The discovery of traces of the high explosive compound Hexogen in the wreckage of a TU 134 Russian passenger jet yesterday is an ominous development. It points to the renewed use of plastic explosives as a weapon of terror against civilian aviation targets.
Plastic explosives have been used in the past to down civilian airliners. Both Pan Am flight 103 over Lockerbie and French flight UTA 772 lost over the Niger desert in 1989 are examples of civilian aircraft destroyed by plastic explosives detonated in the cargo hold.
What is unusual and disturbing about yesterday's discovery is the suggestion that the explosives may have been detonated within the pressurised cabin of the aircraft by a suicide bomber. The detonation of even a tiny amount of Hexogen, or RDX as it is also known, within a passenger jet would lead to immediate decompression along with catastrophic structural failure and destruction of the aircraft. Such explosives are almost impossible to detect - even with the latest generation of explosive detection systems (EDS).
Most modern EDS rely on ion spectroscopy technology to detect the tell-tale vapours or chemical signature of nitrogen-based commercial high explosives. However, military explosives such as Hexogen, RDX or Semtex are chemically bound in such a way as to render them odourless and almost impossible to detect in this way.
To compound matters, to date EDS and X Ray detection systems have been concentrated on luggage and baggage carousels - not on passengers themselves. Since 9/11, the emphasis has been on screening passengers through metal detectors for conventional weapons such as knives and firearms or metal objects capable of being used as weapons.
This week's developments in Russia suggest that terrorists have converted themselves into human bombs by carrying small amounts of plastic explosives on to civilian aircraft.
In such circumstances, even if all passengers were subjected to a minute EDS sweep, the small amount of military high explosives necessary to destroy a passenger jet in mid-flight would be practically invisible to current detection systems.
Dr Tom Clonan is a Fellow of the Inter University Seminar on Armed Forces and Society based at Loyola University, Chicago
