Maybe noxious chemicals -- gas creating mixtures.
FIXOR is a two-component explosive kit, based on a flammable liquid. It has been designed to replace the use of plastic explosives and block TNT as traditional demining and UXO explosive charges. Unlike ammonium nitrate based binary explosives and traditional explosives:
FIXOR can be transported around the world by any method, including commercial passenger aircraft. This makes FIXOR rapidly available to those Customers who require safe, secure, single-purpose, demolition explosives throughout the world.
FIXOR Explosive self-neutralizes after a period of time, becoming a non-explosive. This unique characteristic of FIXOR is very important to those Customers concerned with the proliferation of explosives-based terrorist devices.
FIXOR is in operational use in many landmine affected countries and has been proven effective at destroying a large variety of anti-personnel and anti-tank landmines as well as unexploded ordnance (UXO).
So banning liquids makes complete sense. Because this widely available commercial product is not the only kind of binary explosive.
PLX is another example.