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in the Chemical Labomtory Edited by NORMAN V. STEERE,
140 Melbourne Ave., S.E. Minneapolis, Minn. 55414
LV.
Ozone Hazards* G. T. GATWOOD and 0. F. MURPHY, Cambridge Electron Accelerator Combridge, Massochuseth 02 138
Ozone ( 0 3 )is B colorless gas condensable to a blue liquid and having a eharacteristic pungent odor of new-mown hay, or for urbanites, of subways-the so-called electrical odor. Bssed upon human experience and animal studies, the recommended maximal atmospheric concentration for an 8 hr exposure of ozone is 0.1 part per million parts of air (pprn) by volume or 0.2 milligrams per cubic meter of air. It is detectable by its odor a t concentrations of 0.01-0.015 ppm, well below the allowed levels; however, because olfactory fatigue rapidly develops, reliance for detection should be placed only upon analytical results. Concentrations of 1 ppm produce a disagreeable sulfur-like odor and may cause headache and irritation of the upper respiratory tract which disappear after leaving the exposure. Inhdation of one to two pprn for 2 br produces headache, pain in the chest, and dryness of the throat. Welders who had a severe exposure at an estimated 9 pprn of ozone plus other air pollutants developed pulmonary. edema. Chest X-rays were normal within two weeks, but nine months later the welders still complained of fatigue and difficulty breathing (dyspnea). Human volunteers have inhaled ozone rtt 1.5-2 ppm for 2 hr with tolerable symptoms which subsided after a few days, although 3 hr exposure a t 0.5 pprn ozone enhances the suceptibilit,y to respiratory infections. After exposure to 0.2-0.5 ppm ozone there has been noted tenlporary .reduction in visual acuity and increased peripheral vision; however, no eye irritation was reported by a human subject exposed to 2 pprn ozone for 2 hr. On the basis of animal data, exposure a t 50-60 ppm is presumed to be immediately fatal to human beings. OZONE I S FORMED by electrical arcs and corona, discharges in air or by u h a violet photochemical reactions (which may result, for instance, in the buildup of significant ozone concentrations in the cabin of pressurized aircraft flying above 30,000 ft). Ozone is frequently found in laboratories around high voltage speetrographic and fluorometric apparatus and is being used with increasing frequency in the treatment of drinking water, industrial waste, sewage, and in chemical synthesis. The effect of ozone upon some odorous vapors ha? led to its we simed a t purifying air and reducing CO levels; however,
such a. US8 is considered hazardow because of the concentrations which may be involved. Loesl exhausts and shielding to black ultraviolet rays (welders) should be used to keep ozone concentrations below 0.1 pprn whenever possible. In cases of ozone exposure, removal from exposure and in less mild eases administration of oxygen, plus, of course, exarnimtion by a physician are usudly sufficient,t,reatment. Severe cases should be administ,ered oxygen and observed for potential pdmonary edema. Then steroid therapy should he considered. OZONE CONCENTRATION of air has been difficult to det,ermine bv chemical means, especially a t concentrations of the order of only a few parts per million part8 of air. However, making use of the well-known cracking effect of osone on stretched rubber, B. F. Goodrich developed a. device of relatively simple design to meaxre low oaone concentrations
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feature
directly. A? ozone attacks a n exposed portion of an elongated rubber golf ball thread, the weakening allows the unexposed portion to pull the thread over a pulley which moves an indicat,or needle. Time interval readings on a graduated arc yield curves which when compared with calibration curves for given temperatrm.i allow dhect readings of osone concentrations comparable to chemical methods, which artre sccmat,e t o zk5% in coneentrations of 0.03-0.25 ppm. The omnometer costs $250 with carrying case and can he used to test oaone concentrations in srea.s unaccessible to chemical methods. The Matheson Chemical Company lists a compact osone meter which provides continuous measurements of oaorlc caw centration in the atmosphere by determining the oxidation-redt~etio~? of potassium iodide. I t measures s range of coltcentrat,ion from 0-1.0 ppm/volume, with a sensitivity of 1 0 . 0 1 pprn below 0.5 ppm and +20i, above 0.5 ppm. I t runs on 11,j v ac and sells for $545. HANDLING O F CONCENTRATEI) OZONE is hazardous: in storage it undergoes t,hermal decomposition a t a compara(Continued on page A105)
* Reprinted with permission from Laboratory Safely,anewslettcr of thecampus Safety Association. Requests for reprints should be directed to (,he Editor of Laboratory Safely, Eric Spencer, Brown University, Providence, R. I. 02912. Volume 46, Number 2, February 1969
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t i d y high rate, depending upon temperature, concentrstion and pressure. At low temperatures, for example dry ice temperature of 19.5aK and one atmosphere pressure, the rate of decompasition of 100% osone is less than 10-570 per day, while a t room temperature the rate is over 67,, and a t increasing temperatures the reaction rate may reach that of thermal explosion. The decomposition is cat,alyaed by many substances (01,N?, C03, He), and the presence of minor imporities may establish chains and initiate explosions, the energy for ignition being 6 X 1 0 F joules a t at,mosphere and 298°K. The most important eondit,ions for safe storage of ozone are, then, low t,emperatore and high purity, but p~.ovicianshould also be made for preventing propagation of ally reaction which is initiated. The principle of flame quenching (see references) can be osed t o rednee the possibility ai explosion. An explosion can be developed in any combnstible gas if the flame can be maintained by liberated heat, but if the flame is quenched within a sufficiently short distauce characteristic of each snhstance, no explosion will occur. The quenching diameter (d.) of a. cylinder of ozone-oxygen mixt,ure is related to the ozone concentration a t 1 a t m and 298°K h y the empirical formula: log,o$, 7 6.1X!l - 2.118 log S , whkre d. is i n mlcrnns and X is t,he ozone concentmtia~~ in mole percentage. At 193OK, the equation becomes: loglad. = 6.403 - 2.113 log X. ~h~ relatiallvhip between qoenching diameter and pressure (at 29x0K) is given by log 10d. = 1.953 - 1.111 log P where
P i s in atmospheres. For pure oaone the quenchin& diameter of a cylinder is related to the temperature (at one almospherc initial pressure) by d, = 347.5 - 0.864T where T is the absalnte temperature. These relations were used t o determine that specially purified and heat-treated hallow, porous alumina bubbles of outside diameter between 300 and 4 0 0 ~ could be med to quench flames and cushion explosions of ozone stored under pressure in cylinders, leaving free gas space inside and between the bubbles a t as much as 90% of the empty container volume.
References
American Industrial Hygiene Associntinn. "Hygienic Guide Series." March. 1957. Cambridge Electron Accelerator, Safety ~ ~ lon ozone l ~ ~~ ~ i ~ ~ S.BQ, ~ ~ d ~zO,, . . 1968.
