Document jgoXOYer1w4q19M1z6yE8ZMqZ

PERSONAL PROTECTIVE EQUIPMENT (Tezt continued from page 36-11.) son with glass Findings are summarized below " Plastic specimens with sufficient section tliiAmm passed the drop-ball test of the ASA and the Federal Government for safe ty goggles At 75 F, resistance is compara ble to that of heat treated glass At 0 F, glass is generally much stronger than plas tic However, cellulose acetate 0 060 in. thick passes existing specifications from 0 to 150 F Glass lenses have slightly lower resist ance than plastic to breakage from sharp objects Both glass and plastics have some what less resistance to sharp objects than to rounded objects Tests on resistance to small objects mov ing at high rates of speed were more favor able for plastic lenses than for glass In the evaluation of all these tmjpact tests, the thiclmess of the cross section and the area of the specimen, as well as the compo sition of the material, must be considered Material of the same general type produced by different manufacturers showed differ ent properties The abrasion resistance of plastic was not good, although coated plastics and one allyl casting resin appeared better than oth er plastics The resistance of plastics to hot materi als was equal to, or exceeded, that of glass However, a minimum section of 006 m seems desirable for plastic Hot metal in variably shattered glass lenses but did not break plastic lenses Hot metals tended to adhere to glass All plastics tested showed surface reac tion to some chemicals, but satisfactorily stopped splashes and protected the eyes All plashes appeared satisfactory as lenses, but undesirable cylindrical and pris matic effects might be introduced by curv ing piano meet plastic Shght fogging occurred almost immedi ately on all glass and plastic samples, but on the average complete fogging of plastic took longer to produce than complete fog ging of glass. For spectacle goggles, the frame must be rigid enough to hold the lenses in proper position in front of die eyes If the nose bndge is not adjustable, goggles should be available in enough sizes to fit faces of vari ous shapes. Most manufacturers make a spectacle goggle that has a bndge design which will fit the majority of faces These are not, however, generally recommended for prescnption-ground lenses Frames should be of corrosion-resistant material which will neither irritate nor dis color the skm. Goggles should be of simple design for easy cleaning and disinfection Cup goggles should have cups large enough to protect the eye socket and to dis tribute impact over a wide area of the facial bones. Caps should be flame-resistant, corro sion-resistant, and nommtating to the skin To give the widest possible field of vision, goggles should be fitted as close to the eyes as possible without bringing the eyelashes into contact with the lenses For that rea son also the lenses should be comparatively large. Lenses must not have appreciable distor tion or prism effect Federal Specification CGG-G-501b" limits the nonparallelism be tween the two faces to M pnsm diopter (4 minutes of arc) and both the refraction m any meridian and the difference m re fraction between any two meridians to Mi diopter Both when supported m the eye cups of goggles and when supported on a rubber gasket on a wood tube, lenses are required to withstand the impact of a 22 mm (% in ), approximately 44 gm (156 oz) steel ball dropped from a height of 127 cm (50m ) If corrective lenses are required, it is peferable to grind the correction into a goggle lens Goggles which cover ordinary spectacles may be worn, but they require cups deep and wide enough to admit the whole spectacle The depth noticeably re stricts the field of vision Furthermore, if the correction is critical. "National Safety Council, 425 North Michigan Ave, Chicago Plastic Eye Pro tectors Final Report on the A S S E Re search Project, 1947. ""US Treasury Department, Washington, D C Federal Standard Stock Catalog 38-14