Answer to Question #9399 Submitted to "Ask the Experts"
Category: Radiation Basics
The following question was answered by an expert in the appropriate field:
Before lightning strikes, the air is ionized (plasma) and the lightning can follow the ionized path. Is this ionization the same as radiation ionization for gamma and x rays? Can man-made wireless electricity produced in Tesla coils (25 megahertz and >1 million volts) ionize the air and be hazardous to humans 30 feet away?
Regarding your first question, the process of ionization simply refers to the stripping of one or more electrons from atoms or molecules, leaving the electrons in a more-or-less temporary free state and leaving a positive ion where there had been a neutral atom or molecule. This definition of ionization applies regardless of the source of the ionization. The significant difference between gamma rays or x rays and lightning as sources of ionization lies in the available mechanisms for stripping electrons from the atoms or molecules.
Gamma rays and x rays, as well as other forms of ionizing radiation, are capable of interacting directly with bound electrons of atoms or molecules and transferring sufficient energy to the electrons to overcome the binding energy in the atom and hence remove the electron(s) from the atom or molecule. You may be familiar with gamma and x-ray interactions referred to as the photoelectric interaction and Compton scattering, two common processes wherefrom ionization results. In general, the ionization of air by gamma- or x-ray sources is not sufficient to cause direct electrical harm to people, although some intense sources may produce sufficient air ionization to result in noxious gases such as ozone and nitrogen oxides that can affect the health and well-being of exposed individuals. The gamma rays and x rays produce radiation damage to an exposed individual through the process of ionization of tissue when the gamma rays or x rays interact in the human body, leading to certain chemical/biochemical changes that can have adverse effects on cells and tissues and, ultimately, on the health of the exposed individual.
The process leading to natural cloud-to-earth lightning and air ionization is quite different. In the case of lightning, a large potential difference exists between the cloud and earth and, as the potential increases, it may become sufficiently large so that the associated electric field strength is sufficient to strip electrons from atoms and molecules in the air. The stepwise buildup of stripped electrons proceeds from the cloud toward the earth until the negative charge gets fairly close to the earth, drawing positive charge from the earth toward it and resulting ultimately in the complete breakdown of the ionized air column between the cloud and earth, producing the classic lightning bolt. Such massive discharges are associated with extremely high voltages and high currents, sufficient to cause direct burning of tissue and possible electrical disruption of some bodily functions, such as heartbeat, when a lightning bolt is directed to an individual or, in some instances, to another conductor close to an individual.
The production of ionization in air and the associated visible arcs commonly associated with operation of a Tesla coil are similar to what occurs in the case of natural lightning, but the high-voltage source is produced through a specially fabricated transformer that runs on AC (alternating current) whereas the static voltage potential involved with natural lightning is essentially a DC (direct current) source. Although Tesla coils are not capable of producing air ionization to the same extent as natural lightning, as you have inferred, it is important to be aware of the potential danger associated with the operation of Tesla coil devices. While the user must be extremely cautious to avoid contact with certain elements of the primary (low-voltage) circuitry as well as to show proper respect for the "lightning" arc discharges from the coil, onlookers must also exercise some care. They should stand a sufficient distance away so that they are well beyond the range of the arcs being produced. For the system you describe, 30 feet should be more than sufficient to avoid any possible contact with the arcs from the device. Some electronic devices, such as heart pacemakers, may be affected by the RF (radio frequency) fields associated with operation, and individuals equipped with such devices should probably avoid being in the area at all. Onlookers as well as authorized users should also be aware of the likelihood of producing possibly hazardous ozone and nitrogen oxides through the air-ionization process. This becomes more important when the system is used in closed or poorly ventilated areas and when use is heavy. Even when power has been cut to the coil, significant energy may remain stored in capacitors, and untrained individuals should not approach the system until such capacitors have been drained.
I hope this answers your questions. Stay safe, and enjoy the show.
George Chabot, PhD, CHP