Environment News Service


June 9, 1999

Each of the six blades on the MH-53J Pave Low helicopter that crashed during a training mission last week in North Carolina contained a 500 microcurie source of strontium-90, a radioactive material controlled by the U.S. Nuclear Regulatory Commission (NRC).

The strontium-90 was part of the helicopterís in-flight blade inspection systems (IBIS), which warn pilots when the blades develop stress fractures. IBIS devices release minute amounts of radiation when a leak develops in the pressurized blades, and a radiation detector on each wing immediately notifies the pilot that a blade may fail.

Most military helicopters in the U.S. and abroad contain IBIS devices, according to Major Mitch Hicks, deputy chief of the Air Force Radiation Protection Division (AFRPD). Some civilian helicopters may also use IBIS technology. The small devices are normally heavily shielded, and pose no radiation exposure risk. But after a crash the devices may become unshielded, and may release radioactive powder into the air.

Strontium-90 is a bone-seeking radiation source. If it is inhaled, it can cross the lung membranes into the bloodstream, where it will seek out bone and can lead to leukemia. The crash site on the western side of Fort Bragg, North Carolina, has been cordoned off. Response teams at the site have been warned to wear gloves and bag any IBIS devices or blade parts they locate. So far, four of the six blades have been found and bagged, and no radiation contamination has been detected.

The AFRPD says a person standing a foot from a completely unshielded IBIS strontium-90 source would have to remain exposed for 67 hours before receiving the maximum occupational dose of beta radiation set by the NRC. The crash killed one Air Force crewmember, and injured five others. Pave Low helicopters participated in the rescue of an Air Force F-117A stealth fighter pilot in Yugoslovia in March

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