Aircraft Cabin Bleed Air 

Contaminants: A Review

Gregory A. Day

Civil Aerospace Medical Institute

Federal Aviation Administration

Oklahoma City, OK 73125

November 2015

Final Report

DOT/FAA/AM-15/20

Office of Aerospace Medicine

Washington, DC 20591
NOTICE

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of the U.S. Department of Transportation in the interest 

of information exchange. The United States Government 

assumes no liability for the contents thereof.

___________

This publication and all Office of Aerospace Medicine 

technical reports are available in full-text from the 

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i

Technical Report Documentation Page

1. Report No.

DOT/FAA/AM-15/20

2. Government Accession No. 3. Recipient's Catalog No.

4. Title and Subtitle

Aircraft Cabin Bleed Air Contaminants: A Review

5. Report Date

November 2015

6. Performing Organization Code

7. Author(s)

Day GA

8. Performing Organization Report No.

9. Performing Organization Name and Address 10. Work Unit No. (TRAIS)

FAA Civil Aerospace Medical Institute

P.O. Box 25082

Oklahoma City, OK 73125

11. Contract or Grant No.

12. Sponsoring Agency Name and Address

Office of Aerospace Medicine

Federal Aviation Administration

800 Independence Ave., S.W. 

Washington, DC 20591

13. Type of Report and Period Covered

14. Sponsoring Agency Code

15. Supplemental Notes

16. Abstract

The purpose of this paper is to describe potential health-related risks surrounding human exposure to bleed 

air contaminants generated during “fume events” inside pressurized aircraft. Information was obtained from 

available literature primarily in regard to carbon monoxide, carbon dioxide, ozone, volatile and semi-volatile 

organic compounds, and airborne particles.

The quality of air distributed throughout the cockpit and cabin during air transportation in a pressurized 

aircraft is critically important to human health. Since 1984, public law in the United States has directed 

research in cabin air quality, including investigation of health risks among individuals exposed to toxic fumes 

during flight. 

Quantification of the potential health risks associated with exposure to bleed-air contaminants in cabin air 

is not possible without broad identification and measurement of the representative hazardous constituents of 

bleed air during contaminated air events. Such broad identification and measurement does not exist. Included 

in Public Law 112-95 is the directive to “assess bleed air quality on the full range of commercial aircraft 

operating in the United States.” Carrying out such a mandate requires adequate funding to support required 

research.

17. Key Words

Bleed Air, Bleed Air Contaminants, Cabin Air Quality, 

Fumes, Toxic Fumes, Toxic Fume Events

18. Distribution Statement

Document is available to the public

through the Internet:

www.faa.gov/go/oamtechreports

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Unclassified

20. Security Classif. (of this page)

Unclassified

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Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

iii

Contents

Aircraft Cabin Bleed Air Contami

A Revie

Purpose and Background . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

Bleed Air: A Brief Description . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

Fumes and Fume Events . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2

The Role of Filtration . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Potential Health Outcomes Following Exposure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

CO, CO2, and O3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

VOCs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4

Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Research Needs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5

1

Aircraft Cabin Bleed Air Contami

A Revie

PURPOSE AND BACKGROUND 

The purpose of this paper is to describe potential health-related 

risks surrounding human exposure to bleed air contaminants 

generated during “fume events” inside pressurized aircraft. Information was obtained from available literature primarily in regard

to carbon monoxide (CO), carbon dioxide (CO2), ozone (O3), 

volatile and semi-volatile organic compounds (VOCs, SVOCs), 

and airborne particles. Other constituents of contaminated

cabin air include those arising from ground support equipment 

such as auxiliary power units and aircraft emissions. The latter

group of constituents has been estimated using the Emissions 

Dispersion Modeling System (EDMS) (Moss & Sega, 1994) and 

includes hydrocarbons from incomplete combustion, nitrogen 

oxides from oxidation of nitrogen in combustion air, and sulfur 

oxides from jet fuel

The quality of air distributed throughout the cockpit and cabin 

during air transportation in a pressurized aircraft is critically 

important to human health. For more than 30 years, the topic

of cabin air quality has been of concern. Congressional hearings

in 1983 and 1984 revealed that information describing cabin air 

quality was contradictory, which prompted the U.S. Congres

to mandate a study by the National Academy of Sciences (NAS) 

(Public Law 98-466, 1984). The subsequent report concluded

that there was a lack of data for a scientific evaluation of aircraft 

cabin air quality and associated health effects. The report also

laid the groundwork for necessary research by recommending, in 

part, the implementation of a program for systematic measurement of the concentrations of several components of cabin air 

(NRC, 1986). It should be noted that the NAS report contained

a recommendation to ban cigarette smoking on all commercial 

flights; the following year Public Law 100-202 (1987) made it 

unlawful to smoke in the passenger cabin or lavatory on flights 

of two hours or less in duration

In 1989, the Department of Transportation contracted with 

an independent company to collect measurements aboard 92 

randomly selected aircraft that included both smoking (n=69) 

and nonsmoking (n=23) commercial flights (Nagda et al.,

1989). Among the measured components of cabin air were

CO and respirable particles, both of which were considered 

unique components of environmental tobacco smoke. Reported

concentrations of these and other measured components were 

below permissible exposure limits

In 1994, the U.S. Congress mandated that the Federal Aviation Administration (FAA) establish an aircraft cabin air qualit

research program and to contract with the Centers for Disease 

Control and Prevention (CDC) to carry out studies specific to 

cabin air quality (Public Law 103-305, 1994). Thus, the FAA

amended an existing interagency agreement with CDC’s National Institute for Occupational Safety and Health (NIOSH) 

to conduct studies of the chemical, physical, and microbiological aspects of cabin air quality. Previous work by NIOSH to

study cabin air quality had involved a health hazard evaluation 

of toxic gases on three Alaska Airlines MD-80 700 series test 

flights. Among all constituents, NIOSH investigators assessed

concentrations of several parameters including CO, CO2, O3, 

VOCs, nitrogen dioxide, and total particulate mass, concluding 

that the measured concentrations did not reveal evidence of toxic 

exposures (Sussell et al., 1993). With the amended interagenc

agreement in place, NIOSH designed and carried out a study 

to assess exposures to parameters of cabin air quality on 11 of 

the most common aircraft types during 33 separate flights. Measured parameters of airborne constituents included CO, CO

, 

O3, VOCs, and total particulate mass. Similar to the previous

health hazard evaluation, NIOSH investigators concluded that, 

in general, contaminant levels were low compared to existing 

standards (Waters et al., 2002

In 2000, arising from unresolved issues about aircraft cabin 

air quality and health issues raised by passengers and cabin crew, 

Congress directed the FAA to arrange an independent study 

with the NAS (Public Law 106-181, 2000). The study was to

include the “collection of new data, in coordination with the 

FAA, to identify contaminants in the aircraft air and develop 

recommendations for means of reducing such contaminants.”

The resulting NAS report (NRC, 2002) included a review of 

studies performed since the previous NAS report (NRC, 1986)

It is important to note that many of the principal components 

described in the 2002 NAS report were not specific to bleed air 

or “toxic fume” events (e.g., bacteria and fungi). The authors 

the report noted that studies identified had differed considerably 

not only in the methods used for measuring air contaminants 

but also in the types of aircraft, numbers of flights, and methods 

used to select flights for monitoring

In 2003, in response to the 2002 NAS report (NRC, 2002), 

Congress mandated the FAA to: “1) conduct surveillance to 

monitor ozone in the cabin on a representative number of flights 

and aircraft to determine compliance with existing Federal Aviation Regulations for ozone; 2) collect pesticide exposure data to 

determine exposures of passengers and crew; 3) analyze samples 

of residue from aircraft ventilation ducts and filters after air quality incidents to identify the contaminants to which passengers 

and crew were exposed; 4) analyze and study cabin air pressure 

and altitude; and 5) establish an air quality incident reporting 

system” (Public Law 108-196, 2003)

In 2004, the FAA’s Office of Regulation and Certification 

established a National Center of Excellence (COE) for Airliner 

Cabin Environment Research (ACER, 2004), which in 2007 

was broadened and renamed to the National Air Transportation 

COE for Research in the Intermodal Transport Environment 
2

(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. Additionally, the ACERite COE collaborated in a joint study by the U

Air Force, the National Aeronautics and Space Administration, 

and the FAA that was known as Vehicle Integrated Propulsion 

Research (VIPR) Testing (Hunter et al., 2014). VIPR include

the characterization of jet engine emissions during both routine 

and non-routine operations. At the time of this writing, final

reports were not available and, therefore, were not included in 

this review

Most recently, in 2012, Congress directed the FAA to initiate a study of air quality in aircraft cabins to: 1) assess bleed air 

quality on the full range of commercial aircraft operating in the 

United States; 2) identify oil-based contaminants, hydraulic fluid 

toxins, and other air toxins that appear in cabin air and measure 

the quantity and prevalence, or absence, of those toxins through 

a comprehensive sampling program; 3) determine the specific 

amount and duration of toxic fumes present in aircraft cabins 

that constitutes [sic] a health risk to passengers; 4) develop a 

systematic reporting standard for smoke and fume events in 

aircraft cabins; and 5) identify the potential health risks to 

individuals exposed to toxic fumes during flight.” Additionally,

to the extent practicable, the FAA was to “implement a research 

program for the identification or development of appropriate 

and effective air cleaning technology and sensor technology for 

the engine and auxiliary power unit bleed air supplied to the 

passenger cabin and flight deck of a pressurized aircraft” (Public 

Law 112-95, 2012)

Bleed Air: A Brief Description

Air supplied to a pressurized aircraft cockpit and cabin occurs 

via an environmental control system (ECS). Fresh air from outside

the aircraft, known as replacement or make-up air, enters the 

ECS in most large transport category commercial airplanes via 

the aircraft engines. The compressed air is then “bled” through

ports and is cooled before being mixed in a manifold with recirculated air, ultimately becoming distributed throughout the 

cockpit and cabin. Note that the only exception to the bleed

air function is the Boeing 787 airplane, which is equipped with 

a dedicated air inlet. Thus, breathable air inside a pressurized

aircraft cabin is a combination of both make-up and recirculated 

air. Contaminated air events, or “fume events,” may occur inside the aircraft as a result of the interaction between incoming

make-up air and oils or hydraulic fluids from leaking or failed 

seals in the engine compartment; contaminated air events may 

also arise from leaks in or near the auxiliary power unit (APU)

Such events arising from the ECS and/or APU are considered 

non-routine and extremely rare. Factors inside the engine compartment that influence the generation of contaminants include

types and amounts of oil and hydraulic fluids, temperature, and 

humidity. Factors inside the aircraft that influence contaminant

concentrations include the size of the occupied space and the 

number of complete air changes per hour (i.e., the volume o

make-up air versus the volume of exhausted cabin air). The

2002 NAS report (NRC, 2002) did not refer to any published 

studies describing quantitative measurements of air quality 

under non-routine operating conditions, but it did refer to few 

studies in which researchers had collected measurements of air 

contaminants in aircraft cabins under routine conditions. Those

studies, however, included only small numbers of flights that 

varied considerably in the specific contaminants measured, the 

types of measurement methods used, and the sampling strategies

Consequently, well-characterized cabin air quality under both 

non-routine and routine operating conditions was considered 

non-existent

Fumes and Fume Events

The term “fume” is used commonly to describe any noxious gas, 

smoke, or vapor in the atmosphere. In the case of contaminated

air inside an aircraft cockpit/cabin, the term “fume event” has 

been used to refer to a potentially toxic environment created by 

contaminated bleed air. From a scientific perspective, this term

does not adequately describe such an event. Indeed, fumes are

defined as “solid-particle aerosols produced by the condensation of 

vapors or gaseous combustion products”(Hinds, 1999). Another

term to describe such an event, one that includes fumes and any 

additional constituents, would be preferred. One possibility is

the term “aerosol event,” which by definition includes “solid or 

liquid particles in gas”(Hinds, 1999). However, this term would

also be inadequate because it excludes other possible constituents 

including gases (formless fluids), vapors (liquids converted to 

gaseous state by heating), smoke (visible aerosol resulting from 

incomplete combustion), and mist (liquid-particle aerosol formed 

by condensation). The 2002 NAS report (NRC, 2002) referred

to such events as “air quality events” resulting from the “intake 

of potential contaminants, including engine oils and hydraulic fluids, through the environmental control system into the 

cabin.” Importantly, no matter how such an event is described,

contaminated bleed air should be regarded as a heterogeneous 

mixture of many possible constituents, the exposure to which 

may result in a spectrum of adverse health effects (Chaturvedi, 

2011a, 2011b)

It should be noted that recirculated air in an aircraft cabin 

likely also contains a number of anthropogenic constituents 

introduced, in part, by crew and passengers. These contaminants

may include dusts and fibers, as well as a variety of bioaerosols 

such as microorganisms, bacterial cells, fungal spores, pollen 

grains, skin scales, and viruses. However, because bleed air is not

the source from which these contaminates are generated, neither 

they nor the potential health effects resulting from exposure are 

within the scope of this review
3

The Role of Filtration

To reiterate, bleed air is a heterogeneous mixture of constituents that may include gases, vapors, smoke, fumes, and mist, 

each of which is potentially associated with risk of adverse health 

effect following exposure . It is important to note that bleed air 

is cooled but not cleaned (i .e ., filtered) before being mixed with 

recirculated cabin air . Recirculated air, however, is cleaned using 

high-energy particulate air (HEPA) filtration . HEPA filters, by 

definition, are designed to capture particles but not gases and 

vapors, which pass directly through, and collection efficiency is 

established on the basis of particles that pass through the filter 

(i .e ., penetration efficiency) . HEPA filters must be at least 99 .97 

percent efficient at capturing particles measuring 0 .3 micrometers 

(μm) in diameter (Anna, 2011) . Particles with diameters greater 

than 0 .3 μm but less than 10 μm are regarded as respirable 

(Hinds, 1999), and the goal of HEPA filtration is to collect 

particles in this size range from recirculated air . Aerosols collected 

via HEPA filtration include dusts, fibers, bacterial cells, 

fungal spores, and pollen grains . Unless airplanes are equipped 

with a gaseous filtration system (i .e ., activated charcoal 

imbedded into the weave as on the Airbus A350 and Boeing 

787 aircraft), then gases and vapors pass directly through 

HEPA filters .

Potential Health Outcomes Following Exposure

CO, CO2, and O3

Gases contained in contaminated cockpit/cabin air as 

con-stituents of bleed air include CO from engine exhaust and 

CO2 as a product of incomplete combustion . O3, originating 

in the stratosphere (Grewe, 2006), may enter the cockpit/

cabin from outside the aircraft via the ECS . The Federal 

Aviation Regula-tion (FAR) for ventilation states that the 

passenger cabin must be free from harmful or hazardous 

concentrations of gases or vapors; the CO concentration 

should not exceed one part in 20,000 parts of air, equivalent 

to 50 parts per million (ppm); the CO2 concentration during 

flight must not exceed 0 .5 percent by volume (i .e ., 5,000 ppm) 

(CFR, 2015a) . NIOSH recommends a 35 ppm upper limit 

time-weighted average (TWA) concen-tration for CO for up 

to 10 hours and a TWA concentration of 5,000 ppm for 

CO2 (NIOSH, 2007) . Although it has been reported that 

there is no “safe” level of O3 exposure (Bell et al ., 2006), the 

FAR states that the TWA O3 concentration in the cabin 

should not exceed 0 .1 ppm (100 parts per billion [ppb]) for 

any three-hour period when the aircraft is above 27,000 feet, 

and that O3 levels must not exceed 0 .25 ppm or 250 ppb 

when the aircraft is above 32,000 feet (CFR, 2015b) . NIOSH 

(2007) recommended a ceiling exposure concentration of 100 

ppb for O3 that should not be exceeded . 

Although exposure to CO can produce anemic hypoxia 

following exposure to sufficient concentrations (Bloom &

Brandt, 2001), CO concentrations inside an aircraft are

typically below levels associated with adverse health effects 

(Nagda et al ., 2000) . CO concentrations aboard pressurized 

aircraft have been mea-sured to range between <0 .2 and 2 .9 

ppm (Waters et al ., 2002) . Spengler et al . (2012) collected 

measurements from 83 flights and determined that CO 

concentrations were below 1 ppm . 

Exposure to high CO2 concentrations can lead to symptoms 

such as headache, dizziness, and restlessness and ultimately 

lead to asphyxia . Waters et al . (2002) reported CO2

concentrations aboard pressurized aircraft that ranged between 515 and 

4,902 ppm . Spengler et al . (2012) determined the average CO2

concentration during 83 flights ranged between 863 and 2,056 

ppm, with an average concentration of 1,404 ppm . In contrast 

to the aircraft cabin environment, CO2 is present in ambient 

environments such as office buildings at levels averaging about 

400 ppm (McDermott, 2001) . CO2 is known to be primarily 

generated by people on the aircraft (i .e ., pilots, aircrew, and 

passengers) and, therefore, CO2 concentrations can be used to 

provide an indication of the amount of make-up air provided 

per person (Nagda et al ., 2000) . 

Exposure to O3 may be associated with symptoms ranging 

from irritation to eyes and mucous membranes to chronic respiratory disease (NIOSH, 2007) . Bhangar et al . (2008) reported 

O3 measurements collected on commercial aircraft were highly 

variable; from 68 flights, peak hour O3 measurements ranged 

from 3 to 275 ppb . Spengler et al . (2012) measured O3 on eight 

different airplane models . Among 73 flights, the average O3 concentration was 15 .9 ppb; the highest one-minute measurement 

was 256 ppb; the highest one-hour measurement was 201 ppb; 

and no flight exceeded a TWA concentration of 100 ppb over 

a period of three hours .

It is important to note that O3 reacts with materials in the 

cabin, including seat fabric, carpet, plastic, and clothing to 

emit VOC byproducts (Coleman et al ., 2007) . In controlled 

experiments, the most common VOC emissions detected were 

aldehydes, 6-methyl-5-hepten-2-one, and acetone . Additionally, 

Weschler et al . (2007) observed O3 byproducts emitted from 

surfaces in a simulated aircraft, including emissions from the occupants themselves . These byproducts included acetone, nonanal, 

decanal, 4-oxopentanal (4-OPA), 6-methyl-5-hepten-2-one (6-

MHO), formic acid, and acetic acid . Furthermore, Spengler et 

al . (2012) reported the formation of carbonyls in O3 reactions; 

O3 was also strongly associated with airborne particles . From 

these findings, we must recognize that health risks to aircraft 

occupants may occur from not only exposures to CO, CO2, and 

other bleed air contaminants, but also from exposures to O3 and 

O3-reactive byproducts . 

Additionally, Overfelt et al . (2012) performed controlled studies to identify gaseous emissions from four different thermally 

degraded engine oils . The authors reported analytical results 

indicating that the emissions from oils were complex mixtures 

of CO, CO2, methanol, and water . 
4

VOCs

Vapors contained in contaminated cockpit/cabin air may 

include both volatile and semi-volatile organic compounds 

(VOCs and SVOCs), both of which are chemical compounds 

based on carbon chains or rings that also contain hydrogen with 

or without oxygen, nitrogen, and other elements that represent 

constituents of jet engine oils, hydraulic fluids, and deicing fluids

Simply stated, VOCs are more volatile than SVOCs. VOCs are

characterized by higher vapor pressures than SVOCs that result 

from lower boiling points. Oils from worn seals and/or hydraulic

fluids in the engine compartment may volatilize, producing 

vapors that are subsequently released into the cockpit/cabin 

via bleed ports. Volatilization occurs when these compounds

are converted from a liquid state to a vapor state by the application of heat, the reduction of pressure, or a combination of 

the two processes. Deicing fluids and exhaust from jet engines

may also enter the bleed air supply during ground operations

Health effects resulting from air contaminated with VOCs and 

SVOCs may be associated with symptoms including irritation 

of the eyes and nose, weakness, confusion, euphoria, dizziness, 

and headache. Exposure to higher concentrations could result

in systemic damage (e.g., to liver and kidne

The first NAS report (NRC, 1986) could identify no study 

measuring detectable concentrations of these compounds in 

cabin air. The second NAS report (NRC, 2002) indicated “few

data have been collected on contaminants that might be present 

in engine bleed air under normal operating or upset conditions” 

and “no available exposure data identify the contaminants present in cabin air during an air-quality incident.” Overfelt et al.

(2012) reported that “the specific nature and extent of potential 

decomposition reactions of engine oils and hydraulic fluids are 

largely unknown” and that “the resulting nature and potential 

toxicity of any contaminants in the aircraft cabin from such 

events are highly speculative at the present time.

Among the many possible VOCs and SVOCs representing 

constituents of contaminated bleed air, particular concern has 

been attributed to tricresyl phosphate (TCP; van Netten & 

Leung, 2000), an organophosphate compound that exists as 

a mixture of three isomeric forms: tricresylortho phosphate 

(TOCP), tricresylmeta phosphate (TMCP), and tricresylpara 

phosphate (TPCP). Among these, TOCP is toxic (DHHS,

1978). Both TMCP and TPCP are relatively nontoxic. TC

is an anti-wear additive that represents approximately 3% by 

volume of many commercial jet engine oils; TOCP represents 

only about 0.1% by volume (van Netten & Leung, 2000). Th

recommended upper limit airborne concentration for TOCP, as 

a time-weighted average over up to 10 hours, is 0.1 milligrams

per cubic meter of air (mg/m3) (NIOSH, 2007). Inhalation

exposure to TOCP exceeding this concentration is associated 

with a delayed neurotoxic toxic effect (i.e., several days followin

exposure) manifested by peripheral nervous system abnormalities 

(Eaton & Klaasen, 2001). Additionally, TOCP can affect the

body if it comes in contact with the eyes or skin. Interestingly,

reports indicate that TCP and many other volatile derivatives 

can remain airborne and may be associated with smoke particles 

(van Netten & Leung, 2000, 2001)

To address Public Law 108-196 (2003), ACERite COE 

researchers developed methodologies to analyze residue on 

HEPA filters that were collected from 1) non-incident aircraft, 

2) simulated laboratory experiments, and 3) incident or suspected incident aircraft (Chen, et al., 2010). By analyzing o

samples, the researchers were able to identify a fingerprint of oil

contamination. Ultimately, they used TCP and its isomers in the

correct ratios along with the presence of synthetic hydrocarbons 

as indicative of oil contamination on the analyzed filters and,

thus, in cabin air. They pointed out that such analysis could no

be used as single, definitive evidence of oil-contaminated air;

however, the methods could be used to identify the source of

contamination for aircraft associated with known or suspected

contaminated air incidents

Spengler et al. (2012) measured 64 VOCs in aircraft cabins

during 83 flights and 18 SVOCs on 63 flights. As percentages of

all VOC samples, 91% contained toluene, 90% contained carbon 

tetrachloride and tetrachloroethene, 75% contained m- and pxylene, and 50 to 75% contained benzene, ethylbenzene, o-xylene, 

methylene chloride, hexane, and styrene. The TCP isomer, TMCP,

was detected in only one sample at a concentration of 1 part per 

trillion. We should emphasize that these samples were collected

in one location inside aircraft cabins under routine operating 

conditions. Therefore, the measured constituents were not directly associated with either bleed air or non-routine operating

conditions. The authors reported that the majority of the VOC

concentrations measured in aircraft cabins had median values 

that were similar to or lower than VOC concentrations reported 

in “non-compliant” office buildings. Concentrations of specific

compounds, including carbon tetrachloride, tetrachloroethene, 

benzene, toluene, ethylbenzene, o-xylene, 1,3-budadiene, and 

styrene, on some flights were substantially higher than concentrations expected in offices and homes

Particles

The measurement of airborne particles within an environment 

can provide information on either mass or number concentration, but without subsequent analyses these measurements 

cannot distinguish among constituents comprising the particles

Exposure to particles may result in a variety of adverse health 

effects that range from irritation of eyes, nose, and throat to 

respiratory and other system disorders. Smoke, a visible aerosol

resulting from incomplete combustion, consists of a range of 

particle sizes. Smoke may include ultrafine particles (UFPs), the

diameters of which measure less than 0.1 μm (WHO, 2006), as

well as respirable particles with diameters ranging from 0.3 μm

to 10 μm (Hinds, 1999). Air sampling research has not been

performed aboard aircraft during a smoke event

Spengler et al. (2012) measured airborne UFPs, which the

authors defined as particles measuring in diameter from 6 

nanometers to 0.3 μm, aboard 55 flights under routine operating conditions. Concentrations were reported as 15-minut
5

average numbers of particles per cubic centimeter of air (p/

cm3

). Maximum concentrations from all flights ranged from 1

to 312,000 p/cm3. Particle concentrations from 500 to 10,000

p/cm3 indicated minor events, and concentrations greater than 

10,000 p/cm3

 indicated major events. Both types of events were

associated with elevated O3 concentrations, except on flights 

involving food preparation. Again, it is important to emphasize

that these samples were collected inside aircraft cabins under 

routine operating conditions. As such, the measured constituents

were not directly associated with either bleed air or non-routine 

conditions

DISCUSSION

The NAS stated in 1986 that “empirical evidence is lacking in 

quality and quantity for a scientific evaluation of the quality of 

airliner cabin air or of the probability of health effects of short or 

long exposure to it” (NRC 1986). Among the recommendations

were the need for exposure monitoring, particularly to VOCs, 

and health monitoring. Although much research relevant to

cabin air quality was conducted over the following years, many 

questions remained unanswered. The NAS stated in 2002 that

“no available exposure data identify the contaminants present 

in cabin air during an air-quality incident” (NRC, 2002). Public Law 108-196 (2003) ensued, prompting formation of the

ACER COE (2004), from which much knowledge has been 

added to what is known about cabin air quality. Finally, Public

Law 112-95 (2012) called for a complete assessment of cabin 

air quality, including the identification and measurement of oilbased contaminants, the assessment of bleed air on aircraft, and 

the identification of health risks following exposure

The rare occurrence of air quality events in aircraft cockpits 

and cabins is a very important factor to consider in designing a 

sampling strategy for hazardous constituents of bleed air. Rare

occurrence is also relevant to understanding the associated health 

risks following exposure to those hazardous constituents. The

proportion of such events has been estimated to range in occurrence from 2.7 to 33 events per million aircraft departures

(Mirawski & Supplee, 2008; Overfelt, 2012). The likelihood

of randomly selecting a given flight on which to collect air 

samples during an air quality event is indeed extremely low. A

large number of flights would be required to increase the likelihood of collecting samples during such an event. As an example,

given the higher of the two previous estimates, we would need 

to collect samples from approximately 30,000 flights to expect 

one sample to be collected during a contaminated air event

One of the directives from Public Law 112-95 (2012) was to 

assess bleed air quality on the full range of commercial aircraft 

operating in the United States. Therefore, approximately the

same number of flights for each aircraft type would need to be 

applied to meet this requirement

Another factor to consider is the availability, or lack thereof, 

of a suite of sampling techniques that allows for the broad characterization and evaluation of contaminants within contaminated 

bleed air. Public Law 112-95 directed the implementation of

a research program for the identification or development of 

appropriate and effective air cleaning technology and sensor 

technology for the engine and auxiliary power unit bleed air 

supplied to the passenger cabin and flight deck of a pressurized 

aircraft. We are aware that advances have been made in recent

years in regard to technology to better and more completely 

characterize the various constituents of bleed air. VIPR (Hunter

et al., 2014), the joint research being performed by the U.S. A

Force, the National Aeronautics and Space Administration, and 

the Federal Aviation Administration, holds promise in regard to 

advanced technology for measurement of bleed air constituents 

in a test system. However, because the final results have not

yet been published, further evaluation is not warranted until a 

written report has been issued

Research Needs

Much work is needed to carry out the directives of the Public 

Law 112-95 (2012). This work includes

• the ongoing study of air quality in aircraft cabins through a

comprehensive sampling program for broad characterization

and evaluation of the constituents of contaminated bleed air;

• assessment of bleed air quality on the full range of commercial 

aircraft operating in the U.S

• continued assessment of health risks to passengers who may

be exposed during bleed air events;

• continued development of instrumentation for sensing bleed 

air and cleaning contaminated air in pressurized aircraft

cockpits and cabins;

• continued development and evaluation of current measurement technologies both on the ground and in flight; and

• development of a systematic reporting standard for contaminated bleed air events

CONCLUSION

Quantification of the potential health risks associated with 

exposure to bleed-air contaminants in cabin air is not possible 

without broad identification and measurement of the representative hazardous constituents of bleed air during contaminated air 

events. Included in the 2012 mandate (Public Law 112-95) is

the directive to the FAA to “assess bleed air quality on the full 

range of commercial aircraft operating in the United States.”

Carrying out such a mandate requires adequate funding to support research activities

REFERENCES

ACER COE (Airliner Cabin Environment Research Center of 

Anna DH, ed. The occupational environment: its evaluation,

control, and management. 3rd ed., pp 1626. Fairfa

Virginia: American Industrial Hygiene Association, ISBN 

978-1-935082-15-6, 2011
6

Bhangar S, Cowlin SC, Singer BC, et al. Ozone levels in

passenger cabins of commercial aircraft on North 

American and transoceanic routes. Environmental

Science and Technology 2008;42(11):3938-43. http:/

www.ncbi.nlm.nih.gov/pubmed/1858

Bell ML, Peng RD, Dominici F. The exposure-response curve

for ozone and risk of mortality and the adequacy of 

current ozone regulations. Environmental Health

Perspectives 2006 Apr;114:532-36. http://www.jstor.o

stable/3650933?seq=1#page_scan_tab_contents

Bloom JC, Brandt JT. Toxic responses of the blood. In

Klaasen CD, ed. Casarett and Doull’s toxicology: the

basic science of poisons. 6th ed. New York: McGrawHill, ISBN 0-07-134721-6, 20

CFR (Code of Federal Regulations), Title 14, Part 25, Section 

831. Ventilation. Washington, DC: U.S. Governm

Printing Office. 2015a. http://www.gpo.gov/fdsys/

CFR-2015-title14-vol1/pdf/CFR-2015-title14-vol1-

sec25-831.pd

CFR (Code of Federal Regulations), Title 14, Part 25, Section 

832. Cabin ozone concentration. Washington, DC: 

Government Printing Office. 2015b. http://www.

gov/fdsys/pkg/CFR-2015-title14-vol1/pdf/CFR-2015-

title14-vol1-sec25-832.pd

Chaturvedi AK. Aerospace toxicology: an overvie

Washington, DC: Department of Transportation, Federal 

Aviation Administration, Office of Aerospace Medicine; 

2011a Apr. Report No. DOT/FAA/AM-09/8. http

libraryonline.erau.edu/online-full-text/faa-aviationmedicine-reports/AM09-08.

Chaturvedi AK. Aerospace toxicology overview: aerial

application and cabin air quality. Reviews of

Environmental Contamination and Toxicology

2011b;214:15-40. http://www.ncbi.nlm.nih

pubmed/21913123

Chen Q, Jones, BW, Loo SM, et al. Report to the FAA on the

airliner cabin environment . National Air Transportation 

Center of Excellence for Research in the Intermodal 

Transport Environment (RITE), Airliner Cabin 

Environment Research (ACER) Program; 2010 Aug . 

Report No . RITE-ACER-CoE-2010-1 . https://

www.faa.gov/data_research/research/med_humanfacs/

cer/media/AirlinerCabinEnvironmentReport.pdf

Coleman BK, Destaillats H, Hodgson AT, Nazaroff WW . 

Ozone consumption and volatile byproduct formation 

from surface reactions with aircraft cabin materials and 

clothing fabrics . Atmospheric Environment 2007 

May;42:642-54 . https://www .deepdyve .com/lp/elsevier/

ozone-consumption-and-volatile-byproduct-formationfrom-surface-ZVBDvRPIic

DHHS (Department of Health and Human Services)

Occupational health guideline for triorthocresyl 

phosphate. DHHS, National Institute for Occupational

Safety and Health (NIOSH). DHHS/NIOSH

Publication Number 81-123 0642. 1978. http://w

cdc.gov/niosh/docs/81-123/pdfs/0642.p

Eaton DL, Klaasen CD. Principles of toxicology. In: Klaase

CD, ed. Casarett and Doull’s toxicology: the basic

science of poisons. 6th ed. New York: McGraw-Hill

ISBN 0-07-134721-6 2001, 2001

Grewe V. The origin of ozone. Atmospheric Chemistry an

Physics 2006;6:1495-1511. http://www.atmos-chemphys.net/6/1495/2006/acp-6-1495-2006

Hunter GW, Lekki JD, Simon DL. Overview of vehicle

integrated propulsion research (VIPR) testing

Proceedings of the 225th ECS Meeting; 2014 May 

11-15; Orlando, Florida. Pennington, New Jersey

Eletrochemical Society: 2014. https://ecs.confex.c

ecs/225/webprogram/Paper32125.htm

Hinds WC. Aerosol technology: properties, measurement,

and behavior of airborne particles. 2nd ed. New York

John Wiley and Sons, ISBN 0-471-19410-7, 1999

Moss MT, Segal HM. The emissions and dispersion modeling

system (EDMS): its development and application at 

airports and airbases. Journal of the Air Waste

Management Association 1994 Mar;44(6):787-90

McDermott HJ. Handbook of ventilation for contaminant

control. 3rd ed. Cincinnati, Ohio: American Conferenc

of Governmental Industrial Hygienists, ISBN-10 

1882417380, 2001. http://www.tandfonline.c

Murawski JTL, Supplee DS. An attempt to characterize the

frequency, health impact and operational costs of oil in 

the cabin and flight deck on U.S. commercial aircra

Journal of ASTM International 2008 May;5(5). http:/

www.astm.org/DIGITAL_LIBRARY/JOURNALS/JA

PAGES/JAI101640.ht

Nagda NH, Fortmann RC, Koontz MD, et al. Airliner cabin

environment: contaminant measurements, health risks, 

and mitigation options. Germantown, Maryland:

GEOMET Technologies, Inc.; 1989 Dec. Final Repor

No. DOT-P-15-89-

Nagda NH, Rector HE, Li Z, Hunt EH. Aircraft cabin air

quality: a critical review of past monitoring studies. In:

Nagda N, ed. Air quality and comfort in airliner cabin

West Conshohocken, Pennsylvania: American Society for 

Testing and Materials, 2000. http://www.astm.o

DIGITAL_LIBRARY/STP/SOURCE_PAGES/

STP1393.ht
7

NIOSH (National Institute for Occupational Safety and 

Health). Pocket guide to chemical hazards. 

Department of Health and Human Services (DHHS), 

Centers for Disease Control and Prevention, NIOSH

DHHS/NIOSH Publication No. 2005-149, 3rd

printing, Sep 2007. http://www.cdc.gov/nio

docs/2005-149/pdfs/2005-149.pd

NRC (National Research Council). The airliner cabin

environment: air quality and safety. Washington, DC:

NRC, Committee on Airliner Cabin Air Quality, 

National Academies Press, ISBN 0-309-03690-9, 1986

http://www.nap.edu/openbook.php?isbn=0309036

NRC (National Research Council). The airliner cabin

environment and the health of passengers and crew

Washington, DC: NRC, Committee on Air Quality in 

Passenger Cabins of Commercial Aircraft, National 

Academies Press, ISBN 0-309-08289-7, 2002. http:/

www.nap.edu/read/10238/chapter

Overfelt RA, Jones BW, Loo SM, et al. Sensors and

prognostics to mitigate bleed air contamination events . 

National Air Transportation Center of Excellence for 

Research in the Intermodal Transport Environment

(RITE), Airliner Cabin Environment Research (ACER)

Program; 2012 Apr . Report No . RITE-ACERCoE-2012-5 . https://www.faa.gov/data_research/

research/med_humanfacs/cer/media/

SensorsPrognostics.pdf

Public Law 98-466. 98 Stat. 1825-1826. Oct 11, 1

http://www.gpo.gov/fdsys/pkg/STATUTE-98/pd

STATUTE-98-Pg1825.pd

Public Law 100-202. Section 328. 101 Stat. 1329-382. 

22, 1987. Prohibition against smoking on scheduled

flights and tampering with smoke alarm devices. http:/

history.nih.gov/research/downloads/PL100-202.

Public Law 103-305. Section 304. 108 Stat. 1591-1592. 

28, 1994. Aircraft cabin air quality research progra

http://www.gpo.gov/fdsys/pkg/STATUTE-108/pd

STATUTE-108-Pg1569.pd

Public Law 106-181. Section 725. 114 Stat. 166-167. Apr

2000. Passenger cabin air quality. http://www.gpo.

fdsys/pkg/PLAW-106publ181/pdf/PLAW-106publ181.pd

Public Law 108-196. Section 815. 117 Stat. 2592. Dec 

2003. Air quality in aircraft cabins. http://www.gpo.

fdsys/pkg/PLAW-108publ176/pdf/PLAW-108publ176.pd

Public Law 112-95. Section 320. 126 Stat. 70-71. Feb 

2012. Study of air quality in aircraft cabins. Section 9

126 Stat. 145. Research and development of equipmen

to clean and monitor the engine and APU bleed air 

supplied on pressurized aircraft. http://www.gpo.g

fdsys/pkg/PLAW-112publ95/pdf/PLAW-112publ95.pd

Spengler JD, Vallarino J, McNeely E, Estephan H. In-flight

onboard monitoring: ACER’s component for ASHRAE 

1262, Part 2 . National Air Transportation Center of 

Excellence for Research in the Intermodal Transport 

Environment (RITE), Airliner Cabin Environment 

Research (ACER) Program; 2012 Apr . Report No . 

RITE-ACER-CoE-2012-6 . https://www.faa.gov/

data_research/research/med_humanfacs/cer/media/

In-FlightOnboardMonitoring.pdf

Sussell A, Singal M, Lerner PJ. Health hazard evaluation

report: Alaska Airlines, Seattle, Washington. U

Department of Health and Human Services, Centers for 

Disease Control and Prevention, National Institute for 

Occupational Safety and Health (NIOSH). 1993 Ja

NIOSH Report No. HETA 90-226-2281. http://w

cdc.gov/niosh/hhe/reports/pdfs/1990-0226-2281.p

van Netten C, Leung V. Comparison of the constituents of

two jet engine lubricating oils and their volatile pyrolytic 

degradation products. Applied Occupational and

Environmental Hygiene 2000 Mar;15(3):15, 277-83

http://www.ncbi.nlm.nih.gov/pubmed/1070

van Netten C, Leung V. Hydraulic fluids and jet engine oil:

pyrolysis and aircraft air quality. Archives of

Environmental Health 2001 Mar;56(2):181-6. http:/

www.ncbi.nlm.nih.gov/pubmed/1133

Waters MA, Bloom TF, Grajewski B, Deddens J

Measurements of indoor air quality on commercial 

transport aircraft. Proceedings of the 9th International

Conference on Indoor Air Quality and Climate; 2002 

June 30-July 5; Santa Cruz, California. Indoor Air

2002:782-7. http://www.cdc.gov/nio

nioshtic-2/20033873.htm

Weschler CJ, Wisthaler A, Cowlin S, et al. Ozone-initiated

chemistry in an occupied simulated aircraft cabin

Environmental Science and Technology 2007 

Sep;41(17):6177-84. http://www.ncbi.nlm.nih

pubmed/17937299

WHO (World Health Organization). WHO air quality

guidelines for particulate matter, ozone, nitrogen dioxide 

and sulfur dioxide. Global update 2005. Summary of ris

assessment. Geneva: WHO Press. 2006. http://apps

int/iris/bitstream/10665/69477/1/WHO_SDE_PHE_

OEH_06.02_eng.p