AN INCIDENT in which a plane鈥檚 crew almost suffocated at the controls has
highlighted a possible risk to pilots of cargo aircraft. America鈥檚 aviation
safety watchdog now fears that carbon dioxide gas from evaporating dry ice,
which is frequently used to cool perishable cargo, could starve the crew on the
flight deck of oxygen.
The National Transportation Safety Board (NTSB) is now pressing the Federal
Aviation Administration (FAA) to undertake tests to find out how much dry
ice鈥攕olid carbon dioxide鈥攃an safely be carried on various types of
cargo aircraft. The NTSB believes that current rules might allow a plane to
carry more dry ice than its ventilation system can cope with.
The NTSB鈥檚 concern follows an incident in 1998 at Brownsville, Texas, in
which all four crew on a Douglas DC-8 cargo aircraft fell ill as they taxied to
the runway for take-off. Their symptoms included dizziness, racing heartbeats
and shortness of breath. A fire department analysis of the atmosphere in the
plane noted that oxygen levels were low.
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Dry ice is popular as a refrigerant on cargo planes because it sublimes
directly to CO2 gas, rather than melting to form water which could
corrode the plane. The DC-8 had been carrying frozen seafood cooled by 435
kilograms of dry ice. But the aircraft maker鈥檚 guidelines on carrying dry ice,
based on an FAA standard set in 1974, say the plane ought to be able to carry
more than 2500 kilograms of dry ice.
NTSB investigators now believe the rate at which dry ice sublimes changes
markedly depending on how it is packaged. The dry ice on the DC-8 was spread
among 198 separate containers. This means that it would sublime far faster than
the large lumps of dry ice on which the FAA鈥檚 current sublimation rates are
calculated. As a result, CO2 emissions could have been 鈥渁n order of
magnitude higher than current guidelines would suggest鈥�, the NTSB says.
Paul Schlamm, a spokesman for the NTSB, says the board has written to the FAA
recommending new sublimation tests on different aircraft and ventilation
conditions. FAA spokesman Les Dorr says the agency will respond within 90 days.