The National Academies of Sciences, Engineering and Medicine
Office of Congressional and government Affairs
At A Glance
: Aircraft Cabin Environment
: 06/05/2003
Session: 108th Congress (First Session)
: William R. Nazaroff

Professor, Environmental Engineering, University of California at Berkeley and Member, Committee on Air Quality in Passenger Cabins of Commercial Aircraft, Board on Environmental Studies and Toxicology, Division of Earth and Life Studies, National Research Council, The National Academies

: House
: Committee on Transportation and Infrastructure


Statement of

William W. Nazaroff, Ph.D.

Professor of Environmental Engineering

University of California, Berkeley


Member, Committee on Air Quality in Passenger Cabins of Commercial Aircraft

Board on Environmental Studies and Toxicology

Division on Earth and Life Studies

National Research Council

The National Academies

Before the

Subcommittee on Aviation

Committee on Transportation and Infrastructure

U.S. House of Representatives

June 5, 2003

Good morning, Mr. Chairman and members of the Committee. My name is William Nazaroff. I am a Professor of Environmental Engineering at the University of California, Berkeley and served as a member of the National Research Council (NRC) Committee on Air Quality in Passenger Cabins of Commercial Aircraft. The NRC is the operating arm of the National Academies of Sciences and Engineering.

In 1986, a previous committee of the NRC produced a report requested by Congress entitled The Airliner Cabin Environment: Air Quality and Safety. That report recommended the elimination of smoking on most domestic airline flights and other actions to address health and safety concerns on commercial aircraft and called for efforts to obtain better data on cabin air quality. Subsequently, the Federal Aviation Administration (FAA) took several actions, including a ban on smoking on all domestic flights. However, many other issues regarding cabin air quality were not adequately addressed, and new health questions have since been raised by the public and airline crew members.

In response to these unresolved issues, in 2000, Congress directed the FAA to ask the NRC to perform another study of cabin air quality. The NRC convened a new committee, which produced the 2002 report, The Airliner Cabin Environment and the Health of Passengers and Crew. Specifically the committee was charged to address the following topics:

1. Contaminants of concern, including pathogens and substances used to maintain and operate the aircraft, such as seasonal fuels and deicing fluids.

2. Cabin air supply systems and ways in which contaminants might enter the systems.

3. The toxic effects of the contaminants of concern, their byproducts, and degradation products, and other factors, such as temperature and relative humidity, that might influence health effects.

4. Measurements of the contaminants of concern in the air of passenger cabins during domestic and foreign air transportation and comparison with measurements in public buildings, including airports.

5. Potential approaches to improve cabin air quality, such as an alternative air supply for the aircraft passengers and crew to replace the air supplied through the engines.

The committee did not address the possible effects of ionizing and nonionizing radiation and did not evaluate the potential costs of implementing any of its recommendations.

In its evaluation the committee focused on four aspects of cabin air quality; (1) aircraft systems, (2) exposures on aircraft, (3) health considerations, and (4) air-quality monitoring and health surveillance needs. I will provide background and findings with respect to each of these four issues, and will conclude my remarks with the committee’s overall recommendations for improving cabin air quality.

Aircraft are equipped with environmental control systems (ECS) that are designed to maintain a safe, healthful, and comfortable environment for passengers and crew. The ECS regulates cabin pressure, ventilation, temperature, and humidity control. FAA established design and operational specifications for commercial aircraft as codified in the Federal Aviation Regulations (FARs). There are regulations for levels of ozone (O3), carbon monoxide (CO), carbon dioxide (CO2), ventilation rates, and cabin pressure.

The committee concluded that when the ECS is operated as specified by the manufacturer, it should provide an ample supply of air to pressurize the cabin, meet general comfort conditions, and dilute or otherwise reduce normally occurring odors, heat, and contaminants. The current FAA ventilation design standard of 0.55 pounds of outside air per minute per occupant is less than one-half to two-thirds the ventilation standard recommended by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE) for building environments. The committee did not determine whether the building ventilation standard is appropriate for the aircraft cabin environment.

Contaminant exposures do occur, and can originate outside or inside the aircraft, and in the ECS itself. Exposures can occur under routine operating conditions and under abnormal operating conditions. Contaminant exposures that occur under routine conditions include odors and infectious agents emitted by passengers, O3 that enters with ventilation air during high-altitude cruise, organic compounds emitted from residual cleaning products and other materials in the cabin, and allergens, irritants, and toxicants from other indoor and ambient sources. During abnormal operating conditions, contaminant exposures can result from the intake of chemical contaminants (such as engine lubricating oils, hydraulic fluids, deicing fluids, and their degradation products) into the ECS and thus into the cabin.

During routine operating conditions monitoring data have been collected on only a small number of flights, and studies have varied considerably in sampling strategies, environmental factors monitored, and measurement methods used. There are no published studies that describe quantitative measurements of air quality under abnormal operating conditions.

For routine flying conditions, at cruising altitudes, exposure to O3 is the greatest concern, as studies suggest that O3 concentrations on some flights can exceed the FAA regulatory standards and the Environmental Protection Agency national ambient air quality standards. Pesticide exposures (to d-phenothrin and permethrin) are possible on some aircraft as these pesticides are sprayed on selected international flights to limit the spread of insects. However, no quantitative data are available on passenger or crew exposures to these compounds.

The ECS itself can be a source of contamination because engine oils, hydraulic fluids, or deicing fluids may enter the cabin through the air-supply system from the engines. Many cabin crews and passengers have reported incidents of smoke or odors in the cabin, but no exposure data are available to identify the contaminants and quantify the concentrations in cabin air during these incidents.

With respect to health considerations, the committee concluded that air contaminants can be responsible for some of the numerous complaints of acute and chronic health effects in cabin crew and passengers. However, available health data have not been collected in a standardized, systematic manner. Therefore, establishing a causal relationship between cabin air quality and the health of cabin crew and passengers is extremely difficult.

Among the possible causes of symptoms reported by passengers and cabin crew are the cabin environment itself (including reduced cabin pressure and low relative humidity), contaminants (such as O3, pesticides, biological agents, engine oils, and hydraulic fluids), physiological stressors (such as fatigue, cramped seating, and jet lag), and exacerbation of pre-existing conditions in sensitive groups of people.

The committee reached the following conclusions with respect to exposure conditions and health concerns:

• Reduced cabin pressure may adversely affect health-compromised people, particularly those with cardiopulmonary disease.

• Elevated O3 concentrations have been associated with airway irritation, decreased lung function, exacerbation of asthma, and impairments of the immune system.

• Exposures to allergens (such as cat dander) have been reported to cause health effects, but have not been definitively documented in aircraft.

• Transmission of infectious agents from person to person has been documented in aircraft, but the most important transmission factors appear to be high occupant density and the proximity of passengers. Transmission does not appear to be facilitated by aircraft ventilation systems.

• Low relative humidity might cause some temporary discomfort (e.g., drying eyes, nasal passages, and skin), but other possible short- or long-term effects have not been established.

• Pesticides that are used on some international flights can cause skin irritation and are reported to be neurotoxic, although of low toxicity in humans.

• During abnormal operating conditions, exposure to engine oils, hydraulic fluids, and their degradation products (such as CO and formaldehyde) might occur. No data have definitively linked exposure to these compounds with reported effects in cabin occupants.

Based on the committee’s evaluation and findings on cabin air quality, the committee made the following ten recommendations:

1. FAA should rigorously demonstrate in public reports the adequacy of current and proposed regulations for cabin air quality and should provide quantitative evidence and rationales to support sections of the regulations that establish air-quality-related design and operational standards for aircraft (standards for CO, CO2, O3, ventilation, and cabin pressure). If a specific standard is found to be inadequate to protect public health and ensure the comfort of passengers and crew, FAA should revise it. For ventilation, the committee recommends that an operational standard consistent with the design standard be established.

2. FAA should take effective measures to ensure that the current regulation for O3 is met on all flights, regardless of altitude. These measures should include a requirement that either O3 converters be installed, used, and maintained on all aircraft capable of flying at or above those altitudes, or strict operating limits be set with regard to altitudes and routes for aircraft without converters to ensure that the O3 concentrations are not exceeded in reasonable worst-case scenarios. To ensure compliance with the O3 requirements, FAA should conduct monitoring to verify that the O3 controls are operating properly (see also recommendation 8).

3. FAA should investigate and publicly report on the need for and feasibility of installing air-cleaning equipment for removing particles and vapors from the air supplied by the ECS on all aircraft to prevent or minimize the introduction of contaminants into the passenger cabin during ground operation, normal flight, and under abnormal operating conditions.

4. FAA should require a CO monitor in the air-supply ducts to passenger cabins and establish standard operating procedures for responding to elevated CO concentrations.

5. Prohibition on the transport of small animals in aircraft cabins should be investigated, because of the potential for serious health effects related to exposures of sensitive people to allergens. Cabin crews should be trained to recognize and respond to severe, potentially life-threatening responses (e.g., anaphylaxis, severe asthma attacks) that hypersensitive people might experience.

6. Increased efforts should be made to provide cabin crew, passengers, and health professionals with information on health issues related to air travel. To that end, FAA and the airlines should work with such organizations as the American Medical Association and the Aerospace Medical Association to improve health professionals’ awareness of the need to advise patients on the potential risks of flying, including risks associated with decreased cabin pressure, flying with active infections, increased susceptibility to infection, or hypersensitivity.

7. The committee reiterates a recommendation of the 1986 NRC report that a regulation be established to require that passengers be removed from an aircraft within 30 minutes after a ventilation failure or shutdown on the ground. Furthermore, full ventilation should be maintained whenever on-board or ground-based air conditioning is available.

8. An air-quality and health surveillance program should be established that monitors flights to determine the type and level of contaminants onboard and to document health effects or complaints. The program should be coordinated so that the relationship between health effects or complaints and cabin air quality can be analyzed.

9. A research program should be established to help answer the following high priority questions:

• How is the O3 concentration in the cabin environment affected by various factors (such as ambient concentrations or the presence and effectiveness of catalytic converters), and what is the relationship between cabin O3 concentrations and health effects on cabin occupants?

• What is the effect of cabin pressure altitude on susceptible cabin occupants, including infants, pregnant women, and people with cardiovascular disease?

• Does the ECS provide a sufficient quantity and distribution of outside air to meet the FAA regulatory requirements, and to what extent is cabin ventilation associated with complaints from passengers and cabin crew? Can it be verified that infectious-disease agents are transmitted primarily between people in close proximity? Does recirculation of cabin air increase cabin occupants’ risk of exposure?

• What is the toxicity of the constituents or degradation products of engine lubricating oils, hydraulic fluids, and deicing fluids, and is there a relationship between exposures to them and reported health effects on cabin crew? How are these oils and fluids distributed from the engines into the ECS and throughout the cabin environment?

• What are the levels of exposure to pesticides in aircraft cabins, and what is the relationship between the exposures and reported symptoms?

• What is the contribution of low relative humidity to the perception of dryness, and do other factors cause or contribute to the irritation associated with the dry cabin environment during flight?

10. Finally the committee recommended that Congress designate a lead federal agency and provide sufficient funds to conduct or direct the proposed research program which is aimed at filling major knowledge gaps identified in this report. An independent advisory committee with appropriate scientific, medical, and engineering expertise should be formed to oversee the research program to ensure that its objectives are met and the results publicly disseminated.

Mr. Chairman, that concludes my testimony. Thank you and the members of your committee for the opportunity to participate in this hearing.