Mad About Science

By Brenden Bobby
Reader Columnist

There are many ways to end up on an FBI watch list — and to satiate your curiosity, dear reader, I may have utilized one.

Plastic explosives have been a fixation in entertainment media for decades. I’ve lost count of the number of times I’ve seen a SWAT operator on TV slap a charge on a door and take cover before a massive explosion rips the aforementioned door off its hinges. Video games have also exploited a love for all things explosive by introducing C4 bricks to titles like Call of Duty, or GoldenEye 007 for those of us who feel like broadcasting our advanced age.

C4 from the game ‘Call of Duty.’ Courtesy image.

Are these things real? How do they work? Are they good for anything other than destruction and entertainment? Plastic explosives are indeed real, and their uses span from the mundane to the lethal and totally unexpected.

The first iteration of plastic explosive was a gelatin-based creation called Gelignite, a compound developed by Swedish chemist, Alfred Nobel. Yes, that Nobel — the one with a Peace Prize named after him. 

Gelignite, much like dynamite — which Nobel also invented — is a mixture of chemicals soaked in highly explosive nitroglycerine and saltpeter. Unlike dynamite, Gelignite could be molded into different shapes and attached to things before detonation. If this seems like a completely unnecessary development, you’d be surprised. Gelignite was able to be molded to fit into shapes where a stick of dynamite couldn’t reach, such as a crack in the rock wall of a mine or under the foundation of a building that needed to be demolished in a relatively controlled manner. 

Invented in 1875, military leaders were quick to recognize the potential uses of Gelignite in warfare.

By World War II, plastic explosives were a relatively common tool on the battlefield. Sappers — designated soldiers and engineers with a knack for destroying enemy fortifications — used a substance called Nobel 808, to bring down German walls, vehicles and bunkers. The British were big fans of Nobel 808, and used it extensively throughout the war. Apparently, it smelled like almonds.

The most recognizable form of plastic explosive is C4, as it is most frequently referred to in television, movies and video games. Its history began in World War II, as the British developed a high-explosive substance called RDX. RDX was often mixed with other explosive compounds such as trinitrotoluene, better known as TNT, with the intention of leveling everything Germany had to throw at the Allies. 

Chemists applied RDX to a number of other compounds, including a highly toxic variant known as C3. Eventually, C4 was produced as a highly explosive compound that was safe and stable to store with the consistency of modeling clay. 

Similar to Gelignite, this allowed the Allies to stuff the explosive into cracks and crevices where a stick of dynamite could not fit or might be noticed by the enemy.

The stability of C4 is one of the reasons it’s so appealing to militaries. Storing an immense amount of gunpowder or TNT is extremely unsafe — a rogue electrical discharge, heat or a clumsy handler could spell an explosive doom for anyone in the area. C4 can be thrown, dropped, set on fire and even shot with a gun without detonating.

That’s because C4 can only be detonated by a shockwave. This shockwave is triggered by a blast cap or a trigger rigged up to the explosive, which is usually controlled by radio. When this small shockwave happens, the chemical structure rapidly decomposes into nitrogen, water, carbon oxide and various gasses that release an immense amount of energy in the form of an explosion.

All that said, plastic explosives aren’t all doom and gloom. Though their primary function is to destroy things, they actually serve a tremendous purpose in destroying other things that could hurt people. C4 is extensively used by the U.S. military to dispose of unsafe ordnance, such as compromised artillery shells, legacy landmines recovered from warzones and other tools of destruction that may present a danger to human life.

Additionally, plastic explosives are often used to safely demolish buildings in a controlled manner, when traditional explosives are too dangerous to use. 

Imagine a poorly built, multi-story parking garage that may collapse on a crowded city block at any moment. Teams of architects, engineers and demolition specialists can identify key structures within this garage and rig them with explosive charges. 

These charges are measured to yield a precise amount of force at a precise angle to make the structure implode so it won’t hurt anyone. A similar function can be done if you are exceptionally skilled at Jenga, though I hope you aren’t playing Jenga with C4.

Another really interesting application of plastic explosives is called shock hardening. Certain types of manufactured steel can be blasted by plastic explosives in a precise measurement. The shockwave disrupts the atomic structure of the steel, which reduces its plasticity but makes it far more rigid. This is used for things like steel rails for trains that need to be extra tough, but don’t need to flex very much.

A similar principle is seen on certain models of military tanks, which utilize something called reactive armor. Essentially, plastic explosives are wedged between steel plates on the exterior of the tank. When an incoming shell strikes the tank, the shockwave triggers the plastic explosives to detonate and shock harden the armor, providing some split-second defense to the operators inside.

Stay curious, 7B.