Explosives are materials that are designed to produce controlled violent reactions. These reactions generate large amounts of heat and gas in a fraction of a second. Shock waves produced by these rapidly expanding gases are responsible for much of the destruction caused by an explosion. Other materials are often added by terrorists to an explosive to augment the effect such as incendiary material, projectiles (ball bearings, nails, metal scrap) chemicals or biological contaminants to increase damage and/or casualties. Terrorists tend to not try to use explosives for demolition purposes as that requires considerable technical skill and knowledge. An example of such a failure is the right wing bombing of the Mtamvuna Bridge between the RSA and the former Transkei in 2002.
Certain elements can naturally produce a burning or explosive effect, notably the Alkali Metals (in order of reaction, starting low): Sodium <Na>, Potassium <K>, Rubidium <Rb>, Caesium <Cs> (both rare) and Francium <Fr> (a very rare and radioactive element). These will burn or explode if mixed with water.
Francium would react much more violently than this sample of sodium in water (Ajhalls, public domain)
The first known explosive is Black Gunpowder, a mix of carbon (charcoal) <C>, sulphur <S>, and potassium nitrate (saltpetre) <KNO3> with water <H2O>. When these chemicals are ignited a very rapid chemical reaction – expansion of high temperature gasses – takes place. The products of that reaction are four gases <43%>, water and two solids (56%), which forensic science investigators can easily detect, potassium carbonate and potassium sulphide.
The gases create shock waves that can knock down people, trees, buildings, and other objects and carries the hot gases, which can burn objects and initiate fires. This combination of shock wave and high temperature is characteristic of most kinds of explosives. However, the mixture used in gunpowder is fairly critical and if got wrong may do nothing or just create rapid burning. This may be what happened in the 15 Sept 2017 Parsons Green train ‘bomb’.
Gunpowder: An explosive mixture of charcoal, potassium nitrate, and sulphur often used to propel bullets from guns and shells from cannons. It is relatively easy to make.
Nitrocellulose: The propellant in modern firearm ammunition. It is relatively easy to make.
Dynamite: An explosive made by soaking an inert (inactive or stable), absorbent substance with a mixture of nitro-glycerine or ammonium nitrate, a combustible substance such as wood pulp, and an antacid. Not easy to make and dangerous.
Chemical explosive: A compound or mixture that will explode.
Binary Explosive: Two or more chemicals which, when separate will not explode, but when combined in the correct proportion will explode, either spontaneously or when initiated. A simple example which is well known and warned about on them is mixing pool acid with pool chlorine. When weaponised this mixture also produces toxic chlorine gas.
Nitro-glycerine: An explosive liquid used to make dynamite. Nitro-glycerine is highly dangerous as it is very unstable and explodes if subjected to shock. TNT can ‘sweat ‘ nitro-glycerine, due to heat or age.
TNT: Trinitrotoluene is a high explosive, one of the most commonly used explosives for military, industrial, and mining applications.
IED: An Improvised Explosive Device is a bomb constructed and deployed in ways other than in conventional military action. It may be constructed of military, commercial or home-made explosives. Commercial explosives are widely used in South Africa for mining use and are a popular ‘black market’ item, mostly for criminal use but equally illegally available to terrorists.
Classification of explosives
Explosives can be classified into one of four categories: primary, low, high, and nuclear explosives.
Primary explosives. Primary explosives are generally used to set off other explosives. They are very sensitive to shock, heat, or electricity and, therefore, must be handled with great care. Failure to do so has resulted in the death of many terrorist bomb makers.
Primary explosives also are known as initiating explosives, blasting caps, detonators, or primers.
Low explosives. Low explosives burn only at their surface. But this burn takes place very rapidly, just a few thousandths of a second. This property is utilised in guns and artillery because too rapid an explosion could cause the weapon itself to blow up. Fireworks also are low explosives.
High explosives. High explosives are much more powerful than primary or low explosives. When detonated all parts of the explosive blow up within a few millionths of a second. Some also are less likely to explode by accident. High explosives include ‘Anfo’ – an ammonium nitrate and fuel oil mixture – which is very popular with terrorists as it is very easy to make at home.
Others include dynamite, nitro-glycerine, PETN (pentaerythritol tetra nitrate), picric acid, and TNT (trinitrotoluene). They are the explosive force used in military hand grenades, bombs, and shells. C1 and Semtex plastic explosives are very popular military demolition explosives.
High explosives that are set off by heat or electricity are called primary explosives. High explosives that can only be set off only by a detonator are called secondary explosives. When mixed with oil or wax, high explosives become like clay and are called ‘plastic explosives’. They can be moulded into various shapes to hide them and so are a favourite weapon of terrorists.
Nuclear explosives have not yet been used by terrorists due to the complexity of building them, international controls and lack of availability of the main components.
A SATAC Open Source Article By Andy Grudko