can be expensive or impossible to change a flight.
  • Third, the concentrations of bioeffluents (those gases, vapors, and skin particles that everybody produces) build up more quickly in an aircraft than in a bigger, less-densely populated space like a building. Air quality measurements by an AFA-CWA consultant indicate that you need more ventilation in an aircraft than in an office building or a school to protect against this.

In summary, there is no minimum ventilation standard that applies to the passenger cabin, even though there should be.

Problem 3: Contaminated air supply.

The final problem is that sometimes, the source of the contamination can be the air supply itself.  If your plane is “sitting in traffic” then the auxiliary power unit (APU) or the ground power supply might be sucking in exhaust fumes, including nitrogen dioxide. Also, at altitude, the outside air may contain ozone gas.  The air supply can also be contaminated internally by heated engine oil or hydraulic fluid. This problem is not new – it has been recognized by the airline industry for about 50 years.

How does the outside air get contaminated? Outside air is usually heated and compressed in an engine (either in the APU or the aircraft engines) before it is conditioned, mixed with recirculated air, and then sent to the cabin.

See also: Friends Don’t Let Friends Breathe Oil Fumes

The APU typically sits in the tail of the aircraft. The APU is often used for ventilation and electrical power on the ground, and on many aircraft types, it supplies the cabin with air during take off and ascent when the aircraft engines need all of their compressed air for engine thrust. In some cases, the APU can be used during other phases of flight.

Moving parts in the APU are lubricated with oil and if the system has been overfilled with oil, or if there is a leaky seal or a cracked joint, for example, then the heated oils or the gases that can be generated when the oils are heated, can leak into the air supply. And it’s not just oil within the APU that can contaminate the air supply; the APU inlet can also cause a problem. The inlet is usually located in the belly of the aircraft at the back and it can act just like a vacuum cleaner hose, sucking in whatever it finds nearby. For example, hydraulic fluids, oils, lavatory water, and deicing fluid that spill or spray into the belly from various locations throughout the aircraft will naturally flow towards the back of the aircraft when the aircraft is moving forward. If the APU is operating, those liquids can get sucked into the inlet valve and then mixed into the air that is then supplied to the cabin and flight deck.

During flight, the outside air is compressed in the aircraft engines. Most of that compressed air is used for engine thrust, but a portion of that compressed air is routed to the ventilation systems.

Like the APU, the aircraft engines are full of moving parts that are lubricated with oils – oils that can leak into the air supply. In addition, the air compressors in wing-mounted engines can ingest hydraulic fluids from local hydraulic systems if there is a line break, for example.

Can we prove that this happens? Yes, air supply contamination can be confirmed by aircraft mechanical records and pilot logbook entries. However, airlines need not share these records and they need not monitor the air supply systems or filter the outside air before it is supplied to the cabin and flight deck. Symptoms that crews report are consistent with exposure to the products that contaminate the air supply systems. Airlines are required to report most smoke/fume events to the FAA, but even the FAA has recently acknowledged that the airlines are not reporting many events, as required.

What is in the air? There are two contaminants that raise particular concern: (1) tricresylphosphates (TCPs) used as additives in all aviation engine oils; and (2) carbon monoxide which can be formed when oils and hydraulic fluids are heated to high temperatures. TCPs are neurotoxic which means that they can damage your brain and nerves. Carbon monoxide is an asphyxiant – it reduces your body’s oxygen supply. Remember that you are already getting less oxygen when you are in a pressurized cabin than you would on the ground. Other possible contaminants in aircraft air include nitrous oxides and ozone. Both will irritate your throat and lungs.

You might be told that it isn’t possible to be exposed to TCPs or carbon monoxide. Not true! Scientists have heated two popular engine oils to the temperatures found in an operating aircraft engine and found both TCPs and carbon monoxide in the aerosol/fume that was given off.

So – we know that these contaminants can get into the air supply and we know what those contaminants are. We have reports from hundreds of flight attendants and pilots (in the United States, Australia, Canada, Denmark, France, and the UK, for example) who report symptoms that are consistent with exposure to respiratory irritants, neurotoxins (such as muscle tremors, memory loss) and/or asphyxiants (such as headaches, dizziness, nausea) after exposure to contaminated bleed air.

To sum up:

Problems with aircraft quality include: (1) not enough oxygen; (2) not enough outside air to dilute or flush out contaminants generated inside the cabin; (3) a contaminated air supply; and (4) exposure to insecticides. For information on all of these hazards, visit and view the pull-down menu under “health” on the left side of the page.

You might be told that you have a headache and feel dizzy because you are stressed out, tired, or dehydrated. Even if you are all of the above, don’t forget about the potential problems and health effects associated with cabin air quality. Some symptoms are a nuisance, others are serious.

Reporting Problems:

If you feel that you may be suffering from symptoms due to exposure to airborne chemicals that were supplied to the aircraft cabin via the air supply system, the best thing you can do for yourself is document it. Don’t assume you’ll likely feel better soon so there is no need to report anything. If your health problems persist or return after another incident, the paper trail will be critical. Start by calling your local AFA-CWA safety representative.

If you have symptoms that are visible, have somebody take photos or video as soon as possible. It will help to establish the cause-effect relationship that you want to prove. Symptoms such as stomach cramping, fatigue, muscle pain, and confusion are not visible, but can be documented by a doctor. Video may help. Neurological symptoms may develop during the weeks after an exposure.

It is very important that you see a doctor as soon as possible to document your symptoms. Do not just go home. Get medical attention. It is especially important to have everything documented to protect yourself if your symptoms get worse. We have heard from flight attendants who have seen a doctor for bleed air-related complaints and been sent home with antibiotics. This is unacceptable! If you think that you were exposed to heated oil or hydraulic fluids on board the aircraft, you need to tell your doctor. Tell them when and what symptoms you had during the flight, what symptoms developed after the flight, and what symptoms you have now. Describe the conditions in the cabin. Give them information from the AFA-CWA international website (, under “health”, “air quality”).

Whenever possible, have your doctor perform objective tests to document your condition. For example, if you have respiratory complaints, you might be able to have a lung function test to document any reduced breathing capacity. Nerve conduction velocity tests may be used to confirm nerve damage. If you are dizzy or faint, you may have been exposed to carbon monoxide and a blood oxygen hemoglobin test may be appropriate, although blood must be drawn within a few hours of exposure, and within one hour of exposure if you went on oxygen during the flight. Also, you don’t have to be exposed to carbon monoxide to be exposed to toxic oils or hydraulic fluids.

Note the date, flight number and plane number. Describe the working conditions. Did you notice an odor or visible mist/haze/smoke? Were you aware of any mechanical problems? During what phase of flight did you develop symptoms? Was this the first time?

Keep a copy of everything – every medical record, report, and photo. Keep a record of all phone conversations – names, dates, and a short summary of the conversation. If you have to mail anything, send it by certified mail with a return receipt.

For AFA-CWA members, make sure to file the report with you company immediately.  Also send a copy to your AFA-CWA union representatives.   Reporting to the company is a priority, but to advocate on your behalf, AFA-CWA also needs your information. For more information, contact Judith Anderson at AFA-CWA’s Air Safety, Health & Security Dept. Seattle field office (206-932-6237 or 

Ensuring a Better, Safer, Healthier Aircraft Cabin:

The Association of Flight Attendants-CWA (AFA) is continuing our push for improved air quality in aircraft cabins, both domestically and internationally, to protect both the crew and the passengers.  And we will continue the push until the hazard is eliminated.


Flight Attendant Union Continues to Push for Better Air Quality

AFA Air Safety, Health & Security website

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