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prospective investigations, the Undersea and Hyperbaric Medical Society recommends the following
intervals between diving and flying:
Dive schedule
Minimum interval
1.
Non-decompression dives
a. Less than 2 hours accumulated dive time in the
48 hours preceding surfacing from the last dive
12 hours
b. Multi-day, unlimited diving
24 hours
2.
Dives requiring decompression stops (but not
including saturation dives)
24-48 hours
Table 4.— Recommended intervals between diving and flying
Further information concerning dive times and flying is available from the Professional Association
of Diving Instructors (PADI) and the National Association of Underwater Instructors (NAUI).
Another important consideration in civil aviation operations is the possibility of slow decompression,
including failure to pressurize during climb, which might occur as a result of failures of pressurization
equipment, such as failure of an outflow valve, or incorrect settings of the flight deck pressurization
controls by flight crew. If a slow loss of pressure occurs, the aircraft usually initiates a descent to a safer
ICAO Preliminary Unedited Version — October 2008 II-1-11
altitude; in some cases, on account of high ground, the aircraft is forced to continue flying at an altitude
requiring oxygen. In such cases, the availability of oxygen systems is mandatory and if the planned route
is over high ground that prevents an immediate descent to 10,000 feet or below, additional oxygen is
required to be carried. When cabin pressure is lost, a barometrically triggered valve opens at a given cabin
altitude - usually 10 000 - 14 000 ft (3 050 - 4 250 m) - and releases the masks for passengers. Passengers
are briefed, prior to the flight, about the procedures to be taken to start breathing oxygen when required.
Other forms of decompression symptoms (dysbarisms) such as barotitis, barosinusitis and barodontalgia
are further described in Part III, Chapter 12 of this manual.
COSMIC RADIATION
Radiation consists of a flow of atomic and subatomic particles and of waves, such as those that
characterize heat rays, light rays, and X-rays. All matter is constantly bombarded with radiation of both
types from cosmic and terrestrial sources.
Radiation can be ionizing (i.e. capable of turning atoms and molecules in matter and tissue penetrated
into ions2 and thus causing an electrical effect) or non-ionizing.
Cosmic radiation is the collective term used for radiation coming from the sun (the solar component)
and from the galaxies of the universe (the galactic component).
Ionizing Radiation
Matter consists of a number of simple substances called elements which, as mixtures and compounds,
form all the materials present on earth and in the universe. The basic unit of any element is the atom, and
it is the characteristics of atoms that determine the properties of the elements.
Some elements are naturally radioactive, i.e. they change into other elements with the emission of
atomic particles: radiation. Radiation may be thought of as energy in motion or as transfer of energy.
When radiation energy is absorbed in living tissue, it may have a biological effect which depends not only
on the amount of energy absorbed, but also on the specific effect of the wavelength and on the type of
particles (electrons, neutrons, positrons, etc). If ionization takes place, it frequently results in chemical
changes in matter and in living tissue. These changes may affect the behaviour of living cells and the
organism may suffer obvious injury if enough cells are involved. Unlike light and heat, which are also
forms of radiation, ionizing radiations cannot be directly detected by the body’s senses, except that the
dark-adapted eye, during the 5-6 hours of a transatlantic polar flight, may see a few flashes of light as
cosmic rays directly ionize the retina.
Source and type of radiation
The ionizing radiation to which everyone on earth is exposed comes from the universe, partly from outer
space (galactic radiation of constant intensity) and partly from the sun (solar radiation of increased
intensity during solar flare activity). Furthermore, the earth itself produces ionizing radiation (of intensity
varying with geographical location). Even food and drinking water are sources of ionizing radiation.
In addition to this natural background radiation which has existed for millions of years, there are
2ion: an electrically charged atom or molecule.
ICAO Preliminary Unedited Version — October 2008 II-1-12
modern man-made sources of ionizing radiation: building materials in houses, medical and dental X-ray
examinations, radioactive cargoes, fall-out from atmospheric testing of nuclear weapons, and possibly
　
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