Should we be really concerned about the new "invisible bomb" terrorist treat making the headlines this week? According to the Guardian here a Saudi chemist allied with both ISIS and al-Qaida (however unlikely that is) has the expertise to create invisible bombs and an ambition to target transatlantic flights. The public is warned that these explosives do not contain metals and therefore will not be detected at airport security checks. The public should ready themselves for delays in air travel. Other sources here and here are certain the explosive is a liquid.
Liquid explosives are really nothing special. Wikipedia has a category devoted to it with 17 entries to choose from. A selection: isopropyl nitrate and tetranitromethane. The list even includes binary mixtures such as PLX. Do liquid explosives differ from solid explosives? PLX (used in combination with C-4) has been responsible for the downing of Korean Air Flight 858 in 1987. The chemicals involved in the bombing of Pan Am Flight 103 in 1988 were solid Semtex and PETN. All explosives of this type are solid but malleable, heavy in nitrogen, metals are not involved and the explosives can thus evade airport security. On the other hand, a liquid explosive can be adsorbed into clothing and the Saudi chemist has already had experience in that field. In a nutshell: non-metallic explosives are nothing new, liquid explosives are nothing new. Explosives application: nothing new. Application sophistication: new.