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June 14, 2003 9:01 PM
Flight Attendants Demand Protection from Toxic Cabin Air

 Patricia Friend, International President of the Association of Flight Attendants, AFL-CIO, will testify before the House Transportation and Infrastructure committee to expose the health effects of toxic cabin air in the aircraft cabin. 

While the SARS scare has generated heightened interest in cabin air quality, the virus is not the only cause for serious concern with the quality of aircraft air. The heavy use of recirculated air, fumes from heated engine oils and hydraulic fluid and the use of hazardous pesticides in the cabin can lead to serious debilitating illnesses for crew members and passengers.

Many of the health concerns created by aircraft air quality problems could be more easily addressed if flight attendants had OSHA protections. Instead, the Federal Aviation Administration has sole jurisdiction over health and safety in the aircraft cabin, which has resulted in an injury and illness rate (calculated by days away from work data) of 8 percent, more than four times higher than the national average.

More than 50,000 flight attendants at 26 airlines join together to form AFA, the world’s largest flight attendant union. Visit us @ www.afanet.org .

What You Should Know About The Air You Breathe At Work

Aircraft Air Quality And You

Prepared by the Air Safety & Health Dept., Association of Flight Attendants, AFL-CIO, representing more than 50,000 Flight Attendants at 26 different airlines

There is a lot of talk these days about cabin air quality. AFA is actively working on this very issue. To clear the air (and give you some of the facts) we prepared this bulletin. 

What is the problem? 

Our members report 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 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: (1) not enough oxygen; (2) not enough outside air to dilute whatever is in the cabin air; (3) a contaminated air supply; and (4) exposure to high concentrations of pesticides on selected routes, including Australia, New Zealand, and India. Here's a short course on the first three. Information on pesticides is posted on our web site (www.afanet.org/pesticides.asp ). 

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(1). 

Remember that Joe Public is not exactly in the same fitness and weight category as a rated pilot, and that 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 can not 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 super-fit military types(2) and that a 6000-foot limit would be more appropriate for the rest of us(3). 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 ("HEPA" -- generally considered the champagne of filters), 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. 

First of all, 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 depending on the aircraft type. That is up to 20 times more than in the passenger cabin - but how often do you hear pilots complaining about dryness? 

Second, not all aircraft are equipped with these HEPA 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. 

Third, keep in mind 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? Would it help to use all of the air packs and turn them on full? In the late 1980s, the National Institute for Occupational Safety & Health reviewed approximately 500 indoor air quality investigations in buildings and concluded that inadequate ventilation accounted for 52% of the indoor air quality problems. Remember that this is in buildings not aircraft, but it is an example of the important role that ventilation plays in maintaining the quality of indoor air. 

Certainly, the experts on job-related safety and health hazards at the Occupational Safety & Health Administration tell their compliance officers that "extensive air monitoring may not be warranted because inadequate introduction and/or distributions of fresh air may be the main problem"(4). 

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 Federal Aviation Administration 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." 

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 consultant indicate that you need more ventilation in an aircraft than in an office building or a school to protect against this(5). 

In summary, there is no minimum ventilation standard that applies to the passenger cabin, even though contaminant levels can rise more quickly in an aircraft than in a building because an aircraft is a relatively small space. 

Problem 3: Contaminated air supply. 

The final problem is that sometimes, the source of the contamination can be the air supply itself. First, if your plane is "sitting in traffic" then the auxiliary power unit (more on that later) or the ground power supply might be sucking in exhaust fumes, including nitrogen dioxide. Also, at altitude, the outside air may contain ozone gas.

In addition to exhaust and ozone, the air supply can be contaminated internally. This problem is not new - it has been recognized by the airline industry for at least 20 years. 

How do the ventilation systems work? 

Outside air is usually heated and compressed in one of two places before it is conditioned, mixed with recirculated air, and then sent to the cabin. 

One of those places is the auxiliary power unit (APU) which is an engine that is independent of the aircraft engines. In most cases, it sits in the tail of the aircraft. The APU is often used for air supply 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 cockpit. 

The most likely place for the outside air to be compressed is the aircraft engines. Most of the air compressed in the aircraft engines 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. And finally, just like the APU, the air compressors in tail-mounted engines are like a vacuum cleaner hose and can suck in fluids that may have found their way into the belly of the aircraft. 

Can we prove that this happens? 

Leaks and spills of oils and other fluids are reported infrequently but persistently. In some cases, it has been possible for AFA to confirm symptom reports with airline mechanical records that indicated a leakage or a problem in the APU or engines. Airline mechanical records should be freely available to affected flight attendants, but in fact, they are very difficult to access. The best way to prove that a mechanical problem resulted in a contaminated air supply is to monitor the air supply during an incident, but this has been challenging, partly because of the costs involved. 

Even though the airlines are not required to monitor the air supply, the FAA has formally acknowledged that the air supply, at least on certain aircraft types, can get contaminated in this way. On 8 August 2000, they published an Airworthiness Directive that requires certain modifications to the hydraulic lines and related parts in the APUs of certain McDonnell Douglas aircraft types. The directive was "prompted by reports of smoke and odor in the passenger cabin and cockpit due to hydraulic fluid leaking into the APU inlet, and subsequently, into the air conditioning system" (65 FR 48368, August 8, 2000). This is a step in the right direction but will only address a very small piece of the problem. 

What is in the air? 

There are two contaminants that raise particular concern: (1) tricresylphosphates (TCPs) which are used as an additive in some popular engine oils; and (2) carbon monoxide which is a colorless gas that can be formed when you burn oils and hydraulic fluids to high temperatures. TCPs are neurotoxic which means that they can damage your brain and nerves(6). 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(7).

So -- we know that these contaminants can get into the air supply (because the industry and the FAA say so) and we know what at least some of those contaminants are. We also have reports from hundreds of flight attendants (in the United States, Australia, Canada, Denmark, France, Sweden, and the UK, for example) who report symptoms that are consistent with exposure to neurotoxins (such as muscle tremors, memory loss) and/or asphyxiants (such as headaches, dizziness, nausea). Serious stuff. 

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; and (3) a contaminated air supply. For information on pesticides, contact the AFA international office. Also keep in mind that the health effects caused by any combination of these problems has not been properly investigated. 

You might be told that you have a headache and feel dizzy because you are stressed out, tired, dehydrated, or overweight. 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. 

There are solutions...

To keep you informed, here are some of our recommendations for the researchers, the regulators, and the airlines.

First, we recommend that the justification for the FAA cabin altitude limit is reviewed and that oxygen data be collected from members of the flying public and from flight attendants to examine whether a representative range of people are getting enough oxygen at altitude. 

Second, we recommend that the airlines be required to continuously monitor levels of some airborne contaminants during flights. This would help to define what the contaminant levels are, what the ventilation rates are, and what is acceptable. 

Finally, the air supply needs to be clean. Long-term activities should focus on changing the design of the ventilation system to reduce the chances of the air from getting contaminated in the first place. Short-term activities should focus on installing design modifications and ensuring regular mechanical inspection, including parts replacement and maintenance, and monitoring the supply air. If airlines routed their aircraft to maximize ground time at maintenance bases, more frequent checks would be easier to achieve. 

Whatever the problem, get smart: the passenger cabin is your workplace. 

If you have a problem:





Don't just accept a headache after every shift. If you need to, make a stink. 


End notes 

(1) Cottrell, JJ; Lebovitz, BL; Fennell, RG; and Kohn, GM. "Inflight arterial saturation: continuous monitoring by pulse oximetry." Aviation Space & Environmental Medicine, 66: 126-130 (1995). 

(2) McFarland, RA; Edwards, HT. "The effects of prolonged exposures at altitudes of 8,000 to 12,000 feet during trans-Pacific flights." Journal of Aviation Medicine, 8: 156-177 (1937). 

(3) Ernsting, J. The 10th Annual Harry G. Armstrong Lecture: Prevention of hypoxia-acceptable comprimises." Aviation Space & Environmental Medicine, 49: 495-502 (1978). 

(4) OSHA Technical Manual, Section III, Chapter 2: "Indoor Air Quality Investigation." Published by OSHA's Office of Science & Technology. Occupational Safety & Health Administration, Department of Labor, Washington, DC. January 20, 1999. 

(5) Walkinshaw, D. "Investigating the impacts of occupancy density and ventilation on indoor air quality of offices, classrooms, and aircraft." Indoor Air Technologies Inc. (November 2000). 

(6) Casarett & Doul's Toxicology. 5th Ed. Eds: Casarett, LJ; Amdur, MO; Klaassen, CD. McGraw Hill, 1995. 

(7) Van Netten, C. and Leung, V. "Comparison of the constituents of two jet engine lubricating oils and their volatile pyrolytic degradation products." Applied Occupational & Environmental Hygiene Journal, Vol. 15(3): 277-283 (2000). 

Some extra reading 

Hocking, MB. "Passenger aircraft cabin air quality: trends, effects, societal costs, proposals." Chemosphere, 41: 603-615 (2000). 

National Academy of Sciences/National Research Council "The Airliner Cabin Environment. Air Quality and Safety." Committee on Airliner Cabin Air Quality. National Academy Press, Washington, DC (1986). 

Parliament of the Commonwealth of Australia. "Air Safety and Cabin Air Quality in the BAe146 Aircraft." Prepared by the Senate Rural and Regional Affairs and Transport Legislation Committee. Parliament House, Canberra, Australia. Under October 12, see http://www.aph.gov.au/senate/whatsnew.htm (October 2000). 

Seppanen, OA; Fisk, WJ; and Mendell, MJ. "Association of ventilation rates and CO2 concentrations with health and other responses in commercial buildings." Indoor Air, 9: 226-252 (1999). 

Springston, J. Abstract presented at the American Industrial Hygiene Conference & Exhibition, Orlando, FL (May 2000). 

United States Air Force MIL-E-87145 (USAF) "Appendix B. Respiratory Environmental Thresholds and Physiologic Limitations." 


[1] International Programme on Chemical Safety, "The WHO Recommended Classification of Pesticides By Hazard and Guidelines to Classification 2000-2002" WHO/PCS/01.5 

[2] Ray DE (1991) Pesticides derived from plants and other organisms. In Handbook of Pesticide Toxicology, Ed. Hayes WJ & Laws ER. Pub. Academic Press. 585-636.

[3] WHO (1991b) Safe Use of Pesticides. 14th Report of the WHO Expert Committee on Vector Biology and Control, World Health Organization, Geneva.

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