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Authority: Dr. Clark Thorp, Ph.D., M.D. Acting Chairman, Department of Chemistry and Chemical Engineering, Armour Research Foundation, Illinois Institute of Technology. Subject: OZONE - is Non-Toxic In many discussions on the properties and uses of Ozone, it is stated that Ozone is a toxic substance, that is harmful to the mucous membrane, that it is an irritant or that it is a poisonous gas. These statements are based upon the results of experiments which were carried on by workers who were unaware of the true nature of the gas they were investigating. However, recent authoritative investigation have established that pure Ozone is non-toxic even in concentrations as great as 20 to 50 parts per million of air. Ozone containing oxides of nitrogen, on the other hand, can be toxic in concentrations as low as 1.5 parts per million. Ozone is produced by the action of an electrical spark either upon the atmosphere, or upon pure oxygen. If pure oxygen is used, the pure Ozone is generated. However, if atmospheric air is utilized for its production, the Ozone will be contaminated by certain amounts of oxides of nitrogen, depending upon the type of generator employed, and the nature of the dielectrics, current voltages, etc. In discussing Ozone generators we may state that there are small ozonizers utilizing several small pieces of ordinary window glass or mica as a dielectric superimposed between wire screen or perforated metal plates. Such crude and unscientific construction results in the formation of sparks and abnormal heat. Tests on such units show that the output of nitrogen oxides is equal to and, in many cases, greater than the output of Ozone. The majority of the reports claiming Ozone to be a highly toxic gas are A DIRECT RESULT OF THE USE OF SUCH EQUIPMENT. The reports of the American Medical Association, Dadlez, Elford, and Konrich may be cited as examples. "Although it has not yet been definitely shown why Ozone containing nitrogen oxides is highly toxic, IT HAS BEEN DEFINITELY ESTABLISHED THAT OZONE FREE OF NITROGEN OXIDES IS COMPARATIVELY NON-TOXIC." CONFIRMATION WAS MADE IN 1942 by HILL, A PHYSICIAN SPECIALIZING IN INDUSTRIAL HYGIENE. In 1921, Hill and Aeberly published a series of articles reporting on tests concerning the effects of Ozone, chemically, physically, and physiologically. As a result of these tests a toxic limit for Ozone was established at 1 part per million. It was also stated that 20 parts per million with an exposure of two hours might prove fatal to human beings. After noting the work of Thorp, Hill, realizing that oxides of nitrogen had been present in his previous test, decided to re-run the test on an identical basis to determine if pure Ozone had higher toxic limits. AS A FINAL RESULT OF HIS WORK, HILL STATES: "PURE OZONE IS NOT POISONOUS IN ANY SENSE OF THE WORD AS IT BREAKS DOWN IN CONTACT with the mucous membrane and only oxygen remains." In "Industrial Medicine and Surgery," Toxicity of Ozone