A F O R U M ON SAFETY Hazards in the chemical and chemical process industries are many, but the application of sound and scientific safety principles is saving millions of manhours of lost time a year* Presented here are papers delivered before the Annual Regional Conference of the Philadelphia Safety Council outlining methods used by leading proponents of safe practices
Safe Handling of Fluorine Chemicals HENRY
C.
MILLER.
Pennsylvania Salt Mfg. Co., Philadelphia, Pa.
The hazards in the use of fluorine chemicals need to be looked into, in view of the great increase in production and applications of the chemical in the past 1 0 years J. HKUE has been a large increase in the production of fluorine chemicals during ihe past 10 years, and because of the wide distribution of their use through industry, it is important that safe methods for handling these chemicals Uv known. This higher production of fluorine chemicals is clearly shown by the increase in consumption of acid grade fluorspar, the raw material from which nearly all of the fluorine compounds are made. Acid grade fluorspar consumption has increased from about 15.000 tons in 1938 to well over 120,000 tons in 1948. A partial list of the uses of fluorine chemicals illustrating their wide distribution through industry indudes acid fluorides and fluosilicates as laundry sours, cryolite as an electrolyte component in the manufacture of aluminum, cryolite as an insecticide, anhydrous hydrogen fluoride in the petroleum industry, freons as refrigerants, cryolite in the enamels and glass industry, and of course many fluorine chemicals in the production of the atomic bomb. T h e knowledge of the toxic properties of fluorine chemicals has not kept pace with their expanding utilization, and consequently suspicion of potential health hazards inherent in their use has provoked some public concern. In this paper there is presented a collection of some of the more recent data on the hazards of fluorine chemicals, together with suggested safe handling procedures,
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on the pro-
Fluorine Chemistry For the benefit of those not familiar with fluorine chemistry, the following remarks may be of interest. Fluorine is the most electronegative of all of the elements; there are no oxidizing agents strong enough to liberate it from its compounds. Consequently, fluorine can he liberated only by electrolytic methods in a rather specialized cell. It is made at only a few places in the world, and, contrary to impressions which may be gained from the popular press, it has not been responsible, so far as reliable reports show, for any industrial accidents. However, it is a hazardous substance. One source of confusion in the press is the failure of reporters to distinguish between fluorine and hydrogen fluoride. Elemental fluorine can be made t o combine directly or indirectly with all of the elements except the inert gases. Combined fluorine always exists in the minus one valence state, as fluoride. The raw material from which most of the fluorine compounds are made is fluorspar, or calcium fluoride, a rather widespread mineral. However, good deposits are quite scarce. B y heating fluorspar with sulfuric acid, hydrogen fluoride is made. It is sold as a liquefied gas in pressure cylinders as anhydrous hydrogen fluoride, or as hydrofluoric acid, which is a water solution of
CHEMICAL
hydrogen fluoride. From this acid almostall of the fluorine products are made. Physiological
Effects
Physiologists have shown by animal experiments that fluorine may be one of the necessary trace elements for good health. Rats raised on a fluorine-free diet were in poor health in a few weeks and were not able to bear young (./). li has been shown that drinking water containing fluoride has a beneficial effect on the teeth of children. A rather significant reduction in the incidence of dental caries has been observed and reported for regions where the drinking water contained at least 1 part per million of fluoride (£). At still higher concentrations of fluoride ion, the structure of growing teeth may be changed, so that the surface develops a mottled appearance. Mottled teeth may still be strong and healthy and, while they m a y be somewhat more brittle than, the normal tooth, they have a tendency t o resist decay. On close study, no other chronic effects attributable to fluoride ion were noted in an area where the drinking water contained fluoride ( 3 ) . At still higher intake of fluorides over a period of many years, clinical examinations of industrial workers have shown that the bones of the body are affected, without disabling the worker (6). W h e n fluoride is taken in rather high concentration, chronic fluorosis may appear in man, although the exact level of intake at which this occurs is not well documented (4, 6). Certainly the large percentage of fluoride ion absorbed is excreted. Intake as high as 20 t o 30 milligrams per day of fluoride may b e
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tolerated over rather long periods of time without producing any chronic effect, or visible change in bones and teeth of adults (5, 7 ) . When fluoride is ingested in such large quantities, about 90% is eliminated at once, and at least part of the remaining 10% may be eliminated slowly from the body over a long period after ingestion. These figures are quite well documented and would indicate that although fluorides are regarded as a general protoplasmic poison, t h e y do not act as a chronic poison on man when their intake i s limited to about 10 milligrams a day. Their effect is altered according to the chemical compound and the amounts involved in the specific exposure. Therefore, a discussion of some of the hazards of the individual fluorine compounds is in order. For this purpose a division into classes is convenient. Insoluble Fluorides The water-insoluble fluoride salts will be considered first. Fluorspar and cryolite, the only common members of this class, are found as minerals. Fluorspar has already been mentioned as the important source of fluorine, while cryolite is only a minor source and, in fact, some cryolite is made synthetically from fluorspar. Because of their low solubilit}-, fluorspar and cryolite have low toxicity. T h e y are nonirritating t o the skin, and when inhaled e v e n in relatively large amounts will not cause much coughing or irritation. It has been reported that when inhaled they are slowly absorbed to produce chronic poisoning or fluorosis. T h e reported symptoms of fluorosis, besides the bone changes as revealed b y x-ray, are anorexia, vomiting, constipation, dyspnea upon exertion, and rheumatic pains. These reports on chronic poisoning are not too well documented, however, and more recent work would indicate that a large part of the fluoride absorbed would b e eliminated, and, as pointed out before, considerable amounts can be tolerated in the body without chronic effects {6, 8). The lethal dose for the insoluble fluorides must b e quite large, and this type of poisoning cannot be considered an industrial hazard. Many of these insoluble fluorides are used industrially for their fluxing action on other substances. When they are so used a t high temperatures it is possible that t h e y m a y have sufficiently high vapor pressure t o cause fluorine poisoning; however, authenticated cases of such poisoning have not been reported in the available literature. Soluble Neutral Fluorides T h e soluble nonacid forming fluorides are the next to be discussed. This class would include some of the fluorides and some of the complex compounds of fluorine such as the fluosilicates and the fluoborates. These compounds are
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widely used in the ceramic industry, the electroplating industry, and the laundry industry. The dry salts of these compounds or their neutral solutions in water will not burn the skin. When the soluble fluorides are inhaled as dusts, they are readily absorbed. Within limits, urinary excretion may be expected to take care of the fluoride so absorbed. I t has been shown that over 10 milligrams of sodium fluoride may be ingested daily without storage or harmful effects {5, 7, 12). T h e urinary excretion may be used as a measure of fluoride inhaled or ingested, and it can be used as an index to show when toxic limits have been exceeded. Acute poisoning from sodium fluoride taken orally is of rare occurrence in industry and results almost entirely from accidental ingestion. A lethal dose varies from 5 to 15 grams when taken by mouth. It produces severe cramps, with stomach and intestinal hemorrhages which progress to death from shock. Small amounts of sodium fluoride m a y be swallowed by industrial workers working in a dusty atmosphere and may cause minor nausea and vomiting. A careful study of workers exposed to sodium fluoride vapors coming from an open hearth furnace failed to show any chronic effects that could b e attributed to such vapors (5). T h e toxicity of the soluble fluorides varies greatly. Recent unpublished work has shown that the fluoborates are eliminated much faster without toxic effect than either the fluosilicates or the fluorides. Acidic Fluorine Che-nzcals The third class of compounds t o be discussed is that of the acids and the acid forming compounds. This class includes hydrofluoric acid, fluoboric acid, fluosilicic acid; and, for convenience, this class also includes the salts of these acids that hydrolyze in water to form acid solutions. All of these compounds are extremely corrosive to t h e skin, especially water solutions of the salts and acid. Skin changes caused b y exposure to these compounds range from minor burns to serious ulcers which heal very slowly. Blisters are fairly common and loosened fingernails are said to occur. Hydrofluoric acid is by far the worst offender of this group. In experimental animals, the inhalation of hydrofluoric acid gas in sufficient concentration usually causes fatal edema of the lungs. Experience has shown that the fatal vapor concentration for a man in good health is so irritating to the e y e and to the upper respiratory tract that the only way a lethal dose of the acid fluorides could be received b y inhalation without ample warning would b e by a sudden inhalation of a high concentration of the acid compound as a fine spray or dust. Several such accidents have been reported. However, it is inadvisable t o place full reliance o n this
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warning given by the eyes and nose, a s workers suffering from anemia or cardiovascular diseases might well succumb to circulatory collapse or pulmonary edema after exposure to concentrations which are not too irritating to the eyes and nose. Oxidizing Fluorine Compounds The next group of fluorine compounds contains those having oxidizing powers. This class is new to industry and i n cludes elemental fluorine, the halogen fluorides, and the so-called metal polyfluorides, which are salts of the metals in their highest oxidized state: cobalt trifluoride, silver difluoride, and lead tetrafluoride are common examples. Uranium hexafluoride is an example developed during the recent nuclear energy experiments. Elemental fluorine and the halogen fluorides react vigorously with most oxidizable substances at room temperature, frequently with immediate 'ignition, and with most metals at elevated temperature. These substances can also support the continuous combustion of. glass and asbestos. They form explosive mixtures with w a ter vapor, ammonia, hydrogen, and most organic vapors. T h e metal polyfluorides are considerably less reactive than elemental fluorine and the halogen fluorides. T h e y probably should be classed in activity along with the acids and the acid-forming compounds as far as industrial hazards are concerned. I t is n o t necessary to go into the toxic nature of these substances; naturally, they are extremely toxic. They all react with water to form, among other things, h y drogen fluoride, and thus they combine their oxidizing action along with the action of the acid. Fortunately, however, this extreme activity of these substances has always been recognized and adequate precautions taken. Organic Fluorine Compounds The active organic fluorine compounds form the fifth class to be discussed. This group of compounds may conveniently be divided into two subclasses: those that hydrolyze in water to give hydrogen fluoride, and those that d o n o t hydrolyze but have a toxic effect not associated with hydrogen fluoride. Varying amounts of fluorine may b e introduced into the organic molecule, with varying effect. In general, the first few atoms of fluorine introduced into the molecule are the active ones. After a molecule is pretty well saturated with fluorine, it becomes relatively inactive. The organic compounds that hydrolyze in water j;o form hydrogen fluoride are toxic because of the acid so formed and should be handled like the other acid fluorides. There are other compounds that may not hydrolyze to form hydrogen fluoride but still have high toxicity. In fact, some of the most poisonous known substances belong t o this class, 3855
for example sodium fluoacetate and diisopropyl fluorophosphate. I t is possible that s o m e o f these toxic compounds may be produced in the cracking of the more stable fluoro derivatives. However, as the hazards of these compounds are not caused directly by fluorine, no general statements are required for them. As pointed out above, when a sufficient amount of fluorine has been introduced i n t o the organic molecule, stable inert compounds are formed. These are known a s the fluorocarbons, and present work seems to indicate that they are nontoxic. This is surprising as carbon tetrachloride is a very toxic substance, whereas carbon tetrafluoride is completely nontoxic. inert Fluorine Gate* The last group of compounds constitute t h e inert fluoride gases. Fluorine produces many gaseous compounds, some o f which are extremely stable. T h e o n l y examples well known t o date are the freons (chlorofluoromethanes and -ethanes) and sulfur hexafluoride. The freons are widely used as refrigerants, while sulfur hexafluoride has extremely desirable dielectric properties. They have b e e n thoroughly tested and found t o be completely nontoxic. industrial Hazard* Years of experience in the manufacture o f fluorine chemicals have shown that these materials can be handled with relative safety, providing their hazards are recognized and the necessary precautions taken. Any process that is using fluorine chemicals should be carried o u t in an area that is well ventilated. This applies to the solid, insolub l e fluorides as well as t o the acid gases. If any large amount of fluoride gases or fluorides has t o b e disposed of. the material should be reacted with lime, converting the fluorine content to insoluble calcium fluoride, which can then b e disposed of in the ordinary way. Small quantities of the fluorides could b e disposed of by venting to a high 9tack; however, this procedure is to be avoided whenever possible. The extremely active fluorine gases can be disposed of conveniently by burning them 'with a hydrocarbon. This produces carbon tetrafluoride and hydrofluoricacid. The resulting gas mixture is then scrubbed with a water-lime mixture and the resulting calcium fluoride can be disposed of as a harmless solid. Unreactive gases can be vented without harm t o personnel. Workers in operations involving exposure to fluorine compounds that are acid or acid-forming should be selected initially by medical examination. N o worker with a doubtful chest x-ray or suffering from asthma or other pulmonary complaint, or from cardiovascular disease, should be e m ployed in such operation. Where it is necessary t o work with complete protec-
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tion, including rubber suits, it is important that the worker should have a cardiovascular system with completely normal response t o exercise. Otherwise, serious circulatory collapse can result merely from interference with heat transfer of the body due to the impermeable rubber clothing. Before anyone is allowed to work with any of the acid and acid-forming compounds, they should be provided with the proper safety equipment t o carry out the work they are to perform. If possible, the same men should always be assigned to the work, and they should be thoroughly instructed regarding the hazards involved. I t is very important that each worker be assigned his own protective clothing and be instructed in how to keep this clothing clean. Working with Hydrofluoric Acid The following clothing has been found practical for work with hydrofluoric acid and should be easily adaptable to any work wThere soluble acid fluorides arc involved: gauntlet style neoprene gloves, eye shields with large 8-ineb visor; a chemical respirator with cartridges for acid gases; acid-type neoprene aprons; safety goggles, which, for those m e n who wear glasses, should be special coverall goggles to fit over the glasses. If the worker is to go into an ar^a contaminated with high concentrations of hydrogen fluoride, he must be completely protected by a neoprene suit which is provided with a gas mask of the hose type. It is quite important that each workman be provided with neoprene-sole safety shoes. The release of fluorine chemical:*, whether accidental or otherwise, may leave a film of acid on any object contacted, and touching these object.- will result in an acid burn. In any area exposed to any soluble fluorine chemicals, cotton or canvas gloves should be prohibited, as such gloves are easily contaminated with the solid fluorint compound which can be hydrolyzed to form hydrofluoric acid and then would penetrate through the canvas glove and cause a rather serious burn. Full detail" for handling hydrogen fluoride are given in the Manufacturing Chemists Association Safety Manual H-10 (9) Protective measures against fluorine and the halogen fluorides are not fully developed, and entry into zones contaminated with these compounds should be avoided. Only airline or oxygen masks can be recommended for personal protection against these compounds at the present time. Neoprene gloves and face shields can give only temporary protection against fluorine and the halogen fluorides and, if brought in local contact with fluorine at high concentration, they will inflame. Therefore, safety clothing can give very little protection against such compounds. When working with elemental fluorine at ele-
CHEMICAL
vated pressure, some rather strict safety precautions have b e e n developed. Any apparatus that is t o contain fluorine under pressure should be surrounded by a protective barrier of steel at least V. inch thick, and all valves should be operated b y remote control. Such vigorous precautions are not necessary with fluorine or the halogen fluorides when used a t low pressures. Chlorine trifluoride, for example, at atmospheric temperature, has a pressure of about 15 pounds per square inch. A t such low pressure there is relatively little danger of a serious burn resulting from a failure of well designed equipment if protective clothing is worn and portable safety shields are used. All equipment that comes in contact with fluorine or the halogen fluorides must be completely dry. Tracers of water, paint, oil, metal filings, metal oxides, or any -organic impurities can cause serious explosions Extra heavy steel pipe can b e used for fluorine at high pressure if it i s cleaned and free from oxide scale. Copper tubing for 500 pounds working pressure is also satisfactory for conducting work OD fluorine and halogen fluorides. However, both the steel and copper develop :i protective fluoride film which may be dislodged by flexure or vibration. Where this is not desirable, the use of monel or alloys of nickel is recommended Standard weight pipe and taper-threaded pipe connections are satisfactory for fluorine at low pressure and temperature The recommended lubricant for pipp threads is a* water-base graphite paste which should be applied only to the external thread writh no lubricant OD the first two threads. Copper tubing may be joined b y means of brass flare fittings with the union type nut. Bar stock valves having monel bodies with Z nickel needles packed with tetrafluoroethylene polymer (Teflon) are preferred. Gages for fluorine and halogen fluorides should employ steel Bourdon rubes. After each use all apparatus and piping should be flushed clean of tlie fluorine or fluorine compounds writh an inert gas such as dry nitrogen. All ouilets should be closed immediately u> prevent the entrance of atmospheric moisture. This procedure of flushing is as important for hydrogen fluoride as it is for the halogen fluorides and fluorine There have been some serious accident.* resulting when hydrogen fluoride not flushed from $4 eel apparatus becomes diluted with atmospheric water producing a solution of hydrofluoric acid which can attack steel, generating hydrogen T h e accidents occurred when this hydrogen-air mixture in the pipe win ignited. First Aid In spite of elaborate precautions there will be an occasional accident when working with fluorine chemicals. When
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such accidents occur, the speed in removing the patient from the area and the application of first aid will, i n many cases, determine how serious the accident will be. T h e following is a brief summary of the most recently recommended first aid treatment for the most common of the accidents likely to occur, that is, hydrofluoric acid burns. This treatment has been taken in part from Manual Sheet H-10 (0). The area of the worker's body that was in contact with hydrofluoric acid should be immediately washed with large quantities of water. Following this, an ice-cold saturated solution of magnesium sulfate or iced 70% alcohol should be applied for a t least 30 minutes. T h e physician should be on hand to administer treatment before the completion of the magnesium sulfate or alcohol treatment. If, however, he has not arrived by that time, it is then permissible to apply a generous quantity of paste made from powdered magnesium oxide and glycerol. For many burns this is the only treatment required; however, for the more serious burns the physician may want to prevent further penetration of fluorine ion b y the injection of calcium gluconate. While immediate attention must necessarily be given to the removal of hydrofluoric acid from the skin of exposed workers, the acute exposure to hydrofluoric acid can also lead to shock and circulatory collapse. Therefore, those assisting the worker to wash hydrofluoric acid from his body should watch very carefully for signs of such collapse. Eye Injuries For the treatment of eye injury. Manual Sheet H-10 makes the following statement which, because of its importance, is quoted in full: If liquid hydrofluoric acid has entered the eyes or if the eyes have been exposed to strong concentrations of the vapor, they should be irrigated immediately and copiously with clean water for a minimum of 15 minutes. T h e eyelids should be held apart during the irrigation to insure contact of water with all the tissues of the surface of the eye and lids. A physician, preferably an eye specialist, should be called in attendance at the first possible moment. If a physician is not immediately available, the eye irrigation should be continued for a second period of 15 minutes. After the first 15 minute period of irrigation is completed, it is permissible, as •a first aid measure, t o instill t w o or three drops of a 0.5% pontocaine solution or an equally effective aqueous topical anesthetic. N o oils or oily ointments should b e instilled unless ordered by the physician. Opthalmologists may be interested in a method of treatment for chemical burns of the eye described b y Ralph S. McLaughlin, "Chemical Burns of the H u m a n C o r n e a , " American Journal of Ophthalmology, 29, 1355 (1946). Ingestion of hydrofluoric acid or of the soluble acid fluorides is not a com-
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mon accident. Such compounds cause severe burns of the mucous membranes of the mouth, throat, and stomach. Here, copious irrigation is not feasible, and the treatment in Manual Sheet H-10 (9) recommends that no attempt should be made to pass a stomach tube except by the attending physician. T h e patient should be encouraged to drink a large quantity of water without delay. After the hydrofluoric acid has been diluted with water, white of eggs or mineral oil may then be administered for their soothing effect. T h e patient should be carefully watched for signs of shock or circulatory collapse US). A worker who has been suspected of a possible severe exposure t o gaseous hydrofluoric acid should be carried at once to an uncontaminated atmosphere. Even in the absence of symptoms, a worker must not be permitted to return to work for at least 24 hours after a suspected exposure because of the potential danger of developing severe edema of the lungs. A physician should be called immediately and, if a trained attendant is available, the administration of oxygen should be started at once. The details of the oxygen treatment can be found in Manual Sheet H-10. T h e attending physician will take care of the medication; however, when adequate oxygen is supplied in the manner prescribed, all distress which accompanies suspected exposure to hydrofluoric acid gas "?,'ill usually disappear. A mild sedative., such as aspirin or sodium bromide, may be &iven if thought by the physician to be desirable. Since morphine depresses *he respiratory center, its use in suspected hydrofluoric acid gas exposure merely handicaps further an already embarrassed respiratory system. Therefore, morphine should never be given. This information has recently been distributed. Further information can be obtained from the Universal Oil Products Co., 310 South Michigan Ave., Chicago (10, 11), or in a supplement page which has been issued for Manual H-10 (9) dated December 1948. If sufficient fluoride ion has been a b sorbed b y the blood stream, the blood calcium may b e lowered to a dangerous level. In such cases the patient would suffer from shock from this cause, and the immediate administration of calcium gluconate intravenously is required (13). Nothing should be given by mouth t o an unconscious patient. Summary T o summarize, one of the first things to recognize in the safe handling of fluorine chemicals is the specific hazard involved. This hazard may have been overemphasized in the past. I n small amounts fluoride m a y be necessary for good health. I n high concentrations it is definitely toxic; however*; the symptoms are pronounced and easily recognized, and, after the original effect has
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passed, chronic symptoms are rare. Therefore, in handling most nonacid fluorine chemicals, if adequate protective clothing is worn and proper ventilation provided, there is little danger of any serious industrial hazard from these chemicals. The daily absorption of fluorine by industrial workers can be determined quite closely by urinalysis, while fluorine absorption b y the worker over long periods can b e determined by x-ray studies. Both methods will indicate excess absorption long before serious harm is done. Hydrofluoric acid and acid-forming salts present an additional hazard in that they can cause rather serious burns, often without adequate warning symptoms. However, when this hazard is recognized and first aid treatment is readily available, the dangers of these burns can be greatly minimized. Literature Cited (1) McClendon, J. F., and Foster,, W. C, "Federation Proceedings"; Vol. 4, No. 1, March 1945; Am. J. Med. Sci., 210, 131-2, (1945). (2) Dean, H. T., "Endemic Fluorosis and Its Relation to Dental Caries"; Public Health Reports 53, No. 33, 1443-52 (193S) (Reprint No. 1973). (3) McClure, F. J., and, Kinser, C. A., Public Health Reports, Vol. 58, No. 4S, 1543-58 (1944), and Vol. 59 t No. 49, 1575-91 (1944) (Reprint No. 2588). (4) Roholm, K., "Fluorine Intoxication," H. K. Lewis & Co., Ltd., London (1937). (5) McClendon, J. F., and Foster, W. C, J. of Dental Research, 26, N o . 3, July 1947 (and unpublished information). (60 Agate, J. N., et al. Industrial Fluorosis Medical Research Council Memorandum No. 22; Hie Majesty's Stationery Office, Ix>ndon (1949). (7) Dale, P. D., and MeCauley, H. B., J. Am. Dental Assoc, 37, 131-40 (1948). (8) "Health of Workers Exposed to Sodium Fluoride at Open Hearth Furnaces." U. S. Public Health Bulletin No. 229, page 33 (1948). (9) "Hydrofluoric Acid (Aqueous and Anhydrous) Handling and Discharge of Containers"—Manual Sheet H-10: (1948) Manufacturing Chemists' Association, Inc., 246 Woodward Building, Washington 5, D. C. (10) Carlson, A. J., "A Treatment of Hydrofluoric Acid Casualties—Information for Guidance of Physicians." Universal Oil Products Co., 310 South Michigan Ave., Chicago, 111. (11) Carlson, A. J., "Hydrogen Fluoride Alkylation Plants Safety and First Aid." Universal Oil Products Co., 310 South Michigan Ave., Chicago, 111. (12) Machle, W., Scott, E . W., Largent, E . J., J. Ind. Hyg. Toxicol., 24, No. 7, 189 (September 1942) ; 25, 112-23 (March 1943); 31, 134-8, (May 1949). (13) Rabinowitch, I. M., Acute Fluoride Poisoning, Can. Med. Assoc. J., 52, No. 41, 345-8 (1945).
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