OxyFile #363

This article is apart of a series. Please read the preface (oxy00362) for more details.


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