Static electricity can ignite gasoline fumes

Electrostatic discharge: what to do if it suddenly sparks

Everyone knows it: That brief moment of shock when you shake someone's hand in an unsuspecting way and suddenly there is a radio transmission. So, not in a figurative sense - that might even be desirable - but quite literally: Accompanied by an electric crackling sound and a spark, which is at least visible in the dark, a mini electric shock twitches through the finger. The shock about it is usually greater than the pain itself. The phenomenon of electrostatic discharge can still be quite annoying. But is it also dangerous? In fact, it could be a fire hazard, if one believes so many Internet videos. They come from surveillance cameras at petrol stations and show unsuspecting customers who are refueling their cars when suddenly a jet flame shoots out of the tank - allegedly because of an electrostatic discharge. But can that really happen? In order to be able to answer this question, one must first understand the phenomenon.
Positively charged protons and negatively charged electrons
We humans and everything around us are made up of atoms, and these in turn are made up of different particles: In addition to electrically neutral neutrons, these are positively charged protons and negatively charged electrons. Usually this system is in equilibrium. But everything in our environment reacts with one another, and even if objects appear completely solid to us - they are not: "In a thin, invisible layer on the surface, the atoms and their electrons are only loosely bound and can easily wander," explains Professor Volker Hinrichsen, head of the high voltage technology department at TU Darmstadt. Electrons are extremely wandering companions. Whenever we touch something, we exchange these negatively charged particles with what we touch. It happens all the time and goes completely unnoticed. How intense this exchange is depends on the material. The human skin, for example, is very happy to give off electrons and plastics are extremely happy to accept electrons. However, we only feel this charge exchange when another factor is also involved: friction. "Strictly speaking, friction is the very rapid touching and re-separation of two materials," emphasizes Hinrichsen. With every touch, more and more electrons migrate from one material to the other and the rapid separation prevents the particles from being able to return to their original owner. The two objects that rub against each other are charged differently: one positively, the other negatively. The electrical balance is gone. A person who walks over a carpet made of plastic fibers is really positively charged because he is constantly giving off electrons to the carpet. As soon as he then touches an electrically neutral object - this can be the door handle, the pet or another person - it sparks and the difference in charge is compensated for again in one fell swoop.
How severe the electric shock is depends on the humidity. "At 80 percent humidity, you hardly ever charge yourself, because moist air cannot insulate well," explains Hinrichsen. “You discharge yourself at the same moment you are charging, so you don't even notice it.” With low humidity around 40 percent, as is often the case in winter, you can easily charge up to 10,000 volts - that can be painful. They are only noticeable from around 2000 volts. These small, albeit unpleasant, lightning bolts are not a health hazard, reassured the electrical engineering expert.
It looks different in industry. In some cases, even small charges that humans do not even notice can cause major damage: when manufacturing sensitive microchips, when handling explosive substances or in operating theaters, for example. In such areas, you have to pay close attention to the right equipment. But that is not always the case and possible dangers are easily underestimated, says Bernhard Schmelmer from many years of experience. The engineer has been running an institute for system floor technology in Obernburg, Lower Franconia, for over 30 years and has specialized, among other things, in checking floor coverings for their electrical conductivity. Schmelmer is commissioned, for example, by companies that want to find out whether the expensive conductive floors that are supposed to prevent electrostatic discharges actually keep what the manufacturer promises (they often don't, by the way). Sometimes the appraiser had to hold his breath. In a research institute that worked with explosives. During his measurements, Schmelmer found that the automatic lathe on which the highly explosive ingredients were assembled was not earthed. “It was actually a miracle that it went well for so long,” he recalls.
Car can go up in flames when refueling
Of course, not all of his cases are that spectacular, and he has never had anything to do with a burning car while refueling. But his colleagues do. Although that is extremely rare, it is not impossible, emphasizes Schmelmer. A few prerequisites have to come together for this - a chain of unfortunate circumstances, so to speak: a day with very low humidity. Polyamide seat covers. A driver with a polyester anorak who sits down in the car again while refueling and charges up unnoticed through friction on the seat cover. If there is a spark when pulling out the filler neck, gasoline gases could theoretically ignite.
Even the Physikalisch-Technische Bundesanstalt (PTB) points out this danger. According to its own information, the federal authority has the task of protecting employees and uninvolved third parties from the risk of fire and explosion caused by flammable liquids. "Fuel vapors that escape when refueling can be ignited in particular by electrostatic discharges," says a press release. "The latter can arise in a variety of ways - for example, when clothes rub against the car seat, through defects or unprofessional repairs to the filler neck." Ulrich von Pidoll from PTB on request. “The reasons for this were the introduction of insulating tires with low rolling resistance in combination with plastic tanks with insulated metal components,” he explains. Due to new standards, various product recalls and the exclusive production of conductive car tires, the number of such incidents has fallen dramatically since then. In recent years, the PTB has not heard of any related fires at German filling stations. So no need to panic at the pump, even with a polyester anorak in winter.
By the way, it is hardly possible to protect yourself from electrostatic charge, as it depends on too many external factors that we cannot influence. But you can mitigate the flash a little - for example by choosing the right wardrobe. Expert Bernhard Schmelmer has a hot tip for this: If you use cotton underpants and leather shoes instead of plastic and synthetic materials, you are less charged. "Sweaty feet also help," says the expert with a smile, because they dissipate electricity better. Admittedly: not exactly the sexy solution to prevent the spark from jumping over.