TABLE 5–1 Exposure Sources Relevant to Aircraft Cabin Air Quality

Exposures Related to Normal Operations of the Aircraft

Exposures Related to Incidents

Ozone

Carbon dioxide

Temperature

Relative humidity

Off-gassing from interior material and cleaning agents

Bioeffluents

Personal-care products

Allergens

Infectious or inflammatory agents

Ambient airport air

Cabin pressure/partial pressure of oxygen

Pesticides

Jet exhaust fumes (runway)

Alcohol

Carbon monoxide

Smoke, fumes, mists, vapors from leaks of engine oils, hydraulic fluids, and deicing fluids and their combustion products

FLIGHT ENVIRONMENT

Cabin Pressure

As discussed in Chapter 2, at cruise altitude, the aircraft cabin is typically pressurized to the equivalent of an altitude of 6,000–8,000 ft (1,829–2,438 m), with a corresponding barometric pressure of 609–564 mm Hg and an ambient PO2 of 128–118 mm Hg (see Table 5–2). As specified in the Federal Aviation Regulation (FAR) 25.841, aircraft “cabin pressure altitude” must not exceed 8,000 ft at the aircraft’s highest operating altitude (14 CFR 1986).

The reduced pressure in the cabin environment results in several physiological changes in the passengers and crew. Specifically, the reduced ambient air pressure will cause the gas in body cavities (e.g., middle ear, sinuses, and gastrointestinal tract) to expand in volume by as much as 25%. In the lungs, the lower PO2 in ambient air will reduce the oxygen (O2) pressure in the alveoli from the normal value of 105 mm Hg. That decrease will lower systemic arterial PO2. In healthy people, the arterial PO2 is usually about 5–10 mm Hg lower than the alveolar PO2 (see Table 5–2). It is the arterial PO2 that determines the amount of O2 that is carried by the hemoglobin in the blood, expressed as the percent hemoglobin saturation.



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