Counter Terror Gazette

Liquid Explosives: a guide

23 Apr 2012

Given the ease of concealment of liquid explosives and their close resemblance to benign liquids already carried by most passengers, terrorists have also started to exploit such ‘benefits’ to carry out attacks against civil aviation. The first terrorist attack against civil aviation using liquid explosives was in 1987 targeting Korean Airlines and, since then, there have been several such attacks and attempted attacks, most notably the trans-Atlantic plot of 2006 which resulted in a raft of policy changes and restrictions to carry-on baggage. Amir Neeman describes some of the types of liquid explosives most commonly used by terrorists and highlights some of the specific events in which they were used.

Liquid explosives have been used for military and commercial applications since the late 19th century. The first powerful liquid explosive – Nitroglycerin or NG – was discovered in 1847 and commercialised by the 1860s with solid additives to reduce its inherent high sensitivity to friction and shock. NG has since been used as an active ingredient in the manufacture of explosives, mostly dynamite, and as such employed in the construction, demolition, and mining industries, as well as by the military. Since the discovery of NG, many other types of liquid explosives have been developed and regularly used for similar applications.

Existing in a variety of colours and densities, most liquid explosives perform as well as other regular high explosives (when comparing detonation speed and brisance). However, the commercial and military use of liquid explosives is limited due to their high volatility and toxicity which require unique safety precautions for storage and usage.

Some of the safety concerns have been mitigated by mixing liquid explosives with various solid components which may also enhance their explosive properties (energetic solid substances). Binary liquid explosives (or mixtures) were developed to further enhance the safe handling of liquid explosives since the individual components are safe to handle until mixed, making them even more suited for use by the modern-day terrorist.

Here, in alphabetical order, are just a few of the materials that challenge the aviation security system today…

Typical 3-1-1 compliant package of liquids

Astrolite

Astrolite is the trade name of a family of liquid explosives, invented by the chemist Gerald Hurst in the 1960s while he was employed with the Atlas Powder Company. The Astrolite family is part of the binary liquid explosives, which is the mixture of two non-explosive compounds that rapidly interact to then become liquid explosive. Astrolite liquid explosives are composed of Ammonium Nitrate oxidiser and Hydrazine rocket fuel. They are still used in commercial and civil blasting applications, but have mostly been superseded by cheaper and safer compounds, largely due to the expense and exceptionally poisonous nature of the hydrazine component.

The most common type, Astrolite G, is a mixture of Ammonium Nitrate and Hydrazine at a ratio of 2:1, forming a clear, viscous liquid approximately the consistency of motor oil (density of 1.36 gr/cm³). It is a relatively stable explosive compound, requiring a blasting cap to detonate. Astrolite A is less common and is synthesised by the addition of finely powdered Aluminium to the Astrolite G mixture. Though it has a lower detonation velocity than Astrolite G, the addition of the Aluminium increases its overall explosive effectiveness.

The Astrolite family is remarkably persistent for a liquid explosive due to its low volatility and can be dispersed in an area, be absorbed by the soil, and still retain its full explosive characteristics for a period of approximately four days.

 

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