Environmental Engineering Reference
In-Depth Information
T
HE
AIRCRAFT
CABIN
ENVIRONMENT
As aircraft operators seek to reduce operating costs by operating at higher altitudes,
thereby reducing fuel use, and increasing the capacity of seats within their aircraft
fleet, a number of concerns have arisen amongst the medical profession, aircrew and
passengers regarding the impacts of air travel that the aviation industry is being forced
to address. As an example, the general cabin environment is, by necessity of flying at
high altitude, pressurized. Hence, approximately 50 per cent of the air in the passen-
ger cabin is recirculated, reprocessed cabin air, supplemented by external air. The
recirculated atmosphere typically has low ventilation levels, a low cabin pressure of
0.74 atmospheres (atm), low humidity (15-20 per cent) and reduced levels of oxygen
available to passengers for respiration. At the same time, elevated carbon dioxide (CO
2
)
levels and the presence of 'trace' contaminants such as bio-aerosols (despite the use
of high-efficiency, particle-arresting filters, HEPAs), carbon monoxide, ozone, envi-
ronmental tobacco smoke and other trace organic compounds have all been reported
(Dechow et al, 1997; Hocking, 2000).
1
While all these levels are within acceptable
guidelines, these factors can lead to airborne illness and this has led to agencies such
as the American Society of Heating, Refrigerating and Air-Conditioning Engineers
(ASHRAE), the Federal Aviation Administration (FAA) and the UK Civil Aviation
Authority (CAA) to review various aspects, including both chemical and biological
parameters, of the cabin environment.
The following sections outline the current major concerns regarding the impacts
of the cabin environment upon health for both passengers and aircrew.
P
ASSENGERS
Deep vein thrombosis (DVT)
Perhaps the most controversial of in-flight health effects upon passengers is currently
deep vein thrombosis (DVT). However, DVT is not a new phenomenon and the pos-
sibility of links between immobility and venous thromboembolism was recognized
during 1940 by Simpson, who noted the high incidence (a sixfold increase) in pul-
monary embolism amongst people sleeping overnight in deckchairs while sheltering
from the London blitz - a phenomenon that subsequently disappeared when the
deckchairs were replaced by bunks (Simpson, 1940). As long ago as 1954, Homans
reported venous thrombosis in a 54-year-old doctor after a 14-hour flight, and sug-
gested that prolonged sitting in airplane flights was able to bring on thrombosis in
the deep veins of the legs (Homans, 1954). However, DVT events have recently gained
high levels of media coverage due to high-profile deaths after long-haul flights,
which - when combined with the threat of class-action lawsuits against airlines (an
Australian law firm using three test cases launched legal action in July 2001 against
KLM, Qantas Airways, British Airways and Australia's Civil Aviation Safety Author-
ity) - make DVT a highly contentious issue.
DVT refers to the formation of a thrombosis (blood clot) within a deep vein,
commonly within the thigh or calf. One cause of DVT is poor blood circulation asso-
ciated with prolonged inactivity, such as is found in passengers on long-haul flights,
