Document BRzZQgNa6mb9X5xjvMdYoJ3w

738 LEON F. CURTISS amount of air that can be drawn through the hood is limited by the fact that't adhesives in the paints dry quickly in an air stream and are sometimes difficulty apply. Where hoods are used and additional ventilation also is required, ig essential to provide sufficient make-up air to the room at all times, and it is well, equip each hood with an air flow indicator. Ten changes of air per hour, com-bii with good housekeeping, have been found to produce satisfactory general ventil tion in an average dial-painting room. Hoods for painting dials should be enclosed on all sides except the face, wfi| should have an entrance opening of about one square foot. The glass top sh6\ extend to the front edge of the worktable, and sufficient air should be exhausted maintain an inward flow of 50 to 60 l.f.m. at the face of the hood. Enclosun c the compounding of radioactive paints, that is, mixing the dry powdered pigriiei with the radioactive constituent or mixing the compound with the adh lie should be exhausted at a face velocity of not less than 100 l.f.m. Compounding should be done only by experienced technicians who are aware of the haza d involved in handling relatively large quantities of radioactive substances precautions required in the handling of millicuries of radioactivity should"* observed. ^ ' ` -t1" It is obviously necessary that all ventilation described above should d- hi c i the exhausted air to the outside atmosphere, preferably above the roof oftj building. The air should not be recirculated or exhausted in a way in which ;r be drawn back into the building, either by natural or by forced ventilation^ It must be pointed out that the real criterion in judging the performance ventilation system is the radon concentration in the workroom air at the zone of the workers. Any system that keeps this concentration consistently tolerance is adequate from the standpoint of injuries from radon. Since1! painting should never be permitted even remotely to resemble a dusty operrfj the radon is-the chief offender to be controlled. In rooms where radium luminous compounds are manipulated it is necei to see that ventilating systems are in operation at least a half hour befoi employees start the day's work. This precaution is required to reduce- " ' concentration in the air that results from an accumulation in stagnant ai'Pcl the night. Radioactivity tests of room air samples taken at. the start should be made occasionally to test the effectiveness of this procedure.. -. ^ Repainting ;.Didls. Repainting of radium luminous figures on-diiBCls|g; done with caution. The old compound contains essentially--all the rfldifl: originally, and it must be removed under the same precautions required fo similar radioactive material. Dust must be avoided, and the waste materla|` --he-dispbsed^f--a9-rfli'dio&otive-wftste-f-r-om-oth6F-operaftiO&Sr^SeflSgtlffii compound is soaked off; where this is done, the hands should not be permittedS^, come in contact with the solvent after dials have been immersed in it. The rulrnc' gloves used for protecting the hands should be checked frequently for radio'tfcti.v' contamination. AS RADIANT ENERGY 739 Jb>*Dressing Rooms and Protective Clothing. In plants manufacturing radioH&S luminous dials there is absolute necessity for dressing rooms entirely ifarate from the workrooms. These dressing rooms are to be used by the 'i^tpfcyees to change from street clothes to working costume and for storage of >:!onal effects, including purses and other valuables. Employees should be divided with coveralls, such as smocks, and caps, which they never take from the ant. Laundering and testing for radioactivity of these garments should be the (,i< 'ppnsitoility of management. The coverall should be the external garment worn lirti1 t"nes *n the plant' A double locker system should be installed, and street "cidthing should be kept entirely separate from work clothing. All personal effects He employee should be kept in the locker for street clothing. B. THORIUM POISONING 1. Industrial Use of Thorium In addition to the former use of mesothorium in radioactive luminous fapound, thorium itself is used in the manufacture of gas mantles, which are still considerable demand in this country, mainly for use in portable gasoline lights ^similar lighting devices. In the extraction of thorium from the ore, meso- iium is separated and, usually, refined. The supply of mesothorium is not -cient in quantity, nor is the regularity of production adequate, to permit it to hpete with radium for industrial use. Consequently, there is little demand for 'radioactive substance, and the refining of mesothorium has been limited to ||>r two lahoratories with a few employees under close supervision. The large Band for thorium now is as fuel for nuclear reactors, and refining operations Vat present supervised by the Atomic Energy Commission, A summary of the ^ards and precautions for a laboratory engaged in mesothorium refining has ^-published by Schlundt, McGavock, and Brown.18 TheSe-hazards are similar, i somewhat intensified in degree, to those describedt; in this chapter in potion with the preparation and application ofkfMdioactive luminous |ound. %.&* fin the thorium mantle industry the main hazards are probably from the elation of thoron in the manjlc-spaking, operations, where mantles are soaked ,,is bowls of thorium nitrate .spluth^)itftnd?fromytherinfaa'lationioftduSt^in-;the |Jp'Cut'ting operatioH','wHcre 'COnSIderhble thorium-bearing dust is generated, operations can be controlled by local exhaust ventilation. Concentrations up iX 10-8 curie of thoron per liter of air have been found in thisi industry by ij&.and Goodman,18 but none of the workers studied showed evidence 6f injury fitta^ornexiantraica^tffi^ fjence -between this situation and those where materials containing radium ^manipulated, as far as measurements for control are concernedf'lies'in'the- *H. Schlundt, W. McGavock, Jr,, and Mildred Brown, J. Ind. Hyg., 13, 117 (1931b R. D. Evans and C. Goodman, J. Ind. Hyg. Toxicol., 22, 89 (1940), ,