Document g1ZpNr945LE8Dy7amwVNxxkL

SILVERMAN-HUSAIN--NITROGEN OXIDE-ARC WELDING 141 fwne, since ultraviolet radiation and ozone generation end after welding stops. It is important to point out that although NO, is designated in these curves, it may actually be N02, N,04 or N,03. Low concentrations of N02 are formed in the first 30 minutes of welding, as shown in chart 1. On the basis of Elkins' derivations, if the total oxides are considered as NO, the amounts of N02 formed would also be small. Since time is an important variable in addition to initial NO concentration, this study included recirculation of fumes in the cabinet during and after welding. Such recirculation dilutes the NO formed, and the N02 resulting is also influenced by this factor. Chart 2 represents an experiment similar to that of chart 1, but the total fume generated during welding was largely (95 per cent) removed by filtration. Twenty- Chart 2.--Total oxides, nitrogen dioxide and total fume concentrations during and after arc welding with coated electrodes. Fumes filtered and cabinet air recirculated 0 to 60 minutes. five electrodes were used, compared with 20 for the previous experiment, which probably accounts for significantly greater amounts of total oxides and N02T Nitrogen dioxide concentrations diminish, although most of the fume has been filtered. It should be borne in mind, however, that although the fume has been reduced below the 30 mg. per cubic meter nuisance limit, yet approximately 20 mg. per cubic meter remains. The maximum amount of N02 present in chart 2 is about 10 p.p.m. (approximately 19 mg. per cubic meter). The amounts of iron fume remaining are therefore still sufficient Nfpr reaction with nitrogen oxides. Complete removal of the iron fume is not possible to attain except by ultrafiltration or use of a high voltage electrostatic precipitator. The latter device , would inter fere with the test results because of inherent oxide of nitrogen production.