Tesla noted the hazards of working with his circuit and single-node X-ray-producing devices. In his many notes on the early investigation of this phenomenon, he attributed the skin damage to various causes. He believed early on that damage to the skin was not caused by the Roentgen rays, but by the ozone generated in contact with the skin, and to a lesser extent, by nitrous acid. Tesla incorrectly believed that X-rays were longitudinal waves, such as those produced in waves in plasma. These plasma waves can occur in force-free magnetic fields.

On 11 July 1934, the New York Herald Tribune published an article on Tesla, in which he recalled an event that would occasionally take place while experimenting with his single-electrode vacuum tubes; a minute particle would break off the cathode, pass out of the tube, and physically strike him. "Tesla said he could feel a sharp stinging pain where it entered his body, and again at the place where it passed out." In comparing these particles with the bits of metal projected by his "electric gun," Tesla said, "The particles in the beam of force ... will travel much faster than such particles ... and they will travel in concentrations."