CHAPTER 5: PROVIDING A HEALTHY CABIN ENVIRONMENT
5.1 Chapter 4 looked at the
body's need for an adequate supply of oxygen, removal of carbon
dioxide and protection from harmful atmospheric contaminants.
Against that background, this Chapter deals with the practical
provision of healthy cabin air - the topic about which we received
5.2 Ventilation of the aircraft
cabin is essential for four main purposes:
- to meet the occupants' respiratory needs;
- to clear contaminants and odours from the cabin
- to control the temperature of the cabin environment;
- to maintain cabin pressure when at altitude.
5.3 During our consideration
of respiratory needs in Chapter 4, we found that these were very
substantially more than met in the aircraft cabin by the typical
air supply of 20 cfm per occupant.
Before discussing the other purposes of ventilation, we must first
describe how it is provided.
5.4 Until around 1980, aircraft
cabins were ventilated entirely with fresh air. One of the ways
aircraft manufacturers found to meet the commercial and environmental
pressures to reduce oil consumption which arose at this time was
to reduce the amount of outside air taken from the engines, maintaining
overall air supply by re-circulating some of the air already present
in the cabin. As Boeing noted, the resulting air quality was more
than adequate for respiratory needs, but the air needed to be
filtered for satisfactory contaminant control (p 204).
5.5 All large modern airliners
now use re-circulation of up to 50% of cabin air in their environmental
control systems. Boeing indicated that the typical cabin air flow
of 20 cfm of air per occupant is equivalent to a full change of
cabin air every 2 to 3 minutes, i.e. 20 to 30 times per hour (p
204). As half of the air being changed is re-circulated cabin
air, this is equivalent to an entire exchange of cabin air with
fresh air 10 to 15 times per hour - although,
as noted in paragraph 4(g) of Appendix 5, the mixing arrangements
mean that the actual replacement is a form of progressive dilution.
5.6 Aircraft environmental
control systems work
by taking hot compressed air from the engine compressor stages
and passing it through heat exchangers (pre-coolers) to provide
bacteriologically-sterile air at the appropriate temperatures
and pressures for the aircraft ventilation, air-conditioning,
and pressurisation systems. Air is also provided for de-icing,
cargo heating, pneumatic and hydraulic systems.
5.7 Air for the cabin is
then passed, through ozone converters (see paragraph 4.47) if
fitted, to up to three air-conditioning packs, to produce temperature-controlled
dry sterile air to the cabin air mixing chamber. Here, the fresh-air
flow is combined with up to 50% of air taken from the cabin by
re-circulation fans. The re-circulated air is filtered prior to
passing into the mixing chamber (see paragraphs 5.18ff), and the
rest of the cabin air is exhausted through pressure control valves.
5.8 The mixed air, at a temperature of about 18ºC,
is ducted through to the cabin overhead ventilation system. From
there it is distributed to each of up to six seating zones in
the aircraft, with a separate supply to the flight-deck zone.
Prior to distribution, it may be heated by the addition of hot
air to match the temperature requirements of the individual cabins.
In modern aircraft, as indicated by Airbus Industrie, the conditioned
air flows downward over the cabin occupants, in carefully designed
flow patterns to avoid areas of stagnant air and to minimise draughts
and flow along the cabin (Q 428), to the cabin floor where it
is vented through return-air grilles and either exhausted or re-circulated.
(Air vented from galleys and lavatories is exhausted directly.)
5.9 The exhaustion overboard
is through valves which, by setting the rate of release against
rate at which air is drawn in, control cabin pressurisation including
the rates of pressurisation change on ascent and descent. In modern
aircraft, the environmental control system (including the pressurisation
system) is entirely automatic, being controlled by appropriate
sensors and valves - although some aspects may be manually controlled
from the flight deck, in particular the fresh and re-circulated
air flows, the number of air-conditioning packs in operation and
zone temperatures. There are also parameter level and system warning
indicators on the flight deck, together with manual regulators
which may be needed for emergency purposes.
5.10 A common allegation
is that, to save fuel, flight crew shut down some of the air-conditioning
packs and thereby reduce air quality below the intended standard.
If true, that would be inexcusable. However, we find BALPA's rebuttal
conclusive (p 213). The regulatory emergency requirement noted
in paragraph 3.40 means that there is an inherent over-capacity
in a fully serviceable environmental control system. The automatic
control may well result in packs running at less than full flow
rates while still delivering the required output.
5.11 Many of our witnesses
expressed serious concerns that re-circulatory systems provide
lower quality cabin air than systems using only fresh air (see,
for example, Annex 4). The concerns are centred on reduced oxygen
availability, increased carbon dioxide and other gaseous contaminants,
increased risks of cross-infection, and generally increased "staleness
of air". The root of the concerns would seem to be that,
with the introduction of re-circulation, the fresh air component
of the standard 20 cfm of air per person has been halved to about
10 cfm (see paragraph 3.33).
5.12 The addition of re-circulated air does not affect
the fact that, as noted in paragraph 4.7, the design level of
10 cfm of fresh air per cabin occupant provides more than
ample oxygen for respiration.
5.13 The picture regarding build-up of gaseous contaminants
is less clear-cut. With regard to ozone, cabin air supply at 20
cfm using 50% re-circulation potentially improves the situation
because only half the quantity of ozone is brought into the cabin
compared with a 20 cfm full fresh-air system. With carbon dioxide
and all other contaminants whose source is inside the aircraft,
re-circulation potentially increases build-up, with the equilibrium
level for each contaminant being reached when the rate of its
production is equal to the rate of its removal. For contaminant
control, the important factor is the number of complete changes
of cabin air per unit time (see paragraph 5.5).
5.14 The level of carbon
dioxide in cabin air is important both in its own right (as discussed
in paragraphs 4.13ff) but also as a proxy for satisfactory ventilation.
Until 1996, the FAA/JAA regulatory limit for carbon dioxide in
the aircraft cabin was 30,000 ppm (3%), based on the safety level
used by the National Aeronautics and Space Administration (NASA).
In 1981, ASHRAE set a maximum level of 2,500 ppm as the standard
for ground building environments as a measure of satisfactory
ventilation. In 1989, in the light of concerns about "sick
building syndrome" as described by Mr Gurney (p 234), ASHRAE
reduced this to 1,000 ppm to ensure adequate ventilation for odour
and contaminant control in buildings which by then were using
up to 90% re-circulation of air to conserve energy. Many aircrew
and air passenger groups misinterpreted this move as a reflection
of increased knowledge of carbon dioxide toxicity rather than
as a surrogate measure of adequate ventilation, and demanded the
application of the ASHRAE standard to aircraft cabins (p 204).
5.15 When ASHRAE became aware
of this misinterpretation in 1995, it set up special committees
and working groups specifically to examine all the standards for
contaminants, including carbon dioxide, that should be applied
in the aircraft cabin environment. A September 1999 article
by Dr J N Janczkewski described how ASHRAE was tackling the work.
At the time of writing, the work was still in progress, but the
outcome will be published in ASHRAE Standard 161. The US authorities
already set a workplace limit of 5,000 ppm (0.5%), and FAA and
JAA have adopted the same level (0.5%) as the aircraft cabin standard
(see paragraph 3.33). As discussed in the section on carbon dioxide
as a respiratory gas (paragraphs 4.13ff), cabin levels under normal
re-circulation ventilation conditions with full passenger loads
vary between 0.05 and 0.15%, averaging 0.1%. Cabin air ventilation
standards would therefore seem to be entirely acceptable.
5.16 Because the volume of
air supplied to the cabin continues to provide ample quantities
of oxygen, and because the rate at which cabin air is exchanged
keeps carbon dioxide and other internal-source contaminant levels
to well below those of significance to health, we do not accept
the widely held view that the introduction of re-circulatory ventilation
systems has resulted in any harmful change in the quality of cabin
Nevertheless, the industry should pay attention to these common
perceptions of the effects of re-circulation - for example, by
publicising the results of monitoring as discussed in paragraphs
5.17 We see no case for the
re-introduction of fresh air ventilation to alleviate these perceptions.
The environmental and economic pressures
which led to the introduction of re-circulating systems remain
and, as noted above, we do not find any consequent harmful change.
However, JAA's requirement for only fresh air to be supplied to
the flight deck reinforces the perception that there is something
intrinsically "bad" about re-circulated air (Q 363).
We understand that FAA does not have this requirement. We recommend
the Government to urge JAA to reconsider its requirement for ventilation
of the flight deck with only fresh air.
5.18 The proper functioning
of ventilation systems using re-circulated air depends on the
effectiveness of the filtration arrangements. There are, however,
no FAA/JAA/CAA regulatory requirements for the use of filters
in aircraft ventilation systems, and thus no filtration standards
have been set. This appears surprising, but reflects the regulatory
authorities' remits which are limited to secure arrangements for
physically safe flights and safe landings: as noted by CAA, those
are not known to be under threat from the nature of cabin air
filtration (p 39). Accordingly, where ventilation system filters
are used (as they are in the great majority of aircraft), their
design, specification and maintenance criteria are determined
by agreement between aircraft constructors, airline operators
and filter manufacturers and suppliers. Nevertheless, as BATA
noted, where filters are fitted, CAA requires airlines to implement
reliability monitoring programmes which ensure that filters are
used in accordance with the manufacturers' recommendations, and
that their performance does not fall below manufacturers' standards
5.19 When re-circulatory environmental control systems
became the norm in the 1980s, particle/dust filters became integral
components of the systems. As particle filters did not remove
gases or vapours, activated charcoal filters were sometimes added
for ozone control which, as noted in the supplementary material
submitted by Boeing (p 204), were later replaced by ozone converters.
It was soon realised that passenger and crew complaints about
reduced quality of breathing air could be due to inadequate filtration
of the re-circulated air, and that re-circulation brought a greater
risk of transmission of infection within the cabin. The efficacy
of the filtration systems being used in removing particulates
was also questioned, and improvements were sought and made.
5.20 Most environmental control systems today use
High Efficiency Particulate Air (HEPA) filters. These were developed
for hospital infection control settings where it was vital to
prevent cross-infection and air contamination, and it seemed that
they would be eminently suitable for transfer to the aircraft
cabin. A major advantage of HEPA filters is that they have very
little negative impact on airflow velocity and throughput, and
their efficacy improves with use between changes (pp 165, 204
5.21 The efficiency rating
of HEPA filters is based on their ability to remove a defined
proportion of particles of a given mean diameter set according
to the test method used. Commercially available HEPA filters are
rated from 85% to 99.995% removal efficiency based on liquid droplets
of mean size 0.3 microns (DOP test), or solid particles of mean
size 0.65 microns (Salt Flame test) (p 259).
5.22 As CAA has noted, different
grades of HEPA filter have been, and are still being, used in
different aircraft types (p 39). The current HEPA filter efficiency
standards set for the commercial aviation industry are 99.97%
by DOP test in the USA (ASTM D2986-95), and 99.99% by Salt Flame
test in Europe (BS 3928). All new Boeing and Airbus aircraft are
being fitted with these standards of filter (p 259). Many older
aircraft can be fitted with the latest standard filters, although
there seems to be no easy way of establishing the extent to which
this has been done (QQ 457 & 458).
5.23 Diamond Scientific Ltd made worrying statements
about poor standards in the installation and use of HEPA filters
in ground-based environments (p 225). Pall Aerospace (p 259) and
BATA (p 293) robustly and persuasively refuted such poor practice
in the tightly-controlled aviation industry.
5.24 HEPA filters are changed at intervals based
on the filter manufacturer's recommendations,
according to the filter specification requested by the aircraft
manufacturer. The changes are generally made at fixed aircraft
maintenance intervals, typically every 15 months (p 104) or 6,000
flight hours (p 124). The change intervals are agreed with the
regulating authorities (see paragraph 5.18), but operators may
choose to change them more frequently if aircraft usage and occupancy
are higher than average (p 124). It was alleged by Mr Kahn (p
44, QQ 136-144) that some airlines did not change filters at the
required frequencies or intervals, but this was strongly refuted
by BATA (p 293) and, in the event, Mr Kahn was unable to provide
material to support his allegations (footnote to Q 144).
5.25 A key question about filtration concerns the
efficiency in removing microbiological particles from re-circulated
air. Without efficient filtration, moving from single-pass fresh-air
ventilation systems to re-circulating systems could lead to a
rise in transmission of infectious microbiological particles.
We consider transmission of infection in Chapter 7, and conclude
our consideration of filtration in paragraphs 7.23ff.
5.26 The low humidity of
cabin air is widely felt to be bad for the health of the occupants,
particularly in relation to risks of deep vein thrombosis, the
transmission of viral infections
and, by AsMA and Professors Moyle and Muir of Cranfield University,
as a significant factor in general malaise which some crew and
passengers ascribe to exposure to the cabin environment (pp 198
& 218). Low humidity was also cited as contributory to jet-lag
by the Research Institute for Sport and Exerciser Science (RISES
- p 269) and to eye, nose and respiratory problems by Delta Air
Lines, the Building Research Establishment (BRE) and Boeing (pp
204, 211 & 224).
5.27 "Humidity" is used loosely to refer
to the amount of water vapour in the air. Human comfort generally
depends on "relative humidity" (RH), expressed as a
percentage (% RH) of the maximum water vapour that air at that
temperature can hold. (Above 100% RH, water vapour is precipitated
as mist or, on surfaces, as condensation.)
5.28 At cruising altitudes,
external air is very dry. After pressurising and conditioning,
fresh air is delivered to the cabin at less than 1% RH. The now
standard re-circulation of cabin air means that some water vapour
is added to the cabin atmosphere by cabin occupants and some cabin
activities. Depending on aircraft type, cabin configuration and
passenger load, the relative humidity in the cabin averages around
10-15% within a range from 5%-35% (p 204).
5.29 There are no specific
regulatory limits for cabin relative humidity. As noted by BRE,
the levels normally found in aircraft cabins are well below those
recommended as comfort levels for buildings of 30-70% (p 211).
Nevertheless, many millions of people live healthily in climates
as dry as aircraft cabins. Such dry atmospheres can also be found
outdoors in summer, and indoors in winter (p 204). In addition,
as pointed out by BAE Systems, IAPA and Varig, a low relative
humidity is positively beneficial to the aircraft structure and
equipment in reducing moisture and condensation, thus limiting
corrosion and opportunities for bacterial and fungal growth (pp
200, 243 & 288).
5.30 The dry cabin atmosphere
commonly gives rise to sensations of dryness to the eyes, nose,
mouth and skin. Such "peripheral dehydration" may be
uncomfortable for some. However, it can be easily dealt with by
local application of moisture and it is not itself a threat to
health (Q 215). The key question about low relative humidity in
the cabin is whether it can lead to the loss of so much water
("central dehydration") that the body's normal water
balance is significantly disturbed. There has been some suggestion
that this could lead to potentially adverse conditions such as
abnormal distribution of water around the body and increased viscosity
(thickening) of the blood.
5.31 The body has in-built systems for the maintenance
of water balance, controlled by hormones circulating in the blood,
and urine output through the kidneys. Evaporation of water from
the skin (sweating) and lungs is a major element in the body's
temperature control, the amount being lost varying according to
body temperature, the degree of physical activity being carried
out, and the temperature and RH of the ambient air. In addition,
water is excreted in faeces and urine. When central dehydration
threatens, the body will respond by reducing sweat loss, reducing
urine output, and increasing the sensation of thirst.
5.32 Even in the absence
of sweating, the body loses about 1.5 litres of water a day, one
litre through the skin, lungs and bowel and a minimum of half
a litre through the kidneys as urine. The intake of water from
food and drink is normally about 2.5 litres per day. Water intake
would, therefore, have to be reduced by at least a litre per day
to begin to produce central dehydration. Thus, central dehydration
would not arise during a flight, assuming normal eating and drinking,
unless the body had lost at least a litre of water over and above
its normal losses.
5.33 The definitive experimental work on this topic
was carried out at the then RAF Institute of Aviation Medicine
(now DERA) at Farnborough, Hampshire. This showed clearly that
exposure to 5% RH for 24 hours did not lead to changes in overall
water balance amounting to central dehydration (p 72). Professor
Nicholson also showed that the maximum increase in water loss
for a person spending 8 hours at 0% RH was about 0.1 litre, well
below even the thirst sensation level.
He, Dr Sowood (p 72), and Professor Denison (p 94, Q 214) were
of the firm view that any extra water loss due to the dry cabin
environment is of no significance to health, and that central
dehydration of passengers in low humidity aircraft cabins is a
myth. As Dr Giangrande noted (p 234), the assertion in Q 108 that
breathing dry cabin air means that passengers are not replenishing
their blood plasma is nonsense.
5.34 We received no evidence to indicate that artificially
raising cabin RH levels might be beneficial to passengers in general,
but we were given details by Le Bozec of their vapour (steam)
air humidifier which they claimed would raise cabin RH to 30%.
They said this was fitted widely on long-range business aircraft
and by some airlines, and further large aircraft tests were planned,
but we received no evidence from others about aircraft humidifiers.
From the engineering point of view (see paragraph 5.29) increased
RH would not be beneficial.
5.35 Against this background,
we are satisfied that low cabin humidity is not harmful. Any uncomfortable
dryness of skin, mouth, nose and throat can be alleviated simply
by a sip of water or other local application of moisture and is
not a threat to health. On a long flight, assuming normal fluid
intake, one glass of water can more than offset any additional
loss due to low cabin humidity. The common advice to drink a little
more water than usual is thus sound.
5.36 There may be a tendency
towards central dehydration in those passengers who, before or
during a flight, drink sufficient alcoholic or caffeinated beverages
(such as coffee or cola) to cause excessive production of urine
(diuresis). If the peripheral dryness caused by low cabin humidity
leads such passengers to further consumption of inappropriate
drinks, they may expose themselves to the possibility of central
dehydration. This is a risk factor in DVT, as discussed further
in Chapter 6. Responding to our questions,
Professor Denison (Q 220) and Professor Kakkar (Q 506) were both
of the opinion that, in relation to travel-related DVT, neither
excessive water consumption nor its possible relationship with
the swelling of the lower legs commonly seen during long flights
were of significance.
5.37 As noted by Airbus Industrie,
the heat given off by passengers in a fully occupied cabin is
considerable (Q 445). Incoming air needs to be at or below the
required cabin temperature if that temperature is to be maintained.
The cabin temperature is set according to seating zone from the
flight-deck with a range of control from 18-27ºC, and is
normally maintained in the range 22-24ºC, the same as that
found in many office environments (p 211).
5.38 There are no regulatory standards for cabin
temperature. As noted in the supplementary material submitted
by Boeing (p 204), flight crew normally change cabin temperatures
in response to cabin crew requests based on passenger representations
about their personal comfort. Because passengers are normally
in repose and cabin crew are working, their perceptions of thermal
comfort are likely to be different. Cabin crew may feel uncomfortably
hot and change dress accordingly.
5.39 We received a number
of complaints about cabin temperatures, including inappropriate
settings by crew to encourage passengers to sleep after meals.
Temperature is one of the most quickly sensed aspects of the aircraft
cabin environment. Being too hot or too cold is likely to affect
a passenger's general perception of the whole flight experience.
We endorse ASHRAE's suggestion that further work should be done
to establish guidelines for cabin thermal conditions (as drawn
to our attention by Boeing, p204) and we look to the industry
to carry this forward.
5.40 We have also received
representations from Inflight Research Services (p 240) and Mr
Baker (Appendix 4) about the general lack of personally controlled
air nozzles in current aircraft cabins. Both Airbus Industrie
and Boeing confirmed that such nozzles were available on many
aircraft, but the general absence of air nozzles under personal
control in newer aircraft reflects airlines' preferred cabin layouts
(QQ 463-468, p 204). While we understand (Appendix 5) that, where
fitted, such nozzles deliver the same air as otherwise available,
the directed movement of air can provide personal refreshment.
The absence of individual air nozzles reduces the personal control
passengers have over their flight experience, and we recommend
airlines to review and modify their cabin design considerations
to include such nozzles.
5.41 The main purpose of
cabin pressurisation is to provide passengers and crew with sufficient
oxygen for respiration. As noted in paragraphs 4.7 and 4.8, we
agree that this purpose is met for all those in reasonable health.
There are, however, some other health issues connected with cabin
pressurisation. For the most part these arise from changes in
pressure on ascent and descent.
5.42 In the absence of specific regulation, the rates
of pressurisation change are set at the design stage to minimise
any passenger or crew discomfort within the requirements for safe
aircraft operation. According to the supplementary material from
Airbus Industrie (Q 427) and Boeing (p 204), the reduction in
pressure after take-off is normally limited to the equivalent
of increasing altitude by 500 feet per minute. Human anatomy and
physiology mean that more problems are likely to be experienced
with increasing pressure on descent, and the rate of change for
that is normally limited to the equivalent of 300 feet per minute.
5.43 If changes in cabin
pressure are too rapid, there is insufficient time for the body
to adjust to the substantial changes in the volume of air normally
present, or abnormally trapped, in various body cavities. Pain
in (or damage to) parts of the body caused by such changes is
termed "barotrauma". Barotrauma of the middle ear and
nasal sinuses is experienced by many passengers, particularly
those with current or recent common colds, as discomfort or pain
in the ears, face, nose or head. The symptoms can be relieved
by allowing the pressure of the trapped air to equalise with the
cabin pressure which, Professor Denison noted, is normally achievable
by swallowing, yawning, jaw-moving and nose-blowing (p 94).
5.44 Pain in the head from
pressure changes may be particularly severe for those with active
upper respiratory problems and, quite apart from the infection
risk they may present for others, they may need to take medical
advice about flying. Before take-off, cabin crew should alert
all passengers to the potential for head pain from pressure changes,
and of the simple manoeuvres to prevent or alleviate them.
All cabin crew should be trained in the use of the Valsalva
technique (generating oral pressure against pinched nostrils
and closed pharynx) in order to help passengers to clear ear-block
if simpler measures have failed.
5.45 Abdominal discomfort or pain sometimes occurs
during ascent or descent, but this is usually temporary and relieved
by gas re-distribution in the bowels.
5.46 As noted in paragraphs 7.42ff on vulnerable
individuals, there are some medical conditions of the lungs (such
as previously existing partial collapse of lung tissue or fixed-wall
lung cavities) and of the bowel (particularly after recent surgery),
which can be seriously affected by pressure changes, mainly on
ascent. Passengers subject to these conditions would normally
be under medical care and should have sought advice about air
travel in advance of flying, including informing their airline
if considered appropriate. If passengers are unaware of having
such conditions, however, they may present in flight as medical
emergencies, when descent may be the only practicable remedial
5.47 People who have recently
experienced high-pressure atmospheres, such as scuba and deep-sea
divers or caisson and tunnelling workers, are at risk from the
reduced pressure itself rather than the transitions. They may
have excessive amounts of nitrogen (or other gases such as helium,
depending on the gas mixtures used in their high-pressure environments)
dissolved in their tissues for many hours after being exposed
to high ambient pressures. If they travel by air too soon after
returning safely to sea level, the further reduction in atmospheric
pressure may lead to decompression sickness ("the bends").
Because of the risks of decompression sickness, sub-aqua divers
(particularly occasional leisure divers) should ensure that the
effects of any recent diving will not create an additional hazard
when they fly. If in doubt, they should take professional advice.
These points could usefully be drawn clearly to passengers' attention
at least at the time of booking.
of air quality
5.48 As will be seen from
Appendix 4, cabin air quality was one of the main concerns among
the individuals who made representations to us. Various studies
of cabin air quality have been widely quoted in the evidence received
from airlines, manufacturers, and aircrew and passenger representatives.
However, the studies are mainly of the "snapshot" variety,
leaving questions about whether they are typical, or are used
selectively in support of the witnesses' main contentions. British
Airways (p 99) and BATA (p 124) told us that a number of basic
cabin environment parameters are continuously monitored in-flight,
and recorded in the flight data recorders, including air-conditioning
pack status, airflow rates, cabin pressure and zone temperatures.
5.49 Passengers' perception
of general cabin air quality is one of the key factors in their
assessment of the flight experience as a whole. We recommend that
airlines collect, record and use at least some of the basic cabin
environment data being continuously monitored, not only to give
authoritative substance to their refutation of the common allegations,
but also to provide a better basis for public confidence in these
matters. Indeed, we are surprised that they do not already do
5.50 We noted previously
(paragraph 3.33) that there are regulatory limits for carbon dioxide,
carbon monoxide and ozone. We are satisfied that, under normal
operating conditions, environmental control systems keep cabin
atmosphere levels of these and other contaminants well under control
(see paragraphs 5.14-5.16). We also note that British Airways
is undertaking independent studies of cabin air quality (p 99),
but we have seen no evidence that cabin air is monitored or sampled
either routinely or even under abnormal or unusual conditions
when passengers or crew feel that conditions are not right. We
recommend airlines to carry out simple and inexpensive cabin atmosphere
sampling programmes from time to time, and to make provision for
spot-sample collection in the case of unusual circumstances. This
would be helpful for passengers and staff, and also benefit airlines
themselves. We also suggest that this might form part of Government-sponsored
research, as discussed further in paragraph 9.3,
and note that the Australian Senate Inquiry Report
makes similar recommendations
5.51 A key point in such
monitoring is the basis for comparison. We noted earlier (paragraph
5.15) that ASHRAE is working to set such standards for cabin atmospheres.
Airbus Industrie (Q 469), at least, would welcome this, because
there are no international standards for air quality; and only
building regulation, public place and workplace standards are
currently available for use by the aviation industry. We welcome
the ASHRAE work on cabin air quality standards and recommend the
industry to support and encourage its timely completion and promulgation.
We recommend that, in the light of the outcome, regulators consider
extending cabin air quality standards beyond those for carbon
dioxide, carbon monoxide, and ozone for which they already provide.
63 As noted by Airbus Industrie (Q 445), this volume
of air is needed for temperature control (discussed further in
paragraphs 5.37ff). Back
See also Appendix 5. Back
There are some complicated inter-related issues in all this which
seem frequently to be misunderstood. Dr Murray Wilson stated that
such had found their way into the British Medical Journal
and into a transport paper for the European Parliament (p 255). Back
Air Quality on Passenger Planes, ASHRAE Journal, September
Indeed, we note in paragraph 5.28 that re-circulation is beneficial
in significantly increasing relative humidity in the aircraft
For example, the savings on the total fuel costs of aircraft operation
were indicated by Airbus Industrie to be 1-2% (Q 441), and by
Professor Hocking to be 1-3% (p 236). Back
As noted in paragraph 4.37, filters which can absorb gaseous contamination
are again available. Back
As discussed further in paragraph 7.23, these tests do not necessarily
deal with particles of the most penetrating size - mean diameter
0.1 microns. Back
We noted during our visit to British Airways Maintenance, Cardiff
(see Appendix 5) that filter efficacy was not checked between
Discussed further in Chapters 6 and 7 respectively. Back
Basic physiology and data from Samson Wright's Applied Physiology,
10th edition, 1961. Back
Low Humidity: Dehydration, dipsosis or just dryness? RAF
SAM Report 01/96 and Dehydration and long-haul flights
in Travel Medicine International 1998 Vol 16 No 5. Back
As discussed in paragraph 7.61, the solution for very young babies
is to encourage them to feed. Back
See paragraph 2.14. Back