What is static electricity?
Static electricity is a stationary electrical charge which is built up in a material. This is a very usual phenomenon in our everyday's life: a common example caused by static electricity is the electric shock we suffer when touching a door knob. We also know from the experience that our hair stand straight out from our head when pulling off a wool jersey, and this is also related to electrostatic charge.
Electrical behaviour of matter
All materials are composed of atoms, which in turn consist of smaller particles: protons, neutrons and electrons. A simplified way to represent an atom is a positively charged nucleus, formed by neutrons and protons, and electrons, which have negative electric charge, orbiting around the nucleus.
Under certain conditions, the outer electrons can move from one atom to another; the atom that looses electrons is then positively charged, and the atom that gains electrons is negatively charged. One very common way to move electrons is to rub two different materials together: electrons will be transferred from one to the other and a static charge will be created in both materials.
Two objects with opposite electrical charges attract each other, while objects with the same charge repel from each other. Coming again to the example of the wool jersey, when we take it off it rubs against our hair, electrons move from the hair to the jersey so a positive static charge is created in each of the hairs; that is why the hairs stand up and away from the others.
Static charge accumulation on an object can lead to discharges when the object comes into contact with another: this is what happens when a static charged person touches a metallic door knob and feels a shock.
Lightning is an electrical discharge caused by the built up of static electricity inside the cloud
Static electricity in new working environments
Although the knowledge of static electricity dates back to the earliest civilizations, it has become more and more important since the 20th century with the widespread use of plastics and synthetic materials which intensify the build up of static electricity. The use of these materials are very extended nowadays and we can find them for example in clothes, in plastic seats or in laminated floors.
The effects of static electricity in our everyday activities are diverse, some more perceptible than others. Static electricity can cause unconfortable shocks, disorders and even diseases such as semicircular lipoatrophy related to sick buildings.
Semicircular lipoatrophy is described as a rare condition that consists clinically of a semicircular zone of atrophy of subcutaneous fatty tissue located mostly on the front of the thighs. It is not associated with other symptoms and seems to be reversible after finishing the exposure to risk factors. One of these factors is related to static electricity.
Effect of the flooring on the accumulation of statics
While simply walking, our body can accumulate a large electrostatic charge due to friction with our clothes or with the flooring. Nowadays most of the flooring materials used are isolators, thus avoiding the dissipation of the static charge accumulated in our bodies, and making the static shocks and discharges usual.
The graph below shows the variation of voltage while a person walks on different types of flooring. At the first part of the graph, the person is walking on a synthetic non-conductive quartz based flooring, thus resulting in large negative charges in the body up to 4,2 kV. At the second part of the graph, the person is walking on carpet and in this case the accumulated static charge is also very large but positive, reaching values above 3 kV.
The last part of the graph shows the voltage when the person is walking on ConduStone conductive flooring: the accumulated charge dissipates through the flooring and the statics keeps stable and remains below 1,5 kV, within values considered to be safe for our health.
Graph showing the accumulation of statics in the body by walking on different types of flooring