How Fuel Tankers and Granaries Can Spontaneously Explode

Granaries have been blowing up seemingly at random since the beginning of the Industrial Revolution. Thousands of workers around the world since the late 1800s have died working in seemingly safe conditions due to a phenomenon called “dust explosions.” One explosion in Minneapolis destroyed the world’s largest grain mill, reducing the city’s milling capacity by nearly 50 percent. 1,549 miners died in a dust explosion in a coal mine in China.

Dust explosions have been keeping these industries on edge for over 150 years, causing an estimated 2,000 explosions annually in Europe alone, and to this day, we still aren’t completely sure what causes them. Chemists have tried to solve this problem, but have had no positive results.

“These explosions blow up entire grain towers,” a UW-Milwaukee professor says. “They happen to this day and nobody is quite sure why.”

Robert Balmer, a professor emeritus of mechanical engineering, believes that tackling the problem with chemistry is the wrong approach. His approach comes from an engineering standpoint relating thermodynamics and the behavior of electricity. He hopes to find evidence that a static electric effect has a role in dust explosions.

We’re all familiar with static electricity. If you rub a balloon on your arm for a few seconds and then touch another person, you both experience a small shock. The static electricity is caused by friction between the balloon and your arm. When two objects or particles rub together, they pass electrons back and forth, which can create and imbalance of electrons. The shock comes from the electrons wanting to balance themselves out between the two objects. Where there is a lack of electrons, it will find a way to absorb electrons from a place that has an excess of them.

This video shows what is called the "Corona Effect," a rather mysterious phenomenon that lights up the night sky when a helicopter fires up it's propeller.

In places like granaries, coal mines, and fuel tankers, there is a lot of motion in the air, creating friction. Wheat dust creates friction from being blown about the air, machines kick up dust in coal mines, and washing empty fuel tankers with water creates friction in the mist. This friction gives extra electrons to the air particles, essentially “charging it up.”

The air we breathe is what is called a “dielectric fluid.” Fluids, in the form of gases, liquid, or solids, all have a measurement of how good of a conductor they are for electricity. Water is a strong electric conductor, which is why you don’t jump into water with an operating toaster. Kerosene, on the other hand, is a weak electric conductor. Weak electric conductors do not allow charged particles (ions) to flow freely and recombine to neutralize themselves, leaving them to float around aimlessly looking for something to do and somewhere to go. The dielectric fluid that we breathe leaves many ions free-floating, which can make for a dangerous environment.

If the charge gets built up over a long time, those extra electrons on particles will want to go somewhere without electrons – to “ground” themselves. These charged up particles will come into contact with the “ground” particles” and, if the charge is strong enough, will create an arc of electricity. If you get your friend with a good enough shock using the aforementioned balloon trick, you can see this with your naked eye.

Granaries, coal mines, and fuel tankers are places that are loaded with combustible materials like flour, methane, or petroleum fumes. Arc flashes and combustible materials have a very volatile relationship in nature, and when they are in the same enclosed environment, it can mean disaster in the form of a massive explosion seemingly out of thin air.

Balmer believes that this is the cause of explosions in granaries, coal mines, and fuel tankers, and is working on an experiment that will prove his theory. Stay tuned to find out what Balmer is doing in his lab to prove why these explosions happen and how we can use that information to help avoid these incidents from happening.